Degree/Uni Advice

“You don’t need to memorize every word and be the perfect student. A lot of  stuff you can skim. How do you know what to skim? 3 times a year for every unit in university we meet with the stakeholders (people who will be employing you/accreditation bodies/Australian government) they tell us what they want you to know when you come out of the uni degree. We take that information and for every lecture we put that info into the lecture so your getting what those stakeholders want from you. Every lecture should have a ‘learning objective’ which is a summary of what the stakeholders have told us they want – that is the most important information. STUDY THAT. Treat the learning objectives as questions. If you can answer those questions your doing okay. If you can do that for every lecture – you’re doing okay.” – Phil?

“If you want to know your on the right track learning objectives are the way to go because these are what we’re going to base our questions around. The learning objectives are what industry people and accreditating bodies want you to know”

Hacking Exams

We can only ask you 3-5Q per lecture in an exam. So if you don’t get something let it go. Dont get stuck 3-4 weeks behind just because your trying to remember one topic.

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Introduction to Human Structure & Function (W1)

Lecture #1 (6.3.17)

Structure  = Anatomy (How its put together)

Function = Physiology (How they work together)

11 Different Organ Systems

Integumentary System:

Structures: Skin/Hair/Sweat Glands/Nails

Functions: Protection against hazards/Regulation of body temp/Sensory info

Skeletal System:

Structures: Bones/Ligaments/Cartilage/Bone Marrow

Functions: Protection & Support/Stores minerals/Creates blood cells

Muscular System:

Structures: Skeletal Muscles/Tendons

Functions: Movement/Protection & Support/Heat

Nervous System:

Structures: Brain/Spinal Cord/Peripheral Nerves/Sense Organs

Functions: Controls responses to stimuli/Coordinates other organ systems/Interprets sensory info

Endocrine System:

Structures: Pituitary + Thyroid + Adrenal – gland/Pancreas/Gonads (testes/ovaries)

Functions: Directs chronic changes in other organ systems/Regulates metabolic activity and energy use/Controls structural + functional changes during development

Cardiovascular System:

Structures: Heart/Blood/Blood vessels

Functions: Distribute blood cells, water, nutrients, waste products, O2, CO2/Body temp control

Lymphatic System:

Structures: Spleen/Thymus/Lymphatic vessels/Lymph nodes/Tonsils

Functions: Defends against infection & disease/Returns tissue fluid to bloodstream

Respiratory System:

Structures: Nasal Cavities/Lungs/Larynx/Trachea/Bronchi/Alveoli

Functions: Transports air to alveoli/Provides O2 to bloodstream/Removes Co2 from bloodstream

Digestive System:

Structures: Teeth/Tongue/Salivary glands/Oesophagus/Stomach/Small + Large intestine/Liver/Gallbladder/Liver

Functions: Digests food/Absorbs water & nutrients/Stores energy reserves

Urinary System:

Structures: Kidneys/Ureters/Bladder/Urethra

Functions: Excrete waste products from blood/Controls water balance/Regulated blood ion concentration & pH

Reproductive System:

Structures: Gonads (testes & ovaries)/Reproductive tracts/Mammary glands

Functions: Produce sex cells (sperm & oocytes)/Produce hormones/Support embryo

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Anatomical Landmarks

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PLANES OF MOVEMENT

Frontal/Coronal: An easy cue to remember, imagine moving to your left or right to pick up an actual ‘corona’ drink. Or imagine there is a wall directly behind and in front of you.

Sagittal: ‘Straight up and down’ – starting with S. When we’re talking about our main compound bilateral lifts they’re technically in the sagittal plane because they’re straight up and down.

Or imagine there is a wall directly to your left and right side.

Transverse: ‘Move around the universe/globe.’ – twisting.

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Chemical Level Of Body Organisation AKA Chemistry (W1)

Lecture #2 (7.3.17)

Organic Compound: A collection of elements that contains CARBON (C) AND HYDROGEN (H).

Inorganic Compound: Doesn’t have both C & H – might have either or, but not both.

5 Organic Compounds:

Carbohydrates

C: H: O: 1:2:1 (just for a monosoccharides) = Glucose (C6H12O6)

Anything saccharide / sacch = sugar/CHO.

Disaccharaides: 2 Monosacharides = Sucrose (table sugar)

Polysaccharides: Startch (storage form of glucose in plants)/Glycogen (storage form of glucose in animals)

Lipids

C: H: 1:2 (contains much less O2 than CHOs thus produces twice as much energy)

Important structural element of the cell because they make up the membrane of the cell.

Very similar to lighting a match: CHOs are like trying to burn a half burnt match while lipids are alike to a dry block of wood waiting to be burnt.

We use CHO as a primary fuel because they don’t store very efficiently. Alike to the effect creatine has,  CHO attract about 3x their own weight of water into a cell because they’re hydrophilic as opposed to lipids which are hydrophobic.

Proteins

C: H: O: N (Nitrogen)

Functions of PRO:

Support/Movement/Transport (carrier molecules) /Buffering/Metabolic regulation (enzyme reactions)/Coordination & Control (hormones – insulin/leptin)/Defence (karatin/antibodies)

Protein Structure

Made up of long chains of amino acids.

Protein Shape 

Primrary/Secondary/Tertiary/Quaternary: Need to know?

Nucleic Acids

5 Nitrogenous Bases:

AGCTU: Adenine (A), Guanine (G), Cytosine (C), Thymine (T) Uracil (U) (RNA Only) 

Nucleic Acid Sructure

RNA: Single chain of necleotides

DNA: Pair of necleotide chains

High Energy Compounds

Any organic compound with a phosphate (PO43-) group attached.

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Water (Inorganic)

H but no C.

Hydrophilic: Philic – ‘To love’ – Sugars.

Hydrophobic: Phobic – ‘Fear of’ – Lipids

Sweat: When water becomes a gas. By taking heat energy from your body and turning it into a gas away from your body in order to cool you down.

Acids / Bases / Salts

Acid: Any chemical that can donate a H+ (ion = a charged particle) / Releases H+ into solution.

Lactic acid (before its donated its H) vs lactate (once its donated its H) But both are the same chemical.

Base: Any chemical that can pick up the H+ / removes H+ from solution.

Salt: Compound made of ions other than H+ & OH- 

H+ & pH

Measure of H+ Concentration

More acidic = Lower pH = Greater concentration of H+

Neutral: pH = 7   (H+ = OH-) = Cancel each other out.

E.G. Hydrocloric acid in the stomach @ 2pH.

Acidic: pH < (greater) 7  (H+ > OH-) = More H+ than the base.

Basic/Alkaline: pH > (smaller) 7  (H+ < OH-)

Human body hasn’t evolved to deal with bases as well as acids.

pH Scale

Anything lower than 6 = Acidic

Anything higher than 7 = Base/Alkaline

Every time you move one pH unit (E.G. 7-6) you’re moving a concentration difference of 10. So there’s 10x more H+ at a pH of 5 compared to a pH of 6. If we were to move two units = 100x difference. 3 = 1000. 4 = 10,000, etc.

While moving 5 units down in acidity at a pH of 2 (1 million increase in H+) would only very mildly harm you, if at all. Moving only 4 units up to a pH of 11 (10,000 increase on OH-) could easily kill you.

Buffers: A compound that resists change in pH.

Works to keep your body at a neutral pH. (Bicarbonate buffering system).

A buffer can either donate OR pick up H+ depending on whats required. It can act as an acid and a base. 

 Learning Objectives

4 chemical elements that make up most of the body’s mass:

O:C:H:N

Distinguish between organic and inorganic compounds:

Organic compounds contain H + C whereas inorganic contain only a H OR a C – not both.

List the properties of water that make it important for living things:

Having a high heat capacity and being hydrophobic or hydrophilic.

List the properties of inorganic acids, bases and salts

Inorganic Acids: Any compound that can donate / release a H+ ion

Bases: Any compound that can pick up a H+ ion

Salts: Any compound made of ions other than H+ and CO- (hydroxide)

Describe the pH scale and define acidity and alkalinity

The pH scale is a measure of H+ concentration. Acidity is when a compounds pH is greater than 7, this means that every time we move a concentration level down the H+ concentration increases x10 fold. Whereas alkalinity describes a pH lower than 7, meaning the H+ concentration drops 10x per pH level increase

Identify the normal pH range for human blood

7.35-7.45

Define a buffer

A buffer is a compound that resits change in pH.

List the five organic compounds

CHO/Lipids/Proteins/Nucleic Acids/High Energy Compounds

Distinguish between a carbohydrate, lipid and protein

A CHO has a 1:2:1 ratio of Carbon:Hydrogen:Oxygen for a monosaccharide, a lipid has a 1:2 ratio of carbon:hydrogen as a result producing much more energy than CHO and lastly protein containing Carbon:Hydrogen:Oxygen:Nitrogen

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Organisation Of The Cell (W1)

Lecture #3 (9.3.17)

The basic building blocks for all organs and tissues.

2 Classes Of Cells

Sex Cells: Germ Cells

Somatic Cells: All other Cells (Soma = Body)

Cell / Plasma Membrane

Made up predominately of lipids and proteins.

Functions

Isolation, protection, regulates entry in/out of the cell

Physical isolation: One of the major roles of the cell membrane is to separate the what is inside the cell from what is outside the cell.  It is not only important in keeping what is outside the cell out, but for keeping what is inside the cell in.

Regulates exchange: Acts as an entry control, perhaps like the police at the border of a country.  The cell membrane monitors and controls what comes in and what goes out of the cell.

Sensitivity: First line of defence and detection of environmental changes such as a change in pH of the extracellular fluid or change in chemical composition of the ECF. E.G. Taste buds / Detecting hormone change.

Structural Support: Helps to maintain the shape of the cell and contributes to the structure of whole tissues and organs.

The Cytpoplasm (Thick goo inside the cell)

Cyto = Cell

The cytoplasm contains everything in the cell between the cell membrane and the membrane around the nucleus.

Cytosol: Intracellular Fluid

Nutrients/Ions/Proteins/Wastes

Organelles (‘Like mini organs’)

Structures with specific functions.

Cyotosl Different from Extracellular Fluid (ECF)

The contents of the cytosol differ from the extracellular fluid – the fluid surrounding the cell.

Different ion concentrations

High concentration of proteins in cytosol

Amino acid and energy stores in cytosol

Other inclusions in cytosol

Organelles

Internal structures of cells

Non Membranous Organelles (Don’t have a membrane around it)

Cytoskelton, microvilli, centrioles, cilia, ribosomes, proteasomes.

Membranous

Endoplasmic reticulum, golgi, lysosomes, peroxisomes, mitochondria.

Cytoskeleton

Provide structure and support for the cell.

Actin (red) is the smallest protein making up the microfilements. (Also involved in muscular contraction along with myosin)

The cytoskeleton consists of the following components…

Microfilaments

Made up of actin.

Interact with myosin to change cell chape.

Attachs the cell membrane to the cytoplasm. (Your cytoplasm and cell membrane are liquids being attached by proteins)

Myosin is attached to either end of the cell, actin helps that attachment. When your cell needs to contract they literally ‘walk along each other’ and what that does is pull the end of the cell together.

A component of microvilli. The purpose of microvilli is to increase the surface area of the cell (specifically for the gastrointestinal tract and lungs)

Intermediate Filaments

Support and structure.

Stabilize organelle and cell position. Like tying the cells together.

Unlike the microtubules, which resist compression, intermediate filaments resist tension—the forces that pull apart cells.

Microtubules

Tube like structures. The toughest part of the cell.

They are the primary structures of the cytoskeleton and provide cell strength and rigidity.

Contained in all cells.

Transport system of the cell to move organelles.

Gives structure to other organelles due to their tube like structure.

Nucleus

Largest structure in the cell.

The warehouse that make up your proteins. ‘Holds the codes for the primary sequence of your proteins.’

The nucleus is surrounded by a membrane.

Nucleoli

Within the necleus are structures called Nucleoli which are responsible for making ribosomal RNA

The Nucleoli also contains proteins called Histones which interact with the DNA when genetic info is being read.

Nucleolus (Outer)

Responsible for ribosome synthesises.

Nucleus

The control centre of the cell.

Ribosomes

Converts RNA code into amino acids.

The site of protein synthesis. Proteins are made within cells in specialised organelles called ribosomes.

Before proteins are made, the two ribosomal subunits must join together with a strand of messenger RNA for protein synthesis to begin.

Endoplasmic Reticulum

Endo = In / Exo = Out / Reticulum = A Network

Is a network of membranes attached to the outer envolope of the necleus.

4 Main Functions

Synthesis of proteins, CHO and lipids.

Storage of cytosolic molecules.

Transport.

Detoxification: Neutralise drugs or toxins with special enzymes.

Smooth ER

No Ribosomes associated with it.

Synthesises lipids, cholesterol, steroid hormones, glycogen –all that “slippery stuff”

Rough ER

Has Ribosomes.

Role is to package and modify newly synthesised proteins. (site of protein synthesis)

Golgi Apparatus

Modifies and packages hormones and enzymes from the ER for use in the cytosol.

Maintains the cell membrane.

Mitochondria

Site of energy production for the cell.

 Most of the ATP is produced in the mitochondria as part of aerobic respiration.

Adipose Tissue

White adipose tissue is most abundant. It can appear yellow and owes its color to carotene and related pigments from plant food. White fat contributes mostly to lipid storage and can serve as insulation from cold temperatures and mechanical injuries. White adipose tissue can be found protecting the kidneys and cushioning the back of the eye.

Brown adipose tissue is more common in infants, hence the term “baby fat.” In adults, there is a reduced amount of brown fat and it is found mainly in the neck and clavicular regions of the body. The many mitochondria in the cytoplasm of brown adipose tissue help explain its efficiency at metabolizing stored fat. Brown adipose tissue is thermogenic, meaning that as it breaks down fats, it releases metabolic heat, rather than producing adenosine triphosphate (ATP), a key molecule used in metabolism.

 Learning Objectives

Draw a cell and label its principal parts and briefly say what the organelle does.

Describe the structure and function of each of the following cellular components: cytoskeleton/cytoplasm/mitochondria/lysosomes/ribosomes/golgi apparatus/endoplasmic reticulum/nucleus/ nucleolus/chromosomes

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Cell Membrane & Transport (W2)

Lecture #4 (13.3.17)

Cell Membrane

Also known as the Plasma Membrane / Plasmalemma. Describes ‘the rubber around the balloon that keeps all the chemical reactions inside the cell’

Each cell has a different role associated with that organ and it’s own chemical reactions and compositions.

Cell Membrane Functions

1. Isolation: Inside the cell is where all the chemical reactions for life occur. ‘There’s no point of glucose turning into ATP in the air.’

2. Regulates Environmental Exchange ‘The doors and windows of the cell’ .

A cell has different transporters and carrier proteins that help waste move out of the cell and nutrients (glucose) move in.

E.G. Red blood cell brings in O2 passes out CO2.

3. Sensitivity: ‘The receptors’. E.G. Insulin receptors on your skeletal muscle recognizing chemical signals. Taste.

4. Structural Support: Shape of a cell gives structure to it and that shape is critical to it’s function.

Cell Membrane Major Components: Lipids

Phosopholipid Bilayer

Two layers of lipids that have a hydrophilic head group and a hydrophobic tail. So they come together – water on the inside & outside of the cell. 

Water soluble compounds unable to pass through membrane.

Important for maintaining ICF composition.

That membrane above by itself is selectively permeable. It decides what get’s in and out of the cell because only lipids can get across the hydrophoic tail. E.G. Anything you rub on your skin that is hydrophobic potentially has free access to your body through your skin. E.G. Titanium dioxide from sunscreen into the body.

Phosphate is a great chemical glue for helping compounds join to each other.

The cell membrane called a PHOSPHOLIPID BILAYER because it is made up of phospholipid molecules that form two layers.

Remember last week when we were talking about the organic molecules that are important for cell function, we talked about PHOSPHOLIPIDS. These are special lipids because they have two parts – a LIPID part and a PHOSPHATE part, that is a lipid part and a phosphorous and oxygen component

The LIPID part is made up of long tails of hydrogen and carbon atoms which are hydrophobic.  This means that they don’t like water. The HYDROPHOBIC ENDS will only INTERACT WITH OTHER LIPIDS so they tend to turn towards one another.

The PHOSPHATE end that contains the phosphate groups are hydrophilic which means they like water. This end of the phospholipid is able to form hydrogen bonds with water molecules.

When a phospholipid or a glycolipid enters water, large molecules tend to form droplets or micelles where the hydrophobic (lipid tails) move to the centre and the hydrophilic non lipid heads sit at the outer edge. You have seen oil droplets form on dishwater – these are the miscelles with all of the lipid part of the oil pointing towards the centre of the droplet and the hydrophobic part on the outside. The phospholipids in the cell membrane contribute to this bilayer because the hydrophobic tails face inward away from both the intracellular and extracellular fluid, while the hydrophillic heads face outwards. – highlight on next slide

This DOUBLE or BILAYER is an important feature of the cell membrane because it can control and maintain what is in the cell versus what is outside the cell.

The phosphate head loves water. The hydrophobic tail hates water.

Cell Membrane Major Components: Carbohydrates

CHO that make up part of the cell membrane. E.G. The CHO that hang off your blood cells and give you your blood type.

Common CHO: Proteoglycans, Glycoproteins, Glycolipids

Glyco = sugar

Glycalyx

The region your CHO extend past the cell.

Functions Of The Glycalyx

Lubrication & Protection. E.G. Mucus is a significant form of protection for our body. Bacteria are constantly trying to get into your body – mucus proteins act as a physical viscus barrier of protection. Additionally, helps drag out pathogens. It also lubricates the gastrointestinal tract allowing for smooth passage.

Anchoring & Locomotion: There are enzymes that sit/anchored in the gastrointestinal tract waiting to break down nutrients to get absorbed and pathogens to be removed.

Locomotion: The act of dragging the bacteria through the gastrointestinal tract out of the body. E.G. glucoproteions helping with locomotion through the gastrointestinal tract.

Specificity & Binding: E.G. CHO giving your blood type / signals say you are you.

Recognition: Each of them has a particular pattern that has a particular role.

 

Cell Membrane Major Components: Proteins

Integral Proteins: A key essential part of that membrane. The transporters that help glucose and other hydrophilic compounds get into the cell. It makes sense it needs a lot of those because the cell needs a lot of nutrients.

Peripheral Proteins: Inner or outside surface of the membrane. It’s not part of the cell membrane, it sits just underneath.

Membrane Proteins Summary Image

Membrane Proteins

Anchoring Proteins: Help anchor cells to the rest of the body. E.G. Attaches to cytoskelton. It’s what stops the bulk of your skin cells falling away when you rub your hands together.

Recognition Proteins: Important for the immune response. It tells your immune system that you are you. E.G. Glycoproteins.

Enzymes: E.G. Peptidases (ases = enzyme) breaks down proteins. If they are firmly attached to the cell membrane they are integral proteins, if they are floating around they are peripheral proteins. E.G. Digestive enzymes within the gastrointestinal tract breaking down proteins into amino acids which are then transported to the rest of the body.

Receptor Proteins: E.G. Insulin / hormone receptors. Chemical specific.

Carrier Proteins: ‘The doors and windows’. Transport molecules responsible movement across a cell membrane and around the body. Usually hydrophobic through hydrophilic or vice versa. In this context carrier proteins move/diffuse across the lipid bilayer carrying a cargo across that selectively permeable membrane.

Channels: Always open but can always regulate what comes in and out. Like a particular shape that only recognizes a particular shaped molecule.

Cell Transport

There is no cell that is competently impermeable but it can be selectively permeable = passage of some materials and not others. So if a cell does not need glucose it can keep glucose out through the selectively permeable lipid bilayer because it’s hydrophilic.

Selectively Permuable: Talk about the lipid bilayer and particular proteins allowing certain molecules into and out of the cell.

3 Types Of Transport

Passive Transport: Does not require energy. E.G. Water flowing downhill. Downhill = the concentration gradient.

Active Transport: Requires energy. E.G. If you want water to flow uphill you need a pump/energy.

E.G. Using ATP to pump from high concentration to low concentration.

3 Mechanisms Of Transport: Diffusion/Carrier Mediated/Vesicular Transport

Diffusion

Moving from high concentration to low concentration.

Solute: Any material that is dissolved in a solution.

Solution: A fluid containing a dissolved materials. The solvent + solutes.

Solvent: Water is the major solvent for life.

Concentration Gradient

Chemicals will always flow from high concentration to low concentration without needing to do anything.

E.G. As a part of turning glucose to ATP energy a lot of CO2 is produced in your muscle cells via about 20 different enzymes. You get very high concentrations of Co2 in your muscle cells – now there’s high concentration inside and low concentration outside. CO2 will naturally diffuse across the cell bilayer to outside the cell where it’s picked up by blood cells and carried to the lungs.

Factors Effecting Concentration

Distance: The smaller the distance the more rapidly it moves through diffusion. E.G. Insects being so small so it can allow for rapid diffusion.

Molecule Size: The bigger the molecule the more friction and more its going to be bounced back.

Temperature: A measure of kinetic energy. Hotter = diffuse’s quicker.

Gradient Size: 

Electrical Forces: + and – forces. If you’ve got a lot of + forces in a cell it’s going to take longer to diffuse across the cell as they will be bouncing off each other.

Diffusion Across The Cell Membrane

E.G. After a big sugary meal you have glucose trying to get into your body – you’ve got a high concentration of glucose in your gut and a low concentration in your blood stream. It’s trying to diffuse across but it can’t you need to insert a carrier protein/transporter/channel into that cell membrane to allow glucose to diffuse in. Without that glucose can’t move into the cell.

Osmosis

The net diffusion of water across a membrane.

Osmorality

The concentration of solutes in aqueous solution.

Tonicity

The ability of a molecule to cause a movement of water.

Isotonic Solution: Causes no net movement of water. Same concentration of water inside the cell vs outside.

Hypotonic Solution: A hypotonic solution such as water, causes water to move into the cell and the cells swell. Solute concentration inside cell higher than outside.

Hypertonic Solution: Causes water to move out of the cells and the cells shrink. The water concentration outside the cell is greater than the concentration inside the cell so waters going to flow across that cell membrane. Something that is hypertonic = a lot of salt = water moves towards that hypertonic solution.

Remember: It’s water moving down it’s concentration gradient through a selectively permeable membrane.

Concentration of Solutions

In an isotonic solution the concentration of water inside and outside the cell is the same. So water doesn’t move across the cell membrane.

In a hypertonic solution you’ve got a lot of salt outside the cell – the water inside the cell will try and flood outside the cell to try and even out that concentration gradient. So the cell shrinks as the water leaves the cell.

Carrier Mediated Transport

Specificity: They are proteins.

Saturation Limits: Can only move at a certain rate and bring in so many molecules per sec. Purpose is to regulate cells.

Regulation: Detect which molecule is brought in and out.

Facilitated Diffusion: It is just diffusion that is helped. E.G. Glucose getting into your body across the gastrointestinal tract.

Active Transport

E.G. You’ve got a lot of glucose in a muscle cell and you’ve got less glucose in the blood stream but you want to get more glucose into that muscle cell and clear glucose out of the blood stream. So you use ATP to so you use ATP to pump more glucose into the cell. That is active transport because you are actively helping it via a requirement of energy.

Secondary Active Transport

How our gastrointestinal tract get’s glucose into our body.

A passive process.

ATP isn’t always used straight away. No energy expended in the process

Secondary Active Transport involves moving a substrate down its concentration gradient – like facilitated diffusion.

For the substrate to be carried across, it requires another substrate (in example, glucose wont be transported without Na being transported/bound at same time)

Once the glucose and Na are in the cell, the conc of Na needs to be rebalanced and the ENERGY is EXPENDED here by the SODIUM POTASSIUM PUMP to remove the sodium.

Endocytosis

Endocytosis is a process where materials are packaged into vesicles at the cell surface and imported into the cell. So basically the material that the cell wants is enveloped into a parcel and drawn into the cell.

3 types of endocytosis

Receptor Mediated: Molecules bind to receptors on cell membrane and are drawn into cell

Pinocytosis – ‘cell drinking’

Phagocytosis – ‘cell eating’

 Phagocytosis & Pinocytosis

The second type of endocytosis is PINOCYTOSIS – it is referred to in your texts as CELL DRINKING.

What this means is that the vesicles that are formed at the cell membrane are filled with extracellular fluid.

The only difference to receptor mediated endocytosis is that pinocytosis doesn’t use receptor and the fluid is of interest rather than specific ligands.

The third type of endocytosis is PHAGOCYTOSIS – this is cell eating.

This is where the cell membrane fuses around solid objects and moves them into the cell where they are digested again by lysosomes.  The process of phagocytosis is only performed by specialised cell such as those of the immune system to protect the body from bacteria and other abnormal material.

Exocytosis

Exocytosis is the opposite to endocytosis.

This means that the vesicles of material are created inside the cell and moved to the cell membrane where they are released into the extracellular fluid.

We have already previously talked about this as the Golgi is one of the places where the packaging of the materials occurs.  The material that is released can be a number of things such as hormones or mucous or waste products.

 Learning Objectives

Describe the characteristics of a phospholipid bilayer

Describe how proteins and carbohydrates contribute to the structure and function of

the cell membrane

Explain why the cell membrane is more permeable to lipid soluble substances and

small molecules than to large water-soluble substances

Describe how the following mechanisms facilitate the transport of substances across

cell membranes: diffusion, osmosis, facilitated diffusion, active transport, endocytosis, exocytosis

Describe the effects of isotonic, hypertonic and hypotonic solutions on cells

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Cellular Metabolism (W2)

Lecture #5 (14.3.17)

Metabolism

All the chemical reactions that occur in the body.

Anabolism

The synthesis or ‘build up’ of organic molecules.

Functions

Maintenance/Repair: Structures within the cell need to be maintained and repaired.

Growth

Secretions: E.G. Mucous or hormones that need a constant supply of ingredients.

Nutrient Reserves: E.G. Glucose stored as glycogen in the liver/muscle.  Like squirrels for the winter, cells need to have a supply of nutrients in reserve for emergencies such as a period of extreme activity, or a period of time without nutrient supply. This is important as it acts as a NUTRIENT POOL to supply our mitochondria

E.G. Insulin, which is one of the most powerful anabolic steroids which forces the muscle cells to grow by forcing them to produce proteins to grow larger and take glucose out of the blood stream.

Catabolism

The break down of organic molecules.

Releases energy to synthesize ATP / high energy compounds.

Catabolism not only occurs in the cytosol of the cell but also the mitchondria.

“The break down of organic compounds such as complex carbohydrates to glucose to pyruvates etc etc is how our bodies produce ATP. Human’s acquire these organic compounds by consuming them.

So your body must be starving to need to synthesise organic compounds to then break down to produce ATP. Because this is cannibalism. The body “eats” your muscles (protein) to synthesise into aminio acids, to then use to break down and produce ATP.”

What happens to the excess energy as part of catabolism?

Excess energy given off as heat.

The Relationship Between Catabolic & Anabolic Pathways

Food is digested (NOT catabolism, that’s digestion) into CHO/Fatty Acids/Amino Acids.

Oxidation = taking electrons off chemicals. Which is important because we oxidize our food. We oxidize glucose to turn it into ATP. That energy is used to put chemicals together.

Exergonic: The release of energy.

(gonic = energy) (ex = ‘out’ – passing stuff outside the cell) (endo = ‘in’ passing stuff inside the cell)

Endergonic: Requires energy / The absorption of energy.

Energy depleted end products: Co2 = breath out / H20 = sweat/breath/urin / NH3 (ammonia) = urine

We don’t store the extra amino acids (proteins) it just get’s passed through. “That’s why high protein diets can be risky because they can put pressure on the kidneys, especially for people with diabetes who already have micro vascular damage within the kidneys because your getting rid of a lot of ammonia.

Sources Of Energy To Recycle ATP

We don’t get ATP from food. What we’re doing is getting enough energy from the food to build ATP.

 

We put 1 phospherus on ADP -> we break it off and that releases energy. When we consume glucose we take the energy from glucose and grab an ADP + P -> we use the energy coming from glucose to put it back together. We only have ATP just to store that energy, that’s all it is. 

Cellular Respiration/Metabolism

Glycolysis: The breakdown of CHO which is responsible for anaerobic respiration occurring in the cytosol of the cell using about 10 enzymes. 

E.G. A cheetah can only sprint for a short amount of time because they don’t breath while sprinting as they rely on anaerobic respiration.

Anaerobic Glycolysis: Without air – breaking down – carbohydrate. There’s not enough ATP produced in this process to sustain high bouts of energy without O2.

Krebs Cycle also known as the ‘citric acid cycle’ because that’s the first chemical in the cycle that continues to break down sugar/protein to create energy.

We’ll produce 32 ATP molecules from this process. But the first 2 steps you’re not producing much ATP which is why we can’t use anaerobic respiration very long.

Electron Transport Chain (orange) occurs in the mitochondria which is the part that requires O2 (also why we have to breath in).

Enzymes

A protein.

They are responsible for the synthesis and decomposition of most of the chemicals in the body.

They have great specificity, which means they recognize particular compounds.

Enzymes are called catalysts as they assist the speed of a reaction making it occur faster.  NOTE – they only affect the speed of the reaction not the direction of the reaction or what products are made.

When we have a fever it heats up many bacterial viral proteins and denatures those proteins.

Other Factors Affecting Enzyme & Reaction Rate

How does the body regulate chemical reactions and make sure it has enough ATP but one single cell doesn’t use all the glucose in the body.

Substrate Limitation

If you don’t want a muscle cell turning glucose into ATP you stop glucose entering the muscle cell and that’s what the body does. When there’s the right amount of glucose in the blood stream the muscle cell pulls it’s glucose transporters out of the membrane and puts them away in a cytosol until they’re needed.

Negative Feedback

The cell can use the amount of product being produced to tell it that it has enough product and doesn’t need to use anything else.

Enzyme Modulation

The Electron Transport System

Why do we breath in O2?

The only reason we breath in is to neutralize the byproducts at the end of production of ATP.

The electron transport chain is where the bulk of the ATP is made (about 32 ATP compared to 2 ATP in the citric acid cycle of anaerobic glycolysis).

 Learning Objectives

Define metabolism

Distinguish between catabolism and anabolism

Explain why cells need to synthesize new organic components

Identify the group of macromolecules to which enzymes belong

Proteins made up of amino acids.

Describe how it is that enzymes are highly specific

List the factors that influence the rate of an enzyme controlled reaction

Describe the role and importance of ATP

Distinguish between aerobic and anaerobic respiration

Aerobic requires O2. Anaerobic doesn’t require O2.

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Tissue Level Of Body Organisation #1 + #2 (w2/w3)

Lecture #6 (16/3/17) + Lecture #7 (20/3/17)

What is a tissue?

A tissue comprises of specialised groups of cells which co-ordinate together to perform specific functions of that tissue.

4 Basic Tissue Types

1. Epithelial Tissue (Integument System)

Tissue that surrounds our body and lines the inside of our body such as our respiratory tract.

Is comprised of epithelial cells and main role is to help protect, secrete, absorb and filter.

Important Characteristics

Cellular: Comprises of a high numbers of cells tightly connected together.

Polarity: One side is exposed to the external surface and one side attaches to the internal surface.

Attachment To Underlying Tissue: Such as connective tissue, E.G. basal lamina.

Avascular: Doesn’t have any blood vessels within the tissue

Regenerate: Cells can regenerate to replace any dead or lost cells if the tissue becomes damaged.

Functions of Epithelial Tissue

Protection: Against dehydration, our body contains a lot of water and our skin helps retain it. It also provides a physical barrier to other substances, chemicals and pathogens.

Controls Permeability: Can be very selective to what certain substances are allowed in/out.

Sensory Stimuli: A sensory nerve supply that can help neuroepithelia that can detect touch on the surface on our skin or detect temperate changes etc.

Secretions: Glands that can secrete mucous, fluid (tear ducts) and hormonal releases.

Anatomy of Epithelial Cells

In order to perform the above functions of epithelial tissues, epithelial cells must have specialised structures to perform functions such as secreting fluids and protection. Some of the anatomical properties that allow epithelial cells to do this include:

Apical Surface (Exposed to the Environment): This can be smooth or contain bumps (microvilli) or longer structures called cilia. Depending where the epithelial tissue is it may or may not have adaptations of the surface. What it does is help facilitate the role of the epiethlial cell.

Basolateral Surface: Which is the base or bottom of the cell that is attached to the underlying material.

Cilia: Fine hair like projections that move in a wave to sweep fluids and molecules across their surface. You will find cilia on the apical surface of your epithelial cells of your respiratory tract – cilia there helps keep movement of mucous occurring and helps prevent pathogens coming into your body.

Microvilli: These are small projections of the cell that increase the surface area available to the cell for absorption or secretion of important materials. E.G. In our digestive system epithelial cells will have microvilli that function to increase the surface area of the cell to assist in greater absorption of nutrients.

FOR EPITHELIA TO HAVE A ROLE FOR EXAMPLE IN PROTECTION THEY NEED TO BE JOINED VERY TIGHTLY TOGETHER

Classification of Epithelia

Epithelia can be classified in to categories based on their on shape and number of cell layers

Shape

Squamous (flat ‘egg’ type shape).

Single Squamous = Very thin, allow exchange of gases. Lines our blood vessels to exchange gases/nutrients to underlying connecctvie tissues.

Stratified Squamous = Protection, E.G. Skin.

Cuboidal (cube like)

Columnar (long and elongate)

Simple Columnar = Help filter (pathogens) + Movement of mucous. In the form of cilia or microvilli. E.G. Digestive tracts.

Number of Cell Layers: Can exist in a simple layer (single) or stratified (multi layer).

Difference between simple and stratified in regards to the structure?

A simple epithelium has cells that form a single layer that are attached to the basement membrane. A stratified epithelium, on the other hand, consists of multiple layers of cells where only the basal layers are attached to the basement membrane

Squamous Epithelia

Simple Squamous: Delicate/Smooth. We find them in regions of absorption/diffusion. E.G. Lungs, blood vessels.

Stratified Squamous: We find these layers of cells in regions we experience mechanical stress (skin/mouth).

The skin is keratinized which acts as a waterproofing agent against the surface of the skin that helps prevent dehydration and protects against chemicals.

Cuboidal Epithelia

Simple Cuboidal: Epithelium provides minimal protection and can be found in places where secretion or absorption occurs, E.G. kidney tubules.

Stratified Cuboidal: Rare, E.G. Sweat gland ducts and lining ducts of mammary glands.

Transitional Epithelium: Subject to stretch and recoil E.G. Lining of urinary bladder.

Columnar Epithelia

Simple Columnar: Occur in regions where absorption and secretion is occurring such as in the digestive tract.

Pseudostratified Columnar: 

This is a specialised type of epithelia which is mainly found in the respiratory tract and consists of several different cell types. When you look at it, it appears to be stratified, in that it looks like there are several layers of cells, however ALL CELLS do actually touch the basal lamina – therefore it’s one single layer. E.G. Respiratory tract, male reproductive system.

Stratified Columnar: These epithelia are also rare and provide protection in areas such as the anus and urethra.

Glandular Epithelia

Glands are structures made up of groups of epithelial cells that produce secretions. Pancreas is the only gland that has both endocrine and exocrine glands because it can produce digestive enzymes and also endocrine gland function that releases insulin.

Endorcrine Glands: Produce hormones which go into the extracellular fluid and then into the blood stream for distribution through the body. (They are ductless) E.G. Pituitary and thyroid.

Exocrine Glands: Produce secretions that are discharged out (exo) onto the epithelial surface.  Most of these secretions get to the surface via tubular ducts. E.G. Sweat glands and tear ducts. Exocrine glands can also be classified based on the type of secretion they produce – serous, mucous, mixed.

We can also classify our exocrine glands according to their structure.

SIMPLE have ducts that don’t divide. COMPOUND have ducts that do divide.

TUBULAR – pretty self explanatory they form tubes. ACINAR – they form a sac or a chamber.

2. Connective Tissue

Connective tissue cells are dispersed in a matrix. The matrix usually includes a large amount of extracellular material produced by the connective tissue cells that are embedded within it. The matrix plays a major role in the functioning of this tissue The major component of the matrix is a ground substance which is usually fluid, but can also be mineralized and solid, as in bones.

Main role is to connect epitherlial cells to the rest of the body.

Fills in the gaps, gives structural support to other tissues, can transport materials in the body and stores energy

They can take many forms and include blood, fat and bone

3 main properties that are fundamental to all types of connective tissues

1. They are made up of a specialised type of cell.
2. They have extracellular protein fibres. [Matrix]
3. They contain a fluid known as ground substance which joins with the extracellular proteins to form a MATRIX around the cells. [0Matrix]

Roles Of Connective Tissue

Structural framework to tissues and organs. 

Aid in transporting fluids and dissolved materials.

Protecting organs.

Support, surrounding and connection of tissues.

Store of energy reserves: E.G. Adipose tissue.

Defend body against microbial invasion: E.G. White blood cells to defend against invading microbiols.

Connective Tissues Types

Connective Tissue Proper

Connective tissue proper consists of the matrix (made up of extracellular protein fibres  and ground substance) and several different cell types.

E.G. macrophages, some lipid cells, mast cells, lymphocytes. The role of the different cell types in the connective tissue proper is maintenance and repair and energy storage.

The ground substance is also very viscous because of glycoproteins and proteoglycans. This inhibits pathogen movement

Connective tissue proper is divided into 2 groups:

1. Loose Connective Tissue

“The packing materials of the body” Their role is to fill gaps between organs, cushion and stabilize organs in certain parts of the body.

Areolar, adipose (for energy), reticular.

2. Dense Connective Tissue

Mostly made up of collagen fibres.

Dense regular connective tissues: Tight pattern of fibres. E.G. tendons, ligaments

Dense irregular connective tissues: Strengthen and support areas subject to stress eg around the abdominal organs, nerves and muscles.

  Fluid Connective Tissue

Divided into

1. Blood

The blood has a watery matrix called PLASMA and the cells that make up the rest of the tissue include RED BLOOD CELLS or Erythrocytes, WHITE BLOOD CELLS or LEUKOCYTES and PLATELETS (aid in blood clotting) which are fragments of cells.

2. Lymph

The LYMPH itself is a fluid matrix which is composed of the fluid that passes out of capillaries.  It is also made up of cells that are mainly LYMPHOCYTES which are white blood cells involved in our immune defense.

  Supporting Connective Tissue

1. Cartiliage

The matrix of cartilage is a gel like substance which contains a lot of chondroitin sulfate (proteoglycan – sugar) attached to various proteins that exist in the gel matrix. There is only one cell type in cartilage and these are the cartilage cells called CHONDROCYTES – specialized cells that produce cartilage. The chondrocytes sit in small spaces called LACUNAE which help the transport of materials through the cartilage.

 3 Types of Cartilage

Hyaline Cartilage: Most common type of cartilage. Tough but flexible. E.G. Found between ribs, respiratory tract, elbow and knee joints. Most of our structure in utero is made up of hyaline.

Elastic Cartilage: Contains elastic fibres. Very flexible. Found in the outer flap of the ear, epiglottis and larynx.

Fibrocartilage: A lot of dense collagen fibres. Very tough. Found between spinal vertebrae, in some joints and tendons. Acts as a shock absorber for bones – this is the type of cartilage athletes tend to damage and doesn’t repair well. E.G. Knees have both hyaline and fibro. Hyaline on the bone surface. The fibro pads in the joint absorbs impact and stops bones hitting each other.

The differences between the types are the amounts of ground substance matrix in the ratio to the collagen.

The more ground substance, matrix and less collagen = more elastic. The less ground substance and more collagen = harder.

2. Bone

The bone matrix is made up of mostly CALCIUM SALTS and COLLAGEN FIBRES.

The cells within bone are called OSTEOCYTES and they also lie within LACUNAE in the MATRIX.

Because the matrix of bone is hard it is difficult for the osteocytes to communicate with each other and blood vessels.  The way in which they do this is via canals in the matrix called CANALICULI.

Membrane

A group of epithelial and connective tissues that combine to protect organs and the body.

4 Main Types Of Membranes

A combination of epithelial tissues with different types of connective tissues.

Mucous (epithelial + loose connective tissue)

Lines passageways, lubricates, protects and aids in absorption or secretion.

Serous (epithelial + areolar connective tissue)

They are a thin structure that plays a role in helping attach organs to the body.

2 Components to Serous membranes: 

Parietal (external membrane). Help attach to the body cavety.

Visceral membrane. Encapsulates the organ)

3 Types of Serous Membrane

Pericardium (surrounds the heart), pleura (encases lungs), peritoneum (cover abdominal organs) (also major cavities within the body).

Cutaneous (stratified squamous epithelial + dense connective tissue)

Thick, waterproof and dry (contrast to serous and mucous membranes) E.G. Skin.

Synovial (connective tissue)

Find these between our joints. Their role is to provide the synovial membrane produces synovial fluid to give a cushioning effect to help absorb force/shock.

3. Muscle Tissue

Skeletal Muscle Properties

 Made Up of Muscle Fibres that are…

Multinucleated (multi nuclei) located in the periphery of the fibre.

Cannot divide any further but can be replaced if the muscle gets damaged. E.G. Satellite cells activate during a muscle injury to start to proliferate and form new mature muscle fibres.

The striated appearance of the muscle is mainly due to actin and myosin. These help provide structure and aid in muscle contraction.

We refer to skeletal muscle as striated voluntary muscle.

Skeletal Muscle Formation

Occurs during embryonic stage or muscle damage.

Proliferate: Satellite cells begin to divide.

Differentiation: They start to elongate and maturate.

Fusion: They start to fuse together to generate a mytotube (an immature muscle fibre). This is why you get multiple nuclei in the muscle fibre – because its made up of fused myocytes.

Bundle: When fully mature the nuclei go to the periphery and bundle at tendons to attach to bone.

Cardiac Muscle

Cardiocytes (myocyte): these muscle cells generally have…

One nucleus (can have up to 5) once the organ is formed theres…

Very limited regeneration. After severe damage to the cardiac muscle it undergoes necrosis.

Also have striations.

Joined end to the end by intercalated discs that helps communication between each cardiac cell.

 Pacemaker cell controls electrical impulses to contact the muscle.

Striated involuntary muscle.

Smooth Muscle

Has one nucleus

Has no striations.

Can regenerate.

Involuntary control but can communicate and coordinate with each other through the nervous system.

Non-striated involuntary muscle.

4. Neural Tissue

Made Up of 2 Types of Cells

1. Neurons

Contain a large cell body.

Contains an axon that transmits info to other cells/neurons through electrical impulses and dendrites which receive info form other neurons and take up nutrients.

2. Neuroglia

Are the supports cells made up of astrocytes (provide nutrients), microglia (remove waste), oligodendrocytes (produce a sheath called myloin which acts as an insulation to help the electrical impulse travel faster – conductivity).

Learning Objectives

Identify the four major tissue types in the human body and describe the characteristics of each.

Describe the basic composition and purpose of extracellular fluid.

List the features that distinguish epithelial tissue from other tissue types.

Distinguish between simple and stratified epithelial tissue.

Describe how structure relates to function and location of different types of epithelial tissue.

Define a gland and distinguish between endocrine and exocrine glands.

Describe the general features of connective tissue that enable it to be distinguished from epithelial, muscle and nervous tissue.

Describe the characteristics that distinguish connective tissue proper, fluid connective tissue and supporting connective tissue.

Define a membrane and list the structural and functional characteristics of serous, mucous, cutaneous and synovial membranes.

Assists movement.

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Homeostasis

Lecture #8 (21.3.17)

Homeo = ‘The Same’/ Statis = ‘Static’, ‘Stationary’.

Homoeostasis is about maintaining a stable internal environment / equilibrium.

How do we do this?

By maintaining a stable body temperature.

Body fluid composition. E.G. Supplying the brain with a constant supply of glucose.

Body fluid volume / Blood Pressure

Waste product concentration.

Homeostatic Regulation

Requires all the systems to work together to preserve a stable internal environment.

While we study one system at a time it’s critical to understand no system operates in isolation, they operate in conjunction with all the other body systems.

Homestasis & Disease

Allostatic load is “the wear and tear on the body” which accumulates as an individual is exposed to chronic stress. It represents the physiological consequences of chronic exposure to fluctuating or heightened neural or neuroendocrine response that results from repeated or chronic stress.

2 Mechanisms Of Homeostatic Regulation

Autoregulation (intrinsic regulation)

Local Level: Change occurs automatically within the cell, tissue, organ or organ system.

Extrinsic Regulation:

Systemic Level: (meaning the whole body system). Changes involve the nervous system and/or endocrine systems.

Homeostatic Regulatory Mechanism has 3 Parts

When something happens in the body and we need to respond to it there’s 3 parts to this. First thing is we need to detect that somethings actually happened…

A Receptor: Sensitive to particular environmental changes. E.G. Detecting temperature change /chemical concentration. It then sends that info to…

A Control Centre: Which receives and processes information and  if something needs to be done it sends commands to…

An Effector

Those effectors dictate the commands from the control centre and turn them into a response.

Receptors

Thermoreceptors: Located in the dermis of skin, skeletal muscle, liver and hypothalamus. They are temperature sensitive.

Mechanoreceptors: Receptive to mechanical stimuli such as compression, stretching, twisting. E.G. Tactile barorecptors (internal pressure), proprioceptors (position of limbs/body in space)

Chemoreceptors: Sensitive to changes in chemical concentration. Important for monitoring pH of the body.

Control Centers

Integration of incoming information and issuing of commands to effector sysytems.

Positive v Negative Feedback

Negative Feedback

Opposes a variation from normal.

Most homeostatic regulatory mechanisms involve negative feedback.

E.G. We start with a homeostatic state – something happens like a sudden rise in heat – the negative feedback is going to oppose that variation and bring it back to normal.

Positive Feedback

Exaggerates variations from normal.

Seldom encounter positive feedback in daily life. Positive feedback loops accelerate processes that must proceed to completion rapidly which tends to produce extreme responses.

E.G. Blood clotting following a severe cut, labour/delivery during childbirth.

Positive Feedback Example During Childbirth

The onset of uterine contractions in childbirth -> When a contraction occurs, oxytocin is released -> Oxytocin stimulates further contractions -> Further contractions stimulate more oxytocin release -> This results in contractions increasing in amplitude and frequency. A snowball like effect that exaggeration the deviation from the normal and brings a process to a rapid conclusion -> Delivery occurs

Negative Feedback in the Control of Body Temperature

36.7 – 37.2 (C) is the normal body temperature range.

Thermoregulation

Warm and cold receptors of the sensory nervous system relay information to the heat-loss and heat-gain centres of the hypothalamus which controls heat loss mechanisms and heat retention and generating mechanisms.

The reason you’re more likely to see the blood vessels sitting superficially in hot weather/exercise is because the blood is being prioritised to be sent through the superficial veins rather than the deep veins. This is done in order to accelerate heat loss via the blood being sent very close to the surface of the skin to get evaporate/convective heat loss.

Blood is being sent via the deep veins instead to reduce the amount of heat loss. When the warm blood travels from the trunk to the hand it passes right next to the venus blood returning to the main trunk of the body which is where we get a counter current heat exchange system. This means the warm blood coming from the trunk transfers its heat across to the cool blood which is returning from the hand. [Diagram above]

Shivering Thermogenesis

An involuntary increase in muscle tone that increases the metabolic rate of those muscle tissues by up to 600% above basal level.

Non Shivering Thermogenesis

The release of hormones to increase metabolic activity.

Adrenaline: =Increase metabolic activity in the liver and skeletal muscle via promoting glycogen breakdown.

Thyroid Hormone: Increases basal metabolic rate. Particular in children who tend to loose heat more readily.

Learning Objective

Discuss the homeostatic mechanisms that maintain a constant body temperature

Identify heat loss and heat gain mechanisms

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Nervous System

Lecture #9 (23.3.17)

Afferent = taking sensory info into the CNS. / ‘A for approaching’

Efferent = Info that is exiting the CNS. ‘E for exiting’

Somatic Motor: Skeletal muscle control.

Autonomic: Automatic subconscious processes. Contains the sympathetic and parasympathetic NS.

Neuron

Info comes in via the dendrites -> signal sent along the axon -> down through the telodendria to the synaptic terminal. It’s at the synaptic terminal where that message will be sent off into the next cell in the pathway. Axon Hillock: Where we get initiation of that communication signal.

Myelin Sheath

Is for insulating the axon – it increases the speed at which electrical signals (action potentials) travel along the axon.

Transmembrane Potential & Resting Potential

Transmembrane Potential: Is the electrical potential of the cell’s interior, relative to its surroundings

Resting Potential: Is the transmembrane potential of an undisturbed resting cell – a cell that’s not currently communicating.

Action Potentials

Action potentials are nerve impulses.

Action potentials are propagated (moves along) changes in the transmembrane potential that, once initiated, affect an entire excitable membrane.

Generation of Action Potential

The stimulus that comes along is either big enough to trigger an action potential, or not get one at all. E.G. It’s the same when flushing a toilet, you push the button a tiny bit – nothing happens. A bit more – nothing happens. But you press it enough and you get an ‘all response’. Once you meet the threshold of pressure of pushing the button then you get the response of the flush. Once it’s triggered, everything about it is the same every time – the speed/volume/destination. It’s the same with action potentials.

All-Or-None Principle

A stimulus either triggers a typical action potential, or it does not produce one at all.

 

It takes a particular voltage across the membrane to trigger an opening because their voltage gated channels.

What’s going to happen to generate an action potential?

Informations come in via the dendrites -> we’ll get this upwards local current coming through in the form of Na+ -> – 60mV is the threshold at which we get an opening of our voltage gated Sodium channels.

That allows our Na+ ions to move along their electrical chemical gradient. The high concentration of sodium floods rapidly through the open channel.

We get inactivation of our sodium ion channels which is a trigger point for our voltage gated potassium ion channels to open at +30mV. The huge concentration of K+ wants to flood out to a place of low concentration. + leaving the cell

The transmembrane potential decrease rapidly and K+ channel closes.

The cell is then able to return to it’s resting state.

Another way to explain an Action Potential…

Looking at the membrane potential over time.

In the resting cell we start with a resting membrane potential of -70mV -> as we get a stimulus we get a change in the threshold up to the trigger point of -55mV~ -> There we get the opening of the voltage gated Na+ (sodium ions) channels -> Causing a flooding of Na+  into the cell which increases the membrane potential -> There we get the opening of the voltage gated K+ channels (potassium ions) -> and the flooding of K+ out of the cell.

Depolarization as the Na+ flood in and re-polarizes as the K+ flood out.

Refractory Period: E.G. We’ve pressed the button and we’ve gotten a flush. The toilet has a refractory period. If I press the button again while it’s refilling there is no additional response because the toilet is unable to respond to an additional stimulus until it’s back to it’s resting state. It’s the same with the nerve action potential.

Propagation (move along) of Action Potentials

The exchange of what two ions is responsible for action potential propagation down the axon?

Sodium & Potassium.

The initial AP occurs in the axon hillock but while that’s happening the local current inside the cell created by that AP depolarizes the next section of membrane.

Action potential is generated in a small portion of membrane -> Local current depolarises the adjacent portion of membrane -> Same events take place over and over -> Action potential is propagated through entire excitable membrane -> Action potential only moves forward because previous segment is in refractory period.

Speed of Action Potentials

Different neurons can have different speeds because of the specific characteristics about that neuron.

What happens in the insulted section is we actually getting jumping of the AP to one exposed part of the membrane to the next (node to node). Thus communication is even more rapid.

The diameter of the axon will also determine how quickly the AP travels. The larger the diameter = faster.

Synapse

What happens when that signal get’s the end and it’s time to communicate with the next cell in the pathway? The AP will reach the synapse which is where the communication message is transmitted to the next cell.

When the AP moves along the axon into the synaptic terminal it initiates the migration of the synaptic vesicles to the pre synaptic membrane and it initiates those to fuse with the cell membrane and release the neurotransmitters via exocytosis into the synaptic cleft. On the cell membrane of the postsynaptic neuron we have receptors that bind the incoming neurotransmitters and initiate a response.

So the AP travels along -> triggers the fusing of the vesicles with the cell membrane -> neurotransmitter is released -> diffuses across -> binds with receptors and triggers a response in the next cell.

Electrical & Chemical Synapses

Electrical Synapses

E.G. The heart muscle cells. These cells are connected by gap junctions, which means we have this little pore physically connecting the cytosol of one cell connecting to the cytosol of another. So when we have an AP we can get the electrical signal moving directly via the cytosol into the next cell without having to release a neurotransmitter/diffusion/binding etc that chemical synapses do. Which is vital for the heart to coordinate contraction.

Learning Objective

Distinguish between the anatomical and functional organisation of the nervous system and list the components of each.

Describe the events involved in the generation and propagation of an action potential.

List the factors that affect the speed of action potentials.

Describe the structure of a synapse.

Distinguish between an electrical and a chemical synapse.

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Central Nervous System: Brain & Spinal Cord (W4)

Lecture #10 (27.3.17)

Structures Protecting the CNS

Brain Region & Function

The Meninges

A series of membranes (fluid) that act as a “safety belt and airbag”.

3 Layers Protecting The Brain

(From Deep -> Superficial)

Pia Mater

The first layer that is attached to the surface of the brain.

 

Arachnoid Mater

Helps to provide a smooth surface of the brain and so doesn’t follow the folds of the brain. SUBARACHNOID SPACE contains CSF and acts like an airbag against sudden jolts and movements.

Dura Mater

 Fused to the cranial bones. Very good at protecting the brain.

CerebroSpinal Fluid (CSF)

Circulates in the spaces around the brain.

Provides cushioning / Supports the CNS / Transports nutrients, chemical messengers and waste products.

The choroid plexus allows the fluid out of the blood which becomes the CSF.

 

Blood Brain Barrier (BBB)

Keeps the neuronal tissue protected from the general blood circulation. The blood circulates around the body, when it does it has fluctuations (E.G. Glucose/O2). Also good for protecting against pathogens.

The BBB is produced by cells called Astrocytes which are a type of support cell. The astrocytes play an important role in monitoring what can cross over the endothelium by controlling its permeability.  If the astrocytes become damaged the blood brain barrier is removed.

4 Regions the BBB is Open

Areas of hypothalamus – where hormone diffusion occurs. Hormones produced in the neural tissue of the brain need to get out into circulation.

Capillaries around posterior pituitary – hormone diffusion. Hormones produced need to get out to general circulation.

Pineal gland (regulate our circadian rhythm)– pineal secretions into circulation.

Choroid plexus – capillaries are very permeable

 

White Matter & Grey Matter

Gray Matter

Cell bodies of neurons, neuroglia and unmyelinated axons. The cell bodies of the neurons are arranged in specific areas called nuclei.

Signal integration and command initiation: The place in the neuronal structure where we get incoming info being integrated.

Slower transport of neuronal signals (unmyelinated )

 

Ok so if we were to make a transverse section of the spinal cord and look at it from a superior view, we would see the circular shape of the spinal cord with a central grey shaped pattern that looks a bit like a butterfly, surrounded by white.

White Matter

Myelinated axons.

Carries information from place to place.

Rapid transport of neuronal signals.

Cerebrum

Conscious thought processes, intellectual functions.

Memory storage and processing.

Conscious and subconscious regulation of skeletal muscle contractions.

Cerebellum

Coordinates complex somatic motor patterns. (E.G. Motor control of technincal sporting skills / piano). Heavily involved in neuronal output to the periphery skeletal muscles.

Adjusts output of other somatic motor centres in brain and spinal cord to refine the message being sent.

Diencephalon

The diencephalon has two components…

Thalamus

Relay and processing centres for sensory information. Like a gatekeeper to determine which info coming in is actually going to reach our conscious awareness to the cerebral cortex.

Hypothalamus

Centres controlling emotions, autonomic functions, and hormone production.

The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system through its regulation of the anterior pituitary gland. Other parts of the hypothalamus are involved in memory and emotion as part of the limbic system.

Brain Stem

Mesencephalon (Midbrain)

Processing of visual and auditory data.

Generation of reflexive somatic motor responses. (E.G. Random chaotic events – explosions)

Maintenance of consciousness.

Pons

“The pons contains neurons that relay signals from the forebrain to the cerebellum, along with neurons that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.”

Vast number of neuronal connections from the pons into the cerebellum. A relay centre for lots of info.

Relays sensory information to cerebellum and thalamus.

Subconscious somatic and visceral motor centres.

Medulla Oblongata

Relays sensory information to thalamus and other portions of brain stem.

Autonomic centres for regulation of visceral function (cardiovascular, respiratory, and digestive system activities).

Limbic System

Motivational system

Functional grouping of structures rather than anatomical grouping.

Functions:

Regulation of our emotions.

Links conscious functions of cerebral cortex with unconscious and autonomic functions of brainstem.

Facilitation of memory storage and retrieval.

Important features:

Amygdaloid Bodies: responsible for linking emotions with specific memories. (E.G. A specific song linked to a specific feeling/memory)

Hippocampus: The hippocampus and amygdala are involved in long-term memory formation and emotional responses.

The Cerebrum

Longitudinal Fissure: Splits the brain in half seperating its hemispheres (anterior/sagitally). Transverse fissure: Splits the brain between the cerebrum and the cerebellum.

Sensory & Motor Areas

Primary Motor Cortex (Frontal lobe)

The primary motor cortex (M1) located in the frontal lobe, is the part of the brain that sends neural impulses down the spinal cord to the muscles to drive movement via action potentials.

The initiation of conscious commands to our skeletal muscles and voluntary motor processing.

Primary Sensory Cortex (Parietal lobe)

Receives sensory information (touch, pain, vibration, temperature).

Association Areas

These help the primary cortices in their activity. They make meaning of incoming information.

Somatic Motor Association Area (Frontal lobe)

Coordinates learned movements.

Somatic Sensory Association Area (Parietal lobe)

Monitors activities in primary sensory cortex.

Spinal Cord

 

Posterior Median Sulcus

Shallow groove that runs down the centre of the dorsal surface.

Anterior Median Fissure

Deep groove that runs down ventral surface.

Enlargments

Thickened regions of the spinal cord associated with control of the limbs.

Conus Medullaris

Conical tip, terminates at Filum Terminae.

How is info processed through the spinal cord?

We have neurons picking up info throughout the body. There may be a sensory receptor in the periphery about touch. The info comes in via the dorsal root ganglion (let and right fat bulges) which contains the cell bodies of the sensory neurons. Those neurons then send axons into the CNS to take that info in. Then when its time to send info from the CNS to the periphery (E.G. skeletal movement) that info leaves via the ventral root.

Dorsal Root Ganglia

Small bulges near spinal cord

Contain cell bodies of sensory neurons

Dorsal Roots

Contain axons of sensory neurons

Transport sensory info to spinal cord

Ventral Roots

Contain axons of motor neurons

Relay information to effectors

A Reflex Arc

Ok so we know that the spinal cord receives information from the sensory receptors via the sensory nerves that attach to the spinal cord via the dorsal root.  We know that the information is then processed and a command is generated and sent out to the effector organs and muscles via the motor neurons that travel from the ventral root and to the spinal nerves.

The way in which our homeostatic mechanisms go about this process is known as a REFLEX ARC which is made up of 5 main steps.

1. Stimulus arrival and receptor activation – our receptors can be specialised cells such as our thermoreceptors or mechanoreceptors or the dendrites of sensory nerves, which are sensitive to some sort of environmental change in the internal or external environment.

2. Activation of sensory neuron – stimulation by the receptors leads to generation of action potential in the sensory neurons

3. Information processing – release of neurotransmitter from presynaptic neuron either directly to a postsynaptic neuron or interneuron (intermediate neuron) which relays the information both to the brain and the motor neuron

4. Activation of motor neuron – action potentials are generated in the motor neurons and transported to the effector site

5. Response of peripheral effector – release of neurotransmitters onto effector – could be a muscle or a gland cell.

Point out that an interneuron is not always present in the pathway and that the information can be directly sent to a motor neuron

Learning Objectives

List the structures that support and protect the central nervous system.

Distinguish between white matter and gray matter and describe the roles they play.

Locate the six major regions of the brain and list the functions of each.

Identify the main components of the limbic system and specify their function.

Identify the main regions of the cerebrum

Identify the major sensory and motor areas of the cerebrum and list the functions of each

Describe the role of the association areas

Identify the components of the spinal cord

List the components of a reflex arc and give an example of a reflex response

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Peripheral Nervous System: Sensory & Somatic

Lecture #11 (28.3.17)

Sensory Receptors

Specialised cells or cell processes that detect changes inside or outside the body.

The job of a sensory receptor is to detects a stimulus and transduce it into an action potential which is sent to the CNS.

The frequency of arriving action potentials in CNS brings information about strength, duration and variation of stimulus.

Some information reaches primary sensory cortex and our awareness – the thalamus is the gatekeeper decides what’s relevant for our awareness.

General Senses

Provides information about the body and its environment.

(Temperature, pain, touch, pressure, vibration and proprioception).

Special Senses

Smell, taste, sight, equilibrium (balance), and hearing.

Characteristics of Sensory Receptors

Specificity (type of stimulus)

Free nerve endings: non-specific (they can pick up info about chemical, pressure, temperature, trauma)

The eye’s visual receptors: very specialised so its only light info that’s get’s to them (light only)

Receptive field

(location of stimulus)

Different receptors have their own receptive field for picking up certain info.

Types of Sensory Receptors

Tonic Receptors

Always active and firing off action potentials.

The change that occurs when its time to react to a specific stimulus can either be an increase or decrease in action potentials. They can increase the firing rate or decrease it.

Slow adapting recepotrs (pain)

Phasic Receptors

Normally inactive when in resting state.

They become active when a change in stimulus occurs. They can only increase their firing rate.

Fast adapting receptors (temperature)

Nociceptors: Pain Receptors

They are tonic receptors.

E.G. Skin, joints, bones, blood vessels

They are free nerve endings with Large receptive fields which can make it difficult to pinpoint pain on the body.

3 Main Populations

Pain can come in different types: Temperature, mechanical, chemical. If it’s a really strong stimulus it’s going to activate all 3.

Some are myelinated some are unmyleniated.

Myelinated axons: fast pain, prickling pain

Unmyelinated axons: slow pain, burning, aching sensations

Thermoreceptors: Temperature Receptors

They are Phasic receptors so there’s no activity in the resting state.

E.G. Skin, skeletal muscles, liver

We have more Cold than warm receptors. Cold to warm ratio 3:1

Cold receptors: 10-20 ºC

Warmth receptors: 25-45 ºC

This info travels along same pathways as pain sensations.

Mechanoreceptors: Touch/Pressure/Twist/Stretch Receptors

The cell membranes contain mechanically gated/regulated ion channels.

3 main types

1. Tactile

2. Baroreceptors

3. Proprioreceptors

Tactile Mechanoreceptors

Detect info about texture, shape, pulsation

Fine touch: small receptive fields (finger tips)

Crude touch:  large receptive fields (back)

They can be simple or complex.

6 Types:

Free nerve endings that pick up info about tactile stimuli (skin)

Root hair plexus: whenever we get movement across the skin we get movement of those hairs.

Tactile discs: Takes a little more deeper touch to activate these (skin)

Tactile corpuscles: (eyelids, fingertips)

Lamellated corpuscles: Quite deep – a lot more pressure. (fingers, mammary glands)

Ruffini corpuscles: Picking up info about twist/stertch – deep in skin.

It’s a combination of incoming info about these 6 types of specialised cells that gives the CNS the opportunity to integrate whats happening.

Baroreceptors Mechanoreceptors

Monitor change in internal pressure.

E.G. Blood vessels, respiratory system.

They are a type of mechanically gated stretch receptor.

They’re phasic – normally inacctive byt respond rapidly to changes, then adapt.

Proprioceptors Mechanoreceptor

Monitors the position of our limbs.

3 types:

Muscle spindles: Sending info about movement of the muscle. Skeletal muscle length and stretch reflex.

Golgi Tendon Organs: Detects tendon tension.

Joint Capsule: Detects pressure and tension in a particular joint.

Chemoreceptors

Detect changes in chemical concentration.

Phasic: Normally inactive when in resting state.

E.G. Brain, carotid arteries, aorta

Monitor chemical levels: pH, CO2 and O2 levels

Posterior Column Pathway

Here’s the pathways that information takes to the CNS.

“You don’t need to memorize everything in the next few slides – it’s not that important. Know the name of the pathway, the info it transports, the type of info and where it takes info to/from”

A receptor out in the periphery is picking up info about touch, vibration, ventral pressure or properioception. The ascending info travels in via the dorsal root ganglion -> it brings that info in via the spinal cord -> that neuron than ascends (goes upwards) which synapses … fuck this process.

Spinothalamic Pathway

Taking info from the spine to the thalamus so it must be afferent. E.G. Pain/Temperature.

Spinocerebellar Pathway

From the spine to the cerebellum so must be afferent pathway. This is subconscious and will not reach our awareness.

Incoming info about propreicptetion to the cerebellum (which we know is about movement).

Somatic Nervous System (SNS)

An efferent division of the nervous system. Info is now being initiated in the CNS and sent to the periphery – innervates skeletal muscle.

Output of SNS is under voluntary control unless its a reflex.

Controls skeletal muscle contraction.

Motor pathways

Several centers in cerebrum, diencephalon and brain stem may issue somatic motor commands as result of processing performed at subconscious level

Each pathway from the CNS to the muscle has 2 neruons in it…

Upper Motor Neuron

Cell body lies in a CNS processing center.

These neurons project to and synaps with the lower motor neuron.

Activity within the upper motor neuron may facilitate or inhibit lower motor neuron.

Lower Motor Neuron

Cell body lies in a nucleus of the brain stem or spinal cord

Triggers a contraction in innervated muscle:

The only way we can control muscle so if theres destruction of or damage to lower motor neuron it eliminates voluntary and reflex control over innervated motor unit.

Corticospinal Pathway

Starting in the cerebrul cortex to the spine = must be a efferent pathway.

Conscious control

3 main descending tracts:

Corticobulbar: to cranial nerves, control muscles of eye, jaw, face, neck

Lateral corticospinal: Conscious motor control of skeletal muscles

Anterior corticospinal: Conscious motor control of skeletal muscles

Medial Pathway

Subconscious regulation of: Eye, head, neck and upper limb position in response to visual and auditory stimuli

We also get reflex activity happening here.

–balance and muscle tone

Upper motor neuron cell bodies lie in mesencephalon

Superior colliculi

Inferior colliculi

Lateral Pathway

Subconscious regulation of: Upper limb muscle tone and movement

Upper motor neurons lie in the mesencephalon.

Levels Of Processing

 

Sensory receptors pick up info and send it towards the CNS -> we may get a reflex so that incoming neuron may synapse directly with the lower motor neuron of a somatic -> other info coming in will go to the lower relay and processing centers of the brain -> we may get a commend initiation from here -> some info reaches the thalamus which is the gatekeeper to decide which info will reach our awareness in the cerebral cortex -> at that point we can make conscious commands to innervate our skeletal muscles.

Learning Objectives

Distinguish between the sensory and somatic divisions of the peripheral nervous system.

Describe the role of sensory receptors and explain how they can respond to specific stimuli

Describe how the organisation of a receptor affects its sensitivity

Identify the receptors for the general senses and describe how they function

Identify the major sensory pathways

Explain what is meant by the somatic nervous system

Identify the somatic motor pathways

Identify the level of information processing involved in motor control

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Peripheral Nervous System: Autonomic (W4)

Lecture #12 (30.3.17)

Autonomic Nervous System

Efferent division. (Information Existing the CNS into the periphery)

Responsible for the functions of the:

Cardiovascular system, Respiratory system, Digestive system, Renal (urinary) system, Reproductive system, Subconscious control

Comparison of SNS and ANS

Somatic Nervous System

Controls skeletal muscle

Motor neurons from CNS direct control of skeletal muscle

Autonomic Nervous System

Acts on visceral effectors (internal body organs)

Motor neurons from CNS synapse in GANGLIA

The neuron that comes from the CNS is called the pre-ganglionic neurons

After the synapse it’s then called the post-ganglionic fibres – from ganglia

Ganglion: A collection of neuronal cell bodies that sit somewhere in the periphery.

ANS is under subconcious control so the cell bodies are located deeper within the brain in the hypothalamus as opposed to the cortex of the SNS.  These neurons project down into the brain stem or spinal cord where they synapse with another neuron in the ganglia which heads out into the periphery. The target tissue might me smooth muscle (organs, blood vessels), cardiac muscle, adipose sites and glands.

Divisions of the ANS

Sympathetic NS

Becomes active in times of stress. “Fight or flight”

Prepares the body for energy use and there’s an increase in metabolic rate in order to increase mental awareness.

Anatomically, the Ganglia is close to spinal cord

Short preganglionic, long postganglionic

Increased mental awareness, ­HR, ­MR, ­Resp. Reduces Digestion

Parasympathetic NS

“Rest and repose”

Energy conservation and a reduction in metabolic rate. Works during resting conditions

Anatomically, ganglia close to target organs

Long preganglionic, short postganglionic

Reduces HR, MR, ­Digestion

Organisation of Sympathetic Division of ANS

The neurons that leave the CNS do so through the thoracic and lumbar regions of the spinal cord.

Sympathetic Chain Ganglia: Some neurons leaving the CNS synapse within the sympathetic chain ganglia that then projects to the target organ (eye, mucous membrane, heart)

Collateral Glanglia: Some synapse at one of the collateral ganglias (celiac ganglion, superior mesenteric ganglion, inferior mesenteteric ganglion) and that’s where we get and the ganglion neuron projecting to the target organ (stomach, liver, pancreas, intestines).

Adrenal Medula: The neuron comes from the CNS and projects through the sympathetic chain ganglia through the celiac ganglion and continues to the adrenal gland. Note: The diagram is wrong because it shows there is a synapse in the celiac ganglion for this neuron which is not correct -there’s no synapse in this ganglion. In the adrenal medulla we have some modified neuronal cells that are responsible for releasing adrenal and nor adrenaline into the blood stream.

Neurotransmitters of the Sympathetic Division

The most common neurotransmitter released onto a target organ by the sympathetic division (sympathetic ganglionic neurons) release: Noradrenaline

A small number of sympathetic ganglionic neurons release: Acetylcholine

The adrenal (suprarenal) medullae gland releases: Adrenaline & Noradrenaline

Organisation of the Parasympathetic Division of the ANS

When the neurons leave the CNS they do so in the superior and inferior parts of the spinal cord. The superior ones leave the CNS via the cranial nerves (III, VII, IX, X) X = the vegas nerve, a very large neuronal tract. Ganglionic neurons sit outside the organs and to do with the head and neck region type innervation.

The vegas nerve and pelvic nerve synapses through a intra(within) mural (wall) ganglia = within the wall of the target organ.

 

Neurotransmitters of the Parasympathetic Division

Always acetylcholine.

Autonomic Nervous System

Because of the anatomical differences where the ganglia are close to the CNS for the sympathetic it means the sympathetic division has widespread effects.

Whereas the pre ganglionic neurons of the PNS go all the way to the target organ so they can be controlled we get local effects instead.

Duel Innervation

Innervation: Talking about a nerve going to somewhere and creating a response.

For any one organ we’ve got both sympathetic and parasympathetic neurons coming in. Both subdivisions send neurons to a particular organ.

The effect of two systems on that organ is the OPPOSITE.

Example: The Heart

The sympathetic division becomes active and increases HR (during activity or stress)

Parasympathetic division decreases HR (during rest)

Balance depends on body requirements

Example: The Digestive System

Sympathetic division inhibits activity of digestive system (during activity or stress)

Parasympathetic division stimulates activity of digestive system (during rest)

Balance depends on body requirements

[Left side] We have synapse on the right ganglionic neuron and it projects onto its target organ releasing noradrenaline (green arrow). Left ganglionic neuron: it’s job is to release adrenaline and noradrenaline into the circulatory system which then reach the target organ.

Adrenalin (UK) = Epinephrine (US) / Noradrenaline (UK) = Norepinerphrine (US)

On the parasympathetic side we have this long preganglionic neuron and the gabglion is close to the target tissue were we have the release of acetylcholine.

Regardless of which side we look at, the preganglionic neuron is always releasing acetylcholine.

Learning Objectives

Compare and contrast the autonomic and somatic nervous systems

Identify the divisions of the autonomic nervous system and give the functions of each

Describe the structures and functions of the sympathetic division of the autonomic nervous system and the general effect on target organs and tissues

Describe the structures and functions of the parasympathetic division of the autonomic nervous system and the general effect on target organs and tissues

Outline what is meant by dual innervation

Quiz #2 Prep (W6)

In what way do the pre- and post-central gyrus work together in controlling behaviour?

The postcentral gyrus (primary somatosensory cortex) is first involved in semotosensation which gives the body surface info about where it is and how it interacts with its environment – i.e. touch/pressure. So upon picking up a chair, your post central gyrus receives an interpretation of how heavy the chair is, that info interacts with the precentral gyrus (primary motor cortex) which recruits necessary motor units to lift the object. As you lift the chair and find your postcentral gyrus hasn’t recruited enough motor units it intereacts with the precentral gyrus to adjust its feedback in order for you to correctly recruit enough motor units to life the object. This feedback loop is constantly going back and forth between each gyrus to adjust to the environment as efficiently as possible.

Know how to label a sheep brain and be ready to describe the function of 1-2.

Endocrine System #1 (W5)

Lecture #13 (3.4.17)

Organs & Tissues of the Endocrine System

Comparison Between the Nervous & Endocrine Systems

If it’s released at the synapse  = neurotransmitter. 

If it’s released in the blood = hormone.

Chemical Classes of Hormones

Another reason why cholesterol is important to intake because it’s a building block for our steroid hormones.

Amino Acid Hormones

Tyrosine is important for the creation of catecholamines, which is a term we use to refer to adrenalin, noradrenalin, dopamine et al.

Tryptophan is the building blocks for melatonin released by the pineal gland for circadien rythem regulation.

Peptide Hormones

Steroid Hormones / Lipid Derivatives

Cell Membrane Hormone Action

E.G. Catecholamines, peptide hormones

Hormone (first messenger) reaches the target cell -> the receptor is located in the cell membrane and it binds to it which creates an internal response -> Second messenger -> Metabolic reaction to alter cell activity

Water-soluble hormones cannot diffuse through the cell membrane. These hormones must bind to a surface cell-membrane receptor. The receptor then initiates a cell-signaling pathway within the cell involving G proteins, adenylyl cyclase, the secondary messenger cyclic AMP (cAMP), and protein kinases. In the final step, these protein kinases phosphorylate proteins in the cytoplasm. This activates proteins in the cell that carry out the changes specified by the hormone.

Intracellular Hormone Action

Lipid derived hormones E.G. Steroid hormones

Lipid hormone -> Diffuses through cell membrane -> Forms hormone-receptor complex -> Activates/inactivates specific genes -> Changes target cell structure

Effects of Intracellular Hormone Binding

A steroid hormone directly initiates the production of proteins within a target cell. Steroid hormones easily diffuse through the cell membrane. The hormone binds to its receptor in the cytosol, forming a receptor–hormone complex. The receptor–hormone complex then enters the nucleus and binds to the target gene on the DNA. It’s job is the transcription of the gene which creates a messenger RNA that is translated into the desired protein within the cytoplasm.

Mechanisms of Hypothalamic Control Over Endocrine Function

Hypothalamus: Influences both endocrine and nervous systems

1st Photo: Neurons producing a chemical messenger that get’s released into the blood at the posterior pituitary.

2nd Photo: Neurons project only to the base of the brain releasing their chemical messenger to a set of blood vessels that transport that blood to the anterior pituitary where they regulate the production of hormones.

The Pituitary Gland

Infundibulum: Where pituitary attaches to brain

Anterior Pituitary (Adenohypophysis): Secretes 7 different hormones

Posterior Pituitary (Neurohypophysis): Releases 2 hormones

Hypophyseal Portal System: Specialised capillary system to allow communication between hypothalamus and pituitary

General pattern of feedback control of endocrine secretion

Thyroid releasing hormone (top right) stimulates the anterior pituitary to release thyroid stimulating hormone, which stimulates the thyroid to produce thyroid hormones. The thyroid hormones have their influence over the mitochondria to increase metabolic rate.

Iodine is responsible for the production of thyroid hormones. So what happens if we are iodine deficient. We don’t get as much of the thyroid hormones (T3, T4) being produced so we end of having a absence of ‘negative feedback’ to say ‘turn down your activity of the hypothalamus & pituitary gland’. So in the absence of the thyroid hormones TRH -> TSH is being released a lot more which continually stimulates the thyroid gland which is when we get an enlarged thyroid gland. Because the thyroid is getting all all this stimulation but it can’t do it’s job because it doesn’t have the requisite iodine.

Variations to the General Pattern of Feedback Control of Endocrine Secretion

The PRF stimulates our anterior pituitary lobe to release prolactin which works on the mammary glands to increase milk production. There’s also a prolactin inhibiting factor coming from the hypothalamus to reduce the release. The same is the case of growth hormone, there’s a releasing and inhibiting function – depends on circumstance.

Hormones of the Anterior Pituitary

Thyroid stimulating hormone (TSH): Triggers thyroid hormone release

Adrenocorticotropic hormone (ACTH): Stimulates hormone release from adrenal cortex. (Adreno = adrenalin / cortico = cortex / tropic = promoting growth)

Follicle stimulating hormone (FSH): Follicle development, sperm differentiation

Luteinising hormone (LH): Triggers ovulation in females, stimulates sex hormone adregen production in males

Prolactin (PRL): Mammary gland development, milk production

Growth hormone (GH): Cell growth and replication

Melanocyte stimulating hormone (MSH): Skin pigmentation

Pituitary \Hormones and Their Targets

Posterior Pituitary Hormones

Antidiuretic Hormone (ADH) / Arginine Vasopressin

 Reduces water loss at kidneys / Vasoconstriction of peripheral blood vessels

Oxytocin (OXT)

In females, stimulates smooth muscle of uterus and mammary glands

In males, stimulates smooth muscle of sperm duct and prostate gland

Learning Objectives

List the major glands and tissues of the endocrine system

Compare and contrast the nervous and endocrine systems

Compare the major chemical classes of hormones

Distinguish between cell membrane and intracellular hormone action

Describe the role of the hypothalamus in controlling endocrine activity

Describe the structure of the pituitary gland and its association with the hypothalamus

List the hormones produced by the pituitary gland and specify the function of each

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Endocrine System #2 (W5)

Lecture #14 (4.4.17)

Pancreatic islets (Islets of Langerhans)

Alpha cells: Produce Glucagon. Glucagon is a counterregulatory hormone which has the opposite effects to insulin. When glucose levels are low in the body glucagon releases to  in ↑ glucose levels in the blood.

Beta cells: Produce Insulin. Insulin’s role is to ↓ blood glucose levels in the blood and promote the uptake of glucose into cells

Blood glucose levels are kept to a tight homeostatic range. So whenever it increases the body tries to get it back to baseline levels, whenever it decreases the body tries to get it back up.

Delta Cells: Produce GH-IH (growth hormone inhibiting hormone) – inhibits insulin and glucagon release. Why would you want to inhibit these growth processes?

F Cells: Release pancreatic polypeptide which regulates digestion and appetite regulation.

Pancreas: Hormone Action

Insulin

Beta (b) cells

Uptake food. Responds to ↑ glucose levels

↑ speed of glucose uptake and use

It’s role is to get the glucose into the cell so it can be formed into glycogen and stored.

Glucagon

Alpha (a)  cells

Responds to ↓ glucose levels

When glucose is low it’s role is to stimulate the breakdown of glycogen and fatty acid catabolism.

It stimulates glucose production in liver – gluconeogenesis: the generation of new glucose. (eneration of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids.)

Rising Blood Glucose Levels

Consume food -> Glucose levels IN -> Pancreatic islets detect change -> beta cells release insulin -> insulin triggers the cells to uptake glucose from the blood and use glucose in it’s metabolic processes -> while that’s happening we also get the inhibition of glycogenolysis (lysis = break down) which is the breakdown of glycogen because we’re already getting a surge of glucose into the body we don’t need anymore being liberated from our glycogen stores -> insulin will also inhibit gluconeogensis (inhibit the production of new glucose) because we already have an oversupply -> so it takes it up and reduces the production of glucose and by doing that it decreases the levels of glucose in the blood stream which brings us back to homeostasis.

Declining Blood Glucose Levels

E.G. Fasting causing a drop in blood glucose levels -> alpha cells of pancreatic islets recognise change and produce glucagon which inhibits the cells from uptaking glucose so it remains available in the blood stream -> stimulates glycogenolysis (the breakdown of glycogen into glucose) and also stimulates gluconeogenesis – those substrates will be produced into glucose in the liver to produce new glucose for use and be released into the blood stream to get body back to homeostatic levels.

Adrenal Gland (Suprarenal Gland)

Adrenal Cortex: Corticosteroids

Zona Glomerulosa (outer) – Produces mineralocorticoids (Oid = steroid)

Example: Aldosterone

Acts on kidney to conserve sodium (Na+) and secrete potassium (K+) ions to promote the re uptake of sodium ions back into the body so it’s not lost completely through urine.

Secondary effect is to enhance reabsorption of water

Zona Fasciculata (middle) – Produces Glucocorticoids

Example: Cortisol

Promotes glucose synthesis and glycogen formation in the liver (similar functions to glucagon). It’s released during fasting or times of stress – it’s job is to mobilize fuel stores.

Promotes the breakdown of amino acid and lipid mobilisation which get used for glucose synthesis in the liver.

Reduces inflammation in allergic reactions (E.G. Topical creams)

Zona Reticularis  (inner) – Produces Androgens

Example: Androgens

Unimportant source of androgens in males because the testes produce most of the adregens

Assists in blood cell formation, bone and muscle growth in females.

Adrenal Medulla: Catecholamines

Adrenal Medulla: Inner most portion of adrenal gland

Two types of secretory cells: Primarily secretes adrenaline and small amounts of noradrenaline

  Hormone Actions:

Increases energy utilisation and mobilisation of energy reserves. Adrenalin works alongside glucagon and cortisol to mobilize energy stores in times of stress/emergency.

Increases cardiac activity and blood pressure

Thyroid Gland

Location Of Thyroid

Thyroid Follicles & Parafollicular Cells

The thyroid gland lies across the anterior surface of our trachea.  It is made up of THYROID FOLLICLES which are lined with cuboidal epithelium and contain a COLLOID or viscous solution of proteins.  The follicle cells synthesise THYROGLOBULIN which is  protein that contains the amino acid TYROSINE – the amino acid from which thyroid hormones are made.

Thryroid: Hormone Action

Thyroxine (follicular epithelium)

T4 which has 4 iodide ions. The iodine we consume through our foods helps the regulation of thyroid

Triiodothyronine (follicular epithelium)

T3, 3 iodide ions

T4 and T3 carried in blood by transport proteins

T3 responsible for thyroid hormone actions

Act via intracellular receptors

Calcitonin (Parafollicular cells)

Regulates Ca2+ concentration in the extracellular fluid. If calcium ions get too high then calcitonin get’s released.

Effects of Thyroid Hormones

T3 and T4: Thyroid hormones are about increasing metabolic rate.

Elevate oxygen and energy consumption, body temperature rise in children

Increase heart rate and force of contraction, rise in blood pressure

Increase sensitivity to sympathetic stimulation

Maintain sensitivity of respiratory centers to changes in oxygen and carbon dioxide

Involved in red blood cell formation (increases capacity for oxygen delivery)

Stimulate other endocrine tissues

Calcitonin

Accelerates turnover of bone minerals

Parathyroid Glands

Associated with the thyroid gland are the PARATHYROID GLANDS which lie in the posterior surfaces of the thyroid.  Two types of cells are present in the parathyroid glands – CHIEF CELLS – produce PARATHYROID HORMONE, OXYPHILS – other type of cell and their function is not yet known.

Parathyroid Glands – Hormone Action

Parathyroid hormone (Chief cells) Involved in calcium ion regulation.

Released in response to ↓ Ca2+ concentration

Stimulates bone (osteoclasts – degrade bone) to release Ca2+

Inhibits bone (osteoblasts – job is to produce new bone) uptake of Ca2+

Increases Ca2+ reabsorption in kidneys

Increases gastrointestinal tract absorption of Ca2+ via calcitriol to increase the uptake of calcium in our food

Hormones of the Parathyroid Glands

Regulation of Calcium Ion Concentrations

Organs & Tissues of the Endocrine System

Learning Objectives

Describe the basic structure and location, and identify and describe the main function of the hormones produced by the pancreas

Describe the basic structure and location, and identify and describe the main function of the hormones produced by the adrenal gland

Describe the basic structure and location, and identify and describe the main function of the hormones produced by the thyroid gland

Describe the basic structure and location, and identify and describe the main function of the hormones produced by the parathyroid gland

Questions

Hypothalamic releasing and release-inhibiting hormones are transported from the hypothalamus to the anterior pituitary by way of what?

The hypophyseal portal system

The release of what 2 hormones are stimulated by elevated levels of ACTH?

Aldosterone and cortisol

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Blood (W5)

Lecture #15 (6.4.17)

Transport: Gases (O2), heat, nutrients (glucose), wastes (H+), hormones.

Regulates body temp: Role in thermoregulation

Monitors extracellular fluid pH & ion concentration: Contains buffers that absorbs acids and removes or supplies ions

Minimises fluid loss: Contains Clotting factors

Defence against pathogens: White blood cells

Components of Blood

Haematocrit refers tot he % of RBC. Males have 42-52% of total blood volume and females about 10% lower.  This is one of the reasons why males are naturally superior in athletic “endurance” performance. Anaemia refers to lower red blood cell volume, or more specifically less O2 carrying ability and a high red blood cell fraction above 55% is referred to as polycythaemia.

Heavy components accumulate at the bottom.

Fluid connective tissue

Matrix: Plasma – suspension of proteins

Cell component (formed elements): (Cytes = cell)

Red blood cells (Erythrocytes) Transports O2 to cells

White blood cells (Leukocytes): Involved in immune response

Platelets: Responsible for clotting/reducing fluid loss

Learning Module

Composition & Functions of Plasma

Water: 92%

Transports organic and inorganic molecules, formed elements and heat

Plasma Proteins: 7%

Albumins – Disolved into the plasma, because of that they create osmotic pressure of plasma; transports some hydrophobic molecules such as lipids, steroid hormones

Globulins – transports ions, hormones, lipids; also has role in immune function

Fibrinogen – component of clotting; converted to insoluble fibrin

Regulatory proteins – enzymes, proenzymes, hormones

Other Solutes: 1%

Electrolytes – extracellular fluid ion composition; ions contribute to osmotic pressure; major electrolytes are Na+, K+, Ca2+, Mg2+, Cl–, HCO3–, HPO4–, SO42–

Organic nutrients – Glucose required for ATP production, growth, and maintenance of cells; include lipids, carbohydrates and amino acids

Organic wastes – Carried to sites of breakdown or excretion; include urea, uric acid, creatinine, bilirubin, ammonium ions

Red Blood Cells

Structure:

Flattened, circular. Bi-concave cell

No nucleus, mitochondria or ribosomes. Red.

Function:

Transports O2 from lungs to tissues. Cellular processes produce a waste called CO2 which blood transports from tissues to lungs.

Bi-concave discs:

Gives us a large surface area to volume relation which is useful for the exchange of the surrounding tissues – for O2 to get in and out.

Enables ‘stacking’ in vessels allowing them to move and twist to move through capillaries

Flexibility

No nucleus or mitochondria

Rely on plasma glucose for ATP production

Ensures oxygen delivery to cells and tissues

Short life span

3-4 months. They become damaged and are recycled often. It can’t undergo cellular division to create new red blood cells. Once the RBC have lived their useful life they are broken down and their components are recycled.

Haemoglobin

Haemoglobin accounts for around 95% of the cellular protein.

Haemoglobin is the molecule responsible for the RED pigmentation of RBCs and is also what binds and transports O2 and CO2.

Main RBC cellular protein

Causes red pigmentation

Transports oxygen and carbon dioxide

Complex structure: 2 alpha, 2 beta chains. In each of those chains we have a Heme molecule. The job of the heme molecule is the transport of O2. Right in the center of that we have Fe2+ ion – binds oxygen.

Releases O2 when plasma O2 levels low: tissues

Binds O2 when plasma O2 levels are high: lungs

Abnormal Haemoglobin

Sickle Cell Anaemia

Defect in beta chain of the haemoglobin molecule.

RBC becomes stiff and curved when Hb releases O2 – losses it’s ability to be flexible and stack with other cells.

Problems include:

Blocking of capillaries

Pain and damage to organs

Platelets

Don’t need to memorize the names. 

Structure

Round to spindle-shaped cytoplasmic fragment

Contain enzymes, proenzymes, actin and myosin

No nucleus

Function

Transport of chemicals to clotting process/hemostasis – platelets release chemicals that help to initiate and regulate the clotting process.

Temporary patch formation – the platelets clump together at an injury site to form a ‘platelet plug’ whilst the other components in the clotting process are getting organised to develop a clot.

Contraction of a Clot – the platelets have an important role in shrinking the size of a clot once the clot has formed to reduce the size of the break in a vessel wall. (Where actin and myosin are involved)

Hemostasis (blood clotting)

1. The vascular phase –damage to a blood vessel wall triggers a contraction in the smooth muscle layer that surrounds the vessel. This is called a VASCULAR SPASM. The spasming acts to decrease the diameter of the blood vessel and hence reduce the amount of blood flowing through. The endothelial cells lining the blood vessel release chemicals that make them become sticky to help in the repair process.

2. The PLATELET PHASE – platelets attach to the sticky endothelial cells. This is called PLATELET ADHESION. As more and more platelets arrive on the scene they aggregate to form the PLATELET PLUG. The platelets also begin to release chemicals to stimulate the clotting process.

3. COAGULATION PHASE – in this phase, the chemicals released by the platelets initiate the conversion of FIBRINOGEN – one of the plasma proteins to FIBRIN. The fibrin forms insoluble strands that form a meshwork which enables a clot to form.

4. FIBRINOLYSIS – as the damaged vessel is repaired, a clot will gradually dissolve. This process is called FIBRINOLYSIS and results in the fibrin strands being digested and eventually removed.

White Blood Cells

Major role in immune defense

Specialised characteristics

Migration out of bloodstream: remove pathogens from body

Amoeboid movement: Push their cytoplasm into a part of the cell that is extended out in front of them

Attraction to specific stimuli: Invading pathogens, damaged tissues, and other WBC’s

Phagocytosis: Capable of engulfing (eating) pathogens

Neutrophils: 40/50-70% of WBC

Part of the innate immune response and are the first responders.

Structure

Round cell

Nucleus lobed and may resemble a string of beads

Cytoplasm contains large pale inclusions

Function

Phagocytic: Engulfs pathogens or debris in tissues, releases cytotoxic enzymes and chemicals onto whatever it is to break it down

Eosinophils: 2-4% of WBC

Structure

Round cell

Nucleus generally in two lobes

Cytoplasm contains large granules that generally stain bright red. It’s more dense.

Function

Phagocytic: Engulf anti-body labeled materials, release cytotoxic enzymes, reduce inflammation

Increases in allergic and parasitic situations and releases histamine

Basophils: <1% of WBC

Structure

Round cell

Nucleus generally cannot be seen through dense, blue-strained granules in cytoplasm

Function

Enter damaged tissues and release histamine – useful because they promote inflammation in order to speeed up repair of tissues

Monocytes: 2-8% of WBC

Structure

Very large cell

Kidney bean-shaped nucleus

Abundant pale cytoplasm

Function

Enter tissues to become macrophages (large eating cells) and dendritic cells

Engulf pathogens or debris

Lymphocytes: 20-30% WBC

Structure

Generally round cell, slightly larger than RBC

Round nucleus

Very little cytoplasm

Function

Cells of lymphoid system, providing defense against specific pathogens or toxins. E.G. Chicken pox/measels- specific pathatgons

Three functional classes:

T cells – Thalamus derived (cell mediated response: the T cell itself has to go to the location of the problem to have an affect)

B cells – Bone marrow derived (antibody response)

T and B cells might be dealing with the same pathagon. The T Cell will go to it and B cell won’t go to it, but it will release anitbodies into the blood which will then go the pathagon.

Natural killer (NK) cells (surveillance): Their job is to move around the body looking for potential problems. These NK cells are responsible for locating and killing off thigs like cancerous cells

Learning Module

Learning Objectives

List the major functions of blood

Describe the components of blood

Discuss the composition of plasma and list its functions

List the characteristics and function of red blood cells

Describe the function of haemoglobin

Describe the structure and function of platelets

Categorise the various white blood cells on the basis of their structure and function

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The Heart (W6)

Lecture #16 (20.4.17)

The heart is a double pump that has two main actions:

Pulmonary Circulation: Delivers blood to lungs

Systemic Circulation: Delivers blood to body

Location Of The Heart

Rests in the pericardial cavity/chest wall slightly left of the sternum. The pericardial cavity protects the heart from surrounding tissues.

The base of the heart is at the top where the major blood vessels attach. The apex is at the bottom of the heart designed to help with blood flow.

Features Of The Heart: 4 Chambers

Atria (Atrium)

The 2 most superior chambers at the base.

Thin muscular walls because they only act as receiving chambers – returning from the lungs or body.

Ventricles

Thicker muscular walls (especially left) because they’re responsible for pumping blood into the lungs and body.

Arteries

Carry blood AWAY from the heart. If the ventricles pump blood to the body than you’re going to have arteries attached to them to facilitate moving blood away from the heart.

Veins

Carry blood TO the heart. So if our atria are our receiving filling chambers than you’re probably going to have veins attached to them because their bringing blood back to the heart.

The right ventricle isn’t as large because it’s only ejecting blood into the lungs which are relatively close to the heart.

RIGHT ATRIUM – receives the blood that has been circulating through the body (systemic circulation).  It has two major blood vessels (veins) associated with it, the SUPERIOR VENA CAVA, which receives blood from the head and upper body regions and the INFERIOR VENA CAVA which receives the blood from the trunk and lower limbs.

The right atrium pushes the blood that it receives into the RIGHT VENTRICLE.  The blood travels through an opening that is bound by three fibrous flaps.  These flaps make up a VALVE – the RIGHT ATRIOVENTRICULAR VALVE (AV) valve or TRICUSPID VALVE.  The flaps are attached to the heart by connective tissue fibres called the CHORDAE TENDINAE.  This valve is important for preventing back flow of blood into the atria.  So when the right ventricle contracts, the valve snaps shut so that blood will only flow out of the ventricle and not back into the atria (like a one way door).

RIGHT VENTRICLE – also has a major blood vessel (artery) associated with it the PULMONARY ARTERY.  The PULMONARY ARTERY divides into two branches, the LEFT and RIGHT PULMONARY ARTERIES which carry the blood to the lungs for oxygenation.  The right ventricle also has a valve where the pulmonary artery leaves the ventricle.  This valve is called the PULONARY VALVE and this also prevents back flow of blood when the ventricle relaxes.

You have blood coming from the systemic circuit into the pulmonary circuit and bloods getting oxygenated as we drop off CO2 and pick up O2. We now want to bring that blood back to the heart so it comes via the left side.

Once the blood has circulated via the PULMONARY CIRCULATION and has become oxygenated it travels back to the heart to the LEFT ATRIUM

LEFT ATRIUM – receives blood from the lungs or pulmonary circulation. It has major blood vessels (veins), the PULMONARY VEINS.  The RIGHT PULMONARY VEIN and the LEFT PULMONARY VEIN.  Like the right chambers of the heart it has a VALVE called the LEFT ATRIOVENTRICULAR valve or the BICUSPID VALVE which prevents back flow of blood from the left ventricle into the atrium.

The LEFT VENTRICLE – receives blood from the left atrium.    It has very thick muscle walls as its role is to pump the blood around the systemic circulation.  The left ventricle also has a major blood vessel (artery) extending from it, the AORTA the major artery of the body. There is also a valve that lies between the left ventricle and the aorta, the AORTIC VALVE which prevents back flow of blood into the left ventricle.

Blood flow through left ventricle

This is to show what happens during a contraction.  This is when the ventricles are relaxed.

Point out – atria are squeezing and blood is flowing into the ventricles.  While the ventricles are relaxed the pulmonary and aortic valves are closed to stop back flow of blood into the ventricles.

When the ventricles contract, the bicuspid (and tricuspid) valves close and the aortic and pulmonary valves open.  The bicuspid and tricuspid close to prevent back flow into the atria and the aortic and pulmonary valves open to allow blood to enter the vessels leaving the heart.

Valves Of The Heart

When the ventricles contract, the bicuspid (and tricuspid) valves close and the aortic and pulmonary valves open.  The bicuspid and tricuspid close to prevent back flow into the atria and the aortic and pulmonary valves open to allow blood to enter the vessels leaving the heart.

The Conducting System of the Heart

The heart has it’s own ‘switch board’ called Nodal Cells create an autorhymthic state in the heart.

Ok so we have the general idea that the heart pumps the blood around the body.  But what we haven’t really talked about yet is the specialised way in which this happens.  When our heart beats, the muscles of the atria and ventricles don’t simultaneously contract.  If that happened the blood wouldn’t go anywhere.  What actually happens within a very short time period is that the atria contract first, followed by the ventricles.

This is under a tight control system or CONDUCTING SYSTEM.  We’ve previously talked about cardiac muscle as just being made up of the muscle or contractile cells.  The heart also contains specialised cells that control and co-ordinate our heart beat.  Because our heart continuously beats and is not under hormonal or neural control, this AUTORHYTHMICITY is due to these specialised cells that make up the NODAL SYSTEM.

The NODAL system initiates and distributes the electrical impulses that stimulate our cardiac muscle cells to contract.

The nodal system contains two main elements

The SINOATRIAL NODE (SA node)

Lies in the wall of the right atrium where hundreds of pacemaker cells lay and fire action potentials

The ATRIOVENTRICULAR NODE (AV node)

Which lies at the junction between the atria and the ventricles. Slow rate of spontaneous ventricles.

The nodal system also contains CONDUCTING CELLS which connect the two nodes and spread the electrical impulse throughout the heart muscle.  Point out diff between NODAL and CONDUCTING CELLS

The conducting cells of the SA and AV nodes spontaeneously generate action potentials.  The SA node is faster than the AV node.  Because it is faster, the SA node is the node that sets the pace or rate of heart beats – it is known as the PACEMAKER.

Impulse conduction through the heart

1) The sinoatrial (SA) node and the remainder of the conduction system are at rest. (2) The SA node initiates the action potential, which sweeps across the atria. (3) After reaching the atrioventricular node, there is a delay of approximately 100 ms that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle. (4) Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibers, and also reaches the right papillary muscle via the moderator band. (5) The impulse spreads to the contractile fibers of the ventricle. (6) Ventricular contraction begins.

An Electrocardiogram (ECG)

Detects electrical events of the heart via electrodes (body surface)

Specific nodal, conducting, and contractile components of heart

The Cardiac Cycle

Alternating contraction and relaxation of the atria and ventricles

Systole

Chambers contract

Blood moves to next chamber (in the case of atria) or blood vessel (in the case of ventricles)

Diastole

Chambers relax

Fill with blood

Atrial systole and diastole

Ventricular systole and diastole

Phases of the cardiac cycle

 

Point out early and late systole and diastole where pressure difference – early systole pressures are building but not enough to open Av or semilunar valves.

Early ventricular diastole – relaxation to close semilunar valves to prevent backflow blood is flowing into atria.

Late diastole low pressure in ventricles allows av valves to open and passive filling of ventricles occurs.

Describes how electrical events of the heart work in conjunction with the mechanical events of the heart.

Timing of Heart Sounds

The sound you hear of heart beat is the valves opening.

Cardiac Output

Cardiac Output (Q) = The amount of blood pumped by the heart in one minute (L.min-1)

Cardiac Output = HR x SV

HR = heart rate (bpm or b.min-1)

SV = stroke volume (mL.beat-1)  = The volume of blood pumped from the left ventricle per beat.

Example

If HR is 75 bpm and SV is 80 mL.beat-1

CO = SV (mL.beat-1) x HR (bpm or b.min-1)

= 75 x 80 = 6000 (mL.min-1) = 6 L.min-1

Factors Affecting HR

Factors Affecting SV

Learning Objectives

Describe the location and general features of the heart

Trace the flow of blood through the heart, identifying the major blood vessels, chambers and heart valves

Describe the components and functions of the conducting system of the heart

Identify the electrical events associated with a normal electrocardiogram

Distinguish between systole and diastole

Describe the phases of the cardiac cycle and the changes in pressure and volume that occur during each phase

Describe how the heart sounds are produced

Define cardiac output

Describe the factors that influence heart rate and stroke volume

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Blood Vessels (W7)

Lecture #17 (24.4.17)

Distribution of Blood

Venous system

65-70 % of blood volume. The majority of your blood in your body is sitting in your venous system: about 3.5 litres. Our veins act as reservoirs to temporarily store blood

Everything else (heart, arterial system, capillaries)

30-35 % of blood volume: about 1.5 litres

Blood Vessels

Five classes (listed in order of appearance):

1. Arteries

Conduct blood away from heart

2. Arterioles

Branch into tissues. Like tunnels/networks going into a hill.

3. Capillaries

Inside the tissues there will be capillaries which are responsible for gas/nutrient exchange

4. Venules

Capillary merging.

5. Veins

Return blood to heart

Blood Vessel Structure

Tunica MEDIA – middle layer of the blood vessel wall.  Contains layers of smooth muscle and connective tissue.  This is generally the thickest layer of the blood vessel.  

  Tunica EXTERNA – outermost layer of a blood vessel and forms a connective tissue sheath.  It has an important role in anchoring the blood vessels to the surrounding tissues.

Arteries Structure & Function

The arteries have relatively thick muscular and elastic walls which allows them to change their diameter in response to blood pressure changes

Under the direction of the autonomic nervous system they are able to VASOCONSTRICT (make their diameter smaller) or VASODILATE (make their diameter larger) due to innervation of the smooth muscle in the Tunica media layer.

We have two main types of arteries

Elastic Arteries – transport large volumes of blood away from the heart, highly flexible walls due to large amounts of elastic fibres in the tunica media.

Muscular Arteries – transport blood in the skeletal muscle and internal organs. Thick smooth muscle layer in the tunica media.

Arterioles Structure & Function

Arterioles are much smaller than arteries.  They don’t have as thick a smooth muscle layer in the tunica media as arteries. However, they are still able to change their diameter when influenced by autonomic or endocrine signals.

A change in the diameter of the arterioles affect how much force is needed to move blood through the cardiovascular system.

More effort or pressure is required to push blood through a constricted one than a dilated one.  The effort required is to work against the RESISTANCE of the smaller vessels and so arterioles are known as RESISTANCE VESSELS.

Capillaries Structure & Function

Continuous Capillaries

There are two types of capillaries.

CONTINUOUS CAPILLARIES – most common type of capillary.   Endothelial layer surrounding the vessel is continuous. Found in all tissues except epithelium and cartilage.  Allow the diffusion of water, small solutes and lipid soluble material.  Don’t allow proteins or RBC to escape.  These capillaries have an important role in the brain particularly in the BLOOD BRAIN BARRIER because they are able to tightly monitor what moves across their surfaces.

Fenestrated Capillaries

FENESTRATED CAPILLARIES – have pores in their endothelium which allow rapid exchange of water and solutes.

Organisation of a Capillary Bed

Arterioles can divide into a number of capillaries that will then drain into a venule.

A band of smooth muscle sits at the arterial side of each capillary which is called the PRECAPILLARY SPHINCTER.  The role of the sphincter is to control the flow of blood entering the capillaries.

When the sphincter relaxes, more blood can flow in, when the smooth muscle contracts, less blood can flow in.

Concentrate on artery side only for minute. GO THROUGH SLOWLY

Capillary networks within an area may be supplied by more than one artery or arteriole – Collaterals

Guarantee blood supply to the tissues

Flow of blood into capillary networks is controlled by

Pre-capillary sphincters Direct interconnections with venules called arteriovenous anastomoses. Impportant in regulating flow in the capillary bed.

Capillaries don’t function alone, instead they work in networks called CAPILLARY BEDS

Venules Structure & Function

The capillaries merge to form VENULES.  These are the first vessel on the VENOUS side of the cardiovascular system and contain the blood from which some of the oxygen has been utilised in the tissues.  Many lack a tunica media and merge to form larger veins.

Mechanisms Assisting Blood Flow

Our veins continually merge until they form the superior vena cava and inferior vena cava, the two major veins of the circulatory system.

They have much thinner walls than arteries because the pressure in the veins is not as high as in the arteries.  Veins tend to have a larger lumen diameter than arteries.

The veins also contain VALVES.  We have previously talked about how pressure on the venous side of the circulatory system is quite low and there is not much pressure to oppose the force of gravity.  Valves are specialised flaps that point in the direction of blood flow and snap back shut to prevent any back flow of the blood.

Comparison of Arteries & Veins

Entry & Exit Of Fluid And Dissolved Materials From The Cardiovascular System

Gas/Nutrient exchange only occurs at capillaries

EXAMPLE:

Gases (O2 & CO2) via diffusion down a pressure gradient in the lungs and other tissues

Water via osmosis in the kidneys

Electrolytes down a concentration gradient in the kidneys and gastrointestinal tract

Glucose and amino acids via membrane transporters in most tissues, particularly muscle (for exercising fuel) and GI-tract (absorption)

Learning Objectives

Describe the general plan for the distribution of blood

On the basis of their structure and function distinguish between:

• arteries (elastic and muscular),
• arterioles,
• capillaries (continuous and fenestrated),
• venules and veins (medium-sized and large)
• Describe the mechanisms that assist blood flow in veins
• Describe how and where fluids and dissolved materials (nutrients, gases and wastes) enter and leave the blood vessels

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Cardiovascular Regulation (W7)

Lecture #18 (27.4.17)

Exchange At The Capillaries

Diffusion

Primary source by which we get movement of substances.

Occurs at the capillaries in a number of ways:

Through pores in fenestrated capillaries or between adjacent endothelial cells (e.g. water and electrolytes)

Via transporters or channels in the capillary endothelial cell membrane (e.g. glucose, amino acids)

Lipid soluble (diffuse through a bilayer/endothelial lining) substances can diffuse through the capillary endothelial cell membranes (e.g. steroids/fats)

Blood pressure is clearly not constant. We can see in the aorta that BP is sporadic as heart beats and pressure changes.

As we move further away from the heart BP declines – this is good because we need a pressure gradient in order to enable blood to flow.

BP is low in the capillaries (a good thing) – reduces pressure on those blood vessels (if you had large amounts of BP on those vessels they’d burst). Blood flow is also very slow through the capillaries to enable increased rates of diffusion/osmosis.

How do we get exchange at the capillaries? We can either get them by…

Filtration

Due to hydrostatic pressure

Forces fluid out of capillary

Proteins remain in blood

Filtration: water is forced across the capillary wall due to the driving force of the blood pressure or HYDROSTATIC PRESSURE out of the capillary bed. When water is forced across, molecules that are small enough to move between the endothelial cell membranes also move into the ecf.  Larger molecules such as proteins are unable to cross and remain in the blood.

Reabsorption

Due to osmosis

Blood colloid osmotic pressure (BCOP)

Created due to the presence of the proteins in the blood

Draws fluid into capillary to restore solute concentrations

Reabsorption: occurs due to osmosis.  You will remember that osmosis is the movement of water across a selectively permeable membrane due to a concentration difference.  The OSMOTIC PRESSURE is the pressure needed to move the water across a membrane.  The higher the solute concentration, the higher the osmotic pressure. In the capillary the osmotic pressure of the blood is called the BLOOD COLLOID OSMOTIC PRESSURE.  This pressure is created due to the presence of the proteins in the blood.  This BCOP forces the movement of water back into the capillary in order to restore the solute concentrations on either side of the capillary wall.

Filtration = 24L/day (filtrating 24L of blood a day)

Reabsorption = 20.4L/day (reabsorb 20L of that fluid)

End of the day we lose aboubt 3.5L of fluid per day. (Urine/Water vapor exhaling/Sweat)

Blood Flow

Blood flow is proportional to any change in pressure divided by the resistance How much pressure is being applied and how much resistance is being applied to that liquid medium.

Pressure and resistance determine blood flow and affect rates of capillary exchange

F a DP/R

F = blood flow

P = pressure (from start to end of vessel)

R = resistance (via vessel diameter)

Autoregulation of blood flow

Ok so we know that the heart pumps the blood around the body and that the blood delivers important nutrients, gases and chemical messengers to the cells.  The way in which this is all co-ordinated to ensure that adequate supply reaches each and every cell is under homeostatic control.  This homeostatic control is called CARDIOVASCULAR REGULATION and the goals of cardiovascular regulation are to ensure that

  Blood flow is adequate and appropriate to specific tissues and cells

Neural mechanisms

Endocrine mechanisms

  Blood flow is adequate and appropriate to specific tissues and cells

  Any changes that occur, happen in the right area

  Any changes that do occur don’t have a harmful affect on the vital organs (heart, brain, lungs)

Blood Flow Autoregulation

Ensures adequate and appropriate individual organ blood flow

Generally dictated by metabolism/activity

Achieved via:

 Neural mechanisms

  Endocrine mechanisms

Autoregulation

Individual Tissue Vasodilation =

Increase diameter of blood vessel = decreasing amount of friction = decreasing resistance to blood flow = blood flows more freely.

Via certain metabolic markers to increase flow:

↓O2 or ↑CO2 levels = Vessels dilate to ↑ blood flow through the region + Remove the CO2 and ↑O2

If we have massive decline in O2 saturation in a tissue CO2 usually elevates as a waste product which starts to cause vasodilation of blood vessels feeding that tissue = more blood flow to tissue to increase more O2 to tissue and redistribute excess Co2.

Lactic Acid (LA)  = a build up of an incomplete breakdown  of glucose which limits muscle function)

One way to rid LA is to change PA levels to more alkaline by vasodilating blood vessel we get more buffers which circulate within blood to help neutralize LA buildup.

↑ LA in a particular tissue, the blood vessels dilate

Transport more buffers into the tissue to ↓ LA

↑ Nitric Oxide (NO)

Released by endothelial in relation to a ↑ BP

↑ BP usually means there’s vasoconstriction but NO is produced by the endothelial in the tunica intima to help vasoldilate that vessel.

Causes smooth muscle layer of vessel to vasodilate and ↑ blood flow

Individual Tissue Vasoconstriction

Via reduced metabolic markers, and endothelin, prostaglandins, thromboxane

Maybe we have to much O2 in the tissue and not enough CO2 which will release a substance known as…

Endothelin

Released from the endothelial cells of the blood vessels to act on the smooth muscle layer and cause the vessel to constrict. (Does the opposite of NO)

Prostaglandins & Thromboxane: Protective Mechanisms (Released for damaged blood vessels)

Released by platelets when damage occurs and clotting process is initiated causing the vessel to constrict.

When your finger aches/throbs from a cut that’s prostaglandins and thromboxane vasocontricting that blood vessel to try and minimize the amount of blood flowing to that tissue.

Autoregulation Summary

Overview of vessel diameters, cross-sectional areas, pressures and velocity of blood flow in the systemic circuit

Diameter: Shows that near the heart blood vessels are big with more blood flow and as we move away from it the vessels are much smaller in diameter (capillaries only 1 blood cell).

Velocity: Remembering that slow blood flow at the capillaries/venules is important to allow diffusion/exchange/filtration of gases/nutrients.

Cross sectional: We only have 1 aorta (elastic) but we have many more arterioles branching into all the individual tissues -> within tissues we have millions of capillaries -> we only have one superior/inferior vena cava for our large veins – very small in proportion to the whole blood system. Which links to flow – you IN the surface area of something it takes longer for blood to travel.

Pressure + blood flow at the aorta is high, as we branch further down the blood vessel tree pressure drops down as it disperses blood through the network.

Cardiovascular Pressure

Why is it important to know BP?

We’re trying to get an understanding of the resistance that’s being applied to your blood flow – how hard your heart is working at rest.

Hypertension

Abnormally high BP (140/90)

Increases cardiac workload/stress on the heart which over a long time increases the size of the heart which can not always be good, because if you IN the size of the left ventricle, the actual cavity of the LV where the blood resides becomes smaller and smaller so there’s less SV being produced.

Hypotension

Abnormally low BP (going from sitting to standing innervated by neural mechanisms)

Regulated by:

Neural mechanisms (short-term)

Hormonal mechanisms (long-term)

Blood Pressure

Resting BP = 120/80 (i.e. Systolic/Diastolic) Units are “millimetres of mercury” (mmHg)

Pulse Pressure = Systolic – Diastolic

Mean Arterial Pressure = Average pressure required to push blood into your circulatory system = Diastolic + (⅓ × Pulse Pressure)

Mean Arterial Pressure (MAP)

MAP = CO × TPR

CO (cardiac output)

Product of HR and SV (CO = HR × SV)

TPR – total peripheral resistance

Via overall systemic arteriolar diameter outside local organ autoregulation

Short-Term Neural Regulation

Ok so we said that there are three main ways in which cardiovascular regulation is maintained, via autoregulation, via neural mechanisms and via endocrine mechanisms.

The nervous system plays a major role in adjusting CO and peripheral resistance to make sure that there is adequate blood flow to the tissues and cells.

There are CARDIOVASCULAR CENTRES in the MEDULLA of the brain which are responsible for this control.  Within the CARDIOVASCULAR CENTRES are two divisions – the VASOMOTOR division which control there peripheral resistance of blood vessels and the CARDIAC centres which regulate cardiac output.

The VASOMOTOR division has two groups of neurons, those that monitor VASOCONSTRICTION and those that monitor VASODILATION.

VASOCONSTRICTION: Neural input from the VASOMOTOR vasoconstriction neurons act on the smooth muscle of blood vessels to release NA which causes the smooth muscle to contract and hence reduce the blood vessel diameter.

VASODILATION: Neural input from the VASOMOTOR vasodilator neurons act on the smooth muscle by releasing NO which relaxes the smooth muscle of the blood vessel and hence increases the vessel diameter.

Cardiovascular control center in medulla oblongata that will regulate pressure

Cardiac centers

Cardioacceleratory center: Controls sympathetic activity

Cardioinhibitory center: Controls parasympathetic activity

Responds to pressure detection via BARORECEPTORS which detects how much stretch is occurring in walls of aorta and carotid artery

Sensitive to changes in the stretch of the walls

BARORECEPTOR REFLEX

(Top: Goal to decrease BP. Bottom: Goal to IN BP).

Long-Term Hormonal Regulation

Ok so we said that cardiovascular regulation is maintained by autoregulation at the level of the tissues, neural input and endocrine input.  We’ve talked about autoregulation and neural input, lets now focus on how the endocrine system helps to maintain cardiovascular regulation.

There are four main hormones involved with cardiovascular regulation and their overall goal is to help maintain adequate blood pressure and blood volume.

Antidiuretic hormone (ADH) – vasopressin – released from the posterior lobe of the pituitary gland.  It is released when there is a drop in blood volume or an increase in the osmotic concentration of the plasma.  Another hormone angiotensin II also stimulates its release.  ADH acts on the blood vessels to cause them to vasoconstrict and also acts at the kidneys to conserve water and minimise water elimination.

Angiotensin II – specialised cells in the kidney are senstitive to changes in blood pressure and when blood pressure drops in this region, the kidneys release an enzyme called RENIN.  RENIN is responsible for initiating the production of ANGIOTENSIN II in the blood.  The role of angiotensin II overall is to increase blood pressure and blood volume.  It does this by acting at the adrenal gland to produce ALDOSTERONE which in turn acts on the kidneys to increase Na reabsorption and increase K loss.  It stimulates the thirst response so that we drink more in order to increase our blood volume.  It stimulates the release of ADH which also has water conserving effects.  It acts on the blood vessels to vasoconstrict and therefore elevate blood pressure.

Antidiuretic Hormone (ADH)

Released due to ↓ blood volume, ­ plasma osmotic concentration. E.G. Dehydrated, fasting, post exercise. The plasma in your blood which is 99% water – when you loose blood volume its essentially water leaving your blood plasma – so the volume of blood in your body will drop. When you drop the amount of fluid circulating in your body pressure will also drop. When ADH is released, its trying to do the opposite, its trying to IN your blood plasma concentration by IN re-absorption of fluid in your body.

Its effects blood vessels by causing vasoconstriction

Also acts at kidneys to minimise water loss and IN water re-absorption via your urinary filtrate.

Angiotensin II (AII)

Goal to increase blood pressure and blood volume

Acts at adrenal gland to release aldosterone to stimulate thirst response. So when your thirsty you’re already dehydrated because your blood volume and blood pressure has dropped.

Also stimulates release of ADH to help re-absorption of water at the kidneys.

Causes vasoconstriction to try and IN pressure

Erythropoietin

As we said there are four main hormones that help to regulate the cardiovascular system.  The first two were ADH and AII.

The third hormone is ERYTHROPOIETIN  – it is also released in response to low blood pressure or if the oxygen content of the blood drops quite low.  The role of erythropoietin is to stimulate RBC production which therefore increases the viscosity of the blood and also the oxygen carrying capacity of the blood to restore blood pressure and oxygen content.

Released due to poor renal blood flow and/or low blood oxygen content. If we have low blood O2 content, it may suggest you have low red blood cell count because O2 travels on RBC and it contributes to blood volume.

If you release erythropoietin it increases RBC production -> that IN blood volume -> IN pressure

Atrial Natriuretic Peptide (ANP)

The fourth major hormone involved in cardiovascular regulation is ATRIAL NATRIURETIC PEPTIDE or ANP.  ANP is produced in the cardiac muscle of the right atrium and is released in response to stretching of the atrium.  The role of ANP is to reduce blood volume and blood pressure and it does this by acting on the kidneys to increase Na and water excretion, reduces thirst and inhibits the release of ADH, aldosterone, A and NA and stimulates vasodilation.  The overall aim is to decrease blood volume and blood pressure.

Produced in right atrium

Released in response to atrial stretch. So if our atria are stretching it would probably suggest that we have an IN in blood volume/venous return coming back to the heart.

­ ↑ Na+ loss and water excretion at kidneys = blood plasma volume drops

Also ↓ thirst response

Inhibits ADH, aldosterone, E and NE

ANP also stimulates vasodilation to help drop BP

Summary: Short and long term blood pressure regulation

Learning Objectives

Discuss the mechanisms involved in capillary exchange

Describe how pressure and resistance determine blood flow through arteries, capillaries and veins

Describe how local, neural and endocrine mechanisms regulate blood flow to tissues

Describe the factors that influence blood pressure through the vascular system

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Lymphatic System & Immunity (W8)

Lecture #19 (1.5.17)

Is responsible for defense against threats/pathogens

Hazards & Threats

Pathogens

Viruses, bacteria, fungi, parasites

Internal threats

Cancer cells

Lymphatic System

It picks up fluid and returns it to the blood system.

Tissues and cells responsible for defence against pathogens, chemicals and cancer cells

Lymph: Fluid, similar to plasma (minus proteins)

Lymphocytes (white blood cell type 20-30% of WBC): T-Cells, B-Cells, Natural killer cells. Involved in a defense against a specific threat.

Lymphatic vessels: Network around body, drain into veins

Lymphoid tissues and lymphoid organs: Present throughout body

Lymph

A fluid resembling plasma:

Mostly made up of water

Much lower concentration of suspended proteins than plasma

Also contains other solutes such as electrolytes

Lymphatic Vessels

Ok, so in order for our lymphocytes to detect and respond to some sort of biological attack, they need to be able to move around our body.  The way in which they do this you will remember from our lectures on blood is via the blood circulation. We also noted however that lymphocytes are able to move out of the blood vessels and into the ECF (extracellular fluid).

When we spoke last week about the exchange of fluid at the capillaries, we saw that the CHP (capillary hydrostatic pressure) forces fluid out of the capillaries into the ECF.  We also learned that while 85% of this fluid is reabsorbed by the capillaries, 15% is taken up by  the lymphatic vessels. As this excess fluid in the ECF moves towards the lymphatic vessels, the lymphocytes that have left the blood vessels are able to move through the ECF via this fluid to a site of invasion.

The lymphatic vessels form a network that has a similar design to the blood vessels.  The smallest lymphatic vessel is called a LYMPHATIC CAPILLARY.  The lymphatic capillaries merge to form SMALL LYMPHATIC VESSELS.  The small lymphatic vessels continue to merge to form the MAJOR LYMPH COLLECTING VESSELS which eventually join into the venous system.

Lymph Capillaries

The lymphatic capillaries are the beginning of the lymphatic system.  They have some interesting and unique features that make them different from blood capillaries:

The lymph capillaries originate as BLIND POCKETS or BLIND ENDS

They have a larger diameter than blood capillaries

They have thinner walls than blood capillaries

Lymph capillaries are bound by an endothelial cell layer however the basement membrane of the endothelial layer is missing. 

The endothelial cells of the lymph capillary are not tightly bound but there is an overlap of the cells as they are arranged in the vessel wall.

The region where the cells overlap act as a valve allowing the movement of fluids and extracellular materials into the vessels but not out again.

Lymph forms as interstitial fluid enters the lymphatic capillaries

Lymphatic vessels (green) job is to pick up extra tissue fluid. Once the interstitial fluid enters the capillary that’s when we refer to it as lymph.

Small Lymphatic Vessels

The small lymphatic vessels form from the merging of the lymph capillaries.  The walls of the small lymph vessels are similar to the walls of veins.  In addition, these vessels also contain valves.  The valves are distributed through the vessels at close intervals and where the valve lie in the vessel wall there is a noticable bulge giving the vessel a beaded appearance.  As in veins, the valves in the lymph vessels prevent the back flow of lymph.

Structure similar to veins

Valves purpose is to prevent backflow of lymph

You can identify in a histological slid by the bulge of vessel which is where valve lies giving beaded appearance

Drainage of Lymph into Venous System

The lymphatic vessels are located within the body in the subcutaneous layer called the SUPERFICIAL LYMPHATICS and also amongst the arteries and veins supplying the skeletal muscles and abdominal organs and are called the DEEP LYMPHATICS.

The superficial and the DEEP lymphatics merge to form very large lymphatic vessels called LYMPHATIC TRUNKS.

These lymphatic trunks drain into the…

THORACIC DUCT-  which collects lymph from the body inferior to the diaphragm and the left side of the body superior to the diaphragm, and the RIGHT LYMPHATIC DUCT which collects lymph from the right side of the body superior to the diaphragm.

Lymph from the thoracic duct drains into the LEFT JUGULAR VEIN (found in neck) whilst lymph from the right lymphatic duct drains into the RIGHT SUBCLAVIAN (runs underneath clavicle) VEIN

Lymphocytes

LYMPHOCYTES are one of the WBC types in the body. They represent 20-30% of the circulating white cell population.  Its important to keep in mind though that the number of circulating lymphocytes represents only a small amount of the total lymphocyte number in the body which is around 10 TRILLION!!

Three Classes:

T-Cells – Thymus dependent cells

Involved in direct cellular attack of the pathogen.

Cytotoxic T cells – attack cells infected by a virus via direct contact

Helper T cells – stimulate activation and function of B and T cells

Supressor T cells – inhibit function and activation of B and T cells

B-Cells – Bone Marrow Derived Cells

Don’t go to the cite of infection, but receive info and create antibodies and those antibodies travel to the cite of infection.

Differentiate into PLASMA CELLS

Produce antibodies (immunoglobulins)

Attack antigens = the stimulus to generate the response by the immune system.

NK Cells – Natural Killer Cells

Spend time looking for cells that are abnormal/mutated.

Attack foreign cells, virus infected and cancer cells

Immunological surveillance cells

 

 Lymphoid Tissues

The lymphoid tissues are present as NODULES which are made up of loose connective tissue densely packed with LYMPHOCYTES.

The nodules are around 1mm in size and have a central region called the GERMINAL CENTRE which contains dividing LYMPHOCYTES.

Lymph nodules are commonly found in the connective tissue that lines the respiratory, digestive and urinary tracts.

The group of nodules associated with the digestive system is called the MUCOSA ASSOCIATED LYMPHOID TISSUE (MALT).  Groups of these nodules that are found in the intestine are known as PEYERS PATCHES.  The walls of the appendix  (small pouch at junction of small and large intestine) also contains lymphoid nodules

The TONSILS are also lymphoid tissues.  Most people have 5 tonsils –left and right palatine, single pharyngeal tonsil also know as the ADENOIDS and two lingual tonsils.

Lymphocytes that lie in a nodule cant always destroy bacteria or viruses that they encounter.  If the bacteria or viruses become established we get an infection of which most of you would be familiar with TONSILITIS.  The treatments associated with this include antibiotics and sometimes removal of the nodules.

Nodules

1mm in size

Germinal centre (production of cells in that center)

Found in connective tissues of respiratory, digestive and urinary tracts which are all potential gateways to pathagons – which makes sense why we have the nodules in those areas.

Mucosa Associated Lymphoid Tissue (MALT)

Peyers patches

Appendix (where the small and large intestine join)

Tonsils: 3 types:

Swelling because we have a lot of cells trying to deal with the infection.

Lymphatic Organs: Lymph Nodes

 

Remember: Afferent = approaching – bring something into the target – lymph coming in via the afferent lymphatic vessels.

The job of the lymph node is to filter the lymph and deal with any pathogens

Afferent Lymphatics – Bring lymph to node

Efferent Lymphatics – Remove lymph from node

Filter system – Antigen presentation – to detect new pathogens and present them to the T/B cells so they can respond to it

Early warning system – Swollen lymph glands

There are three different types of lymphoid organs.  The LYMPH NODES, the THYMUS and the SPLEEN

The LYMPH NODES are small organs that range from 1-25mm in diameter.  They are shaped similar to a kidney bean with a small indentation called a HILLUS where blood vessels and nerves attach.  The Lymph Nodes are connected to two types of lymphatic vessels, the AFFERENT LYMPHATICS and the EFFERENT LYMPHATICS.

AFFERENT LYMPHATICS – bring lymph to the lymph node from the peripheral tissues.  They enter the node on the opposite side of the HILLUS.

The EFFERENET LYMPHATICS – take lymph away from the lymph node to the veins.  They leave the node at the HILLUS.

The role of the lymph nodes are to act as FILTERS to remove most of the pathogens and debri from the lymph before it re-enters the circulation. We have mentioned previously how all cells have their own ANTIGENS and it is at the lymph nodes where ANTIGENS of any pathogens in the body are PRESENTED to the lymphocytes.  This ANTIGEN PRESENTATION is one of the first steps in activating the immune response.

The lymph nodes also provide an early warning system thus when there is damage or pathological invasion, there is an increased activity of the lymphocytes in the lymph nodes.  We often refer to ‘swollen lymph glands’ when we have a viral infection or cold.

Lymphatic Organs – Thymus

The THYMUS is found in the MEDIASTINUM which is a collective term for the central tissue mass in the thoracic cavity and includes the heart, lungs and vessels associated.

The THYMUS is the site of DEVELOPMENT AND MATURATION OF T CELLS.  It has two LOBES that are made up of LOBULES which  are made up of a cortex and medulla region.  The CORTEX region of each lobule contains dividing T cells which once mature move to the MEDULLA

Thymus is quite large in young children and reaches its greatest size at about 1-2 years of age. After puberty it begins to become much smaller in size and weighs only about a third of its original weight by the time a person reaches 50 years of age. The dramatic change in size following puberty has been the subject of research where castrated rats have shown no change in the size of their thymus versus intact individuals – study as to why the reproductive hormones reduce the size of the hormones and therefore our immunity.

Located in mediastinum

Role = Development and maturation of T Cells

Lobules

Cortex: Dividing T cells

Medulla: Mature T cells

Lymphatic Organs – Spleen

 It is located in the abdominal cavity near the stomach.  The role of the spleen is to act as a filtering system for the blood, similarly to the lymph nodes as they do for lymph.

The spleen does this by removing abnormal blood cells by phagocytosis, stores iron from recycled red blood cells and activate the B and T cells in response to antigens circulating in the blood.

PICTURE – RED PULP mass of RBCs WHITE PULP – lymph nodules

LYMPHOCYTES are scattered throughout RED PULP

LOTS OF MACROPHAGES around WHITE PULP.

SUDDEN IMPACTS TO LEFT SIDE OF ABDOMEN CAN INJURE THE SPLEEN SPLEEN TEARS VERY EASILY AND SO EVEN A MINOR BLOW CAN TEAR THE CAPSULE AROUND THE SPLEEN.  PROBLEM IS INTERNAL BLEEDING.  DIFFICULT TO REPAIR SURGICALLY,  SUTURES TEND TO TEAR BEFORE THEY CAN BE TIGHTENED ENOUGH TO STOP BLEEDING.  USUALLY PERFORM A SPLENECTOMY.  THESE INDIVIDUALS SURVIVE BUT GREATER RISK TO INFECTION SUCH AS PNEUMOCCOCAL BACTERIA.

Largest lymphoid organ

Acts as a filtering system for blood

Functions

Removes abnormal old blood cells

Stores iron from recycled RBC

Involved in activating B and T cells

Immune Defence

The way in which the body handles foreign invasion is via two general strategies

Non Specific Defence (innate immune response)

Where the type of threat is not distinguished and the response is the same regardless of the type of attack.  Most of these defences are present at birth.

Type of threat not distinguished

Same elimination methods used for all pathogens/threat

Present at birth

Specific Defence (adaptive immune response)

These protect against specific or particular threats.  A specialised mechanism is used for each different pathogen that is encountered.  This type of defence is usually generated after birth as a result of exposure to particular hazards.

Protect against particular threats

Different elimination method for each invasion

Generated after exposure to particular hazard

Involves lymphocytes (T cells and B cells)

We have to have exposure to that hazard so we can create a response – this is where vaccinations come in. When we are vaccinated we introduce a small amount of ‘inactive pathagon’ to the body to allow it to have an immune response. The immune response has memory so it remembers how to respond if it see’s the same threat at a later date.

We need both types of defence to be able to adequately protect against infection and disease.

Non-Specific Defences

Physical barriers

Skin,  tight junctions between cells, sweat and mucous secreting cells

Phagocytes (eating cells)

Microphages (neutrophils, eosinophils), macrophages

Immunological surveillance

NK (natural killer) cells destroy abnormal cells

Interferons

Their job is to interfere with normal functioning/replication of virus’ by increasing resistance of cells to viral infection

Complement System

Destroy target cell membrane by forming Membrane Attack Complex

Inflammatory Response

Localised swelling, redness, heat and pain helps to repair the injury

Fever

Maintained elevated body temperature >37.2 degrees

The heat is helpful because it increases the rate of the chemical reactions responsible for pathogen removal and tissue repair

T Cells

These cells will get involved when the pathogen is inside a cell.

You will remember that specific immune defence is where our immune system acts in response to a specific antigen.

It involves both B CELLS and T CELLS.  Our B CELLS and T CELLS have their own roles in the immune specific response. T CELLS are responsible for what is called CELL MEDIATED IMMUNITY – this is our defense against abnormal cells or pathogens that are within cells.  These guys are not activated when pathogens are present in the ECF and so are important in protecting our cells.

The actions of both B cells and T cells have an important role in specific immune defence.

Respond to a specific antigen

CELL MEDIATED (CELLULAR) IMMUNITY

Protect against abnormal cells and pathogens inside cells

Not activated when pathogens are present in the ECF only when the pathogen is in the cell.

Also help to activate B cells

B Cells

Respond to a specific antigen

ANTIBODY MEDIATED (HUMORAL) IMMUNITY

Located in the ECF body fluids – not the cellular component like before.

Defends against antigens in body fluids

Plasma cells produce vast amounts of antibodies which bind to antigens on pathogens

Bound antibody-antigen complexes destroy antigen alone or in combination with non specific immune defence mechanisms

B CELLS are responsible for ANTIBODY MEDIATED IMMUNITY – that is they defend against antigens and pathogens within the body fluids.  The antibodies produced by B cells are unable to cross cell membranes and so these guys are important for cleaning up the body fluids.

Overview: Immune response (specific defenses)

When we encounter a new pathagon we get the cell mediated immunity via the T cells and the antibody mediated immunity via the B cells. We get a lot of interaction and feedback between these cells. Then there’s a direct attack via the T cells and the antibody attack produced by the B cells. Together they destroy the pathagon/infected cell.

Question: If you came onto contact with a virus for the firs time, what immune response is most effective?

Innate immune response

T-Cells are called “T” because they..

Are removed by the thymus

B-Cells are not involve in the innate immune response

The lymphatic fluid from lower half of the body drains into what structure?

The left subclavian vein

A virus/pathagen within the body fluids that has been prevoously encourtered (e.g. chickenpox) would not cause a second infection due to what?

Humoral immunity

Learning Objectives

List the components of the lymphatic system

Describe the composition of lymph

Describe the organisation of lymphatic vessels

Explain how lymph is formed and how the flow of lymph is accomplished

Distinguish between the following types of lymphocytes:  T cells, B cells and Natural Killer Cells

Identify lymphatic tissues and organs and explain their functions

Explain the differences between non-specific and specific defence

Describe cell-mediated immunity and the role of T cells and describe antibody-mediated immunity and the role of B cells

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Structure of the Respiratory System (W8)

Lecture #20 (2.5.17)

Functions of Respiratory System

Provide area for gas exchange: an exchange of CO2 and O2 at the respiratory membrane

Move air to and from gas exchange surface: getting air in/out of the lungs

Protection from dehydration, temperature and pathogens: hydrating air

Contribute to the production of sounds: voice

Provide olfactory sensation to CNS: smell

Organization of Respiratory System

Upper Respiratory System

nose, nasal cavity, paranasal sinuses, and pharynx

Lower Respiratory System

(larynx – can be classed as both lower and upper) -> trachea -> bronchi -> bronchioles -> and alveoli

derived embryonically from a different region (foregut)

Nose

External Nares  = nostrils

Nasal vestibule (behind the nostril)

Space within flexible tissues of nose

Layer of hairs for trapping large particles

Nasal Septum: the wall between the left and right side of the nose

Nasal Conchae

“shell like structure”

Filters, warms and humidifies air and enables filtration of air

Internal (posterior) Nares

Lined with mucus and small, fine cilia (dashed lines at right)

Pharynx

Chamber shared by respiratory and digestive systems

Extends from internal nares to larynx and oesophagus

Nasopharynx (in the nasal area)

Ciliated epithelium, pharyngeal tonsil, opening to auditory tubes

Oropharynx

Combined passageway where food also passes through. A time where digestive and respiratory system share a common pathway.

Stratified epithelium because you have a higher potential to damage cell walls so its susceptible to chemical and mechanical attack via food. So the stratified nature of the cell provides more layers of defense.

Laryngopharynx

Stratified epithelium, resists abrasion, chemical and pathogen attack

Larynx

Protective cartilaginous structure surrounds GLOTTIS

Important in sound production

Touching vocal folds will trigger the coughing reflex – acts to clear entrance to the glottis. Also any particuls that disturb larynx will also trigger coughing.

When you swallow the larynx moves up and the epiglottis drops down and covers the entrance to the trachea to ensure food/drink doesn’t go down

Three main cartilages:

THYROID CARTILAGE

shield shaped  (Adam’s Apple) forms as a layer of protection to the larynx which is where you have your vocal folds to enable speech

CRICOID CARTILAGE

Protects the glottis and the entrance to the TRACHEA. Only complete ring of cartilage in trachea

EPIGLOTTIS

Forms a lid over the GLOTTIS (=opening into trachea), folds back over glottis during swallowing to prevent entry of food into the respiratory tract

Trachea & Primary Bronchi

Trachea (windpipe)

Tough, flexible tube

Mucosal layer to further protect the respiratory surface that have gotten past the first lines of defense

Contains 15-20 tracheal cartilages: prevents collapse or overexpansion with pressure changes in respiratory system. C- shaped. Muscle connects rings

Primary bronchi

C-Shaped cartilage for support and protection

Right bronchus wider, shorter and descends more steeply than left

Right: 3 secondary bronchi. The R primrary bronchis is wider, shorter and steeper because of the hearts place in the chest cavity.

Left: 2 secondary bronchi

Lung: Gross Anatomy

Blunt cone shaped

tip pointing superiorly

broad base lies on the surface of the diaphragm

Left lung – 2 lobes

Right lung – 3 lobes

Separated by fissures

Hilus

Groove where primary bronchi, pulmonary vessels and nerves enter lungs

Bronchial Tree

Primary bronchi outside lungs

Enter the lungs and divide into secondary bronchi

Right lung has 3

Left lung has 2

Secondary bronchi branch into tertiary bronchi

Each branch of the bronchi walls contain progressively lesser amounts of cartilage and more smooth muscle. So the capacity of your body to regulate where air goes increases as you move further along the branches.

 

Bronchioles

Walls have no cartilage: supported by purely smooth muscle which is important because you can guide where the air goes

Control diameter of conducting airways

Direct airflow toward or away from respiratory exchange surfaces

Influenced by hormonal, sympathetic and parasympathetic input

If you have a SYMPATHETIC response you will bronchodilate: your smooth muscle in the walls of the bronchioles will relax -> airways get bigger which ensures you can get more air to your gas exchange areas in your lungs -> more O2 in your bloodstream.

If you have a PARASYMPATHETIC response you will bronchoconstrict: airways narrow -> you don’t need as much O2 supply

Bronchioles

Pulmonary Lobules

The smallest self contained compartment of the lung which is important to protect against infection and regulation of respiration.

Contains a TERMINAL BRONCHIOLE which branches to form the RESPIRATORY BRONCHIOLES

Respiratory Bronchioles

Most delicate and thinnest branches of the bronchial tree

Deliver air to the gas exchange surfaces of the lungs the ALVEOLI

Alveoli

Are the leaves of your bronchiol tree where the gas exchange occurs.

Alveolar ducts connect to individual alveoli

Alveolar Sacs: Give lung spongy appearance + 200µm in diameter

150 million alveoli per lung: Highly vascularised supplied by capillaries and elastic tissue + Involved in gas exchange

Alveolar Surface

Two types of cells:

Type I: Simple (1 layer) Squamos (irregular shape) Epithelium

You need that thin layer to allow for the gas exchange.

Type II or Septal Cells or Great Alveolar cells: Secrete SURFACTANT which ensures the alveoli can more easily stay open/prevents alveolar from collapsing. Which is why fetus’s <24 weeks are not viable because you can’t keep the alveoli open to ensure gas exchange.

 + Reduces surface tension and prevents alveoli from collapsing

Alveolar Macrophages / Patrol Cells

Patrols the surface and phagocytose that has gone past the other respiratory defences to prevent infection

Respiratory Membrane

Is where gas exchange occurs across respiratory membrane of alveoli

Membrane composed of 3 parts:

What are the components of the respiratory membrane?

1. Squamous epithelial cells of alveolus
2. Endothelial cells of the adjacent capillary
3. Fused basil laminae of the alveolus and endothelial cells

This structure keeps the RESPIRATORY MEMBRANE as THIN as possible so that diffusion can occur very rapidly

Cell linings: Structure ↔ Function

Upper Respiratory Airways

Multiple cell types: ciliated cells (provide cilia to capture debris), goblet cells (provide mucus to capture pathogens/dust), basal cells (differentiate into other cells types after injury)

A single layer of cells, the nuclei are not aligned in the same plane = “ciliated pseudostratified columnar epithelium”

In Oropharynx

To reduce impact of damage: multiple layers to protect against food/drink (= “stratified squamous epithelium”)

In Trachea/Bronchi

Transition from ciliated pseudostratified columnar epithelium (to help move mucous up) to ciliated cuboidal (cube) epithelium and then simple squamous (flat) epithelium

Smooth muscle (for modulating size of airways)

In Terminal Bronchioles

Some ciliated cells, no goblet cells, some “club cells” (secrete surfactant to reduce surface tension, also enzymes for protection) to ensure gas exchange

Smooth muscle (for modulating size of airways)

In Alveoli

Among other types: flat thin cells (squamous) for diffusion

Learning Objectives

Describe the primary functions of the respiratory system

Identify the organs of the respiratory system and describe their functions

Describe the anatomy of the lungs, the structure of a pulmonary lobule and the functional anatomy of the alveoli

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Respiration (W8)

Lecture #21 (4.5.17)

Overview of Respiration

External Respiration

Process by which gases (oxygen, carbon dioxide) are exchanged between the blood stream and air in the lungs

Gas Transport

Transport of gases between lungs and metabolising tissues

Internal Respiration

The movement of O2 out of oxygenated blood into the metabolizing tissues and also the movement of CO2 out of metabolizing tissues into the blood stream.

Process by which gases are exchanged between blood and tissues of the body. E.G. The exchange of O2 going out from the oxygenated blood and into the actual target tissues.

Metabolising tissues

PO2 = 40mmHg

PCO2 = 45mmHg

So O2 will move down the diffusion gradient from the region of high partial pressure of O2 – low partial pressure of O2. Same with Co2, it has a higher partial pressure in metabolising tissues and lower in the blood so it moves out of the metabolizing tissue and into the blood stream.

Blood

PO2 = 95mmHg (much higher partial pressure of O2)

PCO2 = 40mmHg

Steps in External Respiration

Pulmonary Ventilation: Breathing

Gas Diffusion: Exchange between alveolar air and blood in capillaries

Pulmonary Ventilation

Summary: If you decrease the volume of a gas you will increase the pressure.

  Pulmonary ventilation is our breathing aim is to make sure there is enough air flow to keep adequate supplies of O2 at alveoli and remove CO2

Why you need to care? When you have air in your lungs with plenty of Co2 in it and you want to get it out of your lungs you need to increase the pressure of the gas in your lungs to get it outside by letting the lungs. The pressure generated by the earths atmosphere contributes to how we breathe.  Air is able to move into and out of our respiratory tract because the air pressure in the lungs moves from below atmospheric pressure when we breath in and above atmospheric pressure when we breath out. relax.

Boyle’s Law

Inverse relationship between pressure and volume of gas in a container:

         P α 1/V

Air flows from area of high pressure to low pressure

Pressure generated by the Earth’s atmosphere contributes to how we breathe:

Pressure is lower in the lung than outside: air flows in

Pressure is higher in the lung than outside: air flow out.

Pleural Cavity

The lungs lie in a cavity called PLEURAL CAVITY

PLEURAL CAVITY is filled with PLEURAL FLUID which forms a FILM OVER LUNGS.  This film helps to keep the contact between the lungs and the inner chest wall and diaphragm.  USE WET GLASS ON SMOOTH TABLE TOP ANALOGY.  CAN MOVE GLASS BUT VERY DIFFICULT TO PULL GLASS AWAY.

The pleural film helps to maintain lung contact with inner chest wall and diaphragm so that when size changes in the chest wall occur, lung size will also change.

The ribs and diaphragm contribute to the volume of the thoracic cavity.  The way the lungs are shaped helps them to move either superiorly or inferiorly. If they move SUPERIORLY – increase volume, INFERIORLY DECREASE VOLUME

Movement of Diaphragm also related, if DIAPHRAGM moves INFERIORLY (contracting), VOLUME INCREASES, if moves SUPERIORLY (relaxing), volume DECREASES.

Due to the relationship between the PLEURAL fluid and the lungs, when the Chest wall expands, the lungs move with it and the volume of the lungs INCREASES, similarly, the movement of the diaphragm INFERIORLY, INCREASES VOLUME in lungs.

The increase in volume of lungs decreases the air pressure inside the lungs below the pressure of air in the respiratory passageways.  We know that gas moves from a region of high pressure to one of low pressure, therefore AIR MOVES INTO LUNGS.

When the lung volume decreases as ribs move inferiorly and diaphragm superiorly, pressure increases and is higher than that in the resp passageways and AIR MOVES OUT.

Pleural Fluid

Produced by pleural membranes

Forms a film over lungs

Reduces friction and increases surface tension

Maintains lung contact with chest wall and diaphragm

Ribs and diaphragm contribute to volume of thoracic cavity

Pressure

–↑ lung volume = ↓ pressure

–↓ lung volume = ↑ pressure

Respiratory Muscles

In order for us to be able to move air into and out of the lungs, we need to be able to expand and reduce the size of the thoracic cavity.  To do this we need to harness the use of our RESPIRATORY MUSCLES.

Most important muscles used in respiration are DIAPHRAGM and EXTENAL INTERCOSTAL MUSCLES. Both move superiorly and inferiorly for inhalation and expiration and are used during NORMAL BREATHING.

ACCESSORY RESPIRATORY MUSCLES: active when we need to increase depth and frequency of breathing:

  INTERNAL INTERCOSTALS

  STERNOCLEIDOMASTOID

  SERRATUS ANTERIOR

  PECTROALIS MINOR

  SCALENE TRANSVERSUS THORACIS

  TRANSVERSIS ABDOMINIS

  EXTERNAL AND INTERNAL OBLIQUE

  RECTUS ABDOMINIS MUSCLE

Lung volume influenced by respiratory muscles

Most important muscles in respiration:

Diaphragm

External Intercostals

Both move superiorly and inferiorly for inhalation and expiration + used during NORMAL BREATHING

Respiratory Muscles

Muscles Used in INHALATION

Diaphragm: responsible for 75% of air movement

External intercostals: responsible for 25% of air movement

Accessory muscles: Sternocleidomastoid, serratus anterior, pectoralis minor, scalenes

Increase speed and rise of ribs during active breathing

Inspiration (inhalation) is the process of taking air into the lungs. It is the active phase of ventilation because it is the result of muscle contraction. During inspiration, the diaphragm contracts and the thoracic cavity increases in volume. This decreases the intraalveolar pressure so that air flows into the lungs. Inspiration draws air into the lungs.

Muscles Used in EXHALATION

You do not use any extra muscles to breath out at rest. Normally exhalation occurs via normal elastic recoil of the lungs.

Accessory muscles: Internal intercostals and transverse thoracis muscles: reduce width and depth of thoracic cavity

Ways of getting air out faster: Using the abdominals which compress abdomen and force diaphragm upwards

Pulmonary Volumes & Capacities

Focus on top 5.

• Resting tidal volume: the volume of air that goes in or out of the lungs during relaxed normal breathing at rest – usually half a liter.
• Inspiratory reserve volume: the maximal volume of air that can be breathed in beyond a normal inspiration.
• Expiratory reserve volume: the maximal volume of air that can be breathed out beyond a normal expiration.
• Residual volume: the volume of air remaining in the lungs after a maximal expiration
• Minimal volume: if the lung falls below this volume, the alveoli cant stay open anymore and lungs will collapse
• Functional residual capacity (FRC): the volume of air in the lungs at the end of expiration during normal quiet breathing
• Inspiratory capacity: is the volume of air that can be breathed in from a normal expiration during quiet breathing. (Inspiratory reserve volume + tidal volume)
• Total lung capacity: the volume of air in the lungs at a maximal in-breath (a total of all 4 colours in the diagram below)
• Vital capacity: max inhal -> max exhal: volume of air you can move in AND out of your lungs via a maximal inhalation and maximal exhalation

Reading an Expirograph Trace

Vt curves in 1min = normal relaxed breathing

FEV = forced expiratory volume (how much air you can push out of lungs in first second of exhalation – important for testing respiratory disorders.

RR = when counting respiratory rate count only the peaks

Gas Exchange at Respiratory Membrane

RM = Simple squamous cells on the wall of the alveolis.

1. Respiratory membrane is thin: so its a great place for gases to exchange – gases have a short distance to move

2. Cell membranes are made out of lipids and gases are also lipid soluble: So they can move freely and quickly across the membrane without relying on a transport mechanism

3. Differences in partial pressure across the respiratory membrane are large: Gases move from high to low pressure. So your O2 partial pressure is higher in the alveolis and lower in the deoxygenated blood.

4. Lots of alveoli = Large total surface area: 30 to 50m² per lung for gas exchange to occur

5. Blood flow and airflow are co-ordinated: high blood flow around the alveoli + blood and air flow can be modified (width of bronchiols change to get Co2 out)

Partial & Total Pressures

DALTONS LAW – the sum of the PARTIAL PRESSURES of each of the gases in a given mixture equal the TOTAL PRESSURE EXERTED by the GAS MIXTURE.

A pressure of a combination of gases is a sum of its part = the total pressure of the air is the sum of the N2, O2, CO2, H20.

Understand if your blood stream has a lot of CO2 its easier to get it out because the air outside going into your lungs has a low partial pressure of CO2.

GAS EXCHANGE OCCURS ACROSS THE RESPIRATORY MEMBRANE BY DIFFUSION.

Air is a MIXTURE OF GASES – Nitrogen 78.6%, Oxygen 20.9%, CO2 0.04% and some water. Each of these gases is moving around in the atmosphere and their combined pressure contribute to ATMOSPHERIC PRESSURE (760mmHg). We know % of gases in atmosphere and atmospheric pressure is 760mmHg, we can calculate the partial pressures of each of the gases. Eg O2 is 20.9% of 760mmHg , has a Po2 of 159mmHg.

Gas Diffusion

When a gas under pressure contacts liquid, the higher the pressure of the gas, the more gas will go in to solution until a state of equilibrium is achieved.

Increase pressure of gas = more gas goes into solution, decrease pressure of the gas = more gas comes out of solution.

Diffusion of gases occurs at the respiratory membrane + gases move into and out of a solution

Henry’s Law

Amount of gas in a solution depends on: partial pressure of the gas & the “solubility” of the gas

O2 = low solubility in blood

CO2 = ~20x higher

Higher partial pressure? More gas in solution

Lower partial pressure? Gas comes out of solution

Partial Pressures of Gases in Respiratory system

Focus on the relative differences between different parts of the respiratory system.

When oxygenated blood arrives at the metabolizing tissues (muscles) there a much higher concentration / partial pressure of oxygenated blood than there is in your metabolizing tissues. So the O2 will tend to move out of your O2 blood and into metabolizing tissues. The reverse happens for Co2. Explains the difference in 95mmHg oxygenated to 40mmHg metbolising tissues.

Alveolar Air

PO2 = 100mmHg

PCO2 = 40mmHg

Blood

Deoxygenated:

PO2 = ~40 mmHg

PCO2 = 45 mmHg

Oxygenated:

PO2 = ~95 mmHg

PCO2 = 40 mmHg

Metabolising tissues

PO2 = 40mmHg

PCO2 = 45mmHg

Oxygen Transport & Storage

O2 does not easily dissolve in blood plasma: Only 1.5% is transported this way – so it’s not en efficient way to get O2 from your lungs to target tissues.

Different transport mechanisms required: Majority of O2 – 98.5% is transported by RBCs

Temporary storage

Released quickly and easily

from RBCs

Bound to haemoglobin

Act like ‘taxis’

Oxygen and CO2 are not very soluble in blood and so to counteract this problem the RBCs pick take up the gases from the plasma and transport them through the circulation.  This removal of gas from solution contributes to the continual diffusion of gases into and out of the blood.

The important thing about this transport system is that the RBCs are temporary vehicles and the gases are able to leave the RBCs when necessary.  They kind of act like taxis.

Haemoglobin (Hb) molecules in RBC’s carry O2 as oxyhemoglobin

One heme unit can carry up to four molecules of O2: As PO2 ↑, saturation rate of Hb also ↑

PO2 has to drop to 60mmHg before % saturation of Hb is significantly affected

Oxygen Saturation Curve

O2 is bound to Hb molecules in RBCs – remember one heme unit can carry up to four molecules of O2.  The amount of heme units containing oxygen at a given moment is called the HEMOGLOBIN SATURATION. Eg if all heme units are loaded with o2 saturation is 100%, if all heme units only carry 2 molecules of o2 each, saturation is 50%.

As the partial pressure of oxygen increases, the saturation rate of haemoglobin increases.  So at around a partial pressure of 100mmHg of oxygen there is almost 100% saturation of Hb.

As PO2 goes up, Hb binds O2 as it lowers, Hb releases O2 – describe in the tissues, Po2 is low so the oxygen will move from Hb to the tissues, at the alveoli, the PO2 is high and Hb will bind it.

Point out that PO2 has to drop to 60mmHg before % saturation of Hb is significantly affected.

Practical relevance: Carbon monoxide is much more capable of binding to hemoglobin than O2, kicks off all the O2 and you don’t get enough O2 into your body. An improperly working heating system will produce CO. But you can’t see it or smell it.

Carbon Dioxide Transport & Storage

Carbon dioxide is carried in the blood in three ways.

It is converted to a molecule of CARBONIC ACID: CO2 + H2O – HCO3 + H+

  About 70% of CO2 transported this way. Reversible reaction to recover CO2 Hydrogen ions bind to Hb (buffering system), bicarbonate moves out into plasma

  Bound to Hb – about 23% of CO2 is carried bound to Hb.

  Carried in the plasma – around 7%

In form of Bicarbonate ions

CO2 + H2O Û H+ + HCO3-

Reversible reaction

Carbonic anhydrase = enzyme

Approx 70% of CO2 is carried in this biocarbonate ion

Bound to Haemoglobin

Approx 23% transported via haemoglobin

Dissolved in the plasma

Approx 7% carried this way

 

Learning Objectives

Define and compare the processes of external and internal respiration

List the physical principles governing the movement of air into the lungs

Describe the actions of the respiratory muscles responsible for respiratory movement

List the respiratory volumes and capacities as measured using spirometry

Explain the important features of the respiratory membrane

Summarise the physical principles governing the diffusion of gases into and out of the blood

Describe the partial pressures of oxygen and carbon dioxide in alveolar air, blood and the systemic circuit

Describe gas transport in blood

Describe the major steps involved in internal respiration

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Control Of Respiration (W9)

Lecture #22 (8.5.17)

How to Increase Respiration

As just mentioned can our resp system is designed to allow us to increase the capacity or volume of air moving through when we need to. We can increase or decrease the amount of air to meet the body demands within a single breath.

Respiratory rate is NUMBER OF BREATHS P/min – round 12-18 resting, kids around 18-20 bpm.

Tidal Volume – Vt is the amount of air we move in a single resp cycle ie one inspiration and one expiration – around 500mls.

We can INCREASE the respiratory volume that is the amount of air we breathe in and out by increasing our TIDAL VOLUME and our RESP rate.

As we said with a single breath we can change the amount of air reaching the lungs this is due to the CAPACITIES of our lungs.

Control of Respiration

Oxygen is continuously distributed to the cells and tissues. CO2 is continuously taken away. If a change in o2 consumption occurs and the demand increase, the body needs to react fairly quickly.

Two main ways in which this happens

Locally – remember we have talked about CO2 is a vasodilator.  Talk about if oxygen levels at a given tissue decrease, the Co2 levels build up which stimulates the local blood vessels to vasodilate – increase blood flow, increase o2 delivery and CO2 removal.

Centrally – respiratory centres in the brain control respiration RATE and DEPTH.

Regulated by: 

1. Autoregulation (local tissue level)

  Changes in blood flow and O2 delivery in lung and target metabolising tissues

2. Respiratory Centres of CNS (central response)

  Control depth and rate of breathing

Autoregulation

Can happen at…

1. Target Metabolising Tissues

Local changes in O2 and CO2 can result in automatic changes in blood flow and O2 delivery

Target tissues: (a) partial pressure differences and (b) vasodilation due to increased CO2.

High partial pressure of CO2 = blood vessels vasodilate to enable more oxygenated blood to come into tissue.

2. Lungs

Lung perfusion (blood flow)

Alveolar ventilation (air flow)

Local Control of Respiration

Lung Perfusion (blood flow)

When PO2 is low alveolar capillaries constrict (opposite in tissue of the body) blood flow is re-directed toward areas where PO2 is relatively high

High PO2 in alveoli will diffuse into lower PO2 in capillaries

At lungs – two main things happen

  LUNG PERFUSION rate changes – ie blood flow to the lungs increases especially towards capillaries around alveoli where Po2 is high. High Po2 in the alveoli will diffuse into lower Po2 in the capillaries

Alveolar Ventilation (air flow)

ALVEOLAR VENTILATION: airflow into alveoli – is guided by CO2. Where the air goes in the lung and whether it will bronchodilate or bronchoconstrict is guided by concentration of PCO2 in the alveoli.

Bronchioles with high PCO2 will bronchodilate to increase the amount of air flowing through, thereby increasing CO2 output and increasing O2 input.

↑ CO2, diameter of bronchioles increase (bronchodilation)

↓ CO2, diameter of bronchioles decreases (bronchoconstriction)

Airflow is directed to lobules where the CO2 is high

Pressure Relationships between Inhalation/Exhalation

Ventilation

Pre-Prac

As the DIAPHRAGM moves INFERIORLY (contracting), VOLUME INCREASES, if moves SUPERIORLY (relaxing), volume DECREASES.

Inhalation

Exhalation

Factors That Affect The Rate And Depth Of Respiration: Central

Factors That Affect The Rate And Depth Of Respiration: Peripheral

Summary of Ventilation Regulation

Proprioceptors Side Note: One of the reasons we often lift with no shoes/socks on is because we have a lot of proprioceptors in our feet which are important for sending impulses to our brain regarding joint and muscle movements  – specifically of how the ankle and feet are moving in relation to the rest of the body.

Respiratory Regulation of Blood pH

Central Control of Respiration

We can control our respiratory rate voluntarily and involuntarily

Voluntary Control

Conscious control of resp rate and depth

Involuntary Control

Brain control over respiratory muscles and rate and depth of respiration.Brain control of rate and depth

Centres in Medulla and Pons

Control rate and depth of respiration, located in brain stem and work in a hierarchical fashion

Respiratory Control Centers in Medulla Oblongata

Dorsal (towards back) Respiratory Group (DRG)

Ventral (towards front) Respiratory Group (VRG)

Interaction between DRG and VRG determines rate and depth of respiration

Respiratory Control Centres in Pons (Pontine Respiratory Group: PRG)

Apneustic Centre

Pneumotaxic Centre

 

Central Control of Respiration: DRG

Stimulates the muscles of inspiration – they make the diaphragm switch on to contract and breath in then the DRG switches off upon exhalation.

Inspiratory Centre

Motor neuron control of diaphragm and external intercostal muscles

maintains a constant breathing rhythm

Functions for both quiet   and forced inspiration

When DRG activity ceases, allows expiration

Central Control of Respiration: VRG

Functions only during forced breathing during active expiratory and inspiratory centres

Capable of activating the accessory respiratory muscles

Remind students that during normal breathing EXHALATION IS A PASSIVE PROCESS as EVERYTHING RELAXES, EXHALATION OCCURS, (DRG INSPIRATORY CENTRES ARE INHIBITED,  only during forced breathing do we have neuronal input to EXHALATION.

Central Control of Respiration: PRG

Apneustic Centre

Increases the depth of inhalation by stimulating the DRG.

↑ depth of inhalation

Pneumotaxic Centre

(Pneumo = breathing / taxic = rate) Critical in influencing the rate of breathing.

It does that by inhibiting the DRG.

Allow relaxation (therefore control overall rate)

↑ pneumotaxic output, ↑ respiration rate by ↓ duration of each inspiration

↓ pneumotaxic output, ↓ respiration rate but depth ↑ due to more activity in apneustic centres

Respiratory Reflexes

Respiratory reflexes respond to changes in sensory information

1. Chemoreceptor Reflex
2. Baroreceptor Reflex
3. Stretch Reflex (Hering-Breuer Reflex)
4. Protective Reflex

Chemoreceptor Reflex

Chemoreceptors will adapt to chronic stimulus: e.g. if have chronic respiratory disease with altered levels of CO2 and O2, the chemoreceptors will adapt to these, resisting changes

We have chemoreceptors that are sensitive to changes in pH of the blood and CSF present near the carotid artery, aortic arch (peripheral chemoreceptors) and in the medulla oblongata of the brain (central chemoreceptors). These receptors are sensitive to a drop in pH of the blood which can be induced by high levels of CO2. (So when high levels of lactate/H+ are present)

When chemoreceptors detect this change, they send a message to respiratory centres and increase RATE AND DEPTH of breathing.

Point out that DROPS IN O2 LEVELS ARE NOT THE STIMULUS AND THAT THEY HAVE TO DROP BY ALMOST HALF TO STIMULATE RESP CENTRES.  HOWEVER, CO2 LEVELS ONLY HAVE TO RISE BY 10% TO DOUBLE THE DEPTH AND RATE OF BREATHING.

HYPERCAPNIA – increase in PCO2 in arterial blood.  Most common cause is HYPOVENTILATION – low respiratory rate, co2 accumulates in the blood.

HYPOCAPNIA – decrease in PCO2 in arterial blood.  Generally caused by HYPERVENTILATION.

Chemoreceptors respond to changes in pH (H+), CO2 and O2

Where are they located?

Peripheral Chemoreceptors

Carotid artery (carotid bodies) + Aortic arch (aortic bodies)

Central Chemoreceptors

In the Medulla Oblongata

O2 isn’t very important for regulating respiration. Carbon dioxide (CO2) is the most important factor in regulating respiration under normal conditions along with the concentration of H+ and hence pH levels is the most decisive factor for respiration.

If you get asked Q’s on how respiration is regulated make sure you state that O2 is NOT the main driver, that CO2 is.

10%  increase in CO2 (hard to d0) = respiratory system will double your RR and TV

Increased CO2 → more hydrogen ions (H+) in brain and in blood = more acidic blood (pH will drop)

Senses this change in brain [cerebrospinal fluid] → activates central chemoreceptors → stimulate inspiration

Also senses in blood → activate peripheral chemoreceptors in aortic arch and carotid arteries  → increase ventilation

O2 : less important. Needs to drop to about 50mmHg before it has an effect on how respiration if regulated which is a big drop. (95-100mmHg is normal) Acts peripherally

Baroreceptor Reflex

  Signal to CARDIOVASCULAR CONTROL CENTRES in the medulla oblongata to decrease cardiac output, vasodilate to decrease BP.

  Also signal sent to respiratory centres in the medulla – when BP falls, resp increases, when BP rises, resp rate decreases.

Baroreceptors detect changes in blood pressure

  Baroreceptors stretch sensitive in the aorta and carotid sinuses = perihelia reflex

 Main action = signal cardiovascular control centres in medulla 

↓ cardiac output, vasodilate to ↓ BP

 But also: signal sent to respiratory centres in medulla to influence respiratory rate

↑ BP = ↓ respiratory rate

↓ BP = ↑ respiratory rate

Hering-Breuer (stretch) Reflexes

Mostly not important in healthy adults.

Stretch sensitive receptors in smooth muscle of bronchi and bronchioles in the lungs that prevent the lungs from over inflating and help the lungs to deflate. NOT INVOLVED IN NORMAL QUIET BREATHING.

What center is responsible for preventing the lungs from over inflation?

The pneumontaxic centre is a network of neurons that inhibits the actibity of neurons in the DRG, allowing relaxation after inspiration, and thus controlling the overall rate.

An increase in ___ will stimulate the peripheral chemoreceptors to initiate respiration.

pCO2.

Increasing CO2 levels can lead to increased H+ levels. Peripheral chemoreceptors sense arterial levels of H+. When peripheral chemoreceptors sense decreasing pH levels, they stimulate an increase in ventilation to remove CO2 from the blood at a quicker rate. Removal of Co2 from the blood helps to reduce H+, thus increasing systemic pH.

Stretch sensitive receptors i

Largely inactive in adults. May be important in newborns

Inflation Reflex

Stops lung over expansion during forced breathing by activating stretch receptors in the walls of the bronchi to inhibit DRG (i.e. inhalation) and stimulate expiratory centre of VRG: stop inhalation, get active exhalation.

Deflation Reflex

Stops total lung deflation

Inhibit the expiratory centres and excite the inspiratory centres when the lungs are deflating.  Receptors lie in the alveolar wall.

Also receptors in alveolar wall, inhibits expiratory centers and stimulates inspiratory centers

Practical Relevance: It’s suspected the deflation reflex kicks in in newborns taking their first breath. A babies lungs are filled with fluid and the lung is collapsed upon birth – they need to take their first breath to inflate the lungs. The thought is, the deflation reflex kicks in once their born to stimulate their first breath.

Protective Reflexes

Exposure to toxins, chemicals or mechanical stimulation of respiratory tract initiate sneezing, coughing, laryngeal spasms via receptors located in respiratory tract.

       Act to close airway temporarily and suspend respiration

 Sneezing

Triggered by irritation of nasal cavity wall. Air can pass out up to speeds of 160kms/h

 Coughing

Triggered by irritation of larynx, trachea or bronchi

 Laryngeal Spasms

 Triggered by entry of chemical irritants, foreign objects or fluids around glottis

               What will happen if I hold my breath? What mechanisms will come into play?

You can’t kill yourself by holding your breath. As you hold your breath you’re brain senses you’re not getting enough CO2 because the rising PCO2 will eventually force you to take a breath via the chemoreceptors.

This can be dangerous in some situations. E.G. if you walk into a atmosphere that is low in O2, you won’t notice, nor feel an urge to breathe more, because you’re still getting rid of excess CO2. (Unless your blood O2 levels drop 50mmHg~) Instead you’ll simply pass out, which is a bad thing to be doing in a atmosphere that doesn’t have enough O2.

Divers sometimes take advantage of biology to increase their breath-holding time by hyperventilating before they dive. After hyperventilating, the diver feels a reduced urge to breathe and can stay underwater longer. This isn’t because he’s loaded up on oxygen (he isn’t). Rather, it’s because he’s lowered the amount of carbon dioxide in his body. As a result, it takes longer to trigger the brain’s safety mechanism that forces the diver to start breathing again. This practice is dangerous on several counts. The most obvious risk is that both oxygen deprivation and carbon dioxide overload lead to dizziness and can cause a blackout, which will leave the diver lying quietly unconscious at the bottom of a body of water.

Learning Objectives

Describe the factors that influence respiration

Describe the brain centers (medulla oblongata and pons) involved in the control of respiration

Identify and describe the respiratory reflexes (chemoreceptor, baroreceptor, stretch and protective) involved in the control of respiration

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Digestive System (W9)

Lecture #23 (9.5.17)

Functions of the Digestive System

• Ingestion: materials enter via the mouth
• Mechanical processing: chewing – also increases surface area for enzymatic digestion of food particles.
• Secretion: of water enzymes, buffer acids by gut epithelium to break food down.
• Digestion: Process by which large molecules get broken down into small molecules. AKA chemical breakdown of foods for absorption in the intestine.  This occurs with the secretion of different enzymes from the gut.
• Absorption: Taking substances into the cells of the body.
• Excretion: removal of waste products from body fluids.
• Elimination: of undigested components

Components of Digestive System

Digestive Tract

Contents pass through: Oral cavity, pharynx, oesophagus, stomach, small and large intestine

Accessory Organs

Contents don’t pass through: Salivary glands, liver (one of the largest organs), gall bladder and pancreas

Oral Cavity / Buccal Cavity

Functions:

Analysis, mechanical processing, moistening, mixing with salivary secretions

  Lubrication and some digestion of carbohydrates and lipids.

  Lined with ORAL MUCOSA – stratified squamous epithelium

UVULA – dangly bit at the back of the oral cavity helps to stop food from entering the pharynx too early.

  Contains LINGUAL PAPILLAE on the superior surface (DORSUM) these are fine projections assist in moving materials

 Inferior surface contains LINGUAL FRENULUM – fold of mucous membrane that attaches tongue to floor of oral cavity.  Salivary ducts sit on either side of this. LF helps to prevent extreme movements of the tongue but if inhibited too much, cant speak or eat normally, can be surgically corrected.

Longest male tongue is 9.5 cm, longest female is 7cm

Pharynx

Pharynx is the passage way for food, liquids and air.

We’ve already talked about the epithelia lining the pharynx when we talked about the respiratory system. Stratified squamous epilthelium to protect from mechanical damage of food etc.

It also has mucous glands

Contains PHARYNGEAL CONSTRICTOR MUSCLES to push the bolus of food towards the oesphagus

The pharynx is shared by the food that we take in and the air we breath via the trachea.

Epiglottis is involved in making sure we don’t get food into the trachea. It folds down onto the opening of the trachea so food goes down the pharynx.

Muscular propulsion of materials into oesophagus

Passageway for food, liquids and air

Stratified squamous epithelium: Mucous glands

Pharyngeal constrictor muscles: Push bolus of food towards oesophagus

Other muscles involved in support and swallowing

Oesophagus

Function is to transport of materials to the stomach

Muscular tube, ~25 cm in length / 2cm diameter

Upper and lower (cardiac) oesophageal sphincter. A sphincter is a circular muscle that can contract or relax to regulate the flow of substances.

Descends from the mouth down through a gap in the diaphragm called the OESOPHAGEAL HIATUS, empties into stomach in abdominal cavity.

Oesophagus has MUCOSA layer, SUB MUCOSAL layer and Muscularis Externa with ADVENTITIA instead of a SEROSA layer in this region

Also has its own distinctive features:

stratified squamous epithelium

  Large folds of the mucosa and submucosa – allow swallowing of a large bolus (ability to expand)

  Some skeletal muscle fibres are present in the upper third of the oesophagus

 Adventitia (outermost layer of the wall of a blood vessel) rather than serous layer – connective tissue to anchor oesophagus in position.

Layers of the Alimentary Canal

Four basic tissue layers:

Mucosa: a mucous membrane

Submucosa: blood vessels/lymphatics/nerves

Muscularis: Circular + longitudinal muscle

Serosa: outer layer

Lumen = empty space

Stomach

Can store 1-1.5L of contents

Four Major Functions

  1. Storage of ingested food

2. Mechanical breakdown of ingested food

  3. Break down of chemical bonds in food (via acid and enzymatic reactions)

4. Production of a  glycoprotein (intrinsic factor) that is essential for Vitamin B12 absorption in the small intestine

  All of this produces a viscous soupy mix that is highly acidic called CHYME.

Four Main Regions

  The Cardia – smallest part of stomach – large proportion of mucous glands CONTACTS WITH OESOPHAGUS

  The Fundus – contacts with the diaphragm

  The Body – largest part of the stomach – acts as MIXING TANK – has GASTRIC GLANDS involved in the digestive processes that occur in the stomach

  The Pylorus – curved portion of stomach empties into small intestine – sphincter that regulates release of chyme into the duodenum of SI.   Glands in this region secrete hormones such as GASTRIN which stimulates the activity of the gastric glands.

When stomach is empty, RUGAE can been seen and these are TEMPORARY folds that allow the stomach to expand.

Stomach contains extra layers of smooth muscle –circular, longitudinal and oblique layer help to give more strength for the churning to form CHYME. CHYME is partly what we vomit.

 

The Stomach Lining

Mucous produces mucus to protect the inner surface lining of the stomach because of how highly acidic it is.

Parietal Cells: Responsible for producing intrinsic factor (IF) – important for Vitamin B12 absorption + producing hydrochloriuc acid

Chief Cells: Produces pepsinogen – promotes the break down of proteins

Small Intestine

Major role in digestion and absorption of nutrients.

99% of nutrient absorption occurs in SI / Around 6 m in length

3 main sections

Duodenum – closest to stomach – receives stomach juices

 Jejunum middle region where most of the absorption of nutrients occurs

Ileum – final and longest segment of SI.

Small Intestinal Wall

SI has a series of small folds called PLICAE on which villi sit. This increase SA available for absorption of nutrients.

Each villus has a network of capillaries which carry the absorbed nutrients to the liver for further processing before entering the general circulation. 

The villus also contains a LACTEAL which is a lymphatic vessel that is responsible for the absorption of fatty acids and protein – lipid products that are too big to diffuse into blood stream. Enter via lymph through drainage into thoracic duct.

Large Intestine

Main job is the dehydration and compaction of indigestible materials in preparation for elimination.

Begins at end of ileum and ends at anus. Fecal matter is dehydrated as it gets closer to the anal canal as to preserve water.

  3 Main functions

  Reabsorption of water and compaction of intestinal components into faeces

  Absorption of important vitamins

  Storage of fecal material before defecation.

Approx 1.5metres in length

3 parts of the LI

  Caecum –pouch  region at beginning of LI important in compacting fecal material

  Colon – -largest part of LI – has three bands of longitudinal muscle

  Rectum – last part of LI – expandable region for temporary storage of fecal material. 

Movement of fecal matter in the rectum triggers the urge to defecate. Internal anal sphincter not under voluntary control, External anal sphincter –skeletal muscle – under voluntary control

Large Intestinal Wall

Diameter of LI is around 3 X that of SI, however walls are MUCH THINNER.

NO VILLI in COLON.

Lots of GOBLET CELLS to provide mucous to lubricate the lumen as the fecal matter becomes drier and more compact.  No DIGESTIVE ENZYMES PRODUCED HERE.

Peristalsis

How the materials are moved along the digestive tract.

We get the contraction of circular muscle which prevents food bolus from moving backwards and the longitudinal muscle shortens that part of the tract to force the bolus through. It acts as a wave of contractions via the circular and longitudinal muscle.

Diagram applies to any part of the digestive tract.

Salivary Glands

Secretion of lubricating fluid containing enzymes that break down carbohydrates.

Salivary Glands

1. PAROTID SALIVARY GLANDS – lie near the surface of the mandibles (jaws).  Secrete an thick serous secretion contains lots of SALIVARY AMYLASE which breaks down starches. Drain through PAROTID DUCT that empties near the second UPPER MOLAR.

2. SUBLINGUAL SALIVARY GLANDS – lie on the floor of the mouth. produces watery mucous secretion that acts as a lubricant.

  Sublingual ducts that open on either side of the LINGUAL FRENULUM.

3. SUBMANDIBULAR SALIVARY GLANDS – lie in the depression of the floor of the mouth called the MANDIBULAR GROOVE. Secretes a mixture of buffers, mucous and salivary amylase.

Saliva

Produce 1-1.5 litres produced per day / 99% water

1% electrolytes, buffers: to help keep pH of mouth around 7.0,

Glycoproteins: mucins responsible for lubricating saliva

Antibodies, enzymes and wastes (help to remove oral bacteria)

Functions

Lubricate the mouth

Moisten and lubricate material in mouth

Stimulate taste buds by dissolving chemical in food

Initial digestion of carbohydrates

Initiating digestion such as starches using the enzyme SALIVARY AMYLASE.

 

 

Liver

Largest organ in abdominal cavity-  two main lobes, left and right.

Role of liver is to FILTER BLOOD/Regulate blood composition – to ensure nutrient concentration is adequate and to clean up blood removing abnormal cells and pathogens.

Metabolic Functions

  Regulates blood composition

  Removes and stores excess nutrients such as carbohydrates, lipids, amino acids, vitamins

 Extracts toxins from the blood – inactivates drugs, removes waste products including ammonia and old RBC.

Haematologic Functions

  Removes old and damaged RBCs

  Removes pathogens

  Synthesises plasma proteins

  Synthesises and secretes bile (important for lipid digestion)

Liver Strcuture

Hepatic = liver

 

Blood enters from the portal vein from the SI with high concentrations of nutrients -> blood enters blood vessels -> flows through sinusoids -> where hepatocytes can store away excess nutrients -> eventually joins central interlobular vein back to regular circulaton.

Bile produced in the hepatocytes and secreted and collected in the liver so it can head off to the gall bladder.

Gall Bladder

Storage and concentration of bile where it eventually goes down the bile duct to the duodenum (first part of the SI)

Bile

About 1 L of bile produced by liver each day, travels to gall bladder for storage.

  Function of bile is to help digest LIPIDS – breaks lipid droplets apart in a process called EMULSIFICATION (takes large lipid droplets and breaks them down into small lipid droplets) – this makes it easier for enzymes to attack the lipid droplets. Bile salts also promote the absorption of lipids. Most bile salts are reabsorbed in ileum and recycled.

Helps in lipid digestion

Emulsification – ­surface area of lipid droplets for enzyme degradation

Promotes absorption of lipids

Reabsorbed in ileum and recycled

Pancreas

Lies posterior to stomach and extends from duodenum to spleen.

  Lobular textured organ

Point out this is an exocrine and endocrine organ.

  Exocrine organ –produces digestive enzymes and buffers which are delivered to DUODENUM via the PANCREATIC DUCT.

  Pancreas is divided into distinct lobules. Within the lobules the ducts branch to end in blind pockets called PANCREATIC ACINI.

  PANCREATIC ACINI – form exocrine portion (major portion) of pancreas, secrete PANCREATIC JUICE which contains digestive enzymes, water and ions into SI.

  Types of enzymes secreted – alpha amylase – breaks down CHOs

 Lipase –lipids, nucleases – nucleic acids, Proteases and peptidase –proteins.

  PANCREATIC ISLETS form ENDOCRINE PORTION – secrete insulin and glucagon into blood stream involved with glucose storage and release.

Exocrine cells secrete buffers and digestive enzymes

Endocrine cells secrete hormones

Learning Objectives

List the functions of the digestive system

Identify the organs of the digestive tract and the accessory digestive organs

Describe the major structures and regions of the organs of the digestive tract including the oral cavity, pharynx, oesophagus, stomach, small and large intestines

Describe how materials are moved along the length of the digestive tract

Describe the structure and function of the accessory digestive organs including the salivary glands, liver, gallbladder and pancreas

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Digestion & Absorption of Nutrients (W9)

Lecture #24 (11.5.17)

Regulation of Digestion

1. Local Mechanisms

pH of the contents where taking in

Physical stimulation of new materials in the digestive tract

Chemical stimulation

2. Neural Mechanisms

Autonomic control: Sympathetic stimulation + Parasympathetic stimulation

Neuronal reflexes: Short and long

3. Hormonal mechanisms

Digestive tract produces hormones: Gastrin, secretin, cholecystokinin, GIP (gastric inhibitory polypeptide)

Digestion in the Oral Cavity

Digestion begins in the oral cavity as we talked about yesterday.  Mechanical digestion by chewing, tearing flattening to allow greater surface area for enzymic attack.  Also the production of saliva by the salivary glands.

SALIVA

  Glands produce between 1-1.5 litres of saliva per day.  99% of which is water. Rest is electrolytes, buffers – keep pH of mouth around 7.0, glycoproteins (mucins, responsible for lubricating saliva), antibodies (help to remove oral bacteria), enzymes and wastes.

Functions of Saliva

  Lubricate the mouth,

  Moisten and lubricate materials in mouth

  Stimulate taste buds by dissolving chemical in food

 Initiating digestion of carbohydrates such as starches using the enzyme SALIVARY AMYLASE.

Salivary α-amylase

Produced by salivary glands

Initial digestion of carbohydrates

Lingual lipase

Lingual = tongue / Lip = Lipid

An enzyme to breakdown lipids that comes from the toung

Produced by small glands in the tongue

Digestion in the Stomach

Food moves from oral cavity to oesophagus to stomach where next lot of digestion occurs.

As we said both mechanical digestion by stomach churning and moving about, plus production of acid to break down chemical bonds in food.

As food hits the stomach from the oesophagus, the salivary amylase continues to break down carbohydrates until the pH drops below 4.5 as stomach acid levels build up.

As the pH levels drop the enzyme PEPSIN that is secreted from the CHIEF CELLS in an inactive form, is activated and protein digestion begins.  Not all of the protein is digested in the stomach because PEPSIN only acts on certain peptide bonds so it generally breaks the proteins down into smaller parts.

No absorption of nutrients in the stomach due to – layer of mucous to protect the epithelia from acid contents

  No transport mechanisms in the epithelial cells for nutrient uptake

  Digestion is not complete by the time the chyme is ready to leave the stomach (ie not fully broken down).

Mechanical

Churning movements of stomach

Chemical

Acid breaks down chemical bonds

Pepsinogen from chief cells converted to PEPSIN – begin protein digestion

No Absorption of Nutrients

Protective mucous layer

Absence of transport mechanisms

Incomplete digestion prior to exit from stomach

Digestion & Absorption in the Small Intestine

Contents spend around 5 hours in small intestine: Approx 5 hours for materials to pass from duodenum to the end of the illeum – what you eat for breakfast may not leave the small intestine til lunch time.

Absorption enhanced by smooth muscle layer movement: Stirs and mixes

Pancreatic enzymes assist in the breakdown of carbohydrates, lipids and proteins. Bile also assists in the breakdown of lipids

Absorption is enhanced by movement of muscle layer of SI – stirs and mixes SI contents

Digestion & Absorption in the Large Intestine

Less than 10% of nutrients absorbed in large intestine

Prepares materials for ejection from body

Main function is to reabsorb water. Of approx 1500mls of material that enters LI, only around 200mls faeces is ejected. 75% water, 5% bacteria and 20% mix of inorganic matter and indigestible materials.

Site of vitamin absorption

Processing & Absorption of Nutrients

Most of the nutrient absorption occurs in the small intestine.  Each of the organic compounds are treated in a slightly different manner.  However the main aim is to break down the bonds between the CHOs, LIPIDS and PROTEINS and this is called HYDROLYSIS.

All enzymes end with the letters ASE

So – CARBOHYDRASES – digest carbohydrates

LIPASES – digest lipids

NUCLEASES – digest nucleic acids

PROTEASES – digest proteins.

Within each of the classes are specific enzymes that target particular bonds between specific molecules for example one carbohydrase may target bonds between glucose molecules but not other sugars.

As food moves along the digestive tract these enzymes are secreted by the salivary glands, tongue, stomach and pancreas which continually break the food particles down into smaller and smaller fragments.

The villi that sit on the plicae of the small intestine are called the BRUSH BORDER.  The BRUSH BORDER secretes enzymes (called BRUSH BORDER ENZYMES ) that participate in the final breakdown of molecules so that they are ready for absorption into the blood stream.

Hydrolysis

Breakdown of bonds between carbohydrates, lipids and proteins

Classes of Enzymes

Carbohydrases, Lipases, Nucleases (breaking down nucleic acid-DNA/RNA), Proteases

Brush Border Enzymes

Job is to breakdown smaller molecules into their simplest forms. (Final breakdown of molecules prior to absorption)

Secreted from villi of small intestine

Carbohydrate Digestion

SALIVARY AMYLASE and PANCREATIC ALPHA-AMYLASE begin digestion of complex carbohdrates.

SA – begins digestion at mouth, breaking CHOS down into DISACCHARIDES and TRISACCARIDES (2 and 3 sugar molecule compounds).  CHO digestion ceases in stomach when stomach pH drops and inactivates the SA.

At the SI, in the DUODENUM, Pancreatic Alpha Amylase that is secreted from the pancreas and travels to the Duo via the pancreatic duct, breaks down the rest of the complex CHOs – only again into TRI and DI saccharides, no further breakdown until they reach the jejunum.

As the tri and di saccs travel further down SI, they are broken down in to MONOSACCHARIDES by the brush border enzymes.

  Maltase – breaks down the disaccharide maltose into individual glucose molecules

  Sucrase – breaks down sucrose into glucose and fructose

  Lactase – breaks down lactose into glucose and galactose.

Absorption of Monosaccharides

Once the CHOS are broken down into monosaccharides by the brush border enzymes – the SI then absorbs them through the epithelium using FACILITATED DIFFUSION and COTRANSPORT MECHANISMS.

FACILITATED DIFFUSION of MONOSACCHARIDES:

  Uses a carrier protein

  Moves only once monosaccharide molecule at a time

  Does not require ATP

  Will NOT occur if there is an opposing concentration gradient

COTRANSPORT of MONOSACCHARIDES

  Moves more than one molecule at a time

  Uses ATP at some stage of the process

  Will work against a concentration gradient of the molecule

Monosaccharides are absorbed in the SI using both of these mechanisms and diffuse into the capillaries for transport to the liver via the HEPATIC PORTAL VEIN.

Once absorbed, monosaccharides move in to capillaries (villi) for delivery to liver via HEPATIC PORTAL VEIN directly to the liver.

Protein Digestion

Proteins are hard molecules to digest due to complex structure. Need strong mechanical processing in oral cavity first.  Chemical processing in stomach via actions of HCL.  The strong acidic environment is also perfect conditions for the actions of the enzyme PEPSIN which is secreted by the chief cells of the stomach to break down peptide bonds in a protein chain.

Once the chyme moves into the SI, the pancreatic proteases start to work:

  Trypsin – breaks peptide bonds at an arginine or lysine amino acid

  Chymotrypsin – breaks peptide bonds where there is a tyrosine or phenylanine amino acid in the chain.

  Elastase – breaks down elastin chains

  Carboxypeptidase – breaks down peptides into individual amino acids.

Note: if students ask why trypsin and chymotrypsin don’t end in ASE, need to tell them that they belong to the class of PROTEASES.

Amino Acid Absorption

Brush border enzymes in the SI: DIPEPTIDASES break small peptide chains into individual amino acids.

Absorption is then via Facilitated Diffusion and Co transport mechanisms

Once in the ICF, the aas diffuse into the capillaries and are transported to the liver via the HEPATIC PORTAL VEIN so the liver can store away any excess nutrients.

Lipid Digestion

 LINGUAL LIPASE secreted from glands in tongue – begin lipid digestion

  PANCREATIC LIPASE from PANCREAS – further digestion of lipids in SI

Triglycerides are broken down to MONOGLYCERIDES and FATTY ACIDS

Once they have reached the duodenum, bile salts also act to emulsify the lipids into smaller droplets which are easier for pancreatic lipase to digest.  Once broken down the small lipid molecules interact with bile salts to form small complexes called MISCELLES which are able to difuse across the SI epithelium into the intestinal cells where new TRIGLYCERIDES are made

New triglycerides are coated with PROTEINS to form CHYLOMICRONS that are too big to diffuse into capillaries but able to enter the lymphatic LACTEALS due to the large gaps in the endothelium.  The CHYLOMICRONS then travel through the lymphatic system and finally enter the blood via the THORACIC DUCT.

Lipid Absorption

Digestive Secretion & Absorption of Water

E.G. We drink 2L a day, we uptake another 1.5L through digestive secretions, pick up another 1.5L through gastric secretions etc picking up more water until most of it is reabsorpted via the SI

Absorption of Ions & Vitamins

Ions: (Na+, Ca2+, K+, Mg2+, Fe2+, Cl-, I-, HCO3-, NO3-, PO43-, SO42-) are absorbed along the small intestine at closely regulated levels to maintain homeostasis – i.e. we don’t want to take in more into the body than what’s required. The body is selective depending on requirements.

The uptake of ions in the SI involves diffusion and active transport mechanisms. Refer to table 24.4 for examples

• Closely regulated
• Mediated by channel-mediated diffusion
• Co-transport
• Active transport
• Carrier mediated transport

Vitamins: Absorption – occurs in LI

Two main groups: WATER SOLUBLE and FAT SOLUBLE and different transport mechanisms for each.

WATER SOLUBLE – 9, B vitamins (milk and meat), Vitamin C (citrus fruits) abosrbed via channel-mediated diffusion along a concentration gradient.

  All except Vit B12 absorbed by diffusion across intestinal cell epithelium

  Vit B12 is required to be bound to INTRINSIC FACTOR which is produced in the stomach.  When bound to IF, B12 is absorbed via active transport.

FAT SOLUBLE

  A,D,E,K – can dissolve in as lipids are being broken down.

  Absorbed in MICELLES (lipid/bile salt complex)

Via diffusion because its movement straight through the cell membrane

Learning Objectives

Outline the mechanisms that regulate digestion

Describe the role of the oral cavity and its secretions in the digestive process

Explain the role of the small intestine and the contributions of the pancreas, liver and gallbladder in digestion and absorption

Explain the role of the large intestines in the digestion and absorption of nutrients

Describe the events responsible for the digestion and absorption of carbohydrate, fat and protein

List the mechanisms involved in the absorption of water, vitamins and minerals

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Urinary System (W10)

Lecture #25 (15.5.17)

Functions of the Urinary System

Role is to filter blood and rid the body of organic wastes. Most physiological wastes are removed by the urinary system.

Urinary System Has 3 Major Functions

1. Excretion: Removal of organic waste products from body fluids

2. Elimination: Discharge of waste products into the environment

3. Maintenance of blood plasma concentrations, fluid and ion (sodium, potassium, chloride, etc_ homeostasis – ensuring the fluid and ionic composition of the extracellular fluid is balanced by letting them go or up-taking them.

Additional Functions:

Regulation of blood volume and blood pressure: the more BV the greater the BP. BV is a means by which we can regulate BP.

Helps to stabilise blood pH. E.G. If we have excess H+.

Conservation of valuable nutrients

Assists the liver to detoxify poisons

While the main role of the kidneys is in the removal of wastes, the maintenance of fluid volume and ion concentrations are also an essential function performed by the kidney.

The way the Kidney Maintains Fluid and Ion Balance is by:

Regulation of blood volume and pressure – through controlling the amount of water lost in urine.  The kidneys also release the enzyme RENIN – which sets off a cascade of reactions to produce aldosterone which is a hormone responsible for increasing BP promotes water reabsorption, and ERYTHROPOIETIN a hormone released when o2 levels are low and stimulate RBC production.

Regulating plasma concentration of Na, K, Cl and other ions – by controlling how much is excreted in the urine. Also produces hormone CALCITRIOL which promotes Ca absorption in the SI.

Helps to stabilize blood pH by controlling loss of Hydrogen Ions and bicarbonate ions in urine

Conserves valuable nutrients – by preventing their excretion in the urine

Helps the liver –to detoxify the blood.

Components of the Urinary System

ORDER BY WHICH URINE PASSES: COLLECTING DUCT -> RENAL PELVIS -> URETER -> BLADDER -> URETHRA

Excretion is performed in the KIDNEYS – organs that produce URINE -> Urine is a fluid that contains water, ions and small soluble compounds -> Urine leaves the kidneys and travels via the URETERS to the URINARY BLADDER. -> The URINARY BLADDER is a muscular sac for the temporary storage of URINE. -> As it exits from the bladder, URINE passes through the URETHRA which conducts urine to the external environment. -> The elimination of urine is known as URINATION or MICTURITION.

Location of the Kidney

Structure of the Kidney

Kidneys are bean shaped organs that lie on the posterior wall of the abdominal cavity between vertebrae T12 and L3.  They are about 10cm in length and about 3cm thick. They have a prominent indentation called the HILUM which is the entry and exit point for the major blood vessels and nerves associated with the kidney.

Pyramid = where urine production occurs

The RENAL SINUS is an internal cavity within the kidney. The main blood vessels of the kidney that enter through the HILUM, branch in the renal sinus. The kidney has an OUTER CORTEX layer And an inner MEDULLA region. The MEDULLA is arranged into DISTINCT TRIANGULAR structures called RENAL PYRAMIDS.  The tip of the pyramid is known as the RENAL PAPILLA which projects into the RENAL SINUS. Each pyramid is separated by a band of CORTEX called a RENAL COLUMN. A RENAL LOBE consists of a PYRAMID, COLUMN and the overlying CORTEX. –the renal lobes are the site of URINE PRODUCTION. Ducts from the RENAL PAPILLA drain into the MINOR CALYX which merge to form the MAJOR CALYX which again merge to form the RENAL PELVIS.. The kidneys are covered by an outer layer of collagen fibres called the RENAL CAPSULE.

Urine production occurs in microscopic tubular structures called NEPHRONS which are the basic units that make up the kidneys.  Each kidney has roughly 1.25 million nephrons with a combined length of about 145km.

Blood Supply To The Kidneys

Our kidneys receive about 25% of total cardiac output.  What this means is around 1200mls of blood flows through the kidneys in each minute.

Blood is received into the kidney via the RENAL ARTERY which supplies the SEGMENTAL ARTERIES in the renal sinus.  The segmental arteries divide into INTERLOBAR ARTERIES that radiate out through the RENAL COLUMNS (between renal pyramids).  The interlobar arteries deliver blood to the ARCUATE (means curved) ARTERIES which lie along the medulla-cortex border. The ARCUATE ARTERIES supply the CORTICAL RADIATE ARTERIES which reach the cortex regions of the kidney. The CORTICAL RADIATE ARTERIES branch off into smaller ARRERENT ARTERIOLES which supply the capillaries of individual NEPHRONS. From the capillaries, the blood travels into CORTICAL RADIATE VEINS which converge into ARCUATE VEINS that empty into INTERLOBAR VEINS which then drain directly into the RENAL VEIN. That blood then having its organic wastes removed can then join the rest of the body.

Summary

Structure of the Nephron

The nephron is a single unit of the kidney.  There are approximately 1.25 million nephrons in each kidney and their tubular length makes up around 145kms.

Each nephron is responsible for filtering the blood and ensuring a balance of ions and water is reabsorbed into the circulatory system and removes unwanted wastes.

The nephron is made up of a tubular segment – the RENAL TUBULE and the RENAL CORPUSCLE which is the blood supply.

The RENAL TUBULE is where: organic substrates are reabsorbed + approx 90% of water is reabsorbed + waste products are secreted into the tubule.

GLOMERULUS captures filtrate (network of capillaries, where filtration of blood happens) – AFFERENT ARTERIOLE brings blood into nephron, EFFERENT ARTERIOLE carries blood to the tubules of the nephron that form a network of capillaries around them.

Arteriole has smooth muscle and ability to contract/relax.

RENAL CORPUSCLE IS SIGHT OF FILTRATION. Explain blood flows through here and hydrostatic forces push filtrate across GLOMERULAR CAPSULE and into the RENAL TUBULE. Capillaries of GC are FENESTRATED ie PORES to allow filtrate to move out into capsule space.

The renal tubule has TWO TWISTED SEGMENTS

  First is PROX CONVOLUTED TUBULE (Convoluted = twisted)

  Tubule extends into NEPHRON LOOP (descending and ascending limb) which is a chance to concentrate the urine where there’s an uptake of urine

  DISTAL CONVOLUTED TUBULE – continue to get re-uptake of solutes and secretion of substances not required

  COLLECTING DUCT: finally opportunity to adjust composition of fluid

Point out Prox conv and dist con are in CORTEX, LOOP and COLLECTING DUCT in MEDULLA. –These nephrons are called JUXTAMEDULLARY NEPHRONS – account for around 15% of total nephrons.

Rest are CORTICAL nephrons with LOOP quite SHORT.

CORTICAL NEPHRONS responsible for secretion and absorption

JUXTAMEDULLARY NEPHRONS responsible for CONCENTRATION OF URINE.

Renal Corpuscle

The renal corpuscle collects the filtrate which heads off into the proximal convoluted tubule.

Afferent arteriole taking blood in + efferent arteriole taking blood out.

Podocyte are like little filtration slits that allow substances to get out from the capillary. Blood that remains exits out of the efferent arteriole.

Job of the maxula densa and juxtaglomerular cells is to produce a hormone called erythropoietin (EPO) (substance that gets abused in sport). When the blood coming in the afferent arteriole is low in O2 levels that is detected by maxula densa and juxtaglomerular cells to release EPO. The job of EPO is to promote the production of new RBC, in turn increasing the O2 carrying capacity of the blood = better performance with more O2 to muscles during exercise. The problem is if you increase the number of RBC in the blood you also IN the viscosity of the blood = thicker and harder to move through blood vessels.

The other hormone /enzyme (referred to as either or sometimes) that is released is called renin. Renin is released when blood coming through the afferent arteriole is low in pressure. Renin stimulates a hormonal cascade which aims to increase blood pressure and blood flow.

Learning Objectives

Identify the components of the urinary system and describe the primary role that they play in the formation, transport, storage and elimination of urine

Describe the location and structural features of the kidney

Identify the major blood vessels associated with each kidney and trace the path of blood flow through a kidney

Describe the structure of the nephron

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Formation of Urine (W10)

Lecture #26 (16.5.17)

Urine

A fluid containing water, ions and small soluble compounds

Processes of Urine Formation

3 main processes that happen in the formation of urine.

Filtration

In renal corpuscle

Water and small solutes

The force of the blood moving from the afferent arteriole into the glomerular capsule capillaries, squeezes water and solutes across the capillary wall into capsule space.  Solute molecules that are filtered are those small enough to move through fenestrations of capillary and filtration membrane.  Mention that proteins and rbcs are too big to get through membrane.

Reabsorption

Removal of water and solutes from the renal tubular fluid, back into the ECF. Most reabsorbed materials are those that the body uses.  SELECTIVE PROCESS.  Water moves via osmosis.

Secretion

Transport of substances from the ECF into the renal tubules.  Excretion of excess substances that may not have all filtered through GC.  Also method of excretion for drugs.

Urine Eliminated = Filtered – Reabsorbed + Secreted

Renal Corpuscle

Glomerulus

Capillary network: About 50 capillaries

Glomerular Capsule

Cup-shaped chamber

Production of Filtrate

Similar to blood plasma but without the proteins

Proximal Convoluted Tubule

First part of renal tubule

60-70% of filtrate reabsorbed (where most of re-absorption happens)

Reabsorption: Organic nutrients, Ions, Water

Filtrate first enters PCT -> Approx 60-70% of filtrate REABSORBED in PCT ->  reabsorption of organic nutrients (almost all glucose is reabsorbed) -> reabsorption of ions – active and passive transport mechanisms -> reabsorption of water – by osmosis

Not all substances make it through the filtration process and those that are in excess that are not filtered are secreted at the PCT and DCT

Nephron Loop

Reabsorption

THIN Descending Limb – Where a lot of water re-absorption occurs. Permeable to water, Impermeable to solutes

THICK Ascending Limb: Impermeable to water and solutes + Active re-uptake/transport of Na+ and Cl- out of tubule

The Nephron loop is an essential part of the nephron as it plays an important role in the CONCENTRATING URINE

If we’re dehydrated and want to conserve as much water as we can the best we can do is make very concentrated urine so we can conserve as much H2o as possible.

Reabsorption – THIN DESCENDING LIMB – permeable to water, Impermeable to solutes – water flows out, solutes stay in

  THICK ASCENDING LIMB – IMPERMEABLE to WATER and SOLUTES, Na and Cl pumped out by active transport mechanisms. Increases osmotic concentration of fluid surrounding the tubules and forces osmotic movement of water out of thin ascending limb.

Distal Convoluted Tubule

By the time we get here the composition of that filtrate is very different to that which was originally filtered. By this stage we get the selective reabsorption…

Reabsorption

Na+ and Cl- – active transport of (sodium and chloride)

Na+ – K+ exchange pump. I.E. Sodium ions are up taken back into the body at the expense of potassium ions being secreted into the forming urine.

Ca – influenced by PTH and Calcitonin (may have the re uptake of calcium ions if the body is depleted at the time) This is under control of ALDOSTERONE. Ca also reabsorbed under the influence of PTH and Calcitrol

Secretion

  Two important ions that are secreted are H+ and K+ as their concentrations in the body fluids must be carefully maintained.

  K+ are exchanged for Na ions

  H+ are exchanged for Na ions and also secreted as ammonium NH4 ions

K+ – exchanged for Na+ (opposite of what we’re saying with reabsorption)

H+ – exchanged for Na+ and as NH4+ (H+ in excess = low pH = acidic. So we can secrete them into the tubular fluid to get rid of some of those H+)

Only around 15-20% of initial filtrate volume reaches DCT and its composition is quite different from that at the bowmans capsule.

Reabsorption and secretion occur along the DCT. Not all of the materials in the blood are forced into the glomerular capsule, some substances are still in excess and diffuse into the fluid surrounding the renal tubules and are secreted by the PCT and DCT.

Secretion –

Collecting Tubules

 

Last opportunity for the body to adjust filtrate/composition of the fluid prior to entering ureters.

Reabsorption

Na – Na pumps influenced by ALDOSTERONE (adrenal cortex), exchanged for K

Reabsorption of HCO3 (bicarbonate) – in exchange for Cl. HCO3 is a buffer for H+ so its buffering pH – if we have an acidic environment then we can reabsorb bicarbonate ions to increase the buffering capacity of the blood.

  Urea (depending on body requirements)

Secretion

Collecting system is an important site for regulating the pH of the body fluids as it controls the secretion of H and HCO3 (bicarbonate) ions.

  If ECF pH drops, H+ secreted into collecting tubules, HCO3 reabsorbed

  If ECF pH rises, HCO3 secreted into collecting tubules, H reabsorbed.

Filtration Pressure

Like in the other systemic capillaries there is hydrostatic pressure that forces the fluid out of the kidneys and a colloid osmotic pressure that forces fluid back in.

Glomerular Hydrostatic Pressure (GHP)

Hydrostatic pressure = forward pressure of fluid

Due to high BP across capillaries (55mmHg)

Capsular Hydrostatic P – opposes GHP (15mmHg)

HP = GHP-CsHP = 55 – 15 = 40mmHg

Net movement OUT of capillaries

Bp across the capillaries – pushes water and small solute molecules out of capillaries.  THIS P is HIGHER than hydrostatic P at other capillaries due to the arrangement of the capillaries in glomerulus.  Blood flows in via AFFERENT artery and leaves via EFFERENT artery. Diameter of the EFFERENT artery is SMALLER so there is more resistance to get blood flowing into it and hence a higher P generated to force fluid in. – around 50mmHg vs 35mmHg in other systemic capillaries.

GHP is opposed by CAPSULAR HYDROSTATIC PRESSURE (CsHP) – pressure from the capsule to push filtrate back into blood stream – around 15mmHg.

NET HYDROSTATIC P – difference between GHP and CsHP = 50-15 = 35mmHg

Blood Colloid Osmotic Pressure (BCOP)

It’s about there being a higher concentration of solutes somewhere and the water tending to want to drawn in towards that to balance out the concentration gradient.

Due to presence of proteins

Opposes NHP – approx 30mmHg (the draw of fluid back into the capillary)

Net movement back into capillaries

Due to the presence of proteins. Osmotic pressure, water is drawn to a region of high solute concentration.  BCOP draws water out of filtrate and into plasma – opposes NHP – around 25mmHg

Total Filtration Pressure (FP)

FP = NHP –BCOP = 35mmHg – 25mmHg = 10mmHg.

Glomerular Filtration Rate (GFR)

Ok so we know that there is a net force that moves fluid out of the capillaries, across the glomerular capsule and into the renal tubules.

The GFR is the amount of filtrate produced by the kidneys each minute. – around 125ml/min

Clinicians can measure our GFR by measuring the level of CREATININE clearance in our urine. CREATININE is by product of the breakdown of creatinine phosphate in muscle tissue. It filters across the GC and is reabsorbed in only very small quantities so is a good measure of what is going into the kidney and the rate at which it is coming out.

In a single day the glomeruli filter about 180L of filtrate of which about 99% is reabsorbed.  Just as well or we would be spending a lot of time drinking and voiding if we didn’t reabsorb!!!

GFR controlled by three main levels

Hormonal regulation (endocrine system)

Autonomic regulation (nervous system)

Autoregulation (local level)

Glomerular Filtration Rate

GFR is the first step in kidney function and so needs to be tightly controlled.  Need adequate blood flow to the glomerulus and a maintained pressure.  Controlled by:

Autonomic Regulation

Sympathetic innervation

Causes vasoconstriction of afferent arteriole = ↓ GFR because there’s less blood getting there. Important for conserving fluid volume in a state of emergency/exercising though the bladder will release urine as to not carry excess weight around.

Sympathetic tone ↓ GFR during exercise

Innervated by sympathetic fibres – one direct effect on GFR to vasoconstrict afferent arterioles and DECREASE GFR to slow production of filtrate.  Activated in response to a large drop in BP or heart attack.

Sympathetic tone also decreases GFR during exertion or exercise, blood flow increases to skin and muscles and decreases to kidneys.

  Hormonal Regulation

RENIN ANGIOTENSIN SYSTEM and Natriuretic peptides

  Renin released by JGA when BP drops (usually due to decrease in BV), or if JGA cells stimulated by Symp NS, or decrease in osmotic concentration at macula densa.

  Renin converts angiotensingoen – circulation plasma protein to AI, converted by ACE to AII which then acts to increase BP by vasoconstriction, stimulate aldosterone release which acts on DCT to increase Na reabsorption, acts at CNS to increase thirst response.

 Natriuretic Peptides: Job is to promote water loss. Released in response to an increase in BP – dilate afferent arteriole and constrict efferent arteriole to increase GFR and increase urine production, thereby decreasing blood volume and bp.

Autoregulation – local level

Regardless of change in systemic bp, the afferent and efferent arterioles can dilate and constrict to maintain a constant BP at the glomerulus. Eg if BP drops, afferent arteriole dilates and efferent arteriole constricts to increase blood flow and increase BP.

Renin-Angiotensin System

Renin is released when BP or blood flow is low. Once its in the blood renin joins with angiotensinogen to become angiotensin I -> as it travels along the lungs it comes in contact with a ACE which converts angiotensin I into angiotensin II -> Angiotensin II stimulates wide spread vasocontstriction which will aid in increasing BP -> also stimulates adrenal cortex to stimulate aldosterone which will help with the reuptake of Na+ -> if we uptake more Na+ we tend to bring more water as well which will help to increase blood volume -> the other thing angiotensin does is to increase the release of ADH from the posterior pituitary which limits the production of fluids (another method to increasing blood volume that will help increase BP when its low)

Hormonal Influences on Volume and Concentration of Urine

Antidiuretic Hormone (ADH)

Increases permeability of collecting tubules to water -> More water is reabsorbed

Aldosterone

↑ Aldosterone, ↑ Na+ reabsorption

“Water follows salt” so more water is reabsorbed

Natriuretic Peptides (ANP and BNP)

(Atrial natriuretic peptid + Brain Natriuretic Peptide)

Opposite action of ADH

More water is eliminated by stimulating production of urine

Concentration of Urine

The kidneys are able to control the concentration of urine by controlling the amount of water reabsorbed.

Water is reabsorbed by osmosis in the PCT and DESCENDING LIMB of LOOP.  Rest of the TUBULE is fairly SELECTIVELY IMPERMEABLE TO WATER.

That is water cannot move out of these regions of the tubule by osmosis without the influence of the hormone ANTIDIURETIC HORMONE.  When ADH is present, channels open in the tubule membrane and water can move out by osmosis due to the high concentration of solutes in the medulla region.

When ADH is present, water can move out of collecting tubules by osmosis and produce a concentrated urine with a small volume.

In the absence of ADH, the collecting tubule is impermeable to water and urine produced is dilute and large in volume.

Summary of Renal Function

1. Proximal convulated tubules: a lot of small molecules the body still needs 2. Secretion of components we don’t need. 3. Nephron loop we get reuptake of water. 4. And then the active reuptake of some solutes. 5. Distal convualted tubule: Selective reabsorption depending on bodies requirements. 5. Secretion continues. 6. May get some final uptake of water under influence of ADH.

Learning Objectives

Outline the processes involved in the formation of urine

Describe the major functions of each portion of the nephron

List and describe the factors that influence filtration pressure and the rate of filtrate formation

Describe how hormones influence the volume and concentration of urine

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Skeletal System (W10)

Lecture #27 (18.5.17)

Functions

Support soft tissue and vital organs

Protection/Creates Body Cavities – Thoracic cavity, pelvis, nasal cavity (Dorsal: posterior and ventral: anterior)

Facilitates Movement

Storage of minerals such as calcium

RBC formation from red bone marrow

270 at birth – 206 bones by adulthood as they fuse.

Classifications of Bones

Long Bones: Humerus, femur, radius, ulna, tibia

Short Bones: Carpals (8 carpals that make up the wrist joint) / Tarsal (7 bones that make up your foot)

Flat Bones: Cranium, Sternum

Irregular Bones: Vertebrae

Sesamoid: A bone developed within a tendon: Patella

Axial Skeleton

Forms the vertical axis of the body

Consists of about 80 bones

Adjusts the positions of the head, neck & trunk

Performs respiratory motions

Stabilizers & positions the appendicular skeleton. Working with the axial skeleton can aid in mitigating deficiencies in the appindecular skeleton.

 

 

Cranial Bones

Parietal: Form the most superior and lateral aspects of the skull

Temporal: Protects temporal lobe and forms of jaw line

Frontal: Forming superior aspects of our eye sockets (orbits)

Occipital:

Sphenoid: One complete bone, forms floor of your skull, the most anterior aspect of your brain is almost sitting on your sphenoid bone

Ethmoid: Sits on top of the sphenoid bone,

 

Facial Bones

Nasal: Breaking your nose will often fracture the nasal bone

Maxillae: Anchoring cite for the upper row of your teeth + forms the medial/inferior borders of your eye socket

Zygomatic: Gives facial definition + forms lateral aspect of your eye socket

Lacrimal: Important in regards to nasal cavity

Palatine: Comes from the word ‘pallet’ – posterior to the maxilla – a bit further back behind the roof of your mouth

Vomer: Important for nasal cavity

Mandible: Anchoring cite for lower row of teeth

Foramen: Hole in a bone is known as a foramen – it’s important for the spinal chord to anchor to our brain

Hyoid Bone

Structure:

U-shaped

Suspended from the temporal bones by ligaments & muscles

Why do we have it? It’s the attachment cite to your tongue 

Attachment site for infrahyoid & suprahyoid musculature above and below the hyoid bone

Vertebral Column

Cervical: C1 = ‘Atlas’

Thoracic: 12 thoracic vertebrae because we also have 12 ribs – paired together = 24 ribs. Act as an attachment cite for ribs. Each ribs attach to thoracic vertebrae. T1 anchoring cite to rib 1, T2 – rib 2 etc.

Lumbar: They have larger vertebral bodies because they’re supporting so much of our mass from our trunk

Sacrum: Fused vertebrae not individual bones

Coccyx: Different for everyone, some have 2, some 3, or 1.

Thoracic and sacrum that give that ‘C shape’ are known as “primary curves” – the reason is because they’re there at birth.

Our cervical and lumbar vertebrata are known as “secondary curves” – they develop after birth as we learn to crawl and walk they thicken out to accommodate the weight we will be distributing throughout our body

Differences in Vertebrae

Cervical vertebrae is small because its only supporting the head. Thoracic is a bit bigger because it has to support some of the upper limbs.

Vertebral foramen also differ in size. Big in cervical because we have large bundles of spinal nerves there. As we progress down the spinal cord because thinner and we start to branch out with more nerves from the sides.

Spinous Processes: Bony projections you can feel when you palpate your back. These cites are important because they become the cite for soft tissue attachment. Bigger spinous processes in our thoracic and lumbar because we have larger muscles attaching so they need a bigger anchoring point.

Thoracic Cage

Thorax

Manibrium

Body

Xiphiod process

True ribs: 1-7 are because they have a direct attachment to your sternum via intercostal cartilage attachment

False ribs: 8-12 they have an indirect attachment or no attachment. There costal cartilage blends into the corresponding rib – E.G. rib 10 costal cartilage is blending into rib 9 – collectively their blending into costal collage 8.

Floating ribs: Ribs 11-12 not attached to sternum. When you get hit in the wrong spot of your back you can puncture your lung.

Appendicular Skeleton

Bones of the upper / lower limb and those which connect  them to the trunk/axial skeleton.

 Two bones connect each upper  limb, together = pectoral/shoulder girdle: Arrangement of bones that help attach your arms to your axial skeleton.

Two coxal bones plus sacrum and coccyx = pelvic girdle: Arrangement of bones that help attach your legs to your axial skeleton.

Pectoral (Shoulder) Girdle

Includes: Clavicle / Scapula

 

Upper Extremity (Limb)

Humerus 

Forearm:

Radius: Ulna: Important for stability and soft tissue structures where muscles can attach to.

Ulna: runs medial down towards your little finger. Is a bigger and thicker bone, it articulates with the humerus. Radius runs laterally and rotates and follows the thumb.

Carpals: 8 (short bones)

Metacarpals: 5

Phalanges: You have a proximal and distal phalanx for your thumb whereas our 4 fingers also have a middle phalanx so we can ‘hook and claw’ our fingers. Same as phalanges of feet.

Pelvic Girdle

You’re pelvis is 2 coxal bones separated by left and right not 1.

Sacrum

Coccyx

Lower Extremity (Limb)

Consists of the following: Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges

Tibia is weight bearing. Fibula has no weight bearing – it’s there as an attachment cite for muscle and soft tissue structures.

Tarsals: 7

Metatarsals: 5

Articular System

Articulations are known as joints – it’s where 2 or more bones meet.

Structure of joint determines type and ROM

Each joint reflects a compromise between the need for strength and mobility

  Joint Classification

Structural Classification:

Fibrous: Cranial bones fused together via fibrous tissue

Cartilaginous: Allow some degree of movement but still relatively strong/stable. E.G. Pubic symphsis

Synovial: Shock absorption and support + filled with synovial fluid

Functional Classification:

Synarthrosis: Immovable

Amphiarthrosis: Slightly moveable

Diarthrosis: Freely moveable

Synovial Joints

Unstable from a structural perspective so there’s a lot of soft tissue structures to support it.

Articular Cartilage: Create cushioning to reduce friction between bones

Articular Capsule: Joint capsule protecting integrity of joint

Synovial Membrane: Secretes…

Synovial fluid: Gives nutrients to articular cartilage to help restore/regenerate

Ligaments: ACL / PCL / MCL / LCL – prevent excessive stretch in certain plane of movement

Bursa: Synovial fluid filled sacs – ‘gel pads’ that try to minimize/reduce friction in areas of high movement – suprapateller bursa to minimize friction of quad rubbing on femur.

Tendon Sheaths: Membranous sheath to help reduce friction. A tendon sheath is a layer of synovial membrane around a tendon. It permits the tendon to stretch and not adhere to the surrounding fascia.

Angular Movements

Rotational Movements

Special Movements

Learning Objectives

List the primary functions of the skeletal system

Identify the bones of the axial skeleton (as shown in Figure 7.2)

Identify the curvatures of the spinal column and their functions

Distinguish between different types of vertebrae

Identify the bones of the appendicular skeleton (as shown in figure 8.2)

Describe the importance of articulations

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Muscle Tissue 1 (W11)

Lecture #28 (22.5.17)

Muscle Histology

Functions of Muscle Tissue

Production of body movement

Stabilizing body positions

Storing and moving substances within the body (reservoir of water, calcium, ATP, glycogen)

Generating heat (thermogenesis) maintaining core temp

Properties of Muscle

Electrical Excitability: Skeletal muscle relies on electrical stimulus via the CNS to function

Contractility: Ability to contract/shorten/lengthen

Extensibility: Means the muscles can be stretched to their normal resting length and beyond to a degree certain

Elasticity: Means that if muscles are stretched they recoil to their original resting length

Skeletal Muscle Histology

Most attached to skeleton

Striated (striped) which are made from protein filaments which make up contractile elements of the muscle

Voluntary

Attached to bones at either end by tendons

Origin: Fixed end. Like an anchoring point that doesn’t move.

Insertion: Most moveable end. Muscle will move from its insertion back to its origin when we cause it to contract. E.G. Brachialis moving from its insertion point back to its origin.

Main body – belly where we have muscle fibers/contractile proteins

Cardiac Muscle Histology

Only found in the heart

Striated & involuntary

“Intercalated discs” (purpleish disc shapes) & cell junctions to increase speed for nerve impulses to the heart (helping send action potentials from the sino atrial node to the atrial ventricular node)

Autorythmicity: the ability to contract on its own without external nervous stimulation/neural input

Smooth Muscle Histology

Single nucleus centrally located

Not striated (though still has contractile proteins but they’re not arranged in a uniform striated structure)

Involuntary

Slow & rhythmical contractions (peristalsis)

Lines hollow organs & blood vessels

Found in: Stomach & intestines, Urinary bladder, Uterus

Connective Tissue: EPE

Skeletal muscle has 3 layers of connective tissue. The endomysium which surrounds a single muscle fibre. The perimysium which surrounds a collection of muscle fibres into a fascicle. And the epimysium which surrounds a collection of fascicles to create the outermost layer surrounding a whole muscle.

Epimyosium (upon/wrapped around)

A thin membranous sheet.

Perimyosium (around the muscle fascicles)

Endomyosium (within the muscle fascicles)

All three extend from the deep fascia to protect the muscle = they all blend at the end of each muscle to help facilitate part of your tendon.

Tendons

Help anchor our muscle to bone

Why do we have tendons? For muscular attachment

Add useful length/thickness to muscles – longer muscles have higher potential to produce more force because they have a bigger leverage momentum

Reduce muscle strain??? (See Jill Cook’s research)

Add strength to muscle action: As said beofre,If you increase the length of the muscle you potentially increase its leverage capabilities, therefore increasing its force production

Macroscopic & Microscopic Anatomy of Skeletal Muscle

Skeletal muscle is composed of individual cells known as muscle fibers

They are long cylindrical shape. The importance of having them long/cylindrical is that they need to run the entire length of the muscle belly.

 Numerous nuclei on the periphery because they’re so large

Groups of muscle fibres are known as Fascicles

Muscle belly made up of groups of fascicles

Skeletal Muscle Characteristics

Skeletal muscle fibers are big! Up to 30cm long

Multinucleate : Hundreds of nuclei within a single fiber

Myoblasts: Immature muscle cells

Multinucleated: On the periphery of the cell to help relay that message to one end of the muscle fiber to the other.

Myosatellite cells: Help with regeneration/development of muscle

Muscle Fiber/Cell

SARCOLEMMA:

Plasma membrane of skeletal muscle fibers. Monitor movement of substances in/out of the muscle fiber.

SARCOPLASM:

Specialized cytoplasm

TRANSVERSE (T) TUBULES:

Runs to the outside of the fiber carries nerve impulse to sarcoplasmic reticulum – helps relay neural stimulus that we get from CNS through that entire muscle fiber

MITOCHONDRIA

Energy production via ATP for movement. We can manipulate the amount of mitochondria by specific types of training – more anaerobic/power based training decreases the number of mitochondria than someone who does endurance based training.

MYOFIBRILS:

Contractile element of the fiber

Are 2um in diameter

Extend the entire length of the muscle otherwise the muscle wouldn’t function

Contain myofilaments called actin and myosin that give the muscle their striated appearance.

SARCOPLASMIC RETICULUM:

Encircles each myofibril

Stores and releases Ca2+ (calcium) – muscles require calcium in order to contract

As it butts against the T-tube it forms a triad

MYOFILAMENTS:

Thick myofilament: Myosin

Thin myofilament: Actin + troponin/tropomyosin (regulatory proteins)

Myofilaments do not extend the entire length of a muscle fiber, rather they are organized into compartments called “Sarcomeres” – like carriages of a train that are linked together

Muscle Proteins

Myofibrils are made from 3 types of proteins

Contractile proteins: Myosin & Actin

Regulatory proteins: Troponin & Tropomyosin

Structural proteins: Dystrophin

Hundreds of these sarcomeres linked together to create the entire muscle fiber.

Sarcomeres

Functional unit of a myofibril

Several characteristics:

Z Lines/Discs: The peripheries of an individual sarcomere – also the anchoring point for your thin filaments

A Bands: Helps us get vertical striations – it’s where we have an overlap of myosin and actin

I Bands: Thin actin filaments only

H Band/Zone: No overlap – it’s simply where our myosin is contained

M Line: Midpoint – the anchoring point for the thick filaments (myosin) whereas the actin attaches tot he periphery of the sarcomere

When skeletal muscle contracts the z line has to come closer to the other z line towards the middle of the sarcomere – they need to shorten. If we have lots of these shortening at the same time = shortening the muscle belly = contraction of muscle. If we want to relax the muscle belly then we need to make sure the z lines move away from each of the M lines – they relax = muscle stretches/lengthens.

Neuromuscular Junction

Interface between the ending of the motor nerve & skeletal muscle fiber point

Sliding Filament Theory

The process we get a shortening of the sarcomeres -> shortening the skeletal muscle itself.

Neural impulse get’s sent down the dendrites -> arrives at synaptic bulb -> ACh is released at the synaptic cleft -> binds to receptors on the sarcolemma -> opens up Na+ or K+ channels and changes the resting membrane potential -> this sends info down the t-tubules -> when the stimulus hits the sarcomplasmic reticulum it get excited and stimulates the release of calcium -> calcium moves its way into the individual sarcomeres -> unlocks a mechanisms which enables muscle to contract -> end process being that our sarcomeres will all shorten in unison to cause the muscle belly to contract

a) The active site on actin is exposed as calcium binds to troponin – calcium is the key to the lock

b) The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge. (known as cross bridge cycling)

c) During the power stroke, the phosphate generated in the previous contraction cycle is released. This results in the myosin head pivoting toward the center of the sarcomere (towards the M line), after which the attached ADP and phosphate group are released.

d) In order to release myosin head from the active site a new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach.

e) The myosin head hydrolyzes ATP to ADP and phosphate, which returns the myosin to the cocked position.

If there is no calcium or not enough ATP then this cycling process will stop.

Learning Objectives

List the structural and functional differences between skeletal, cardiac and smooth muscle tissue

Describe the organisation of whole muscle including the arrangement of tendons and connective tissue

Identify unique characteristics of skeletal muscle fibers

Describe the structure of a sarcomere

Outline the key steps involved in the contraction of a skeletal muscle fiber

Muscle Tissue 2 (W11)

Lecture #29 (23.5.17)

No more action potential to muscle/Relaxation: Sarcomplasmic reticulum is no longer excited -> now starts to reabsorb calcium within the sarcomeres -> calcium starts to become less available in the sarcomeres -> when that happens the troponin/tropomyosin molecules start to ravel back around the actin (they’ve locked off the active sites) -> when there are no active sites available there is no attachment site for the myosin heads to interact with so that cross bridge cycling disappears -> when that occurs = muscle relaxes back to resting state

Factors Influencing Total Muscle Tension

Muscle Fiber Diameter

Larger muscle fiber diameter will have a significant impact on force production relative to one that’s small

Greater fiber diameter produces larger forces due to a greater number of myofibrils (which house contractile proteins myosin/actin that faciliate cross bridge cycling)

Larger fibers are associated with larger motor units that have a greater innervation ratio. Bigger diameter = theoretically more cross bridges which therefore leads to more force production

Muscle Fiber Length

Generally, a longer length muscle will have a greater ability to produce force relative to a shorter muscle because it has a greater leverage capacity

All muscles have an optimal zone of overlap – an optimal length at which they will produce maximal tension/force

Practical: So the optimal zone of overlap is usually the most challenging part of a lift that produces the most amount of force/tension.

The force that a muscle fiber can exert varies with muscle length, or the degree of overlap between the thick and thin filaments

The length that provides an optimum overlap maximizes the number of cross-bridges that can be formed

Contraction Velocity

The speed at which you contract influences muscle fiber recruitment

The force that a muscle fiber can exert varies with the velocity (magnitude and direction) of the contraction

The variation in force is mainly due to changes in the average force exerted by the cross-bridges

“You would think the quicker you do something, the more force you produce – its actually the opposite, the slower you perform a movement the more force you will produce. The faster you do it, the less time there is for the cross bridges to engage with one another effectively. The reason being there is not enough time for the myosin heads to attach to the actin filaments effectively – cross bridge cycling is compromised.”

But what about RATE of force production?

Jay: Yeah rate of force is higher but total force is lower mate you’re right. The thing that separates good athletes is how much % of their maximal force output they can produce in a short given time (ie a counter movement jump)

-20 (negative speed) is during the eccentric lengthening phase

Size and type of motor unit

Motor Unit: A motor neuron and all the muscle fibers it innervates

E.G. Here we have 3 different coloured motor units innervating different fibers within one fascicle

Recruitment of motor units

Henemens size principle: small to large

Why? Large motor units are recruited last because the muscle fiber membranes are less excitable

Frequency of stimulation: 

Manipulating the number of action potentials to change force production measured in Hertz – looking at electrical impulses per sec.

Creating muscle tension via a muscle twitch / Summation / Tetanus

Muscle Size

A muscle with a larger cross sectional area has a higher potential for myosin/actin filaments – therefore greater cross bridge cycling – produce more force

The maximum force that a muscle can exert depends on its physiological cross-sectional area (PCSA), which is a measure of the number of cross-bridges that are in parallel

Recruitment of Motor Units

Modulation of muscle tension involves the concurrent variation in the number of active motor units and discharge rate

We can switch motor units on/off to help regulate force production depending on the weight we have to lift or overcome.

Motor units are recruited in a set order from smallest to largest (hennemans size principle)

How?

Because the small motor units have a small surface area, fewer ion channels and therefore a higher resistance

The ability to recruit motor units and activate additional motor units, changes the tension within a muscle

The graph suggests motor unit 5 is the largest of the motor units because it takes the highest amount of frequency to recruit and when we do recruit it, it creates a spike in force production to around 50% of its MVC (10sec)

Force is produced by increased motor unit recruitment and discharge rate modulation

The start of each line represents recruitment

Discharge rate: Amount of electrical stimulus per sec

An increase in each line represents an increase in discharge rate

Our body commonly recruits in synchronous, a-synchronous and preferential recruitment

A-Synchrounous: Most common (smallest to largest)

Synchornous: Works as one in unison. But our body rarely ever works like this, if you were to recruit ALL the motor units in the muscle belly you’re going to get full muscle contraction – we don’t need that.

Preferential: Engaging large motor units first and small motor units last. E.G. Baseball players practicing with heavier bats first before the lighter normal bats.

Size & Type of Motor Unit

Slow: E.G. Postural Muscles / Fast Fatigue: 400-800m Runner / Fast Fatigable: 50-200m Sprint / Oly Lifters

Frequency of Stimulation

The force that a motor unit exerts depends on the rate (frequency) at which the motor neuron discharges action potentials

You could ramp a stimulus up to 100Hz or 1000Hz – it’s not going to make that muscle work any harder because all muscles have a saturation point. Simply increasing the stimulus doesn’t mean you’re going to increase the motor units recruited – once you’ve recruited all those motor unit that’s as far as you can go. You can keep increasing the stimulus but those motor units will remain saturated so force production will plateau and eventually drop off.

Twitch

The frequency at which you send a stimulus affects tension production.

One single stimulus (electrical impulse) to a motor unit that generates a contraction and relaxation sequence within all muscle fibers within a MU.

3 Main Steps

Latent Period – Takes about 5mm for the stimulus to travel down the MU, travel across the synaptic cleft, depolarize the sarcolemma of that muscle fiber, and relay the action potential generated thorough T- Tubules to SR (sarcoplasmic reticulum) then Ca2+ is released then the cross bridges are enabled.

Contraction Phase – cross bridges form / recruit muscle fibers.

Relaxation Phase – Electrical impulse then disappears. Relaxation takes longer than contraction because it has to reverse the above process – reabsorbing calcium for example.

Ca2+, cross bridges release

Treppe: 

Repeated stimulation after relaxation phase has been completed

Step-like increase in tension (rise in stages up to between 30-50 stimulations after which it remains constant)

Tension increases due to Ca2+ not being reclaimed back into the SR prior to the next AP

Force production slowly increases over time via the repeated stimulus because we’re reducing the amount of time for the sarcoplasmic reticulum to recuperate calcium from the sarcomere. So it leaves more active sites available for cross bridge cycling and therefore a slow increase in force production as seen below.

Summation (Wave Summation)

Repeated stimulation before relaxation phase has been completed

A second stimulus arrives before relaxation phase ends

Thus a second more powerful contraction occurs

Once again, it’s reducing the amount of time for the SR to recuperate or reabsorb calcium so there are calcium molecules in the sarcomere = more cross bridges are occurring.

Complete Tetanus: The Way Our Body Functions

Stimulation that eliminates relaxation period

AP arrive so rapidly that the SR can not reclaim the Ca2+ pumped out, thus no relaxation phase occurs at all, thus prolonging muscle contraction

Used for almost all normal muscular contractions for a steady increase in force production. Eventually that muscle will become saturated and we’ll overstimulate.

Tetanus (Medical) = can cause things like locked jaw due to complete stimulation of your muscles and no relaxation.

Muscle Contraction

Isotonic Contractions

Concentric

When muscle torque is greater than load torque, the muscle performs a concentric contraction as whole-muscle length decreases/shortens.

Eccentric

When muscle torque is less than load torque, the muscle performs an eccentric contraction as whole-muscle length increases while still producing tension. Most muscle damage occurs. Why and how though?

Isometric Contraction

When the two torques are equal, the muscle performs an isometric contraction. Muscle length doesn’t change.

However, muscle fiber length decreases by about 25% during a maximal isometric contraction / as fatigue increases.

Important for posture and resisting forces of gravity (soleus/axial muscles)

Learning Objectives

Describe the mechanisms responsible for tension production during muscle contraction

Identify the arrangement of motor units in skeletal muscle and describe their role in tension production

Distinguish between isotonic and isometric contractions

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Integration of Body Systems (W11)

Lecture #30 (25.5.17)

Levels of Organisation

Integration of Physiological Systems

None of the physiological systems works on its own. The systems work together to maintain homeostasis

The successful functioning of each physiological system is reliant on the successful functioning of other physiological systems

Integumentary System

Skin, hair, sweat glands, nails

Integration with other systems:

Outer mechanical first barrier of protection against environmental hazards

Hairs guard entrance to respiratory system

Skin synthesises Vitamin D3 needed by skeletal, muscular, endocrine and digestive systems

Skeletal System

Bone, cartilages, ligaments, bone marrow

Integration with other systems:

Provides mechanical support, stores energy reserves, stores calcium and phosphate reserves

Red blood cells produced in bone marrow which aids in the cardiovascular system

Movement of ribs important in breathing – working with respiratory system

Muscular System

Skeletal muscles, tendons

Integration with other systems:

Generates heat that maintains normal body temperature (thermogenesis)

Skeletal muscle contractions help move blood through veins –  aids cardiovascular system

Muscles cause lungs to fill and empty – aids respiratory system

Nervous System

Brain, spinal cord, peripheral nerves, sense organs

Integration with other systems:

Monitors pressure, pain and temperature, adjusts tissue blood flow patterns

Controls skeletal muscle contractions – skeletal system

Modifies heart rate and blood pressure – cardiovascular system

Controls pace and depth of respiration – respiratory system

Endocrine System

Hypothalamus, pituitary, thyroid, pancreas, adrenal glands, gonads

Integration with other systems:

Adjusts metabolic rates and substrate utilisation, regulates growth and development

Erythropoietin (EPO) regulates production of red blood cells

Adrenaline and noradrenaline stimulate respiratory system

Glucocorticoids have anti-inflammatory effects

Cardiovascular System

Heart, blood, blood vessels

Integration with other systems:

Delivers oxygen, hormones, nutrients and white blood cells, removes carbon dioxide and metabolic wastes, transfers heat

Red blood cells transport oxygen and carbon dioxide between lungs and peripheral tissues

Lymphoid System

Lymphatic vessels, lymph nodes (filter lymph), spleen (filters blood), thymus (maturation of t-cells), tonsils

Integration with other systems:

Provides specific defences against infection, immune surveillance, eliminates cancer cells

Returns tissues fluid to circulation

Tonsils protect against infection at entrance to respiratory tract

Lymphatic vessels carry lipids absorbed in digestive tract to blood system – digestive system reliant on lymphatic system for absorbed lipids to get into body

Respiratory System

Nasal cavities, sinuses, larynx, trachea, bronchi, lungs, alveoli

Integration with other systems:

Provides oxygen and eliminates carbon dioxide

Assists urinary system in regulation of pH by eliminating carbon dioxide

Converting enzyme along capillaries of lung converts angiotensin I to angiotensin II

Digestive System

Teeth, tongue, pharynx, oesophagus, stomach, small and large intestine, liver, gall bladder, pancreas

Integration with other systems:

Absorbs organic substrates, vitamins, ions and water required by all cells

Secretions of the digestive system (acids and enzymes) provide non-specific defence against pathogens

Absorbs fluid to maintain normal blood volume

Urinary System

Kidneys, ureters, urinary bladder, urethra

Integration with other systems:

Excretes waste products, maintains normal body fluid, pH and ion composition

Kidney cells release renin which elevates blood pressure

Acidic pH of urine provides non-specific defence against urinary tract infections

A Stable Internal Environment

Body Temperature

Muscular System = thermogenesis

Cardiovascular System = transport of heat around of body via blood

Nervous System = redistribution of blood flow away from the periphery

Endocrine System = release of hormones for non-shivering thermogensis (thyroid hormone)

Body Fluid Composition

Nutrient Concentration

Oxygen & Carbon Dioxide Levels

Body Fluid Volume

Digestive System = How we uptake and absorb fluids

Cardiovascular System = How we transport fluids around the body

Endocrine System = Important hormones for urine production

Nervous System = Altering filtration rate

Urinary System = To rid any excess fluid

Waste Product Concentration

Blood Pressure

Learning Objectives

Provide an overview of the human body

Describe how the physiological systems are integrated to ensure optimal functioning of the human body