3.1.2 Transport in Animals

Question 1

Do small animals need specialised transport systems?

Answer 1

no

Question 2

Why do small animals not need specialised transport systems? 3 points

Answer 2

1. Small size means that they have a high enough surface area to volume (SA:V)
2. The distances that molecules and ions will need to move will always be short. This means that diffusion (which is too slow over long distances) is an adequate method of transport
3. Their demand for oxygen uptake and CO2 removal are not too high due to the low metabolic rate, and respiration rates

Question 3

Do large animals need specialised transport systems?

Answer 3

yes

Question 4

Why do large animals need specialised transport systems? 4 points

Answer 4

1. Large size means they have a low surface area to volume ratio (SA:V), this makes it difficult for enough substances to be exchanged across the outer body surface to meet the needs of all cells in the organism
2. Many body cells are a great distance from the body surface, therefore diffusion would be too SLOW
3. Their demand for oxygen uptake and CO2 removal are very high respiration rate in the muscles during movement, requiring high rates of oxygen supply.
4. Endotherms, must maintain a constant body temperature, usually higher than that of their surroundings, using physiological mechanisms. Therefore high metabolic rates, including a high rate of respiration, hence they need high rates of oxygen uptake

Question 5

What are the uses of transport systems in animals? 7 points

ogacuhw

Answer 5

Transport of:
oxygen
glucose
amino acids
carbon dioxide
urea
hormones
white blood cells

Question 6

What is an open circulatory system?

Answer 6

An open circulatory system is one in which the transport medium (blood/haemolymph) is not always contained within vessels.

Question 7

Who has an open circulatory system?

Answer 7

insects

Question 8

what are the insectoid version of blood?

Answer 8

haemolymph

Question 9

how does an open circulatory system work? 3 points

Answer 9

haemolymph that circulates around the body (being pumped by a tubular heart) and directly bathes the body cells.

The main body cavity, in which haemolymph bathes the body cells, is called the haemocoel. No capillaries and no tissue fluid

No capillaries and no tissue fluid are needed as the haemolymph is in direct contact with the body cells. The body cells exchange materials directly with the haemolymph.

Question 10

What are the disadvantages of an open circulatory system? 2 points

Answer 10

1. much pressure is lost as the blood flows into the main body cavity (haemocoel) and hence flow rates of the haemolymph are low (limiting rate of delivery of glucose etc. to body cells).
2. haemolymph cannot be redistributed or directed more/less to different parts of the body at different times, as there are no vessels to redirect flow

Question 11

what is a closed circulatory system?

Answer 11

closed circulatory system is one in which the blood is always enclosed within blood vessels and does not come into direct contact with the cells of the body (except from the endothelium of the blood vessels)

Question 12

What are the advantages of an close circulatory system? 2 points

Answer 12

1. the high pressure generated by the heart can be well maintained, giving faster blood flow rates and hence faster oxygen and glucose delivery to body cells.
2. blood flow can be specifically directed to different parts of the body according to need (due to the action of smooth muscle in varying the lumen diameter of arterioles), e.g. muscles can receive more blood (and hence more oxygen) during exercise.

Question 13

what are the types of closed circulatory systems?

Answer 13

single and double

Question 14

what is a single circulatory system?

Answer 14

A single circulatory system is one in which the blood flows through the heart only once in a complete circuit of the body.

Question 15

what animals have a single circulatory system?

Answer 15

Fish

Question 16

How does a single circulatory system work?

Answer 16

The heart has one atrium and one ventricle, which pumps the deoxygenated blood to the gills, in which the blood becomes oxygenated. The oxygenated blood then flows directly onwards to body tissues, delivering oxygen, before returning to the heart.

Question 17

What are the disadvantages of a single circulatory system (compared to a double)?

Answer 17

a great deal of the hydrostatic pressure generated by the heart is lost as the blood flows through the gill capillaries; this means that the flow rate of blood (and hence rate of oxygen and glucose delivery) to respiring body tissues is not very high.

Question 18

what is a double circulatory system?

Answer 18

A double circulatory system is one in which the blood travels twice through the heart for each complete circulation of the body.

Question 19

What animals have a double circulatory system?

Answer 19

Mammals

Question 20

How does a double circulatory system work? 3 points

Answer 20

In the first (pulmonary) circulation, deoxygenated blood is pumped by the heart to the lungs

the blood is oxygenated and then returns to the heart. In the second (systemic) circulation, oxygenated blood is pumped by the heart to the brain and body to supply cells with oxygen

the deoxygenated blood then returns to the heart.

Question 21

What are the advantages of a double circulatory system ?

Answer 21

1. It is a highly effective system for active,
   endothermic organisms because a new boost of high hydrostatic pressure can be given to the blood that has already become oxygenated, sending it around the body with high velocity to supply oxygen and glucose to respiring tissues (and remove waste carbon dioxide) at the very high rate that is required.
2. It is advantageous however that the pulmonary circulation (to/from the lungs) operates at lower pressure, avoiding damage to the thin‐walled lung capillaries and alveolar epithelium.

Question 22

What is the route taken by the blood in the pulmonary circuit (to lung)

Answer 22

Right ventricle of the heart → pulmonary artery → pulmonary arteriole → lung capillaries → pulmonary venule → pulmonary vein → left atrium of the heart

Question 23

What is the route taken by the blood in the systemic circuit

Answer 23

Left ventricle of the heart → aorta → artery → arteriole → capillaries → venule
→ vein → vena cava → right atrium of the heart

Question 24

What is an artery?

Answer 24

An artery is a major blood vessel that takes blood away from the heart

Question 25

What are key features of an artery?

Answer 25

1. The walls of an artery are very thick and are strong enough to withstand the high pressure of the blood that has just been pumped by the heart.
2. The artery walls are elastic (containing many elastic fibres made of elastin protein), allowing them to stretch and recoil in response to the pressure fluctuations.
3. The walls contain much collagen and a thick layer of smooth muscle for strength.
4. smooth muscle in the artery wall can contract to decrease the lumen diameter in order to maintain blood pressure if necessary (e.g. if pressure has fallen due to blood loss).
5. The lumen (internal space) of an artery is relatively narrow, which helps to maintain the high pressure of the blood (as the blood is confined to a small space, which a high proportion of blood in contact with the artery walls).
6. The endothelium (lining) is smooth, reducing friction, and is pleated (folded) allowing for expansion of the lumen without risk of the lining tearing.

Question 26

Why do the arteries not need valves?

Answer 26

There is a steep enough hydrostatic pressure gradient to keep the blood flowing away from the heart in arteries at all times, due to the powerful contractions of the ventricle walls.

Question 27

how thick are the artery walls?

Answer 27

around 0.7mm

Question 28

What is an arteriole?

Answer 28

An arteriole is a blood vessel that branches off an artery, carrying blood away from the heart towards capillaries.

Question 29

How is an arteriole different to an artery/what are its key features?

Answer 29

1. Arteriole wall structure is similar to that of an artery, though arterioles tend to have even narrower lumens and slightly less thick walls than arteries.
2. Smooth muscle can be used to
   control and redistribute blood flow to different parts of the body according to need.
3. the circular smooth muscle in the wall of the relevant arteriole will contract (whilst longitudinal smooth muscle relaxes), constricting the lumen; this is called
   vasoconstriction. The blood flow through the capillary network beyond that arteriole is reduced.
4. the longitudinal smooth muscle contracts (whilst circular smooth
   muscle relaxes), expanding (dilating) the lumen; this is called vasodilation. The blood flow through the capillary network beyond that arteriole is increased
5. ring‐shaped sphincter muscles in their walls, which control lumen diameter and hence blood flow into shunt vessels. Shunt vessels branch off the arteriole and allow blood to bypass a capillary network (e.g. in the skin) and flow directly from an arteriole, via the shunt, into a venule. This is particularly important during thermoregulation.

Question 30

What do some arterioles have that some don’t?

Answer 30

ring‐shaped sphincter muscles in their walls, which control lumen diameter and hence blood flow into shunt vessels. Shunt vessels branch off the arteriole and allow blood to bypass a capillary network (e.g. in the skin) and flow directly from an arteriole, via the shunt, into a venule. This is particularly important during thermoregulation.

Question 31

What is a capillary?

Answer 31

Capillaries are the narrowest type of blood vessel, with a very small lumen diameter (often no larger than the diameter of a single red blood cell); they have very thin, permeable walls.

Question 32

What are features of a capillary?

Answer 32

1. very thin, permeable walls.
2. An exchange surface with a huge surface area (as the capillaries are numerous and branch repeatedly).
3. one layer of thin, flattened cells (the endothelium), providing a short diffusion distance; there is a little collagen present but no smooth muscle.
4. The permeability of the capillary walls is further increased by the presence of pores. Water, small molecules (e.g. glucose, amino acids, urea) and ions (e.g. Na+, Cl‐) can easily pass through these pores; however plasma proteins, platelets and red blood cells cannot fit through. Some types of white blood cells (e.g. macrophage) can change shape so dramatically (using their cytoskeleton) that they are able to squeeze through the pore

Question 33

what is a venule?

Answer 33

A venule is a small vein, formed when multiple capillaries re‐join. Venules themselves merge together to form larger veins, which carry blood back to the heart.

Question 34

What are features of a venule?

Answer 34

The walls of a venule are quite thin (yet impermeable) and contain little collagen and no smooth muscle

there is no need for substantial strength to withstand high blood pressure at this point in the circulatory system as most of the hydrostatic pressure generated by the heart has already been lost.

Question 35

what is a vein?

Answer 35

A vein is a blood vessel with large internal lumen diameter but thin walls, carrying blood back towards the heart

Question 36

what are the features of a vein 5 points

Answer 36

1. no need for substantial strength to withstand high blood pressure at this point in the circulatory system as most of the hydrostatic pressure generated by the heart has been lost. Hence as well as the walls being thin, there is little collagen and little smooth muscle.
2. little need for elasticity in the vein’s walls as the blood pressure will be fairly steady, not be rising and falling as it would in an artery; hence there are few elastic fibres.
3. The inner lining of the vessel is a layer of endothelium. This provides a smooth surface, reducing friction. Unlike the endothelium of an artery, the vein’s endothelium is not pleated as there is no need for the vein’s lumen to be able to expand
4. large lumen diameter of the vein reduces the proportion of blood in contact with the wall, reducing friction. This means that the blood has less resistance to overcome and allows an adequately high flow rate to be achieved, despite the low hydrostatic pressure of the blood in the vein.
5. Valves

Question 37

what blood vessel has valves?

Answer 37

veins

Question 38

why do veins need valves

Answer 38

The blood in a vein should be moving towards the heart but the hydrostatic pressure of the blood in a vein can be so low that there is a risk of backflow, e.g. due to gravity. Veins therefore contain semilunar valves to prevent the backflow of blood.

Question 39

how to valves work?

Answer 39

vein squashed by contraction of nearby skeletal muscles
the valves only allow the blood in the vein to move towards the heart, not away from it.
keeps the blood in veins moving towards the heart only.

Question 40

What is tissue fluid?

Answer 40

Tissue fluid is the extracellular solution that directly surrounds (bathes) the body cells in an animal. Tissue fluid is formed from blood plasma when some water and solutes are squeezed out through the capillary wall at the arteriole end of capillaries due to the hydrostatic pressure of the blood being stronger than its oncotic pressure at this point

Question 41

what is in tissue fluid? OGAS

Answer 41

oxygen, glucose, amino acids and salt ions

Question 42

what is not in tissue fluid?

Answer 42

Plasma proteins, red blood cells and platelets are too large to be filtered through the capillary wall so, though present in blood, are absent from tissue fluid.

Question 43

What is the function of tissure fluid?

Answer 43

Body cells absorb the materials they need from the tissue fluid (e.g. glucose and oxygen for aerobic respiration, amino acids for protein synthesis).

Meanwhile the body cells also excrete waste (e.g. carbon dioxide and urea) into the tissue fluid (avoid it building up to toxic levels in the cells).

Question 44

where is tissure fluid reabsorbed?

Answer 44

Most tissue fluid is reabsorbed by the blood at the venule end of the capillaries (where the hydrostatic pressure is now less strong than the oncotic pressure).

some (excess) tissue fluid instead drains into blind‐ending lymph capillaries and is now referred to as lymph. Lymph flows in lymph vessels until eventually re‐joining the blood, when lymph vessels merge with veins near the heart

Question 45

what happens if there is an excess of tissue fluid? what may cause this?

Answer 45

If there is an over‐accumulation of tissue fluid in a particular part of the body (due to rate of tissue fluid formation exceeding the rate at which tissue fluid is removed), a condition called oedema occurs. High blood pressure is one possible cause of this.

Question 46

what is hydrostatic pressure?

Answer 46

the pressure created by water in an enclosed system. Water and dissolved solutes will move from a region of higher hydrostatic pressure to a region of lower hydrostatic pressure by mass flow.

Question 47

what causes hydrostatic pressure?

Answer 47

the contraction of the ventricle wall of the heart generates the high hydrostatic pressure of blood, such that blood is then forced out of and away from the heart in arteries.

Question 48

hydrostatic pressure from arteries to veins

Answer 48

The blood arriving at the arterial/arteriole end of capillary still has relatively high hydrostatic pressure. By the time the blood reaches the venous/venule end of the capillary, the hydrostatic pressure has significantly fallen.

Question 49

what is oncotic pressure?

Answer 49

tendency of water to move back from the tissue fluid into the blood by osmosis. This tendency is due to the presence of soluble plasma proteins in the blood but not in the tissue fluid

Question 50

what causes oncotic pressure?

Answer 50

the presence of soluble plasma proteins in the blood but not in the tissue fluid

Question 51

what happens to oncotic pressure as solute conc increases?

Answer 51

Oncotic pressure becomes more negative as solute concentration gets higher

Question 52

oncotic pressure from arteries to veins

Answer 52

there is actually little difference in the oncotic pressure at the arterial/arteriole end of capillaries compared to the venous/venule end of capillaries (in both cases, it is around ‐ 3.3kPa)

Question 53

Why does tissue fluid form at the arteriole ends of capillaries and re‐enter the blood at their venule ends,?

Answer 53

At the arteriole end of a capillary, the hydrostatic pressure of the blood (generated originally by the contraction of the heart and tending to push fluid out of the blood through capillary walls) is stronger (at around 4.6kPa) than the oncotic pressure (‐3.3kPa)
this results in tissue fluid being formed as water and some solutes are pushed through the
permeable capillary walls.

At the venule end of a capillary, the hydrostatic pressure has fallen so much (down to around 2.3kPa, due to the fluid loss that has already occurred) that it is now less strong than oncotic pressure (still around ‐3.3kPa), hence some fluid re‐enters the blood at this
point.

Question 54

what happens with a -ve Net flitration pressure?

Answer 54

fluid reabsorbed into the capillaries

Question 55

what happens with a +ve Net flitration press

Answer 55

fluid leaves the capillaries

Question 56

how to calculate net filtration pressure

Answer 56

Hydrostatic pressure + oncotic pressure

Question 57

What is the composition of blood?

RB,WB,P,PP,O,G,U,L

Answer 57

1. Red blood cells present - from bone marrow
2. Many white blood cells present - from bone marrow
3. Platelets (thrombocytes) present - from bone marrow
4. Plasma proteins (e.g. albumin) present - from body cells
5. High [O2] at the arterial end of the capillary - the blood has passed through the lungs and is oxygenated.

Low [O2] at the venous end of the capillary - oxygen
diffuses out of the blood through the permeable
capillary wall and is used up by respiring body cells, hence the blood leaving the tissue is deoxygenated.

6. High [glucose] at the arterial end of the capillary - glucose has passed into the blood as it flows through the liver and the walls of the small intestine.Low [glucose] at the venous end of the capillary - glucose passes out of the blood through the permeable capillary wall and is used up by respiring body cells.
7. Low [urea] at the arterial end of the capillary - urea has been removed by the kidneys.High [urea] at the venous end of the capillary - urea has passed from body cells into tissue fluid and now passes through the permeable capillary wall into the blood.
8. Lipids present - entered the blood via secretions from the liver, via the flow of lymph (containing lipids) into the bloodstream or directly from the small intestine.

Question 58

What is the composition of tissue fluid?

RB,WB,P,PP,O,G,U,L

Answer 58

1. No RBCs present - too large to be filtered out
2. Few/some WBCs usually present - some are able tto change thier shape to fit through the small pores
3. No platelets present - too large to be filtered out
4. Few/no plasma proteins present - too large to be filtered out
5. O2 is present - O2 diffuses out of the blood through the permeable capillary wall. The conc can change due to respiring cells
6. Glucose is present - glucosediffuses out of the blood
   through the permeable capillary wall. The conc can change due to respiring cells
7. Urea is present - it is released as a waste product from body cells into the tissue fluid.
8. Lipids present - most types of lipid will pass freely
   through the capillary wall; they may then be taken up
   by body cells and used in respiration if needed or stored in the form of lipid droplets.

Question 59

What is the composition of lymph?

RB,WB,P,PP,O,G,U,L

Answer 59

1. No RBCs present - lymph is derived from tissue fluid, which does not contain RBCs
2. WBCs present - lymphocytes enter the lymph as it flows through lymph nodes.
3. No platelets present - lymph is derived from tissue fluid, which does not contain platelets
4. No plasma proteins present - lymph is derived from tissue fluid, which does not contain plasma proteins
5. Low [O2] present - lymph is derived from tissue fluid, from which the O2 has already been taken up and used by respiring cells.
6. Little/no glucose present - lymph is derived from tissue fluid, from which the glucose has already been taken up and used by respiring cells.
7. Urea is present - lymph is derived from tissue fluid, into which urea has been released by body cells.
8. High [lipid] - especially after a meal has been digested: lipids (e.g. fatty acids) are absorbed directly from the small intestine by lymph vessels called lacteals (which are present inside the fingerlike villi that increase the surface area of the wall of the small intestine).

Question 60

what happens to hydrostatic pressure as it flows round the double circulatory system?

Answer 60

hydrostatic pressure of the blood changes significantly as it flows around a double circulatory system

Question 61

Why does the hydrostatic pressure of the blood drops as it flows from the arteries towards the capillaries? 3 points

Answer 61

1. Given that it is the heart which generates the high hydrostatic pressure as it contracts, blood further from the heart will have lower pressure as some hydrostatic pressure has been lost.
2. As blood flows from arteries to arterioles to capillaries, it is flowing through vessels which have an increasingly large ‘total cross‐sectional area.’ This is because the blood vessels divide in to more and more (smaller) vessels. Despite the small lumen of each individual capillary, the capillaries are so very numerous that collectively, they actually have a greater total lumen than the arterioles, just as the arterioles collectively have a greater total lumen that the arteries. The fact that the blood is effectively flowing into a more voluminous space means that it loses pressure.
3. As blood flows through the capillaries, some water (plus small dissolved solutes) is squeezed out through the capillary endothelium, to become tissue fluid. This reduces the blood volume and so causes a fall in blood pressure.

Question 62

which part of the heart produces the most hydrostatic pressure?

Answer 62

the cardiac muscle in the wall of the left
ventricle (which is extremely thick) can generate very high hydrostatic pressure, so the blood (which leaves the left ventricle via a large artery called the aorta) can reach all parts of the body served by the systemic circulation.

Question 63

How in the right ventricle wall differ to the left ventircle wall?

Answer 63

the right ventricle wall has thinner cardiac muscle, and so does not generate such high hydrostatic pressure. This is appropriate because it is only pumping blood to the lungs
The pulmonary circulation operates at lower pressures, since the delicate lung capillaries would be damaged by higher pressure.
The slower flow rate of blood through the lung capillaries also allows more time for gas exchange.

Question 64

LABEL THIS HEART DIAGRAM

Answer 64

Label printed sheet.

Question 65

what divides the heart? Whats its function?

Answer 65

vertical septum divides the heart such that deoxygenated blood on the right side is completely separated from and cannot mix with the oxygenated blood on the left.

Question 66

what areas of the heart has the thinnest walls?

Answer 66

The wall is thinnest for the right and left atria ‐ the cardiac muscle only needs to contract powerfully enough to generate sufficient hydrostatic pressure of the blood to push it into the ventricles below;

Question 67

what area of the heart has moderate thickness?

Answer 67

The wall of the right ventricle has a moderately thick layer of muscle ‐ this can generate sufficient hydrostatic pressure to push the blood around the pulmonary circulation (in which the delicate lung capillaries could rupture if the blood pressure was too high);

Question 68

what area of the heart has the thickest wall?

Answer 68

The cardiac muscle is thickest in the wall of left ventricle – this has to contract so powerfully that the force generated can increase the hydrostatic pressure of the blood very significantly. This in turn enables the blood to be pushed around the whole systemic circulation, including overcoming gravity to send blood up to the brain.

Question 69

what is the cardiac cycle?

Answer 69

The cardiac cycle is the repeating sequence of events that make up each heartbeat, composed of atrial systole (contraction of the atria), ventricular systole (contraction of the ventricles) and then diastole (relaxation).

Question 70

what is atral systole?

Answer 70

contraction of the atria

Question 71

what is ventricular systole?

Answer 71

contraction of the ventricles

Question 72

what is diastole?

Answer 72

relaxation of the heart

Question 73

how long is a typical cardiac cycle?

Answer 73

The typical length of the cardiac cycle at rest is around 0.8s

Question 74

how is the cardiac muscle coordianted?

Answer 74

The muscle contractions involved in the cardiac cycle are coordinated by electrical activity

Question 75

What occurs on the right side of the heart (Cardiac cycle)?

Answer 75

1. Deoxygenated blood at low pressure enters the right atrium from the superior vena cava (a vein bringing blood from the head and arms) and inferior vena cava (a vein bringing blood from the lower body).
2. The cardiac muscle in the wall of both atria contracts (atrial systole). This increases the hydrostatic pressure of the blood in the atria, such that it becomes higher than the pressure in the ventricles.
3. The consequence on the right side of the heart is that the tricuspid atrioventricular valve is pushed open, allowing blood to flow from the right atrium into the right ventricle down the pressure gradient
4. The walls of the atria now relax and the cardiac muscle in the walls of both ventricles contracts (ventricular systole), from the base upwards. This increases the hydrostatic pressure of the blood in the ventricles, such that it becomes higher than the pressure in the atria.
5. The consequence is that the atrioventricular valves are both pushed closed, preventing blood flowing back from the ventricles into the atria. The closing of the tricuspid and bicuspid valves produces the first heart sound (‘lub’).
6. Due to the ventricular pressure becoming so much higher than the atrial pressure, there could be a risk of the atrioventricular valves not only being pushed closed but actually inverting and become damaged and leaky. This is prevented by the tendinous cords which have a fixed length: they allow the valves to close but not be pushed back further into the atria. The tendinous cords are themselves held at the correct length by the contraction of tiny papillary muscles, located on the, inner ventricle walls.
7. Due to ventricular systole, the hydrostatic pressure of the blood in the right ventricle is now higher than the pressure of the blood in the pulmonary arteries. This causes the semilunar valve at the base of the pulmonary arteries to be pushed open, allowing the flow of blood from right ventricle into pulmonary arteries down the pressure gradient.
8. Both ventricle walls now relax (ventricular diastole), resulting in the blood pressure in the ventricles falling below the blood pressure in the arteries.
9. As a consequence, the semilunar valves are pushed closed, preventing backflow of blood from the arteries into the ventricles. The closing of the semilunar valves produces the second heart sound (‘dub’).
10. The whole cardiac cycle (which has typically taken around 0.8s to complete) now repeats. At rest, the heart rate (number of cardiac cycles or number of beats per minute) is typically around 75bpm.

Question 76

What occurs on the left side of the heart (Cardiac cycle)?

Answer 76

1. Oxygenated blood at low pressure enters the left atrium from the pulmonary veins (one from the left lung and one from the right lung).
2. The cardiac muscle in the wall of both atria contracts (atrial systole). This increases the hydrostatic pressure of the blood in the atria, such that it becomes higher than the pressure in the ventricles.
3. The consequence on the left side of the heart is that the bicuspid atrioventricular valve is pushed open, allowing blood to flow from the left atrium into the left ventricle down the pressure gradient.
4. The walls of the atria now relax and the cardiac muscle in the walls of both ventricles contracts (ventricular systole), from the base upwards. This increases the hydrostatic pressure of the blood in the ventricles, such that it becomes higher than the pressure in the atria.
5. The consequence is that the atrioventricular valves are both pushed closed, preventing blood flowing back from the ventricles into the atria. The closing of the tricuspid and bicuspid valves produces the first heart sound (‘lub’).
6. Due to the ventricular pressure becoming so much higher than the atrial pressure, there could be a risk of the atrioventricular valves not only being pushed closed but actually inverting and become damaged and leaky. This is prevented by the tendinous cords which have a fixed length: they allow the valves to close but not be pushed back further into the atria. The tendinous cords are themselves held at the correct length by the contraction of tiny papillary muscles, located on the inner ventricle walls.
7. Due to ventricular systole, the hydrostatic pressure of the blood in the left ventricle is now higher than the pressure of the blood in the aorta. This causes the semilunar valve at the base of the aorta to be pushed open, allowing the flow of blood from left ventricle into the aorta down the pressure gradient.
8. Both ventricle walls now relax (ventricular diastole), resulting in the blood pressure in the ventricles falling below the blood pressure in the arteries.
9. As a consequence, the semilunar valves are pushed closed, preventing backflow of blood from the arteries into the ventricles. The closing of the semilunar valves produces the second heart sound (‘dub’).
10. The whole cardiac cycle (which has typically taken around 0.8s to complete) now repeats. At rest, the heart rate (number of cardiac cycles or number of beats per minute) is typically around 75bpm.

Question 77

what is the average heart rate?

Answer 77

The heart rate (number of cardiac cycles or number of beats per minute) is typically around 75bpm.

Question 78

Cardiac cycle graph 1, 2, 3 and 4

Answer 78

1. When ventricular pressure becomes higher than atrial pressure (due to the start of ventricular systole), the bicuspid valve is pushed closed
2. When ventricular pressure becomes higher than aortic pressure (due to continued ventricular systole), the semilunar valve is pushed open
3. When ventricular pressure falls lower than aortic pressure (due to the start of ventricular diastole), the semilunar valve is pushed closed
4. When ventricular pressure falls lower than atrial pressure (due to continued ventricular diastole), the bicuspid valve is pushed open.

Question 79

What does each cross over on the cardiac cycle grpah represent? 1, 2, 3 and 4

Answer 79

1. When ventricular pressure becomes higher than atrial pressure (due to the start of ventricular systole), the bicuspid valve is pushed closed
2. When ventricular pressure becomes higher than aortic pressure (due to continued ventricular systole), the semilunar valve is pushed open
3. When ventricular pressure falls lower than aortic pressure (due to the start of ventricular diastole), the semilunar valve is pushed closed
4. When ventricular pressure falls lower than atrial pressure (due to continued ventricular diastole), the bicuspid valve is pushed open.

Question 80

what type of muscle is the heart made of?

Answer 80

cardiac muscle

Question 81

what are some ket features of cardiac muscle?

Answer 81

Cardiac muscle never fatigues

requires plentiful oxygen supply at all times (as it cannot use anaerobic respiration)

can contract very powerfully

myogenic

Question 82

what does cardiac muscle do?

Answer 82

The powerful contractions of cardiac muscle generate a force which increases the hydrostatic pressure of the blood inside the heart. The contraction of the wall of the left ventricle is so powerful that the hydrostatic pressure of the blood increases enough to send it even up to the brain (against gravity).

Question 83

the cardiac muscle is myogenic, what does this mean and what causes this?

Answer 83

Cardiac muscle has another noteworthy and unique property: it is myogenic.
This means that it can initiate its own contractions (at regular intervals) independently of stimulation by motor neurones.
It is the sino‐atrial node (SAN) that is responsible for the myogenic nature of cardiac muscle

Question 84

What is the SAN?

Answer 84

It is the sino‐atrial node (SAN) that is responsible for the myogenic nature of cardiac muscle.
The SAN (also known as the ‘pacemaker’) is a specific patch of cardiac muscle in the wall of the right atrium

Question 85

What is the AVN?

Answer 85

atrioventricular node (AVN)

Question 86

What are purkyne fibres?

Answer 86

Conductive tissue

Question 87

How is the cardiac cycle coordinated? 10 points

Answer 87

1. The SAN is responsible for initiating the cardiac cycle: approximately once every 0.8s, the SAN, found in the wall of the right atrium, generates electrical impulses. These are emitted from the SAN and are transmitted over the atrial walls.
2. The electrical impulses trigger the contraction of the atrial walls, i.e. atrial systole.
3. Note that the wall of the right atrium starts to contract very slightly earlier than the wall of the left atrium. This is because the contraction is triggered by the electrical impulses that have originated from the SAN, which is in the wall of the right atrium.
4. The electrical impulses that are spreading over the atrial walls can NOT spread directly downwards onto the ventricular walls. This is due to the presence of a non‐conductive band of collagen protein that forms a horizontal septum in the wall of the heart between the atria and the ventricles.
5. The only point on this horizontal septum that is able to conduct the impulses downwards is the AVN, located in the (vertical) septum at the junction of the RA, LA, RV and LV.
6. However, before conducting the electrical impulses downwards, the AVN delays them for approximately 0.1s. This delay is important: it allows time for the ventricles to fill with blood from the atria before the ventricle walls start to contract. This delay introduced by the AVN is therefore important in maintaining a high stroke volume and hence cardiac output.
7. The AVN now conducts the electrical impulses down to the bundle of His. This is made up of many parallel conductive Purkyne fibres (also called Purkyne tissue). The impulses are thus conducted down to the apex (base) of the heart.
8. From the apex, the electrical impulses are conducted upwards and outwards over the ventricle walls by further Purkyne fibres which radiate out from the apex.
9. These impulses trigger the contraction of the ventricle walls from the base upwards. This directionality is important as it means the blood in the ventricles is correctly forced upwards, into the pulmonary arteries (on the right side) or the aorta (on the left side).
10. There then follows a period in which the cardiac muscle relaxes (diastole). The atria refill with blood. The whole cycle then repeats.

Question 88

What does ECG stand for?

Answer 88

Electrocardiogram

Question 89

what is an electrocardiogram?

Answer 89

The measurement of the electrical changes occurring in a patient’s heart

Question 90

what is a P wave?

Answer 90

this corresponds to the electrical activity which triggers atrial systole. Electrical impulses are being generated by the SAN and transmitted over the atrial walls. These impulses trigger the contraction of the cardiac muscle in the atrial walls

Question 91

what is the QRS complex?

Answer 91

this corresponds to the electrical activity which triggers ventricular systole. Electrical impulses are passed on by the AVN and transmitted down the bundle of His to the apex of the heart, from where the impulses spread upwards over the ventricular walls in Purkyne fibres. These impulses trigger the contraction of the cardiac muscle in the ventricular walls (from the apex upwards).

Question 92

what is a T wave?

Answer 92

this corresponds to the electrical activity that occurs during diastole. Even though the cardiac muscle is now relaxing, electrical activity is detected due to the active transport of ions across the plasma membranes of the cardiac muscle fibres. This phase is essential in preparing the heart for the beginning of the next cardiac cycle.

Question 93

how to determine a heart rate from an ECG?

Answer 93

1. Determine the length of one complete cardiac cycle, e.g. from the start of one P wave to the start of the next P wave. For a healthy subject at rest, this will often be around 0.8s. If the trace shows more than one complete cardiac cycle, determine themean cycle length.
2. Divide 60 by the (mean) length of one cycle, e.g. 60 ÷ 0.8.
3. This will give the heart rate in beats per minute, e.g. 75bpm.

Question 94

what is cardiac output?

Answer 94

Cardiac output is the volume of blood that leaves the heart each minute (with units usually given as cm3min‐1):

Question 95

how do we calculate cardiac output?

Answer 95

cardiac output = stroke volume x heart rate

Question 96

what is stroke volume?

Answer 96

volume of blood leaving the heart in one cardiac cycle, usually measured in cm3

Question 97

Draw a normal ECG

Answer 97

notes

Question 98

what is Tachycardia? Draw it

Answer 98

A heart rate significantly higher than normal, over 100bpm. Occurs during exercise (increasing cardiac output such that muscles receives faster delivery of oxygen and glucose) or during a ‘fight or flight’ response (due to the effects of adrenaline and the sympathetic nervous system on the SAN). However, if tachycardia occurs without these contexts or can suggest an abnormality in the function of the SAN, which is generating electrical impulses more frequently that is ideal.

IF SOMETHING IS TACHY IS BREAKS FASTER

Question 99

What is Bradycardia? Draw it

Answer 99

A heart rate significantly lower than normal, below 60bpm. This can be caused by the individual having very high fitness levels (and therefore a heart that is so strong and efficient that it can produce the necessary cardiac output without beating as many times per minute). However, in other individuals, bradycardia
could lead to low cardiac output and low blood pressure; in this case, an artificial pacemaker may be fitted in order to increase the heart rate

Question 100

What is Atrial fibrillation? Draw it

Answer 100

very frequent additional electrical impulses are generated in the atrial walls (not only originating at the SAN), giving an appearance on the ECG of many consecutive P waves in rapid succession. This leads to the atrial walls fluttering (fibrillation) as they contract incompletely but rapidly and repeatedly. Only some impulses are pass on to the ventricles, seen as occasional QRS complexes on the ECG. Cardiac output falls as the ventricles may be contracting without being full of blood and the patient’s blood pressure will likewise fall.

Question 101

What is Ventricular fibrillation? Draw it

Answer 101

there is no clear pattern of electrical signals; the electrical activity is chaotic, with few or no identifiable P, QRS or T waves. The ventricle walls may be twitching, but do not have synchronised contraction from the base upwards. The cardiac output will drop dramatically, the blood pressure will fall significantly and there will be no detectable pulse. The patient’s heart will go into cardiac arrest; they will quickly become unconscious and could die if the electrical activity cannot be corrected very quickly.

Question 102

What is Ectopic heartbeat? Draw it

Answer 102

this is scenario in which extra heart beats occur that are out of the usual rhythm. This is seen on an ECG as an additional cardiac cycle that does not fit the usual rhythm; additionally this cycle will itself usually show an unusual shape (e.g. a QRS complex that does not have the normal pattern of electrical activity). An occasional ectopic heartbeat (up to one per day) is common and does not give cause for concern, but if they occur frequently then treatment is required.

Question 103

What is an Erythrocytes, what is its functions and how is it specialised?

Answer 103

What:
Red blood cells

Function:
Transport oxygen from the lung alveoli to body cells, for use in respiration

Specialisations:
No organelles, e.g no nucleus, no ribosome and no mitochonsria (Organelles present in immature erythrocytes, but are broken down once enough haemoglobin is produced, it is then mature. This is good as there is more space for heamoglobin so more oxygen can be carried

Biconcave disk shape, increases SA and therfore rate of diffusion increases, plus allows the cell to be flexible

Small, 7 um, therefore is able to fit through narrow blood capillaries, also creates a large SA:V ratio, increasing the rate of diffusion

Question 104

what is the role and quantity of heamoglobin in rbc’s?

Answer 104

Red blood cells have huge quantities of haemoglobin protein in their cytoplasm. Since red blood cells have no nucleus (nor any mitochondria), there is more space for haemoglobin.
The role of this haemoglobin (and therefore of the red blood cells) is to transport oxygen from the lungs (which are the site of oxygen uptake) to the body tissues (where cells require oxygen for use in aerobic respiration).

Question 105

how many iron irons are in 1 haemoglbin?

Answer 105

4

Question 106

how many oxygen atoms can 1 heamoglbin bind with?

Answer 106

4

Question 107

what is loading of O2 in blood?

Answer 107

Oxygen reversibly combines with haemoglobin to form oxyhaemoglobin. Specifically, oxygen will bind to haemoglobin where there is a region of high oxygen availability, i.e. at the lung alveoli. This helps to maintain a steep concentration gradient for oxygen, so that it keeps diffusing from the alveoli into the red blood cell at a high rate.

Question 108

what is dissociation of O2 in blood?

Answer 108

when the blood later reaches a region of low oxygen availability, e.g. respiring body tissues, the oxyhaemoglobin dissociates; this means that the oxygen is now released from the haemoglobin. The released oxygen will then move by diffusion out of the red blood cells into the surrounding tissue, where it be used immediately in aerobic respiration in the cells’ mitochondria.

Question 109

what is the reversible reaction between haemoglobin and oxygen?

Answer 109

Hb + 4O2 ⇌ Hb(O2)4

Question 110

What shape is an oxygen dissociation curve?

Answer 110

Sigmoidal

Question 111

Describe the oxygen dissociation cureve from Left‐to‐right: the loading of oxygen onto haemoglobin 6 points

Answer 111

This can be interpreted as corresponding to the
loading of oxygen onto haemoglobin via a process called co‐operative binding:

1. Remember that each haemoglobin has four haem groups (one on each of the four polypeptide chains) and hence can carry up to four oxygen molecules (one per haem group) at any one time. Full (100%) saturation is when all the haemoglobin is carrying the maximum number of oxygen molecules, i.e. four per protein.
2. As the blood flows into the lungs towards the alveoli, it is effectively flowing into regions of increasing oxygen partial pressure.
3. However, haemoglobin with no oxygen molecules yet attached actually has quite a low affinity for (i.e. low readiness to bind with) oxygen. Hence the first oxygen to bind to a haemoglobin does so slowly or with difficulty. This corresponds to the initial shallow phase of the sigmoidal graph.
4. The binding of the first oxygen molecule triggers a small change in the haemoglobin’s 3D shape (tertiary structure). This causes an increase in the affinity of haemoglobin for oxygen.
5. As a result of this, the second and third oxygen molecules combine very readily with the haemoglobin (quickly and easily). This corresponds to the steep phase on the graph.
6. The fourth and final oxygen however has difficulty binding, due to the low probability of it colliding with the one remaining haem group which is still free. This corresponds to the final shallow phase on the graph.

Question 112

Describe the oxygen dissociation cureve from Right‐to‐left: release of oxygen (dissociation) from haemoglobin

Answer 112

1. The steep part of the curve corresponds to the (fall in) partial pressure experienced by oxyhaemoglobin in blood that is flowing into a respiring tissue.
2. The steepness of the curve at this point is significant because it shows that even a small, further decrease in oxygen partial pressure will result in a large decrease in the percentage saturation of haemoglobin with oxygen. In other words, a small drop in oxygen partial pressure is resulting in a great deal of release (dissociation) of oxygen from haemoglobin.
3. This is an important effect because it means that tissues that are respiring aerobically (depleting oxygen from the surrounding fluid, causing a decrease in oxygen partial pressure) will have more oxygen released to them due to more dissociation of oxygen from oxyhaemoglobin. The particular steepness of the curve (at partial pressures corresponding to those found in body tissues) means that more oxygen is released to those tissues (for a given drop in oxygen partial pressure) than would be the case if the graph were a straight line rather than a sigmoidal curve.

Question 113

What is the Bohr Effect

Answer 113

At high CO2 concentrations, the dissociation curve shifts to the RIGHT; this phenomenon is called the Bohr Effect (or Bohr Shift).
High CO2 concentrations occur in muscle tissue during exercise; since more energy is needed for muscle contraction, the rate of respiration has increased. This in turn means that more CO2 is being produced as a waste product.

Question 114

How to rememeber which way the bohr effect shifts the graph?

Answer 114

bohR = Right

Question 115

How to rememeber which way the bohr effect shifts the graph?

Answer 115

bohR = Right

Question 116

What is feotus haemoglobin?

Answer 116

All body cells in a foetus, developing in its mother’s uterus, require oxygen for aerobic respiration. However, the foetus does not have access to atmospheric air and is not able to breathe (ventilate). Instead, the foetus relies entirely on diffusion of oxygen across the placenta, from the mother’s blood into the foetal blood.

In order for this mechanism to be effective, it is crucial that the foetal haemoglobin has a higher affinity for oxygen than the mother’s haemoglobin. In fact, a foetal haemoglobin molecule has a different composition of polypeptide chains in its quaternary structure (2 α-globin plus 2 γ‐globin) compared to ‘adult’ haemoglobin (2 α‐globin plus 2 β‐globin); it is essentially a different protein and hence has different properties.

Question 117

what is adult haemoglin made of?

Answer 117

2 x alpha-globin 2x beta-globin

Question 118

How to rememeber which way the foetal haemoglobin shifts the graph?

Answer 118

foetaL = Left

Question 119

What is the significance of foetal heamoglin?

Answer 119

The foetal haemoglobin has higher affinity for oxygen. This means that it combines more readily with oxygen to form oxyhaemoglobin and can become fully loaded (saturated) with oxygen even at low oxygen partial pressure.

The significance of this property is as follows:
1. At the placenta, the partial pressure of oxygen is very low.

2. At this low partial pressure, maternal haemoglobin will be caused to release oxygen via dissociation of the oxyhaemoglobin contained within red blood cells in the mother’s blood.
3. This oxygen diffuses across the placenta, from the mother’s blood into the foetal blood. (Note that the placenta is a highly efficient exchange surface, with large surface area, rich blood supply and thin barrier to diffusion.)
4. Despite the low oxygen partial pressure, the foetal haemoglobin is able to combine with oxygen to form oxyhaemoglobin; this is due to its higher affinity for oxygen, compared to maternal haemoglobin. The foetal haemoglobin is able to become wellsaturated with oxygen under the low oxygen conditions found at the placenta, even though these same conditions are causing maternal haemoglobin to release oxygen.
5. In this way, the foetus is able to obtain sufficient oxygen across the placenta such that its body cells can be supplied with enough oxygen for their aerobic respiration to be maintained.

Question 120

What is the significance of the gradual replation of foetal haemoglin?

Answer 120

This is significant because foetal haemoglobin, if present in a child, would have too high an affinity for oxygen to fulfil its role. Specifically, foetal haemoglobin would not be able to release oxygen readily enough to muscles during exercise, when a higher rate of oxygen dissociation from haemoglobin is required in order to sustain a higher rate of aerobic respiration.

In any case, the child is now breathing atmospheric air (which results in a much higher partial pressure of oxygen at the lungs than there was at the placenta); there is therefore no longer any advantage or necessity in having the foetal form of haemoglobin, with such a high affinity for oxygen.

Question 121

What are some other cases where the dissociation curve shifts to the left?

Answer 121

Haemoglobin of animals adapted to high altitude (e.g. the llama) or those that are mud‐dwelling – having very high affinity for oxygen allows sufficient oxygen to combine with haemoglobin at the alveoli, despite the lower partial pressure of oxygen in the atmosphere/environment; this means that the body cells are still supplied with sufficient oxygen to respire aerobically despite the low availability of oxygen in the surroundings.

Myoglobin – this is a protein found in muscle fibres that has very high affinity for oxygen; oxygen that has diffused into a muscle fibre (that has not been immediately consumed in aerobic respiration) binds very readily to myoglobin, keeping the concentration gradient for oxygen between the blood and the muscle fibre’s sarcoplasm (cytoplasm) very steep.

Question 122

How does carbon dioxide transport work?

Answer 122

All body cells produce carbon dioxide as a waste product from respiration. This carbon dioxide typically diffuses (moving passively down its concentration gradient) from the cells, through the capillary wall, into the blood plasma. Most of this CO2 then continues to diffuse down its concentration gradient, moving into the cytoplasm of red blood cells by passing through their cell surface membranes. Once in the cytoplasm of a red blood cell, there are two possible reactions that the CO2 may undergo. Both of these are very significant to body function as they stimulate release of oxygen from haemoglobin. The first possibility is that a CO2 molecule can react directly with an amine (‐NH2) group at the end of one of the four polypeptide chains of a haemoglobin molecule. This forms carbaminohaemoglobin. (Since haemoglobin comprises four polypeptide chains, there are actually four amine groups available on each haemoglobin protein molecule which can each react with a CO2 molecule.) This reaction results in a change to the 3D shape (tertiary structure) of the haemoglobin protein. If the haemoglobin was carrying any oxygen, this oxygen will now be released, since carbaminohaemoglobin has decreased affinity for oxygen (i.e. lower tendency to combine with oxygen and higher tendency to release it).

Alternatively, the carbon dioxide that has diffused into the cytoplasm of a red blood cell may undergo a reaction with water. This reaction occurs at a very high rate, catalysed by an enzyme called carbonic anhydrase, which is found in large quantities in the cytoplasm of all red blood cells. The product from this reaction is called carbonic acid (H2CO3). The carbonic acid may then dissociate (split up) into a hydrogen ion (H+) plus a hydrogencarbonate ion (HCO3‐). he hydrogen ions released by the above reaction then bind to haemoglobin molecules, forming haemoglobinic acid. This results in a change to the 3D shape (tertiary structure) of the haemoglobin. If the haemoglobin was carrying any oxygen, this will now be released, since haemoglobinic acid has a lower affinity for oxygen. Meanwhile, the hydrogencarbonate ions produced by the above reaction move by facilitated diffusion (down their concentration gradient) out of the red blood cells, into the blood plasma. In fact, most of the CO2 molecules released by body cells end up being
carried round the body in the blood plasma in the form of hydrogencarbonate, having first undergone reaction with water (catalysed by carbonic anhydrase) in the red blood cells’ cytoplasm. To balance the loss of negative charge (HCO3‐ ions) from the red blood cells, negatively charged chloride ions (Cl‐) move by facilitated diffusion into the red blood cells. This phenomenon is called the Chloride Shift. As noted above, the reactions that CO2 molecules undergo once they have entered red blood cells lead to the release of oxygen from haemoglobin (i.e. the dissociation of oxyhaemoglobin). The oxygen released will immediately diffuse out of the red blood cells and into the surrounding body cells, where it is consumed in aerobic respiration. This effect is highly significant: the higher the respiration rate in a particular tissue, the more CO2 is produced as waste; if more CO2 diffuses into red blood cells then there is an increased rate of reaction of the CO2 with water, forming more carbonic acid, which dissociates to H+ and HCO3‐ ions; if more H+ are produced, then there is more binding of H+ to haemoglobin, forming haemoglobinic acid; since this is accompanied by a release (dissociation) of oxygen from the haemoglobin, the overall effect is that tissues with a higher respiration rate (where cells are producing and releasing more CO2) will correspondingly have more oxygen released to them. The reason that this is so significant is that oxygen is therefore released to body tissues according to their current needs, enabling their current rate of respiration to be maintained. A particular example would be that during exercise, muscles have increased respiration rate (as they must produce more ATP to provide energy for muscle contraction); they produce CO2 at a higher rate, and, via the mechanisms described above, this in turn triggers more release of oxygen to the muscle, due to increased dissociation of oxygen from haemoglobin. The muscle can thus maintain its high rate of respiration during the period of exercise.

Question 123

Summarise the reaction catalysed by carbonic anhydrase, and the subsequent dissociation
of carbonic acid:

Answer 123

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

Question 124

Summarise the reaction catalysed by carbonic anhydrase, and the subsequent dissociation of carbonic acid:

Answer 124

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

Question 125

A note about pH: The pH (hydrogen ion concentration) of the blood is remarkably stable as it is buffered (i.e. corrected back to the set point) by both of the following reversible reactions:

Answer 125

H+ + Hb ⇌ HHb

H+ + HCO3- ⇌ CO2 + H2O

The forward reactions occur more when pH falls, acting to remove excess H+ ions from the solution and increase the pH; the back reactions occur more when pH rises, acting to donate H+ back into the solution and decrease the pH. This buffering effect tends to correct the pH back to the set point and is an example of negative feedback.