3.1.2 Transport in Animals Flashcards

Question

What are key features of an artery?

Answer 1

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.

Answer 2

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.

Answer 3

around 0.7mm

Answer 4

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

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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

Answer 9

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.

Answer 10

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.

Answer 11

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

Answer 12

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

Answer 13

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.

Answer 14

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.

Answer 15

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

Answer 16

oxygen, glucose, amino acids and salt ions

Answer 17

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.

Answer 18

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).

Answer 19

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

Answer 20

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.

Answer 21

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.

Answer 22

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.

Answer 23

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.

Answer 24

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

Answer 25

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

Answer 26

Oncotic pressure becomes more negative as solute concentration gets higher

Answer 27

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)

Answer 28

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.

Answer 29

fluid reabsorbed into the capillaries

Answer 30

fluid leaves the capillaries

Answer 31

Hydrostatic pressure + oncotic pressure

Answer 32

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.

Answer 33

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.

Answer 34

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).

Answer 35

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

Answer 36

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.

Answer 37

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.

Answer 38

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.

Answer 39

Label printed sheet.

Answer 40

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.

Answer 41

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;

Answer 42

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);

Answer 43

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.

Answer 44

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).

Answer 45

contraction of the atria

Answer 46

contraction of the ventricles

Answer 47

relaxation of the heart

Answer 48

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

Answer 49

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

Answer 50

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.

Answer 51

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.

Answer 52

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

Answer 53

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.

Answer 54

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.

Answer 55

cardiac muscle

Answer 56

Cardiac muscle never fatigues requires plentiful oxygen supply at all times (as it cannot use anaerobic respiration) can contract very powerfully myogenic

Answer 57

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).

Answer 58

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

Answer 59

``` 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 ```

Answer 60

atrioventricular node (AVN)

Answer 61

Conductive tissue

Answer 62

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.

Answer 63

Electrocardiogram

Answer 64

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

Answer 65

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

Answer 66

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).

Answer 67

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.

Answer 68

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.

Answer 69

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

Answer 70

cardiac output = stroke volume x heart rate

Answer 71

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

Answer 72

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

Answer 73

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

Answer 74

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.

Answer 75

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.

Answer 76

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.

Answer 77

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

Answer 78

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).

Answer 79

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.

Answer 80

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.

Answer 81

Hb + 4O2 ⇌ Hb(O2)4

Answer 82

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.

Answer 83

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.

Answer 84

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.

Answer 85

bohR = Right

Answer 86

bohR = Right

Answer 87

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.

Answer 88

2 x alpha-globin 2x beta-globin

Answer 89

foetaL = Left

Answer 90

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.

Answer 91

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.

Answer 92

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.

Answer 93

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.

Answer 94

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

Answer 95

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

Answer 96

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.

3.1.2 Transport in Animals Flashcards

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