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Biology A-Level > Transport in Mammals (Chapter 8) > Flashcards

Transport in Mammals (Chapter 8) Flashcards

1
Q

What is the mammalian circulation system?

A

A closed double circulation consisting of a heart, blood vessels and blood

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2
Q

What is the function of arteries?

A

To transport blood, swiftly and at high pressure, to the tissues, away from the heart

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3
Q

What are the three layers of muscle in the walls of arteries and veins?

A 
Tunica intima (an inner endothelium)
Tunica media
Tunica externa
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4
Q

Describe the tunica intima

A

Very smooth, minimising friction with the moving blood

It is made up of flat cells (squamous epithelium) fitting together like jigsaw pieces

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5
Q

What does the tunica media contain?

A

Smooth muscle, collagen and elastic fibres

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6
Q

What does the tunica externa contain?

A

Elastic fibres and collagen fibres

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7
Q

What are the distinctive characteristics of an artery wall?

A

Its strength and elasticity

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8
Q

Why must artery walls be very strong?

A

To withstand the very high blood pressure of the blood leaving the heart

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9
Q

How are artery walls strong?

A

They are thick

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10
Q

How does the composition of the artery wall provide strength and resilience?

A
  • (Nearer the heart) the tunica media contains large amounts of elastic fibres, allowing the wall to stretch as pulses of blood surge through at high pressure
  • (Further from the heart) tunica media has fewer elastic fibres but more muscle fibres
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11
Q

Why is the elasticity of artery walls important?

A
  • It allows them to ‘give’, which reduces the likelihood that they will burst
  • It allows artery walls to stretch as the high-pressure blood surges into them when the ventricles contract (reducing the pressure) and then recoil inwards as the pressure drops when the ventricles relax (giving the blood a little push)
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12
Q

What are arteries called when they branch into smaller vessels?

A

Arterioles

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13
Q

Describe the walls of arterioles

A
  • Similar to arteries, but have a greater proportion of smooth muscle
  • This muscle can contract, narrowing the diameter of the arteriole and so reducing blood flow, to help control the volume of blood flowing to different tissues at different times
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14
Q

What is the function of capillaries?

A

To take blood as close as possible to all cells, allowing rapid transfer of substances between cells and blood

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15
Q

What are capillary beds?

A

Networks of capillaries

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16
Q

What are adaptations of capillaries?

A 
Small size (approx 7μm in diameter) 
Extremely thin walls (one layer of endothelial cells)
Tiny gaps between endothelial cells
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17
Q

Why is the small size of capillaries important?

A
  • Allows them to bring blood as close as possible to each group of cells in the body as they are approx the same diameter as an RBC
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18
Q

Why are the thin walls of capillaries important?

A
  • RBCs are brought within 1μm of the cells outside the capillary, needing the oxygen
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19
Q

Why are the gaps between the cells in capillary walls important?

A
  • They allow some components of the blood to seep through into the spaces between the cells in all the tissues of the body, forming tissue fluid
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20
Q

What is the function of veins?

A

To return blood to the heart

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21
Q

What does the low blood pressure inside a vein mean for the vein?

A
  • That there is no need for veins to have thick walls

- Their tunica media is much thinner than in arteries and has far fewer elastic fibres and muscle fibres

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22
Q

How is blood returned to the heart if it has low blood pressure (e.g. from your legs) ?

A
  • Many veins run within or close to several leg muscles, so when you tense these muscles, they squeeze inwards on the veins, temporarily raising the pressure
  • Veins also contain semi lunar valves which allow blood to move towards the heart but not away, so the squeezing of muscles only squeezes it upwards
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23
Q

What is plasma?

A

A pale yellow liquid in blood consisting of mainly water with other substances dissolved in it

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24
Q

Give examples of solutes in blood plasma

A

Nutrients e.g. glucose
Waste products e.g. urea
Protein molecules - plasma proteins which always stay in the blood

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25
Q

What is tissue fluid?

A

Leaked plasma between the cells in tissues which has leaked through the gaps in the cells of the capillary wall

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26
Q

How is tissue fluid different from blood plasma?

A
  • Far fewer protein molecules (too large to fit through gaps in capillary walls)
  • No RBCs (but some WBCs)
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27
Q

Why does plasma move out into tissue fluid at the arterial end of the capillary bed?

A
  • The blood pressure inside the capillary is enough to push fluid out into the tissue (down a pressure gradient) and there is no change in water potential as proteins remain in the capillary
  • The hydrostatic pressure is greater than the difference in water potential between the blood and tissue fluid
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28
Q

Why does tissue fluid move back into capillaries at the venous end of the capillary bed?

A
  • Water moves from high water potential to low water potential
  • Since tissue fluid lacks the high concentrations of proteins that exist in plasma, and the pressure is lower, fluid moves into the capillaries from a higher water potential to a lower water potential
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29
Q

Overall, does more blood flow into or out of capillaries?

A

Out of

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30
Q

What is oedema, how is it caused and how is it avoided?

A
  • Oedema is the build up of tissue fluid
  • If blood pressure is too high, too much fluid is forced out of capillaries and may accumulate in the tissues
  • One of the main roles of arterioles is to reduce the pressure of blood that enters the arterioles, in order to avoid this
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31
Q

What is the muscle of which the heart is made called?

A

Cardiac muscle

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32
Q

What do the coronary arteries do?

A

They branch from the aorta and deliver oxygenated blood to the walls of the heart itself

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33
Q

What is the septum?

A

A wall of muscle in the heart, separating the right chambers from the left

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34
Q

What is the left AV valve called?

A

Bicuspid (mitral) valve

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35
Q

What is the right AV valve called?

A

Tricuspid valve

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36
Q

What is your average heart rate?

A

70 beats per minute

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37
Q

What is the cardiac cycle?

A

The sequence of events that makes up one heart beat

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38
Q

What are the three stages of the cardiac cycle?

A

Atrial systole
Ventricular systole
(Ventricular) diastole

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39
Q

What happens during atrial systole?

A
  • The muscle in both of the atrial wall contracts
  • The pressure developed is not very great, because the muscular walls of the atria are only thin, but it is enough to force the blood in the atria into the ventricles through the AV valves
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40
Q

Why does blood from the atria not go back into the pulmonary veins or venae cavae?

A

Because these have semi lunar valves to prevent backflow

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41
Q

What is another word for white blood cells?

A

Leucocytes

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42
Q

Where are WBCs made?

A

In the bone marrow

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43
Q

What is different about the structure of WBCs compared to RBCs?

A
  • WBCs all have a nucleus
  • Most WBCs are larger than RBCs (except lymphocytes)
  • WBCs are either spherical or irregular in shape, never biconcave discs
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44
Q

What is the function of haemoglobin?

A
  • To carry and distribute oxygen in RBCs around the body

- It loads oxygen in the lung capillaries and unloads it in the tissue capillaries

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45
Q

How many oxygen molecules can each haem group carry?

A

1

46
Q

How many oxygen molecules can a haemoglobin molecule carry at one time?

A

Up to 4 (8 atoms)

47
Q

What is the equation for the reaction of Hb with O2?

A

Hb + 4O2 <==> HbO8

48
Q

What does the term ‘partial pressure’ mean?

A

Concentration

49
Q

What is a dissociation curve?

A

The percentage saturation of Hb with oxygen plotted against the partial pressure of oxygen

50
Q

What does the Hb dissociation curve show?

A
  • At low partial pressures of oxygen, the % saturation of Hb is very low (the Hb has combined with only a very little oxygen)
  • At high partial pressures of oxygen, the % saturation of Hb is very high (the Hb has combined with large amounts of oxygen
51
Q

Why is the Hb dissociation curve S-shaped?

A
  • When an oxygen molecule combines with a haem group, the whole Hb molecule is slightly distorted
  • This distortion makes it easier for a second oxygen molecule oxygen molecule to combine with the second haem group (and the third and fourth/final)
  • Therefore the curve rises steeply
  • In this part of the curve, a small change in partial pressure of oxygen causes a very large change in the % saturation of Hb
52
Q

What is the Bohr effect?

A

The presence of a high partial pressure of CO2 causes Hb to release oxygen

53
Q

Why is the Bohr effect useful?

A

High concentrations of CO2 are found in actively respiring tissue, which need oxygen

54
Q

What are phagocytes?

A

WBCs that destroy invading microorganisms by phagocytosis

55
Q

What are the two types of phagocytes and what do they look like?

A

Neutrophils - most common, lobed nucleus, granular cytoplasm

Monocytes - less rounded, bigger, U-shaped nucleus

56
Q

What are lymphocytes?

A

WBCs that destroy microorganisms, some by secreting antibodies which attach to and destroy the invading cells

57
Q

What do lymphocytes look like?

A

Spherical, smaller, large nucleus

58
Q

What happens during ventricular systole?

A
  • The thick, muscular walls of the ventricles squeeze inwards on the blood, increasing its pressure and pushing it out of the heart
  • As soon as the pressure difference in the ventricles becomes greater than the pressure in the the atria, this pressure difference pushes the AV valves shut, preventing blood going back into the atria
  • The blood rushes upwards into the aorta and pulmonary artery, pushing open the semi lunar valves
59
Q

Why doesn’t the high pressure blood flow back into the low pressure ventricles during ventricular diastole?

A

Because of the semi lunar valves in the aorta/pulmonary artery, which snap shut

60
Q

What happens during diastole?

A
  • The whole of the heart muscle relaxes
  • Blood from the veins flows into the two atria
  • Some of the blood trickles downwards into the ventricles, as the AV valves open before atrial systole and because the pressure in the ventricles is lower than the pressure in the atria
61
Q

What does myogenic mean?

A

That it naturally contracts and relaxes, it does not need to receive impulses from a nerve to make it contract

62
Q

What does a double circulation system mean?

A

That the blood travels twice through the heart for one complete circuit of the body (through the systemic and pulmonary circulations)

63
Q

What does tissue fluid do?

A
  • Forms the immediate environment of each individual body cell
  • Exchanges of materials between cells and the blood occur
64
Q

How much fluid from the capillaries eventually seeps back into them?

A

About 90%

65
Q

How is the remaining 10% of fluid collected and returned to the blood system?

A

By a series of tubes - lymph vessels or lymphatics

66
Q

What are lymphatics?

A
  • Tiny, blind-ending vessels, which are found in almost all tissues of the body
  • They contain tiny valves, which allow the tissue fluid to flow in but stop it from leaking out
67
Q

Describe the structures of the valves in the lymph vessel walls and why this is important

A
  • They are wide enough to allow large protein molecules to pass through
  • Very important because such molecules are too big to get into the capillaries, and so cannot be taken away by the blood
68
Q

What is the fluid inside lymphatics called?

A

Lymph

69
Q

How is lymph different from tissue fluid?

A

Similar - diff place and diff composition

  • in liver, both have high conc of protein
  • in small intestine, both have high conc of lipid
70
Q

What do the lymphatics join up to form?

A

Lymph vessels - these transport the lymph back to large veins beneath the collarbone - subclavian veins

71
Q

What is the movement of fluid along the lymphatics caused and controlled by?

A

Contraction of muscles around the vessels

Valves keep it going in the right direction (like veins)

72
Q

What do lymph vessels have in their walls?

A

Smooth muscle

73
Q

Is lymph flow slow or fast compared to blood flow?

A

Slow

74
Q

What are located at intervals along the lymph vessels?

A

Lymph nodes

75
Q

What do lymph nodes do?

A

Involved in protection against disease
- bacteria and other unwanted particles are removed from lymph by some types of WBCs as the lymph passes through a node, whilst other WBCs within the nodes secrete antibodies

76
Q

What is other name for RBCS?

A

Erythrocytes

77
Q

What is the main function of haemoglobin?

A

To transport oxygen from the lungs to respiring tissues

78
Q

Describe the structure of RBCs

A
  • Shaped like a biconcave disc
  • Very small
  • Very flexible
  • No nucleus, mitochondria or ER
79
Q

Why are RBCs shaped like biconcave discs?

A
  • To increase the SA:vol ratio which means that oxygen can diffuse quickly into or out of the cell
80
Q

Why are RBCs very small?

A
  • Capillaries can be only 7μm wide, still allow RBCs to squeeze through them, so bringing oxygen as close as possible to cells which require it
  • No Hb molecule is far from the CSM and the Hb molecule can therefore quickly exchange oxygen with the fluid outside the cell
81
Q

Why are RBCs very flexible?

A
  • Some capillaries are even narrower than diameter of RBC

- Therefore the cells are able to deform so that they can pass through these vessels (bc of cytoskeleton)

82
Q

Why do RBCs have no nucleus, mitochondria or ER?

A
  • The lack of these organelles means more room for Hb, maximising the amount of oxygen which can be carried by each RBC
83
Q

Describe the reaction which is catalysed by carbonic anhydrase and the reaction that follows

A
  • CO2 + H2O <=> H2CO3

- H2CO3 <=> H+ + HCO3- (the carbonic acid dissociates)

84
Q

How does CO2 cause the release of oxygen (Bohr effect)?

A
  • Hb readily combines with the H+ ions (formed from the second reaction - dissociation of carbonic acid) forming haemoglobinic acid (HHb)
  • In doing so, it releases the oxygen which it is carrying
  • The Hb ‘mops up’ the H+ ions which are formed when CO2 dissolves and dissociates
85
Q

How does Hb help to maintain the pH of the blood close to neutral?

A
  • A high conc of H+ ions means a low pH - if the H+ ions were left in solution, the blood would be very acidic
  • By removing the H+ ions from solution, haemoglobin helps to maintain the pH of the blood close to neutral
  • It is acting as a buffer
86
Q

How does CO2 conc affect the saturation of haemoglobin with oxygen curve?

A
  • A high conc means a lower curve
87
Q

How is CO2 carried in the blood (3 ways)?

A

1) As hydrogencarbonate ions (HCO3-) formed by the dissociation of carbonic acid in the cytoplasm of RBCs which diffuse out of the RBC into the blood plasma, where they are carried in solution (85%)
2) As CO2 molecules carried in solution (5%)
3) As carbaminohaemoglobin by combining directly with the terminal amine groups of some of the Hb molecules (10%)

88
Q

What is the significance of the oxygen dissociation curves of adult oxyhaemoglobin at different carbon dioxide concentrations (the Bohr effect)?

A
  • At low partial pressures of oxygen, where oxygen is
    needed e.g. in active tissues, Hb will release oxygen
  • At high partial pressures of oxygen e.g. in lung capillaries, where oxygen is not needed (but needs to be taken up by the Hb), Hb will not release oxygen, and will instead take it up
89
Q

What happens when blood reaches the lungs?

A
  • The relatively low conc of CO2 in the alveoli compared with that in the blood, causes CO2 to diffuse from the blood into the air in the alveoli, stimulating the CO2 of carbaminohaemoglobin to leave the RBC, and HCO3- and H+ ions to recombine to form CO2 molecules once more
  • This leave the Hb molecules free to combine with oxygen, ready to begin another circuit of the body
90
Q

What happens to the partial pressure of oxygen at high altitudes?

A
  • At a height of about 6500m air pressure is much less
  • Therefore the partial pressure of oxygen in the air drops from 20kPa at sea level to 10kPa and in the alveoli from 13 to 5.3
91
Q

What does high altitude mean for Hb?

A
  • Haemoglobin becomes less saturated (about 70%) in the lungs and less oxygen will be carried around the body - the person mat begin to feel breathless and ill
92
Q

What happens if someone suddenly changes altitudes?

A
  • They could develop altitude sickness with symptoms of an increase in the rate and depth of breathing and a general feeling of dizziness and weakness
  • Can become more serious: arterioles in the brain dilate, increasing the amount of blood flowing into the capillaries, so that fluid begins to leak from the capillaries into the brain tissues - this can cause disorientation
  • Fluid may also leak into the lungs, preventing them from functioning properly
93
Q

What happens if someone gradually acclimatises to high altitude over a few months?

A
  • The number of RBCs in the blood increases from making up about 40-50% of the blood to as much as 50-70%
  • This increases the amount of Hb in their blood so more blood can be carried around the body
94
Q

What adaptions do people who live permanently at high altitudes show?

A

1) Broad chests - providing larger lung capacities
2) Larger heart - especially on the right side which pumps blood to the lungs
3) More Hb in their blood than usual

95
Q

What is the largest artery in the heart?

A

The aorta - it branches to the head and then arches over downwards for the main flow towards the body

96
Q

What is the other main artery in the heart?

A

The pulmonary artery

97
Q

What are the two large veins that bring back blood from the head and from the body?

A

The venae cavae

98
Q

What are the other main veins in the heart?

A

The pulmonary veins - bringing blood back from the right and left lungs

99
Q

Why are the walls of the ventricles much thicker than the walls of the atria?

A

Because the ventricles need to develop much more force when they contract
- their contraction has to push the blood out of the heart and around the body

100
Q

Why is the wall of the right ventricle thinner?

A
  • The force produced must be relatively small, because the blood goes only to the lungs, which are very close to the heart
  • If too high a pressure was developed, tissue fluid would accumulate in the lungs, hampering gas exchange
101
Q

Why is the wall of the left ventricle thicker?

A
  • It has to develop sufficient force to supply blood to the rest of the body organs
  • For most of the organs, most of the time, the high pressures that the left ventricle is capable of producing would be too great and arterioles help to reduce this pressure before blood flows into the capillaries
  • However, during vigorous exercise, when muscles are working hard, the arterioles supplying blood to them dilate, increasing blood flow
  • The left ventricle must be able to develop enough force to ensure that there is still sufficient blood reaching other organs, especially the brain
  • Kidneys require high pressure blood all the time, to carry out ultrafiltration
102
Q

Why does the heart have its own built in controlling and coordinating system?

A
  • The individual heart muscle cells cannot be allowed to contract at their own natural rhythms
  • If they did, parts of the heart would contract out of sequence with other parts, the cardiac cycle would become disordered and the heart would stop working as a pump
103
Q

Where is the cardiac cycle initiated?

A

In a specialised patch of muscle in the wall of the right atrium - the sinoatrial node (SAN or pacemaker)

104
Q

How does the SAN initiate the cardiac cycle?

A
  • The muscle cells of the SAN set the rhythm for all the other cardiac muscle cells - their natural rhythm is slightly faster than that of the rest of the heart muscle
  • Each time the muscles of the SAN contract, they set up a wave of electrical activity which spreads out rapidly over the whole of the atrial walls
  • The cardiac muscle in the atrial walls responds to this excitation wave by contracting, at the same rhythm as the SAN
  • Therefore, all the muscle in both atria contracts almost simultaneously
105
Q

What is the delay in the contraction of the ventricles after the contraction of the atria cause by?

A
  • A feature of the heart that briefly delays the excitation wave in its passage from the atria to the ventricles
  • There is a band of fibres between the atria and ventricles which does not conduct the excitation wave
  • Therefore, as the wave spreads out from the SAN over the atrial walls, it cannot pass into the ventricle walls - the only route is via a patch of conducting fibres, situated in the septum, known as the atrioventricular node (AVN)
106
Q

What does the AVN do?

A
  • It picks up the excitation wave as it spreads across the atria and, after a delay of about 0.1s, passes it on to a bunch of conducting fibres called the Purkyne tissue, which runs down the septum between the ventricles
  • This transmits the excitation wave very rapidly down to the base of the septum, from where it spreads outwards and upwards through the ventricle walls
  • As it does so, it causes the cardiac muscle in these walls to contract, from the bottom up, so squeezing blood upwards and into the arteries
107
Q

What is fibrillation?

A

When the heart wall simply flutters rather than contracting and then relaxing as a whole caused by the excitation wave becoming chaotic

108
Q

Describe pressure in atrial systole

A

The pressure of the blood is higher in the atrium than in the ventricle, and so forces the atrioventricular valve open

109
Q

Describe pressure in ventricular systole

A

The pressure of the blood is higher in the ventricle than in the atrium

110
Q

Describe pressure in ventricular diastole

A

The pressure of the blood in the arteries is higher than in the ventricles

111
Q

What is hydrostatic pressure?

A

The pressure that the blood is exerting on all of the blood vessels

112
Q

Why is the hydrostatic pressure lower further from the heart?

A
  • Loss of fluid/blood plasma from the capillaries
  • Capillary bed has a large volume overall, therefore lower pressure
  • Reduced resistance to blood flow as there are more, smaller vessels

Biology A-Level (44 decks)

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