Transport in Mammals

Question 1

What are red blood cells?

Answer 1

1. They are also called erythrocytes
2. Their red colour is caused by the pigment haemoglobin, a globular protein
3. The main function of haemoglobin is to transport oxygen from the lungs to respiring tissues

Question 2

What shape are red blood cells and why?

Answer 2

• Red blood cells are shaped like a biconcave disc
  1. The dent in each side of a rbc increases the amount of surface area in relation to the volume of the cell
  2. This gives it a large SA:V ratio
  3. This large surface area means that oxygen can diffuse quickly into or out of the cell

Question 3

What is the size of red blood cells and why?

Answer 3

• Red blood cells are very small (diameter of 7 mu meters compared with 40 mu meters of normal liver cell)
  1. This small size means that no haemoglobin molecule within the cell is very far from the cell surface membrane, and the haemoglobin molecules can therefore quickly exchange oxygen with the fluid outside the cell
  2. It also means that capillaries can only be 7 mu meters wide and so bring oxygen as close as possible to cells which require it

Question 4

Are red blood cells flexible and why?

Answer 4

• Red blood cells are very flexible
  1. Some capillaries are even narrower than the diameter of a red blood cell
  2. The cells are able to deform so that they can pass through these vessels
  3. This is possible because the cells have a specialised cytoskeleton, made up of a mesh-like network of protein fibres that allows them to be squashed into different shapes, but then springs back to produce the normal biconcave shape

Question 5

Do red blood cells have nucleus, mitochondria or er and why?

Answer 5

• Red blood cells have no nucleus, no mitochondria and no endoplasmic reticulum
  1. The lack of these organelles means that there is more room for haemoglobin, so maximising the amount of oxygen which can be carried by each red blood cell

Question 6

What are white blood cells?

Answer 6

1. White blood cells are sometimes known as leucocytes
2. They are made in the bone marrow as are red blood cells
3. They are all concerned with fighting disease even though there are many different types of wbcs

Question 7

How can you distinguish a white blood cell from a red blood cell?

Answer 7

1. White blood cells all have a nucleus, although the shape of this varies in different types of white cell
2. Most white blood cells are larger than red blood cells, although one type, lymphocytes, may be slightly smaller
3. White blood cells are either spherical or irregular in shape, never looking like a biconcave disc

Question 8

What are phagocytes?

Answer 8

1. Phagocytes are cells that destroy invading microorganisms by phagocytosis
2. The commonest type of phagocyte (neutrophils) can be recognised by the lobed nuclei and granular cytoplasm
3. Monocytes are also phagocytes

Question 9

What are lymphocytes?

Answer 9

1. Lymphocytes also destroy microorganisms. but not by phagocytosis
2. Some of them secrete chemicals called antibodies which attach to and destroy the invading cells
3. There are different types of lymphocytes. which act in different ways, though they all look the same
4. Lymphocytes are smaller than most phagocytes, and they have a large round nucleus and only a small amount of cytoplasm

Question 10

What is the role of haemoglobin?

Answer 10

• Oxygen is rand-sorted around the body inside red blood cells in combination with protein haemoglobin
• Overall each haemoglobin molecule can combine with four oxygen molecules (eight oxygen atoms)
• It must be able to pick up oxygen at the lungs and release oxygen within respiring tissues

Question 11

What is a dissociation curve?

Answer 11

-The percentage saturation of each sample can be plotted against the partial pressure of oxygen

Question 12

What is the saturation of haemoglobin like at low partial pressures of oxygen?

Answer 12

Very low: the haemoglobin is combined with only a very little oxygen

Question 13

What is the saturation of haemoglobin like at high partial pressures of oxygen?

Answer 13

Very high: it is combined with large amounts of oxygen

Question 14

What is the mammalian circulatory system?

Answer 14

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

Question 15

What is the structure of an artery?

Answer 15

1. An inner endothelium, called the tunica interna made up of a layer of flat cells (squamous epithelium)
   - This layer is very smooth, minimising fiction with the moving blood
2. Tunica media containing smooth muscle, collagen and elastic fibres
3. Tunica externa containing collagen fibres and elastic fibres

Question 16

What are the features of arteries and their adaptions?

Answer 16

1. Elasticity:
   - Allows the artery to ‘give’ to prevent the likelihood that they will burst
   - Allows the artery walls to stretch as the high-pressure blood surges in to them and then recoil inwards as the pressure drops (The overall effect is to ‘even out’ the flow of blood)
2. Thick walls to maintain high pressure

Question 17

What are arterioles?

Answer 17

1. As arteries reach the tissue to which they are transporting blood, they branch into smaller and smaller vessels, called arterioles
2. Arterioles are similar to arteries but have more smooth muscle
3. This muscle can contract narrowing the diameter of the arteriole or it can cause the arteriole to dilate (overall to control the blood flow to the tissue)

Question 18

What is the function of capillaries?

Answer 18

1. Take blood as close as possible to all cells, allowing rapid transfer of substances between cells and blood
2. Capillaries form a network throughout every tissue in the body except the corner and cartilage, (capillary beds)

Question 19

How are capillaries adapted for their function?

Answer 19

1. Small size, so closer
2. Slows down flow of red blood cells, blood close to cells
3. Walls extremely thin (made up of a single layer of endothelial cells)
   - SHORt diffusion pathway so diffusion more affective
4. Many Tiny gaps between the individual cells that form the endothelium, important in allowing some components of the blood to seep through into the spaces between the cells in all the tissues of the body (these components form tissue fluid)
   - Allows named cell/substance to leave the the blood
   - By the time the blood reaches the capillaries, it has already lost a great deal of the pressure originally supplied to it by the contraction fo the ventricles
5. Large surface area to volume ratio so more exchange (NOT faster)

Question 20

What is the function of veins?

Answer 20

1. To return blood to the heart
   - Low pressure, so no need for thick walls, and although same three layers as arteries the tunica media is much thinner and has far fewer elastic fibres and muscle fibres

Question 21

How do veins keep the blood flowing in the right direction?

Answer 21

1. Veins contain valves, formed from their endothelium
   - These valves allow blood to move towards the heart but not says from it
   - Thus when you contract your leg muscles, the blood in the veins is squeezed up through these valves, but cannot pass down through them

Question 22

What is blood plasma?

Answer 22

Mostly water with substances dissolved in it such as glucose and urea that are being transported from one place to another in the body. Solutes also included plasma proteins which remain in the blood all the time

Question 23

How is tissue fluid different from blood plasma?

Answer 23

• Tissue fluid occupies the space between your cells (leaked plasma)
• Similar composition but contains far fewer protein molecules as these are too large to escape easily height the tiny holes in the capillary endothelium
• RBCs are also too large so none in tissue flood but some WBCs can squeeze through and move freely around in tissue fluid

Question 24

How is the volume of fluid which leaves the capillary to from tissue fluid determined?

Answer 24

1. At the arterial end of a capillary bed, the blood pressure inside the capillary is enough to push fluid out into the tissue
2. The high conc. of proteins in the plasma and not in tissue fluid leads to an osmotic moment of water back into the capillaries from the tissue fluid
3. The net result of these competing process is that fluid tens to flow OUT of capillaries onto tissue fluid at the arterial end of a capillary bed and INTO capillaries from tissue fluid near the venous end of a capillary bed
4. Overall however rather more fluid flows pout of capillaries than into them, so they there is a net loss of fluid form the blood as it flows through a capillary bed

Question 25

What are lymphatics?

Answer 25

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

Question 26

What is the fluid inside lymphatics called?

Answer 26

• Lymph
  1. Lymph is virtually identical to tissue fluid (but different place)
• Lymphatics join up to form larger lymph vessels, that gradually transport lymph back to the large veins that run just beneath the collarbone the subclavian veins)
• As in veins the movement of fluid along the lymphatics is largely caused by contraction of muscles around the vessels, and kept going in the right direction by valves
• The lymph vessels also have smooth muscle in their walls which can contract to push the lymph along
• Lymph flow is also very slow

Question 27

What is the shape of the dissociation curve and why?

Answer 27

• S-Shaped Curve
  1. When an oxygen molecule combines with one haem group, the whole haemoglobin molecule is slightly distorted
  2. The distortion makes it easier for a second oxygen molecule to combine with a second haem group
  3. This in turn makes it easier for a third oxygen molecule to combine with a third haem group
  4. It is then still easier for the fourth and final oxygen molecule to combine

Question 28

Why is the dissociation curve shape significant?

Answer 28

1. Up to an oxygen partial pressure of around 2kPa, on average only one oxygen molecule is combined, however it become successively easier for the second and third oxygen molecules to combine, so the curve rises very steeply
2. Over this part of the curve, a SMALL change in the partial pressure of oxygen cause a VERY LARGE change in the amount of oxygen which is carried by the haemoglobin

Question 29

What is the Bohr shift?

Answer 29

A change in the shape of the dissociation curve of haemoglobin caused by a change in the carbon dioxide concentration

Question 30

How does haemoglobin behave in the blood?

Answer 30

• Picks up oxygen at the lungs and readily releases it when in conditions of low oxygen partial pressure
• Amount of oxygen the haemoglobin carries is affected not only by the partial pressure of oxygen, but also by the partial pressure of carbon dioxide
• Carbon dioxide is continually produced by respiring cells and it diffuses from the cells and into blood plasma, from where some of it diffuses into the red blood cells

Question 31

What does haemoglobin combine with in the blood?

Answer 31

1. Haemoglobin readily combines with the hydrogen ions forming haemoglobinic acid, HHb. In so doing it releases the oxygen which it is carrying

Question 32

What two key reactions occur in the blood?

Answer 32

-In the cytoplasm of red blood cells, CARBONIC ANHYDRASE, catalyses:
1. CO2 + H2O (equilibrium arrow with carbonic anhydrase over it) H2CO3
2. The CARBONIC ACID DISSOCIATES:
H2CO3 (equilibrium arrow)H+ + HCO3-

Question 33

What is the impact of the haemoglobin in the blood? 1

Answer 33

1. ‘Mops up’ the hydrogen ions which are formed when carbon dioxide dissolves and dissociates
2. A high concentration of hydrogen ions means an ACIDIC LOW pH environment and if the hydrogen ions were left in solution the blood would be very acidic
3. So by removing the hydrogen ions form solution, haemoglobin helps to maintain the pH of the blood close to neutral (acts as a BUFFER)

Question 34

What is the impact of the haemoglobin in the blood? 2

Answer 34

1. The presence of a high partial pressure of carbon dioxide causes haemoglobin to release oxygen
2. This is called the BOHR EFFECT
   - High concentrations of carbon dioxide are found in actively respiring tissues, which need oxygen; these high carbon dioxide concentrations cause haemoglobin to release its oxygen even more readily than it would otherwise do

Question 35

What would the dissociation curve for haemoglobin look like?

Answer 35

It lies below and to the right of the ‘normal curve’

Question 36

What are the ways that carbon dioxide is transported in the blood?

Answer 36

1. Binds to haemoglobin (as it combines directly with the terminal amine groups of some of the haemoglobin molecules) to from carbaminohaemoglobin (10%)
2. Forms carbonic acid (which in turn causes the Bohr shift), of which the HCO3- ions diffuse out (85%) and this causes the blood to be slightly alkali
   - To balance out this negative charge, there is the chloride shift where Cl- ions go into the erythrocyte (RBC)
3. Dissolves in blood plasma (5%)

Question 37

What happens to the blood when it reaches the lungs?

Answer 37

1. The relatively low concentration of carbon dioxide in the alveoli compared with that in the blood causes carbon dioxide to diffuse from the blood into the air in the alveoli
2. This stimulates the carbon dioxide of carbaminohaemoglobin to leave the rbc, and hydrogencarbonate and hydrogn ions to recombine to form carbon dioxide molecules once more
3. This leave the haemoglobin molecules free to combine with oxygen, ready to begin another circuit of the body

Question 38

What are the limitations of oxygen transfer?

Answer 38

1. Haemoglobin combines very readily, and almost irreversibly, with carbon monoxide
2. CO in rbc combine with the haem groups in the haemoglobin molecules, forming carboxyhaemoglobin (a very stable compound)
3. Treatment of carbon monoxide poising involves administration of a mixture of pure oxygen and carbon dioxide: high concentration of oxygen to favour the combination of haemoglobin with oxygen rather than CO and CO2 to stimulate and increase in breathing rate

Question 39

What happens at high altitudes?

Answer 39

1. The partial pressure of oxygen is much lower (in the air it is around 10kPa, and in the lungs the partial pressure of oxygen is about 5.3kPa)
2. This will mean that your haemoglobin will become only about 70% saturated in the lungs
3. Less oxygen will be carried around the body, and the person may begin to feel breathless and ill
   - May suffer from altitude sickness if travel too fast and in a short period of time

Question 40

Why will you feel ill from altitude sickness?

Answer 40

The arterioles in their brain dilated, increasing the amount of blood flowing into capillaries, so that fluid begins to leak form the capillaries into the brain tissues which can cause disorientation or into lungs preventing them from functioning properly

Question 41

How have people adapted to high altitudes?

Answer 41

1. The number of red blood cells increases: however takes a long time to happen at least 2 to 3 weeks before any change
2. If permanently live:
   - Especially broad chests, providing large lung capacities than normal
   - Larger hearts especially the right side, which pumps blood to the lungs
   - More haemoglobin in their blood than usual, so increasing the efficiency of oxygen transport from lungs to tissues

Question 42

Describe the internal and external structure of the mammalian heart

Answer 42

Internal:

1. The heart has four chambers, right and left atria and right an left ventricles
2. The right side of the heart is divided from the left by a wall of muscle tissue called the septum
3. The atria and ventricles have valves between them, which are known as atrioventricular valves
4. The one on the left is the mitral or bicuspid valve and the one on the right is the tricuspid valve

Question 43

What is the difference in thickness of the walls of the different chambers?

Answer 43

1. The atrial muscular walls are thin and do not exert much pressure when they contract, but it is enough to force the blood in the atria down through the atrioventricular valves into the ventricles: the semilunar valves prevent back flow
2. Thick, muscular walls of the ventricle increase pressure and push it out of heart and around the body.
   - The walls are much thicker than the walls of the atria because the ventricles need to develop much more force when they contract and their contraction has to push the blood out of the heart and around the body

Question 44

What happens in atrial systole?

Answer 44

1. Both atria contract
2. Blood flows from the atria into the ventricles
3. Back flow of blood into the veins is prevented by closure of the valves in the veins (semi lunar valves prevent back flow)

Question 45

What happens in ventricular systole?

Answer 45

1. Both ventricles contract
2. The atrioventricular valves are pushed shut by the pressurised blood in the ventricles
3. The semi-lunar valves in the aorta and pulmonary artery are pushed open
4. Blood flows from ventricles into the arteries

Question 46

What happens in ventricular diastole?

Answer 46

1. Atria and ventricles relax
2. The semilunar valves in the aorta and pulmonary artery air pushed shut
3. Blood flows from the veins through the atria and into the ventricles

Question 47

Which ventricle has a thicker muscular wall and why?

Answer 47

1. The force produced in right side has to be smaller as blood only goes to lungs which are close to heart
2. The left ventricle has to develop sufficient force to supply blood to all the rest of the body organs

Question 48

Why is cardiac muscle different?

Answer 48

It is myogenic so it naturally contacts and relaxes as it does nor need to receive impulses from a nerve to make it contract

Question 49

Why can individual hear muscle cells not be allowed to contract on their own?

Answer 49

Parts of the heart would contract out of sequence with other parts and so the cardiac cycle would become disorder and the heart would stop working as a pump

Question 50

How is the cardiac cycle initiated?

Answer 50

1. In the sinoatrial node (SAN or pacemaker) in the wall of the right atrium
2. Each time muscles of SAN contract, they set up a wave of electrical acitivity which spreads out rapidly over the whole of the atrial walls
3. The cardiac muscle in the atrial walls responds to this excitation wave by contracting, at the same rhythm as the SAN and so all the muscle in both atria contacts almost simultaneously

Question 51

How is it that the muscles of the ventricles do not contract until after the muscles of the atria?

Answer 51

1. This delay is caused by a feature path hear that briefly delays the excitation wave in its passage from the atria to the ventricles
2. There is a band of fibres between the atria and ventricles which does not conduct the excitation wave
3. As a result as the wave spreads out from the SAN over the atrial walls, it cannot pass through the ventricle walls
4. The only route through is via a patch of conducting fibres in the septum, known as the atrioventricular node (AVN)

Question 52

How does the AVN work?

Answer 52

1. The AVN picks up the excitation wave as it spreads across the atria and, after a delay of about 0.1 seconds passes it onto a bunch of conducting fibres called the Purkyne tissues which runs down the septum between the ventricles
2. This transmits the excitation wave very rapidly down to the base of the septum, from where it spreads outwards and upwards though the ventricle walls
3. 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

Question 53

What is fibrillation?

Answer 53

• When the excitation wave becomes chaotic, passing through the ventricular muscle in all directions, feeding back on itself and restimulating areas it has just left
• Small sections the cardiac muscle contract while other sections are relaxing
• The result is fibrillation, in which the heart wall simply flutters rather than contracting as a whole and then relaxing as a whole

Question 54

What is the purpose of the lymph system?

Answer 54

1. About 90% of the fluid that leaks from capillaries eventually seeps back into them and the remaining 10% is collected up and returned to the blood system by means of lymph vessels or lymphatics
2. It is important for this 10% to be returned as if it was not the 10% and then 10% would build up and it also allows the tissue to be cleared from pathogens before it goes to the blood at the lymph nodes
   - There is a high pressure in the bloodstream to stop pathogens from coming in

Question 55

How are red blood cells involved in the transport of carbon dioxide?

Answer 55

1. Carbon dioxide reacts with terminal amine of haemoglvoun
2. To form carbaminohaemoglobin
3. Carbonic anhydride catalysed formation of carbonic acid
4. Carbonic acid dissociates to HCO3- and H+
5. Hydrogen carbonate diffuse out into plasma

Question 56

Why do multicellular organisms require transport systems whilst unicellular organisms do not?

Answer 56

Multicellular:

1. Small SA:V ratio
2. Larger size means long distances to reach cells
3. Diffusion is too slow
4. Transport system decreases time to supply cell
5. Require bulk/mass flow
6. Transport system means efficient supply to cells of nutrients