7.1-7.6 Mass Transport

Question 1

When is mass transport used?

Answer 1

Over large distances, efficient movement of substance to and from exchange surfaces

Question 2

What type of structure does haemoglobin have?

Answer 2

Quaternary structure - four polypeptides each associated with a haem group (4 oxygens can be carried by a single molecule)

Question 3

What type of protein is haemoglobin and why is it soluble?

Answer 3

Globular protein
Curled up - hydrophilic side chains face outwards (soluble) and hydrophobic side chains face inwards (maintain structure)
Therefore soluble and good for transport in the blood

Question 4

What are the haemoglobins?

Answer 4

A group of chemically similar molecules found in many different organisms

Question 5

What is the process by which haemoglobin binds with oxygen?

Answer 5

Loading or associating
Takes place in lungs

Question 6

What is the process by which haemoglobin releases its oxygen? Where does it take place?

Answer 6

Unloading or dissociating
Takes place in the tissues

Question 7

What does a high affinity (chemical attraction) mean?

Answer 7

Take up oxygen more easily
Release it less easily

Question 8

What does a low affinity mean?

Answer 8

Take up oxygen less easily
Release it more easily

Question 9

What is the role of haemoglobin?

Answer 9

Transport oxygen (oxygen is not soluble)

Question 10

What must haemoglobin do to efficiently transport oxygen? How does it do this?

Answer 10

Readily associate with oxygen at the surface where gas exchange takes place
Readily dissociate from oxygen at those tissues requiring it

Changes shape in the presence of certain substances

Question 11

How does oxyhaemoglobin form?

Answer 11

Prosthetic haem group contains Fe2+ which combines reversibly with an oxygen molecule, forming oxyhaemoglobin

Question 12

Why are there different haemoglobins?

Answer 12

Shape of the molecule
Different shape so there is a different affinity for oxygen

Question 13

What is the oxygen dissociation curve?

Answer 13

The rate at which oxygen associates, and also dissociates, with haemoglobin at different partial pressures of oxygen (pO2)

Question 14

What is partial pressure?

Answer 14

The pressure exerted by oxygen within a mixture of gases; it is a measure of oxygen concentration

Question 15

Explain the shape of the oxygen dissociation curve

Answer 15

1. The shape of the haemoglobin molecule means it is difficult for the first oxygen molecule to bind to haemoglobin –> binding of the first oxygen occurs slowly, (relatively shallow curve at the bottom left corner of the graph)
2. After the first oxygen molecule binds to haemoglobin, the haemoglobin quaternary shape changes so it is easier for the next haemoglobin molecules to bind which speeds up binding of the remaining O2 (steeper part of the curve in the middle of the graph)
3. As the haemoglobin molecule approaches saturation it takes longer for the fourth O2 to bind due to the shortage of remaining binding sites (levelling off of the curve in the top right corner of the graph)

Question 16

What is cooperative binding?

Answer 16

The shape change of haemoglobin leading to easier oxygen binding

Question 17

What does it mean if the curve is further to the left?

Answer 17

The greater is the affinity of haemoglobin for oxygen (it loads oxygen readily but unloads it less easily)

Question 18

What does it mean if the curve is further to the right?

Answer 18

The lower is the affinity of haemoglobin for oxygen (so it loads oxygen less readily but unloads it more easily)

Question 19

What is the Bohr effect?

Answer 19

Haemoglobin has a reduced affinity for oxygen
Greater conc of CO2, more readily the haemoglobin release its oxygen

Question 20

Explain the behaviour of haemoglobin at the lungs (gas-exchange surface) due to carbon dioxide concentration

Answer 20

• Conc. of CO2 is low because it diffuses across the exchange surface and is excreted from the organism
• Affinity of haemoglobin for oxygen is increased (high conc of O2 in lungs) so oxygen is readily loaded by haemoglobin
• Reduced CO2 has shifted the oxygen dissociation curve to the left

Question 21

Explain the behaviour of haemoglobin at rapidly respiring tissues (eg muscles) due to carbon dioxide concentration

Answer 21

• Conc of CO2 is high
• Affinity of haemoglobin for oxygen is reduced (low conc of oxygen in muscles) oxygen is readily unloaded from the haemoglobin into the muscle cells
• Increased CO2 has shifted the oxygen dissociation curve to the right

Question 22

Describe how oxygen is loaded, transported and unloaded in the blood

Answer 22

1. Haemoglobin carries oxygen/has a high affinity for oxygen
2. In red blood cells
3. Loading of oxygen takes place in the lungs at high partial pressure
4. Unloads oxygen to respiring cells or tissues at low partial pressure
5. Unloading due to higher carbon dioxide concentration

Question 23

Why do different species have different types of haemoglobin?

Answer 23

Adapted to their environment so their haemoglobin has different oxygen transport properties
- Less O2 in environment = high affinity haemoglobin
- High metabolic rate = haemoglobin with a low affinity for O2 so that O2 released more easily at the respiring tissues
- Type of Hb relies on the environment and metabolism of the organism

Question 24

What is myoglobin and its uses?

Answer 24

Conjugated protein (similar to haemoglobin)
Stores O2 in the muscles
Left of haemoglobin so has a high affinity for oxygen
Only releases oxygen when pO2 is low eg during exercise

Question 25

Why do large organisms have a transport system?

Answer 25

1. SA: volume decreases
2. Diffusion distances are too great - the time taken for substances (glucose and oxygen) to diffuse would be far too long
3. High metabolic rate, more active organisms need a larger/faster supply of oxygen

Question 26

What are the features of a transport system?

Answer 26

• Medium to carry materials eg blood
• Form of mass transport where medium is moved in bulk
• Closed system of tubular vessels containing medium
• Mechanism for moving transport medium eg pump for pressure difference –> plants: evaporation of water
  animals: muscular contraction

Question 27

What is the circulatory system in mammals?

Answer 27

Closed, double circulatory system where blood is confined to vessels and passes twice through the heart from each complete circuit of the body - keeps pressure high so substances delivered to the rest of the body quickly

Question 28

How is the heart structured?

Answer 28

The heart is divided into four chambers. The two top chambers are atria and the bottom two chambers are ventricles
The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart

Question 29

What is the location and function of the aorta?

Answer 29

Connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs

Question 30

What is the location and function of the vena cava?

Answer 30

Connected to the right atrium and brings deoxygenated blood back from the tissues of the body (except the lungs)

Question 31

What is the location and function of the pulmonary artery?

Answer 31

Connected to the right ventricle and carries deoxygenated blood to the lungs where its oxygen is replenished and carbon dioxide is removed

Question 32

What is the location and function of the pulmonary vein?

Answer 32

Connected to the left atrium and brings oxygenated blood back from the lungs
Unusually for a vein, it carries oxygenated blood

Question 33

What is the function of the coronary arteries?

Answer 33

Heart requires its own blood supply for aerobic respiration
The heart receives blood through coronary arteries on its surface
Build up could lead to angina or a heart attack (myocardial infarction)
Brings glucose and oxygen to the heart muscle which are needed for aerobic cell respiration providing the energy for contraction

Question 34

What is the wall of the heart made from?

Answer 34

Cardiac muscles - never gets tired and can continuously contract and relax
Cardiac muscle is myogenic so can contract on its own

Question 35

How are arteries structures related to function?

Answer 35

Muscle layer is thick compared to veins
- Constricted/dilated to control volume of blood passing through them
- Withstand force of pumping action and resists vessel bursting under pressure

Elastic layer relatively thick compared to veins
- Stretched and recoils to maintain high blood pressure
- Smooth pressure surges created by the beating of the heart

No valves
- Constant high pressure so tends not to flow backwards

Collagen provides strength

Endothelium is smooth so reduces friction and folded to prevent damage to artery

Narrow lumen so high bp

Question 36

How are arterioles adapted for their function?

Answer 36

Muscle layer thicker than arteries
- Contraction allows constriction of the arteriole
- Restricts flow of blood so control movement into capillaries

Elastic layer thinner than in arteries
- Bp is lower
- Close to heart, muscle cells can contract and partially shut off blood flow to particular organs

Question 37

How are veins adapted to their function?

Answer 37

Muscle layer thin compared to arteries as withstands low pressure and allows skeletal muscles to squeeze veins

Carry blood away from tissues so their constriction and dilation cannot control the flow of blood to tissues

Elastic layer thin compared to arteries
- Low pressure of blood within the veins will not cause them to burst and pressure is too low to create a recoil action

Wall thin
- Pressure low so no risk of bursting
- Flattened easily aiding flow of blood

Valves
- No back flow of blood and pressure goes towards the heart

The lumen of the vein is much larger than that of an artery

Lots of collagen for protection from external sources

Smooth endthelium layer reduces friction

Question 38

How are capillaries structure related to their function?

Answer 38

Walls mostly of lining layer - endothelial cells
- Extremely thin so short diffusion distance
- Rapid diffusion between blood and cells
Smooth endothelium layer reduces friction

Greater c-s area than arterioles decreases rate of blood flows, allows more time for diffusion to occur

Numerous and highly branched - increased SA so more exchange in capillary bed

Narrow diameter
- Permeate tissues, no cell is far from a capillary and short diffusion pathway

Lumen so narrow that RBC are squeezed flat against the side of the capillary
- Closer to cells and reduces diffusion distance

Gaps or pore in walls allow some nutrients to move in and out

Question 39

What is tissue fluid?

Answer 39

Contains glucose, amino acids, fatty acids, ions in solution and oxygen and supplies to tissues
Means by which materials are exchanged between blood and cells
Formed from blood plasma

Question 40

How does tissue fluid form?

Answer 40

1.Ultrafiltration: Arterial end of capillary –> high hydrostatic pressure so fluid forced out through endothelium (is tissue fluid)
- Cells and large blood proteins are too large

2. Exchanges of materials between the tissue fluid and the cells
   - Simple diffusion: oxygen and carbon dioxide
   - Facilitated diffusion: ions
   - Active transport: glucose and amino acids
   - Osmosis: water through lipid bilayers

Question 41

What 2 other forces oppose the high hydrostatic pressure?

Answer 41

• Hydrostatic pressure of the tissue fluid outside the capillaries, which resists outwards movement of liquid
• The lower water potential of the blood, due to the plasma proteins, that cause water to move back into the blood

Question 42

How does tissue fluid return to the circulatory system?

Answer 42

• Venule end of the capillary the blood at lower pressure than tissue fluid due to loss of tissue fluid.
• Blood plasma water potential has decreased due to the retention of blood proteins
• Hence, water return to the blood down the pressure gradient and via osmosis

The tissue fluid contains carbon dioxide and waste materials

Question 43

What happens to the excess tissue fluid?

Answer 43

• Drains into lymph vessels
• Have very thin walls, like capillaries, and tissue fluid can easily diffuse inside, forming lymph

Question 44

How does the lymph move?

Answer 44

Hydrostatic pressure of the tissue fluid that has left the capillaries
Contraction of body muscles that squeeze the lymph vessels- valves in the lymph vessels mean lymph moves towards the heart and away from tissues

Question 45

What happens during diastole?

Answer 45

• Blood returns to the atria of the heart through the pulmonary veins and vena cava
• Atria fills so pressure rises –> Atrioventricular valves open
• Atria and ventricles both relaxed, blood enters ventricles from atria
• Pressure lower than in aorta and pulmonary artery so semi lunar valves close (dub)

Question 46

What happens during atrial systole?

Answer 46

• Contraction of atrial walls push blood into ventricles
• Ventricles relaxed
• Semi lunar valves closed
• Atrioventricular valves open

Question 47

What happens during ventricular systole?

Answer 47

• Blood pumped into pulmonary arteries and the aorta
• Ventricles contract (increases blood pressure)
• Atrioventricular valves close (Lub)
• Then, pressure rises in ventricles further
• Once pressure exceed that in aorta and pulmonary artery blood forced in (semi lunar valves open)
  Pushes blood away from the heart

Question 48

What is the function of valves?

Answer 48

Keep blood flowing in one direction

Question 49

What are the atrioventricular valves?

Answer 49

Between atrium and ventricle
Prevent back flow when contraction of ventricles means ventricular pressure is greater than atrial pressure
When closed blood moves to aorta and pulmonary artery not atria

Question 50

What are the semi lunar valves?

Answer 50

In aorta and pulmonary artery
Prevent back flow of blood into the ventricles when the pressure is higher than in ventricles

Question 51

What are the pocket valves?

Answer 51

Occur throughout the venous system
Ensure that when the veins are squeezed blood flows towards heart

Question 52

What are the main 4 risk factors of CVD?

Answer 52

Smoking
High blood pressure
Blood cholesterol
Diet

Question 53

Why is smoking a risk factor?

Answer 53

Carbon monoxide reduces oxygen carrying capacity
- Lead to raised blood pressure (risk of coronary heart disease and strokes)
- Blood may be insufficient to supply heart muscle during exercise (chest pain or heart attack)

Nicotine
- Production of adrenaline and increase HR and raises blood pressure (CHD/stroke)
- Makes platelets more sticky (risk of thrombosis and strokes/myocardial infarction)

Question 54

Why is high blood pressure a risk factor?

Answer 54

Caused by stress, diets, lack of exercise
- Heart must work harder to pump blood into already high pressure arteries so could fail
- More likely to develop an aneurysm and burst (haemorrhage)
- To resist the higher pressure within them, the walls of the arteries tend to become thickened and may harden, restricting the flow of blood

Question 55

Why is blood cholesterol a risk factor?

Answer 55

Low-density lipoproteins deliver cholesterol to tissues so increase risk of atheromas (build up of fatty deposits) and heart disease

Question 56

What does conjugated protein mean?

Answer 56

Contain a non-protein component (haem group)

Question 57

What is the function of veins?

Answer 57

Transport blood slowly, under low pressure, from the capillaries in tissues to the heart
Carry deoxygenated blood

Question 58

What is the function of capillaries?

Answer 58

Exchange metabolic materials between the blood and the cells

Question 59

How do you calculate the mitosis index?

Answer 59

Cells in mitosis/Total number of cells

Question 60

Why is diet a risk factor for CVD?

Answer 60

High levels of salt raise blood pressure
High levels of saturated fat increase low-density lipoprotein levels and hence blood cholesterol concentration