3.4.1 Mass transport in animals

Describe the role of red blood cells and haemoglobin in oxygen transport.

• Red blood cells contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion path

• Hb associates with/binds /loads O2 at gas exchange surfaces where partial pressure of O2 (pO2) is high

• This forms oxyhaemoglobin which transports O2 (each can carry 4O2 - one at each Haem group)

• Hb disassociates from/ unloads O2 near cells/tissues where pO2 is low

Describe the structure of haemoglobin.

• Protein with a quaternary structure

• Made of 4 polypeptide chains

• Each chain contains a Haem group containing an iron ion (Fe2+)

Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve. (Areas with low pO2)

• Hb has a low affinity for O2

• So O2 readily unloads / dissociates with Hb

• So % saturation is low

Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve. (Areas with high pO2)

• Hb has a high affinity for O2

• So O2 readily loads/ associates with Hb

• So % saturation is high

Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve.

1. Binding of first oxygen changes tertiary / quaternary structure of haemoglobin

2. This uncovers Haem group binding sites, making further binding of oxygens easier

Describe evidence for the cooperative nature of oxygen binding.

• At low pO2, as oxygen increases there is little/ slow increase in % saturation of Hb with oxygen→ when first oxygen is binding

• At higher pO2, as oxygen increases there is a big/ rapid increase in % saturation of Hb with oxygen→ showing it has got easier for oxygens to bind

What is the Bohr effect?

Effect of CO2 concentration on dissociatian of oxyhaemoglobin → curve shifts to right

Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin.

1. Increasing blood co2 eg. due to increased rate of respiration

2. Lowers blood pH (more acidic)

3. Reducing Hb’s affinity for oxygen as shape /tertiary/ quaternary structure changes slightly

4. So more / faster unloading of oxygen to respiring cells at a given pO2

Explain the advantage of the Bohr effect (eg. during exercise)

More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced

Explain why different types of haemoglobin can have different oxygen transport properties.

• Different types of Hb are made of polypeptide chains with slightly different amino acid sequences

• Resulting in different tertiary/ quaternary structure / shape → different affinities for oxygen

What happens when the oxygen dissociation curve shifts left?

• Haemoglobin has a higher affinity for O2

• More O2 associates with haemoglobin more readily at a lower pO2

• This helps organisms living in low O2 environments, e.g. underground or foetuses

What happens when the oxygen dissociation curve shifts right?

• Haemoglobin has a lower affinity for O2

• More O2 dissociates from Hb more readily

• This supplies more O2 to respiring tissues, e.g. in active organisms with high metabolic rates.

Describe the general pattern of blood circulation in a mammal.

Closed double circulatory system - blood passes through heart twice for every circuit around body:

1. Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to the left side

2. Oxygenated blood in left side of heart pumped to resr od body; deoxygenated returns to the right

Suggest the importance of a double circulatory system

• Prevents mixing of oxygenated/deoxygenated blood

→ So blood pumped to body is fully saturated with oxygen for aerobic respiration

• Blood can be pumped to body at a higher pressure (after being lower from lungs)

→ Substances taken to / removed from body cells quicker / more efficiently

Name the blood vessels entering and leaving the heart & lungs (right side)

• Vena cava - transports deoxygenated blood from respiring body tissues → heart

• Pulmonary artery - transports deoxygenated blood from heart → lungs

Name the blood vessels entering and leaving the heart & lungs (left side)

• Pulmonary vein - transports oxygenated blood from lungs → heart

• Aorta - transports oxygenated blood from heart → respiring body tissues

Name the blood vessels entering and leaving the kidneys.

• Renal arteries - oxygenated blood → kidneys

• Renal veins - deoxygenated blood to vena cava from kidneys

Name the blood vessels that carry oxygenated blood to the heart muscle

Coronary arteries - located on surface of the heart, branching from aorta

Suggest why the wall of the left ventricle is thicker than the right

• Thicker muscle to contract with greater force

• To generate higher pressure to pump blood around entire body

What happens during Atrial systole?

• Atria contract → volume decreases, pressure increases

• Atrioventricular valves open when atrial pressure exceeds ventricular pressure

• Semilunar valves remain closed.

• Blood is pushed into the ventricles

What happens during Ventricular systole?

• Ventricles contract → volume decreases, pressure increases

• Atrioventricular valves shut when ventricular pressure exceeds atrial pressure

• Semilunar valves open when ventricular pressure exceeds arterial pressure

• Blood is pushed out of the heart through the arteries

What happens during Diastole?

• Atria and ventricles relax → volume increases, pressure decreases

• Semilunar valves shut when arterial pressure exceeds ventricular pressure

• Atrioventricular valves open when atrial pressure exceeds ventricular pressure

• Blood enters the atria via veins and flows passively into the ventricles

When are semilunar valves closed?

Artery pressure is higher than ventricular pressure, preventing back-flow of blood from artery to ventricles

When do semilunar valves open?

Ventricular pressure is higher than arterial pressure, so blood flows from the ventricles into the arteries

When are atrioventricular valves closed?

Ventricular pressure is higher than atrial pressure, preventing back-flow of blood from the ventricles into the atria

When do atrioventricular valves open?

Atrial pressure is higher than ventricular pressure, so blood flows from the atria into the ventricles

Describe the equation for cardiac output

Cardiac output (volume of blood pumped out of heart per min) = stroke volume (volume of blood pumped in each heart beat) x heart rate (number of beats per min)

How can heart rate be calculated from cardiac cycle data?

Heart rate (beats per minute) = 60 / length of one cardiac cycle (seconds)

Whats the function of arteries?

To carry blood away from heart at high pressure

Explain how the structure of arteries relates to their function

• Thick smooth muscle tissue→ can contract and control / maintain blood flow/pressure

• Thick elastic tissue→ can stretch as ventricles contract and recoil as ventricles relax, to reduce pressure surges/even out blood pressure/ maintain high pressure

• Thick wall→ withstand high pressure / stop bursting

• Smooth / folded endothelium→ reduces friction / can stretch

• Narrow lumen→ increases / maintains high pressure

Whats the function of arterioles?

direct blood to different capillaries / tissues

Explain how the structure of arterioles relates to their function

• Thicker smooth muscle layer than arteries

Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries

Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries

• Thinner elastic layer → pressure surges are lower (as further from heart/ ventricles)

Whats the function of veins?

carry blood back to heart at lower pressure

Explain the structure of veins relates to their function

• Wider lumen than arteries → less resistance to blood flow

• Very little elastic and muscle tissue → blood pressure lower

• Valves → prevents back-flow of blood

Whats the function of capillaries?

Allow efficient exchange of substances between blood and tissue fluid (exchange surface)

Explain the structure of capillaries relates to their function

• Wall is a thin (one cell) layer of endothelial cells → reduces diffusion distance

• Capillary bed is a large network of branched capillaries → increases surface area for diffusion

• Small diameter/ narrow lumen → reduces blood flow rate so more time for diffusion

• Pores in walls between cells → allows larger substances through

Explain the formation of tissue fluid

At the arteriole end of capillaries:

1. Higher blood/ hydrostatic pressure inside capillaries (due to contraction of ventricles) than in tissue fluid (so net outward force)

2. Forcing water (and dissolved substances) out of capillaries

3. Large plasma proteins remain in capillary therefore, forming tissue fluid

Explain the return of tissue fluid to the circulatory system

At the venule end of capillaries:

1. Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)

2. (Due to water loss) an increasing concentration of plasma proteins lowers water potential in capillary compared with tissue fluid

3. Water enters capillaries from tissue fluid via osmosis down a water potential gradient

4. Excess water taken up by lymph vessels and returned to circulatory system through veins

Suggest and explain causes of excess tissue fluid accumulation

• Low concentration of protein in blood plasma

Water potential in capillary not as low → water potential gradient in reduced

So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis

• High blood pressure → high hydrostatic pressure

increases outward pressure from arterial end AND reduces inward pressure at venule end

So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis

Lymph system may not be able to drain excess fast enough

What is a risk factor? Give examples for cardiovascular disease

• An aspect of a person’s lifestyle or substances in a person’s body/environment

• That have been shown to be linked to an increased rate of disease

• Examples - age, diet high in salt or saturated fat, smoking, lack of exercise, genes