Mass Transport in Animals

Haemoglobin

• Group of chemically similar molecules found in many different organisms

• Has a quaternary structure - four polypeptide chains with haem group per polypeptide

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

• red blood cells contain lots of Hb

• (No nucleus and bioconcave - more space for Hb, high SA:V and short diffusion distance)

• Hb associates with oxygen at gas exchange surfaces where partial pressure of oxygen (pO2) is high

• This forms haemoglobin which transports oxygen

• (Each can carry four oxygen molecules, one at each haem group)

• Hb dissociates from / unloads oxygen 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 and an iron ion (Fe2+)

Describe the loading, transport and unloading of oxygen in relation to the oxyhemoglobin dissociation curve

Areas with low pO2 - respiring tissues:

• Hb has a low affinity for oxygen

• So oxygen readily unloads Hb

• So % saturation is low

Areas with high pO2 - gas exchange surfaces:

• Hb has a high affinity for oxygen

• So oxygen readily loads Hb

• So % saturation is high

Explain how the cooperative nature of oxygen binding results in a S-shaped (sigmoid) oxyhemoglobin dissociation curve:

• binding of first oxygen changes tertiary structure of haemoglobin

• This uncovers the haem group binding sites, making further binding of oxygen easier

Describe evidence for the cooperative nature of oxygen binding

• at low pO2 as oxygen increases there is slow increase in % saturation of Hb with oxygen

• (When oxygen is binding)

• At higher pO2, as oxygen increases there is a rapid increase in % saturation of Hb with oxygen

• (Showing it has got easier for oxygen to bind)

What is the Bohr effect?

Effect of CO2 concentration on dissociation of oxyhemoglobin → curve shifts to the right

Explain the effect of CO2 concentration on the dissociation of oxyhaemoglobin

• increasing blood CO2 e.g. due to increased rate of respiration

• Lowers blood pH (more acidic)

• Reducing Hb’s affinity for oxygen as tertiary structure changes slightly

• So faster unloading of oxygen to respiring cells at given pO2

Describe evidence for the Bohr effect

At given pO2 % the saturation of Hb with oxygen is lower

Explain the advantage of the Bohr effect (e.g. during exercise)

More dissociation of oxygen → faster aerobic 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 structures

• So they have different affinities for oxygen

Explain how organisms can be adapted to their environment by having different types of haemoglobin with different transport properties

Curve shifts to the left - Hb has higher affinity for O2

• more O2 associates with Hb more readily

• At gas exchange surfaces where pO2 is lower

• E.g. organisms in low pO2 environments - high altitudes, underground, or foetuses

Curve shifts to the right - Hb has a lower affinity for O2

• more O2 dissociates from Hb more readily

• At respiring tissues where more O2 is needed

• E.g. organisms with high rates of respiration/ metabolic rate (may be small or active)

Describe the general pattern of blood circulation in a mammal

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

• deoxygenated blood in the right side of the heart pumped to lungs; oxygenated blood returns to left side

• Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right

Suggest the importance of the 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 higher pressure (after being lower from lungs)

• (Substances taken to / removed from body cells quicker/ more efficiently)

Draw a diagram showing the general pattern of blood circulation in a mammal, including the names of key blood vessels

Name the blood vessels entering and leaving the heart and lungs

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

• Pulmonary artery - transports deoxygenated blood from heart → lungs

• 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 heart and lungs:

• renal arteries - oxygenated blood → kidneys

• Renal veins - deoxygenated blood to vena cava from kidneys

Name the blood vessels that carry oxygenated blood to heart muscle

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

Label a diagram to show the gross structure of the heart

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

• thicker muscle to contract with greater force

• To generate higher pressure to pump blood around entire body

Explain the pressure + volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood (atrial systole)

• atria contract

• So their volume decreases, pressure increases

• Atrioventricular valves open when pressure in atria exceeds pressure in ventricles

• Semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles

• So blood pushed into ventricles

Explain the pressure + volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood (Ventricular systole)

• ventricles contract

• So their volume decreases, pressure increases

• Atrioventricular valves shut when pressure in ventricles exceeds pressure in atria

• Semilunar valves open when pressure in ventricles exceeds pressure in arteries

• So blood pushed out of heart through arteries

Explain the pressure + volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood (Diastole)

• atria + ventricles relax

• So their volume increases, pressure decreases

• Semilunar valves shut when pressure in arteries exceeds pressure in ventricles

• Atrioventricular valves open when pressure in atria exceeds pressure in ventricles

• So blood fills atria via veins and flows passively to ventricles

Explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted e.g. to identify when valves are open/ closed

Semilunar valves are closed:

• pressure increases (named) artery higher than in ventricle

• To prevent backflow of blood from artery to ventricles

Semilunar valves open:

• when pressure in ventricle is higher than in (named) artery

• So blood flows from ventricle to artery

Atrioventricular valves closed:

• pressure in ventricle higher than atrium

• To prevent backflow of blood from ventricles to atrium

Atrioventricular valves open:

• when pressure in atrium is higher than in ventricle

• So blood flows from atrium to ventricle

How can heart rate be calculated from cardiac cycle data?

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

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 minute)

Explain how the structure of the arteries relates to their function

(Function - carry blood away from heart at high pressure)

Thick smooth muscle tissue - can contract and withstand blood pressure

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

Thick wall - withstands high pressure / prevents bursting

Smooth / folded endothelium - reduces friction / can stretch

Narrow lumen - increases / maintains high pressure

Explain how the structure of arterioles relates to their function

(Function - division of arteries to smaller which can direct blood to different capillaries / tissues)

• 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)

Explain how the structure of capillaries relates to their function

(Function - allow efficient exchange of substances between blood and tissue fluid (exchange surface))

• wall is a thin (one cell) layer of endothelial cells - reduces diffusion distance

• Capillary bed (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 - allow larger substances through

Explain how the structure of veins relates to their function

(Function - carry blood back to heart at lower pressure)

Wider lumen than arteries - less resistance to blood flow

Very little elastic and muscle tissue - blood pressure lower

Valves - prevent backflow of blood

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 tissue fluid (so net outward force)

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

3. Large plasma proteins remain in capillary

Explain the return of tissue fluid to the circulatory system

At the venue 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 below that of tissue fluid

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

4. Excess water taken up by lymph capillaries 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 is reduced

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

• Lymph system may not be able to drain excess fast enough

High blood pressure (e.g. caused by high salt concentration) → high hydrostatic pressure

• increases outward pressure from arteriole 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