7- Mass Transport in Animals

Describe the structure of a haemoglobin molecule.

• Protein with a quaternary structure

• Four polypeptide chains

• Each polypeptide chain is associated with a haem group

• Each haem group contains an Fe²⁺ ion

State and explain how many oxygen molecules can be transported by a single haemoglobin molecule in humans.

• Four oxygen molecules

• Each haemoglobin has four haem groups and therefore four Fe²⁺ ions

• Each Fe²⁺ ion can combine with a single oxygen molecule

What is the name of the process by which haemoglobin binds with oxygen?

• Oxygen loading or

• Oxygen association

Where does oxygen loading take place in humans?

In the lungs

What is the name of the process by which haemoglobin releases its oxygen?

• Oxygen unloading or

• Oxygen dissociation

Where does oxygen unloading take place in humans?

In respiring tissues

What does it mean if haemoglobin has a high affinity for oxygen?

• It takes up oxygen more readily

• It releases oxygen less readily

What does it mean if haemoglobin has a low affinity for oxygen?

• It takes up oxygen less readily

• It releases oxygen more readily

Describe and explain the position of the oxygen dissociation curve in the lungs.

• Carbon dioxide concentration is low

• This means pH is high

• Affinity of haemoglobin for oxygen increases

• Haemoglobin takes up oxygen more readily

• Oxygen dissociation curve shifts to the left

Describe and explain the position of the oxygen dissociation curve in respiring tissues.

• Carbon dioxide concentration is high due to respiration

• This means pH is low

• Affinity of haemoglobin for oxygen decreases

• Haemoglobin releases its oxygen more readily

• Oxygen dissociation curve shifts to the right

What is the name of the graph showing the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen?

The oxygen dissociation curve

What can the effect of carbon dioxide concentration on the position of the oxygen dissociation curve be described as?

The Bohr effect

Explain the shape of the oxygen dissociation curve at A

• Gradient of the curve is shallow

• The shape of haemoglobin makes it difficult for the first oxygen molecule to bind

Explain the shape of the oxygen dissociation curve at B

• Steep gradient

• Binding of the first oxygen molecules changes the quaternary structure of haemoglobin, causing it to change shape

• This makes it easier for the next oxygen molecule to bind

• This is known as positive cooperativity

Explain the shape of the oxygen dissociation curve at C

• Graph plateaus

• Majority of the Fe²⁺ ions are bound to an oxygen molecule already

• This makes it less likely for the final oxygen molecule to find an unbound Fe²⁺ to bind to

State the relationship between the affinity of haemoglobin for oxygen and the position of the oxygen dissociation curve on the axes.

The further to the left the curve, the greater the affinity of haemoglobin for oxygen

Which types of species would have haemoglobin with a higher affinity for oxygen?

Species living in habitats with a low partial pressure of oxygen

Why is the llama oxygen dissociation curve further to the left than the human oxygen dissociation curve?

• Llamas live at high altitudes

• Partial pressure of oxygen is lower here

• Therefore llamas need haemoglobin with a higher affinity for oxygen than humans

State the relationship between surface area to volume ratio of an organism and its need for a specialised transport system.

The lower the surface area to volume ratio, the greater the need for a transport system

State the relationship between how active an organism is and its need for a specialised transport system

The more active the organism, the greater the need for a transport system

What can the circulatory system of mammals be described as?

A closed, double circulatory system

Why is the circulatory system in mammals described as closed?

Blood is confined to vessels

Why is the circulatory system in mammals described as being a double circulatory system?

• Blood passes through the heart twice

• For each complete circuit of the body

Why is it an adaptation that the circulatory system in mammals is a double circulatory system?

• When blood passes through the lungs, its pressure is reduced to prevent the lungs from bursting

• As it is a double circulatory system, blood is returned to the heart

• This increases blood pressure again before it is circulated to the rest of the body tissues

• This means substances are delivered to the rest of the body quickly

• This is necessary because mammals have a high body temperature and therefore a high rate of metabolism

Describe and explain how substances move from blood vessels into cells, after they have moved a long distance via a transport system.

• Via diffusion

• There is a large surface area

• Diffusion distance is short

• There is a steep concentration gradient

• Therefore, diffusion is rapid enough for cells to obtain the substances they need (no transport system is needed)

What is the function of the pulmonary artery?

• To transport deoxygenated blood

• From the right ventricle

• To the lungs

What is the function of the vena cava?

• To transport deoxygenated blood

• From the body

• To the right atrium

What is the function of the renal vein?

• To transport deoxygenated blood

• From the kidneys

• To the right atrium (through the vena cava)

What is the function of the pulmonary vein?

• To transport oxygenated blood

• From the lungs

• To the left atrium

What is the function of the aorta?

• To transport oxygenated blood

• From the left ventricle

• To the body

What is the function of the renal artery?

• To transport oxygenated blood

• From the left ventricle (through the aorta)

• To the kidneys

How is the renal vein connected to the vena cava?

Via other veins

How is the renal artery connected to the aorta?

Via other arteries

Which type of blood do arteries transport, and which artery is the exception?

• Oxygenated blood

• The pulmonary artery- transports deoxygenated blood

Which type of blood do veins transport, and which vein is the exception?

• Deoxygenated blood

• The pulmonary vein- transports oxygenated blood

Which type of blood does each side of the heart deal with?

• The right side deals with deoxygenated blood

• The left side deals with oxygenated blood

Describe the structure of the atria.

• Thin-walled

• Elastic so that they can stretch as they collect blood

Describe and explain the structure of the ventricles compared with the atria.

• Much thicker muscular walls than the atria

• So they can contract strongly to pump blood over a longer distance

What is the difference in structure between the right and left ventricle?

• Right ventricle has a thinner muscular wall as it only has to pump blood to the lungs

• Left ventricle has a thicker muscular wall as it has to pump blood to the rest of the body

What is the name of the left atrioventricular valve?

Bicuspid valve

What is the name of the right atrioventricular valve?

Tricuspid valve

What are coronary arteries?

Blood vessels which supply the heart with oxygen

What do coronary arteries branch from?

The aorta

Describe the stages leading to a myocardial infarction (heart attack).

• Coronary arteries become blocked

• Area of the heart muscle is deprived of blood and therefore also oxygen

• The muscle cells in this region are unable to aerobically respire

• These cells eventually die

What are the three stages of the cardiac cycle?

• Diastole

• Atrial systole

• Ventricular systole

What happens during atrial systole?

• Atrial walls contract simultaneously

• Atrioventricular valves open as atrial pressure > ventricular pressure

• Blood is pushed from the atria into the ventricles

• Ventricles remain relaxed

• Semi-lunar valves are closed

What happens during ventricular systole?

• Atria relax

• After ventricles have filled with blood, ventricular walls contract simultaneously

• Atrioventricular valves close as ventricular pressure > atrial pressure

• Semi-lunar valves open as ventricular pressure > arterial pressure

• Blood is pushed from the ventricles into the aorta and pulmonary artery, and then out of the heart

What happens during diastole?

• Blood enters atria through pulmonary vein and vena cava

• Atria are relaxed and fill with blood

• Atrioventricular valves open slightly

• Ventricles are relaxed and fill slightly with blood

• Semi-lunar valves are closed

Which structures prevent the backflow of blood?

Valves

What are the three types of valve?

• Atrioventricular valves

• Semi-lunar valves

• Pocket valves

Where are atrioventricular valves located?

Between the atria and ventricles

Where are semi-lunar valves located?

In the aorta and pulmonary artery

Where are pocket valves located?

In veins

What equation is used to calculate cardiac output?

Cardiac output = heart rate x stroke volume

What is the cardiac output a measure of?

The volume of blood pumped by one ventricle of the heart in one minute

What is the heart rate a measure of?

The rate at which the heart beats

What is the stroke volume a measure of?

The volume of blood pumped out of the heart at each beat

What is cardiac output usually measured in?

dm³ min^-1

What do the labels A-J represent?

A- atrial systole

B- ventricular systole

C- diastole

D- semi-lunar valve opens

E- semi-lunar valve closes

F- atrioventricular valve closes

G- atrioventricular valve opens

H- aortic pressure

I- ventricular pressure

J- atrial pressure

What are the four different types of blood vessels?

• Arteries

• Arterioles

• Capillaries

• Veins

What do arteries do?

• Transport blood from the heart

• Into arterioles

What are arterioles, and what do they do?

• Smaller arteries

• Transport blood from arteries

• Into capillaries

What are capillaries, and what do they do?

• Tiny vessels that link arterioles to veins

• Exchange metabolic materials (e.g. glucose, carbon dioxide, oxygen) between the blood and cells of the body

What do veins do?

• Carry blood from capillaries

• Back to the heart

Which type of blood vessel carries out exchange as well as transport?

Capillaries

What are the layers making up arteries, arterioles and veins from the outside inwards?

• Tough fibrous outer layer

• Muscle layer

• Elastic layer

• Endothelium

• Lumen

What is the structure of an artery?

• Thick muscle layer

• Relatively thick elastic layer

• High overall thickness of the wall

• No valves

Why do arteries have a thick muscle layer?

So that they can constrict and dilate in order to control the volume of blood passing through them

Why do arteries have a relatively thick elastic layer?

• Elastic layer can stretch and recoil

• Maintains a high blood pressure within the arteries

Why do arteries have a thick wall overall?

Prevents the artery from bursting under high pressure

Why do arteries not have valves?

Blood is under high pressure so does not flow backwards

What is the structure of an arteriole?

• Muscle layer is thicker than in arteries

• Elastic layer is thinner than in arteries

Why do arterioles have a thicker muscle layer than arteries?

• Allows constriction of the lumen

• Restricts the flow of blood/ controls its movement into capillaries

Why is the elastic layer thinner of arterioles than in arteries?

Blood is under lower pressure in the arterioles than in the arteries

What is the structure of a vein?

• Thin muscle layer

• Thin elastic layer

• Low overall thickness of the wall

• Valves

Why is the elastic layer thin in veins?

They do not need to maintain a high pressure

Why do veins have a thin wall overall?

Pressure is low so there is no risk of bursting

Why do veins have valves?

• Pressure is low so there is a risk of blood flowing backwards

• Valves prevent backflow in veins so that blood only travels towards the heart

What is the structure of a capillary?

• Wall only consists of the endothelium

• Numerous and highly branched

• Narrow lumen

• Gaps between endothelial cells

Why is it useful that capillary walls only consist of the endothelium?

• They are extremely thin (only one cell thick)

• Short diffusion distance

• Rapid diffusion between blood and cells

Why is it useful that capillaries are numerous and highly branched?

• Large surface area

• Rapid diffusion between blood and cells

Why is it useful that capillaries have a narrow lumen?

• Cells are close to capillaries

• Short diffusion distance

• Rapid diffusion between blood and cells

AND

• Red blood cells are squeezed flat against the side of the capillary

• Brings red blood cells close to the cells requiring oxygen

• Short diffusion distance

Why is it useful that capillaries have gaps between endothelial cells?

White blood cells can escape in order to deal with infections within tissues

What is the name of the liquid solution that bathes cells?

Tissue fluid

What does tissue fluid contain?

• Water

• Glucose

• Amino acids

• Fatty acids

• Ions in solution

• Oxygen

• Waste products like carbon dioxide

Why is tissue fluid useful for cells?

• It provides a mostly constant environment for the cells it surrounds

• It supplies important substances to cells

Outline the formation of tissue fluid and how it returns to the circulatory system. (8 marks)

• Capillaries are narrower than arteries

• Blood passing through capillaries at arterial end has a high hydrostatic pressure

• Forces small molecules to move out of the blood plasma (plasma proteins and blood cells are too large so stay in the blood) into the surrounding cells

• Known as ultrafiltration

• At the venous end of the capillary, hydrostatic pressure is low due to the loss of tissue fluid

• Water potential is also low as plasma has lost water but still contains proteins

• Tissue fluid is forced back into the capillaries at venous end down a hydrostatic pressure gradient

• Water enters the blood plasma from surrounding tissues via osmosis down a water potential gradient

Why would a high concentration of salt in the blood plasma lead to a build-up of tissue fluid?

• Tissue fluid has a lower water potential

• So less water is returned to the capillary via osmosis

• Also, higher salt leads to higher blood pressure

• More tissue fluid is forced out of the capillary

What is the movement of tissue fluid out of the blood plasma resisted by?

• High hydrostatic pressure of the tissue fluid already outside of the capillaries

• The lower water potential of the blood as it moves through the capillaries

What happens to the excess tissue fluid that has not returned to the blood capillaries?

• It is transported through lymphatic capillaries as lymph via the lymphatic system

• Eventually returns to the bloodstream

What allows lymph to move around the body, despite it not being pumped around by the heart?

• The hydrostatic pressure of tissue fluid

• Contraction of body muscles which squeeze lymph vessels