Transport in Animals

Question 1

What is a single circulatory system?

Answer 1

A circulation in which the blood flows through the heart once during each circulation of the body e.g. fish

Question 2

What is a double circulatory system?

Answer 2

A circulation in which the blood flows through the heart twice during each complete circulation of the body
e.g. mammals

Question 3

What is an open circulatory system?

Answer 3

The blood is not always in vessels e.g. insects

Question 4

What is a closed circulatory system?

Answer 4

The blood is always in vessels e.g. fish

Question 5

Advantages of closed circulatory system?

Answer 5

it is possible to maintain a high blood pressure
there is an increased rate of flow and so delivery of substances flow can be diverted and directed

Question 6

Features of arteries:

Answer 6

Carry blood at high pressure, so artery wall must be able to withstand the pressure
wall is thick with a thick layer of collagen to provide strength
the endothelium is folded which prevents damage as it can stretches under pressure
Must be able to maintain that high pressure
there is a thick layer of elastic tissue to cause recoil and a return to original size
there is a thick layer of smooth muscle which narrows the lumen

Question 7

Features of veins:

Answer 7

Carry blood at low pressure so the walls do not need to be thick
Lumen is relatively large to ease the flow of blood
The walls have thinner layers of collagen, smooth muscle and elastic tissue. They do not need to stretch and recoil and are not actively constricted to reduce blood flow.
Contain valves to prevent blood flowing in the wrong direction. As the walls are thin, the
vein can be flattened by the action of the surrounding skeletal muscles. Pressure is applied to the blood, forcing it to move along in the direction dictated by the valves.

Question 8

Features of capilliaries:

Answer 8

Walls consist of a single layer of flattened endothelial cells that reduces the diffusion distance for the materials being exchanged
The lumen is the same diameter as a red blood cell (about 7μm). This ensures that the red blood cells are squeezed as they pass along the capillaries. The diffusion distance is shorter, so they are more likely to give up their oxygen

Question 9

How is tissue fluid formed?

Answer 9

At the arterial end of a capillary, the blood is under high pressure due to contractions of the heart (hydrostatic pressure). This is greater than the osmotic (oncotic) pressure pulling water into the capillary from the tissues. This will tend to push the plasma fluid out of the capillaries, leaving large protein molecules behind. It can leave through tiny gaps (fenestrations) in the capillary wall to form tissue fluid. At the Venule end hydrostatic pressure decreases as you move further away from the heart, therefore the oncotic pressure is now higher, thus water moves back into the capillaries.

Question 10

What are the stages of the cardiac cycle?

Answer 10

1. When both the atria and the ventricles are relaxed, blood flows into the atria from the major veins.
2. The blood flows through the atrioventricular valves into the ventricles
3. The atria contract simultaneously, pushing blood into the ventricles
4. Blood fills the atrioventricular valve, causing them to snap shut and preventing the blood from flowing back into the ventricles
5. When the pressure in the arteries is higher than the pressure in the ventricles, the semilunar valves shut
6. The walls of the ventricles contract, starting from the bottom
7. When the pressure in the ventricles is higher than the pressure in the arteries, the semilunar valves is pushed open and blood is pushed out of the heart. The contraction only lasts for a short time
8. The ventricles relax
9. When the pressure in the ventricles drops to below that of the atria, the atrioventricular valves open again
10. When the pressure in the ventricles drops to below that of the arteries, the semilunar valves shut again

Question 11

How is heart rate co ordinated with SAN and AVN?

Answer 11

SAN starts the excitation wave which spreads over the wall of the atria until it reaches the AVN
The atria contract (atrial systole) and this contraction is synchronised
There is a delay at the AVN then the excitation spreads down septum and into the bundle of His and the Purkyne fibres
This causes the ventricles to contract (ventricular systole) from the apex (bottom)

Question 12

Formation of haemoglobonic acid:

Answer 12

As Carbon dioxide diffuses into the blood, some of it enters the red blood cells and combines with water to form carbonic acid, catalysed by carbonic anhydrase.
CO2 + H2O → H2CO3
This carbonic acid then dissociates to form Hydrogen ions and Hydrogencarbonate ions
H2CO3 → H+ + HCO3-
The Hydrogencarbonate ions diffuse out of the red blood cell into the blood plasma. The charge in the red blood cell is maintained by the chloride shift; the movement for chloride ions into the RBC.
Hydrogen ions could cause the contents of the RBC to become very acidic, so the haemoglobin acts as a buffer. They oxyhaemoglobin dissociates releasing the O2, and the hydrogen ions are taken up by the haemoglobin to form haemoglobonic acid.

Question 13

Fetal haemolglobin:

Answer 13

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin
Fetal Hb takes up oxygen in lower partial pressure of oxygen
The placenta has a low partial pressure of oxygen
At low partial pressure of oxygen, in the placenta, adult oxyhaemoglobin will dissociate releasing the oxygen