Ch 8 Transport in humans

Question 1

Adaptations of arteries

Answer 1

1. The thick walls of the arteries allow the arteries to withstand high blood pressure due to the pumping action of the heart
2. The thick layer of elastic tissues allows the arteries to distend and recoil. When the heart contracts, blood is forced out of the heart. This exerts a high blood pressure against the wall of the arteries, and the arteries extend. When the heart relaxes, the arteries recoil due to the elasticity of their walls. This causes the blood to flow forwards, maintaining a continuous blood flow.
3. In the arterioles, the thick layer of muscles contract or relax to change the size of the lumen. This regulates the amount of blood flow to different parts of the body.

Question 2

Adaptations of veins

Answer 2

1. The large lumen reduces the resistance to the blood flow inside the veins.
2. Valves are present to prevent the backflow of blood.
3. The force for blood flow in veins is provided by the contraction of skeletal muscles lying next to the veins. When the muscles contract, the veins are squeezed and blood is forced to flow towards the heart.

Question 3

Adaptations of capillaries for exchange of materials

Answer 3

1. The highly branched capillary bed provides a large surface area for rapid exchange of materials between the blood and body cells
2. Each artery eventually branches into a very large number of capillaries. The total cross-sectional area is much greater in the capillary beds than in any other part of the circulatory system. Blood flows slowly in the capillaries. This allows a longer time for exchange of materials.
3. The one-cell thick capillary wall provides a short distance for rapid diffusion of materials.

Question 4

Arteries and arterioles - Blood pressure

Answer 4

Blood pressure is high due to the pumping action of the heart. Blood pressure changes periodically as the heart contracts and relax.

Question 5

Arteries and arterioles - Rate of blood flow

Answer 5

Rate of blood flow in the arteries is high under the pumping force of the heart. When the arteries branch into arterioles, the total cross-sectional area of the arterioles increases, the flow rate drops.

Question 6

Capillaries - Blood pressure

Answer 6

The small diameter of capillaries results in a high resistance to blood flow. This lead to a significant drop in blood pressure along the capillaries.

Question 7

Capillaries - Rate of blood flow

Answer 7

The total cross-sectional area is the greatest. Rate of blood flow drops to nearly zero. This provides more time for the exchange of materials between blood and body cells.

Question 8

Veins and venules - Blood pressure

Answer 8

The blood has overcome great resistance of the blood vessel walls after travelling a long distance away from the heart. The blood pressure drops to nearly zero.

Question 9

Veins and venules - Rate of blood flow

Answer 9

The force from the pumping heart can no longer drive blood forwards. Rate of blood flow increases due to contraction of skeletal muscles lying next to the veins.

Question 10

Adaptions of heart for pumping blood

Answer 10

1. Cardiac muscles: can contract and relax continuously without fatigue
2. Ventricles: have a thick muscular wall that provides a strong force of contraction to drive blood over a long distance to all parts of the body
3. Bicuspid valve, tricuspid valve, semilunar valves: prevent backflow of blood in the heart to ensure blood flow in one direction
4. Heart tendons: prevent the bicuspid and tricuspid valves from turning inside out

Question 11

Formation of tissue fluid

Answer 11

1. At the arteriole end of the capillary bed, the pressure of blood in the capillaries is higher than the pressure of the fluid surrounding the body cells. This forces some components of the plasma out of the capillary walls to form tissue fluid. Plasma proteins, red blood cells and blood platelets are too large to pass through the capillary walls. They remain in blood. White blood cells can squeeze through the capillary walls. The composition of tissue fluid is similar to blood, except for the absence of red blood cells, blood platelets and plasma proteins.
2. As plasma proteins remain in the blood, the water potential of the blood at the venule end of the capillaries is lower than that of tissue fluid. Water in the tissue fluid is drawn into the capillaries by osmosis.
3. Most tissue fluid returns to the blood at the venule end of the capillaries. Due to hydrostatic pressure of the tissue fluid, a small amount of tissue fluid drains into the lymph capillaries, which carry the excess tissue fluid back to the blood circulation