section 2. (3)compare the structure of arteries, capillaries and veins in relation to their function

Question 1

what is the difference between the functions of veins and arteries and capillaries?

Answer 1

The function of arteries and veins is to carry blood over relatively long distances from one organ to another, whereas capillaries form branching networks to carry blood over relatively short distances within organs

Question 2

What is the basic structure of arteries?

Answer 2

• The walls of arteries are much thicker as it carries blood away from the heart at high pressure
• Major arteries close to the heart also have thick layers of smooth muscle in their walls to withstand the increases in pressure as the heart pumps
• The walls also have a large proportion of elastic fibres in both the inner and middle layers – this allows for the arteries to stretch according to the increases in volume of blood. As the heart relaxes the artery walls return to their original position, hence pushing the blood along – maintaining a constant flow in one direction.
• Arteries near the surface of the skin, the changes in the arteries diameter can be felt as a pulse.

Question 3

What is the basic structure of veins?

Answer 3

• The walls of veins are thinner than the walls of arteries, as the blood they receive from the capillaries is at a much lower pressure.
• The walls have fewer elastic fibres and the lumen is wider (to allow for easier blood flow)
• Veins have two mechanisms for keeping the blood flow constant and in one direction. Firstly many veins are close to muscles, hence when the muscles contract they compress the walls of the vein – pumping blood forwards. Veins also have valves (small pocket like folds of the endothelium lining the lumen of veins), they are spaced along regular intervals in veins. They work much like one-way swinging doors – as the blood is forced through the valve opens, however once the pressure drops and the blood flow decreases, the valve shuts – preventing backflow of blood.

Question 4

What is the basic structure of capillaries?

Answer 4

• They are extremely tiny microscopic vessels that bring blood into close contact with the tissues, for the exchange of chemical substances between cells and the bloodstream.
• The one cell thick endothelial layer is a continuation of the lumen arteries and veins
• Diffusion is a relatively slow process and hence the structure of capillaries is suited to slowing down the flow of blood
• In order to maximize the exchange of substances between the blood and cells capillaries have, thin walls (more efficient diffusion) a small lumen (forces blood cells to pass through in single file, slowing down the rate of flow and maximizing their exposed surface area)
• They form an expansive blood flow network, such that no cells are far from blood supply