Describe the structure of the arteries, veins and capillaries and relate this to their function.

figure 7

Arteries
Arteries transport blood away from the heart; there are two types the pulmonary arteries and systemic arteries. Pulmonary arteries carry blood from the heart to the lungs where the blood picks up oxygen. Systemic arteries deliver blood to the rest of the body.
It has thick muscular and elastic walls as blood is pumped through at a high pressure, from the heart and so that they can expand and contract to push the blood through to the capillaries. They are under sympathetic nervous control that adjusts their diameter to increase or decrease their resistance to the flow of blood. As the arteries get nearer to the tissue they get narrower, these are known as arterioles.

Veins
As blood flows from the capillaries it enters slightly larger vessels know as venules, from here they join the veins. Veins carry deoxygenated blood with the exception of the pulmonary vein back to the heart. The walls are made up of elastic and muscular fibres and are thinner than arteries; it has a larger lumen than the arteries. The veins include valves to ensure the blood does not flow back in the wrong direction.

Capillaries
Capillaries are found at the end of the arterioles, they are the smallest blood vessels in the body; they take the blood through the tissue. They are only one cell thick this helps with diffusion of oxygen and glucose. (Wright, 2007)