What is the structure and function of the arteries?

Answer 1

Arteries are blood vessels which carry oxygenated blood away from the heart to the body under high pressure. (Note that the pulmonary artery is the only artery which carries deoxygenated blood to the lungs where it is oxygenated and returns in the pulmonary vein to the heart).

The structure of the artery is adapted to this function in several ways.

The walls of the arteries are very thick in order to withstand the high pressure. The artery wall is made up of 3 layers, each of which is adapted to serve the function of the arteries.The tunica intima is the inner wall of the artery, and is made up of a layer of smooth endothelium, which reduces friction, covered by a surface of elastic fibres which allow the artery to expand and recoil.The overall function of the elastic fibres is to even out blood flow. When pressure is high they expand, so pressure decreases, and when pressure is lower they recoil, causing an increase in blood pressure. They are not entirely successful in this as a pulse can be felt in the arteries, however this pulse is helpful in propelling blood along through the arteries, together with the action of the smooth muscles.The tunica media is the middle layer, and this comprises a layer of smooth muscle, elastic fibres and collagen. The elastic fibres allow the artery to expand under pressure and then to recoil, causing another surge of pressure which carries the blood forward through the vessels.The tunica externa is the outer layer of the artery wall, and is made up of collagen and elastic fibres. The function of the tunica externa is to prevent over-distention (or over-expansion) of the artery. It is a tough protective outer layer which prevents the artery from bursting when pressure is high.Another characteristic of the artery walls that helps them to serve their purpose is the tiny blood vessels called the vaso vasorum which supply the artery walls with the essential nutrients that they need, including oxygen and glucose which are required for aerobic respiration.The middle and inner layers of the artery wall are nourished by diffusion.Arteries further from the heart will have fewer elastic fibres, as the pressure is less, but more smooth muscle to propel blood along the vessels.

Answer 2

Arteries carry blood away from the heart, therefore they need to be muscular and elastic to withstand high blood pressure.