compare the structure of arteries, capillaries and veins in relation to their function
Veins carry blood back toward the heart. They carry the same quantity of blood as the arteries but not at the same high pressures. Veins have the same three layers as the arteries: endothelium, smooth muscle and connective tissue. However, the layers are not as thick. The veins also contain valves that prevent the backflow of blood.
Capillaries have walls that are only one endothelium cell thick, as they have to allow diffusion of materials through their wall to reach the cells found in the tissues in which the capillary is located.