What are the structural and functional differences between arteries and veins?

Arteries have a much thicker muscular layer than veins, as this allows them to contract strongly and generate a high pressure to allow blood to be quickly transported to tissues in the body. Arteries also have a thick elastic layer, which allows them to stretch and recoil under pressure, which is a feature not necessary in veins as the blood is at a low pressure. Veins also have valves which prevents the backflow of blood whilst it travels against the direction of gravity.