There are three types of blood vessels: arteries, veins and capillaries.
Arteries and veins have the same basic three-layered structure but hte proportions may vary:
Innermost layer - endothelium is one cell thick and surrounded by the tunica intima. It has a smooth lining which reduces friction with minimum resistance to blood flow.
Middle layer - tunica media has elastic fibres and smooth muscle.Thicker in arteries than in veins. In arteries the elastic fibres allows the arteries to stretch accommodating changes in blood flow and pressure as blood is pumped from the heart.
Outer layer - tunica externa contains collagen fibres which results overstretching.
Capillaries have thin walls which are only one…