Arteries carry blood from the heart to the rest of the body. They are thick walled, muscular and have elastic tissue in the walls to cope with the high pressure caused by the heartbeat. The inner lining of endothelium is folded, allowing the artery to expand, helping it to cope with high pressure.
Veins take blood back to the heart and are wider than equivalent arteries, with very little elastic or muscular tissue. Veins contain valves to stop the blood flowing backwards. Blood flow through the veins is helped by contraction of body muscles surrounding them.
Capillaries are the smallest of the blood vessels and are where metabolic exchange occurs. Substances are exchanged between cells and the capillaries. There are networks of cappilaries in tissue which increase the surface area for exchange. Cappilary walls are one cell thick which speeds up diffusion of substances such as glucose and oxygen into and out of cells.
Arterioles have thin muscular walls, generally one or two layers of smooth muscles. They are a blood vessel with a small diameter, and branch out from an artery to a cappilary. Arterioles receive autonomic nervous system innervation and respond to various circulating hormones in order to regualte their diameter.
Bibliography
CG Partnership handout, wk 24
Wikipedia/image
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