The Structure Of Arteries, Veins, Capillaries, and Arterioles

Blood circulates around the body through three kinds of blood vessel: veins, arteries and capillaries the heart pumps the blood through the blood vessels to enable food and oxygen to get to all the cells in the body.
Arteries carry blood away from the heart and to the body cells they divide into smaller vessels called arterioles.
Arterioles divide into microscopic vessels called capillaries.
Capillaries join up to form veins.
Veins return the blood to the heart.

Arteries have a thick wall with an outer layer of fibrous muscle and a thick layer of elastic tissue and smooth muscle there is then a thin layer of folded endothelial tissue when the ventricles contract, blood enters the arteries at high pressure which stretches the endothelium and the elastic walls. When the ventricles relax the artery wall keeps the blood pressure up, if the blood pressure drops too much between heartbeats organs such as the kidneys would not function,

Arterioles are tiny branches of arteries that lead to the capillaries they regulate blood flow by constricting and dilating this is done by the control of the sympathetic nervous system. Arterioles are the main regulators of blood pressure and blood flow.

Capillaries are tiny blood vessels their walls are only a cell thick which enables materials such as oxygen, water, salts, and carbon dioxideto exchange between the contents of the capillaries and the tissue surrounding them. There are capillaries in most organs and tissues in the body the capillaries are supplied with blood by arterioles and drained by venules.
A venule is a small blood vessel which allows deoxygenated blood to return from the capillary bed to a larger vein.

Veins consist of 3 layers of tissue that are thin and less elastic than arteries, veins have valves that help blood to return to the heart and prevent it from flowing backwards, blood flow though veins is helped by muscle contraction for example when a muscle contracts it bulges and presses on the walls of the veins which pushes blood to the vein when the muscle relaxes the valve closes this helps the blood return to the heart.





references
cgp handout arteries and veins
cgp handout the heart and blood vessels
http://www.youtube.com/watch?v=PgI80Ue-AMo