Blood Circulation - Structure of Arteries, Veins & Capillaries

Arteries are the blood vessels that carry the oxygenated blood away from the heart, they are also responsible in helping the push of the rapid flow of blood when both ventricles are relaxed and the heart is refilling. Varying in size which is depicted by how far away from the heart they are their structure consists of three layers of tissue.

1. Tunica Adventria - This is the strong outer covering consisting of fibrous tissue which allow the arteries and veins to stretch due to the pressure that is exerted on the walls by the blood flow.


2. Tunica Media - This is the middle layer of the walls of arteries and veins, composed of smooth muscle and elastic fibers which allows them to stretch more gentle each time the heart pumps blood into them, then return back to their original shape.


3. Tunica Intima - The inner most layer of the arteries and veins composed of an elastic membrane lining and smooth endothelium that is covered by elastic tissue.

Veins are the opposite to arteries whereby they carry the deoxygenated blood back to the heart. Although thinner than arteries they share the same composition with the same three layers with less muscle and elastic tissue in the tunica media. With some veins containing valves to make sure that the flow of blood travels to the heart not backwards, the pressure in a vein is less than that of an artery so no pulse can be found in a vein compared to that of an artery where a pulse can be obtained.

Capillaries are the smallest of the blood vessels within the body. Composed of a single layer of endothelial cells they operate as a link between arteries and veins where the exchange of blood and tissue takes place in the capillary bed.