The structure of arteries, veins ad capillaries and their function

There are three main types of blood vessels these are veins, arteries and capillaries. Their main job is to transport blood around the body.

Arteries

The walls of arteries contain smooth muscle fibre that contract and relax under the instructions of the sympathetic nervous system. The functions of arteries are, they transport blood away from the heart, they carry oxygenated blood and they transport blood under higher pressure more than veins. Arteries also don't have valves (except for the semi-lunar of the pulmonary artery and the aorta.)

Capillaries

Capillaries are extremely narrow blood vessels. They are around 5-20 micro-metres in diameter. Capillary walls are only one cell thick this is because of the contents of the capillary and the surrounding tissues. Capillaries are supplied with blood by arterioles and they are drained by venules. Their function is to not only transport blood but to supply tissues with components and also removes waste from the surrounding cells.

Veins

The walls of veins have three layers of tissue that are thinner than arteries. Veins include valves that aid the return of blood to the heart by preventing blood from flowing in reverse, this is important as it prevents waste materials returning to the bodies tissues. The job of veins is to get blood from the tissues and return deoxgenated blood back to the heart.