Arteries are adapted to their function in blood transport from the heart.

Arteries differ slightly from the veins and a lot from the capillaries. Veins take deoxygenated blood back from the body. This blood that is taken back to heart is under very low pressure because of this the veins have valves, these valves stop the blood from going back down the wrong way. They do this by only opening in one direction. When the pressure form the blood builds up it forces the valves to open and let the blood through but because they only open in one direction it cannot return back. The veins are made from the same materials as the arteries but are different in terms of thickness. The muscle around the veins is very thin this is because the blood is not at a high pressure. Because of the low pressure the blood has not got a pulse unlike the arteries, which do. They also have a larger lumen then the arteries to let more blood through.

When the blood flows through the arteries the arteries split up into arterioles these then divide again into capillaries. They take blood to all of the tissues in the body. The capillaries are very small. They are also very thin vessels. They are made of one cell thick endothelium. These vessels link up the arteries with the veins. When the blood enters the capillaries it slows down, this takes away most of the pressure and allows for exchange of chemicals to take place more efficiently. The slowing down of the blood also results in the capillaries having no pulse or valves. The capillaries are so small that the lumen is only big enough for one red blood cell to squeeze through. The capillaries have no elastic tissue or muscle; this is because they do not need to expand and contract to let the blood flow through. When the chemical exchanges have taken place via diffusion through the one cell thick endothelium the capillaries start to merge together into veins. Capillaries also expand in heat and contract in cold this is so that less heat is lost through the blood when it is cold and more heat is lost when it is hot. Here is a diagram from Microsoft Encarta 99 explaining what has just been mentioned.

Disorders of arteries are inflammation, infection also the lining around the vessels can degenerate. The most common arterial disease is arteriosclerosis. This is when the artery wall hardens. Before this occurs fatty deposits occur on the inner arterial walls. When this happens the blood flow can slow down. This causes the wall to lose its elasticity. This may affect all of the arteries in the body. When arteriosclerosis takes place a clot can occur due to red blood cells collecting where the fat deposits are. This can be treated by clot dissolving enzymes called urokinase and streptokinase.

Arteries have to undertake the pressures of the blood being pumped from the heart at 93mmHg. They are special in the way that they have thick muscle walls and are very elastic. If they were not elastic then the blood cannot be pushed though them at high pressures and the pulse would not happen. They are different from the veins in many ways; they do not have valves, they do not have thin muscular walls, blood is passed through the veins at low pressure this does not happen in the arteries, also veins have a large lumen whereas the arteries do not. They differ a lot from the capillaries too; capillaries are one cell thick obviously the arteries are not, the capillaries have no pulse, and a very small lumen a lot smaller than the arteries. The arteries, the veins and the capillaries all have different roles to play in the transport of blood around our bodies. They have been designed for these different roles, the arteries take blood away from the heart, the capillaries ensure that chemicals can be exchanged and the veins take the blood back to heart. This is all done in balance and is regulated by the heart and brain.