the old fruit correctly pointed out, an artery carries blood
from the heart.
The heart pumps blood out from the left ventricle to the aorta. This is the main artery. The aorta then divides and branches out into many smaller arteries. These smaller arteries feed the different body regions with blood.
The arteries deliver the oxygen-rich blood to the capillaries, and the capillaries deliver the waste-rich blood to the veins for transport back to the heart. It is in the capillaries that the exchange of oxygen and carbon dioxide between blood and tissue occurs.
Each artery has three layers (generally speaking):
- an outer layer of tissue called the adventitia - this layer varies a lot between different arteries, and contains fibroelastic tissue, nutrient vessels, and nerves. It also connects the artery with its surrounding tissues.
- a muscular middle - consists mostly of smooth muscle cells and various elastic tissues.
- an inner layer of endothelial cells, called the intima. This inner layer is very smooth so that the blood can flow easily with no obstacles in its path. The cells are also generally oriented to be parallel to the direction of the flow of blood.
There are two types of arteries:
- elastic arteries (or conducting arteries) - these are bigger arteries. They have more elastic material in their walls, and their function is to conduct large amounts of blood away from the heart. Examples are the aorta and the pulmonary artery.
- the muscular arteries - once the blood has reached the general region it is aimed for, smaller arteries take over, such as the radial artery. These have more smooth muscle cells.
The muscular wall
of the artery, along with the artery's elsticity helps the blood circulate
. When the heart beats, the artery fills with blood, and expands. When the heart relaxes, the artery contracts, pushing the blood along.
The artery's expansion and contraction rhythm is therefore exactly the same as the heart's. This is the reason you can measure a pulse at the radial artery (at the wrist) or any other artery for that matter. You are actually measuring the number of times the artery is contracting per minute, but this is the same as the number of heartbeats.
Incidentally, the pulmonary artery carries deoxygenated blood. All other arteries carry oxygenated blood away the heart, but the pulmonary artery pumps deoxygentated blood to the lungs. In the lungs blood is oxygenated and returns to the heart via the other exception, the pulmonary vein (excpetion in that it, unlike other veins, carries oxygenated blood).Thanks dwardu for that last insight.