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Once blood leaves your heart, it enters the rest of your circulatory system, which
is an intricate network made up of three types of blood vessels: arteries, veins, and capillaries. Each of these
has its own special design and function.
Arteries are the blood vessels that carry blood rich in oxygen from the heart to all the organs and cells in your
body. Arteries have muscular walls that allow them to grow larger (dilate) or smaller (constrict) as needed. The
largest artery in the body is called the aorta. The aorta runs from the chest into the abdomen and receives blood
directly from the powerful left ventricle of your heart.
All of your arteries have important functions, but some may be referred to more often such as the femoral artery
in your upper leg and the radial artery in your forearm. These are the vessels through which your cardiologist,
radiologist or vascular surgeon, for example, can insert the tubes that are used for cardiac catheterizations,
arteriograms or angioplasties. Arteries decrease in size the closer they are to the cells they are nourishing.
Very small arteries are known as arterioles.
Veins are the blood vessels that carry "used" blood that is low in oxygen back to the heart. Veins have thinner
walls than arteries and contain numerous one-way valves that help keep blood moving toward the heart. The largest
veins are called the superior vena cava and inferior vena cava. These veins bring blood from the upper and lower
body directly into the right atrium. The smallest veins are known as venules.
Arteries and veins are connected to each other by tiny, microscopic vessels called capillaries. But these tiny
vessels do far more than act as connectors, for it is in the capillaries that the all-important transfer of
oxygen and nutrients to the cells takes place. Capillary walls are so thin that oxygen passes from the arterial
blood through them into the cells in your organs and tissues, while waste products such as carbon dioxide pass
into the capillaries to be carried back by the veins to the heart and lungs.
We have described how the heart and blood vessels supply needed oxygen to the body. Now we will describe how the
heart itself receives the oxygen it needs. Your heart requires large amounts of oxygen to do its job well, but it
does not get that oxygen from the blood that is passing through its chambers. Your heart has its own system of
blood vessels, called coronary arteries, that travel around the heart muscle to provide blood and oxygen to all
parts of the heart.
There are two primary coronary arteries that branch off into smaller vessels. The right coronary artery (1) feeds
the right atrium and ventricle and the bottom of the left ventricle. The left main coronary artery (2) supplies
blood to the rest of the heart. This artery has two main branches, the left anterior descending (3) and the
circumflex (4). These quickly branch into smaller vessels (see illustration).
Copyright ©2005 Michigan Heart & Vascular Institute. All rights reserved.
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