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In this article:
Key Points
- The coronary arteries supply blood to the heart, and when they become blocked (such as with plaque), angina – or chest pain – can occur.
- Capillaries are tiny vessels that form bridges between arteries and veins.
- Blood flows through arteries at high pressure, but it flows through veins at a lower pressure.
Blood travels through your body via a network of tubes called vessels, also known as the vasculature. This network makes it possible for blood to make one round-trip from your heart to the rest of your body and back again in about one minute. Three types of blood vessels carry blood: arteries, capillaries, and veins. The space inside each vessel is called the lumen.
The arteries
Arteries carry bright red blood filled with oxygen away from the heart throughout the body. The aorta, the body's main artery, carries this oxygen-rich blood from the heart to smaller arteries—which in turn deliver blood to the rest of the body—and to the coronary arteries, which supply only the heart.
The heart pumps blood into the aorta with great force. Artery walls are thicker than those of other vessels, which helps protect them from being damaged by the high pressure caused by the heart's pumping action. Artery walls also have muscles that help the blood keep moving through the cardiovascular system. When the heart is working very hard, such as when you exercise, the lumen of the artery can widen so that more oxygen-rich blood can be delivered to meet the body's need for fuel.
Your doctor measures the pressure of the blood against the walls of the arteries by taking your blood pressure. Learn more in Blood Pressure.
The coronary arteries divide into many branches and supply blood to all parts of the heart, providing it with a constant supply of oxygen to help it work continuously. Some types of heart disease can narrow coronary arteries, preventing sections of the heart from receiving adequate oxygen. If this happens, you may feel chest pain or discomfort, a serious condition known as angina. A coronary artery can also become totally clogged with plaque, preventing blood and oxygen from reaching a section of the heart. This can cause a part of the surrounding heart muscle to die and stop functioning, resulting in a heart attack. Learn more in Coronary Artery Disease and Angina Basics.
The capillaries
The capillaries are the bridges between the arteries (which carry bright red, oxygen-rich blood away from the heart) and veins (which bring dark blue, oxygen-poor blood back to the heart) for the blood's round-trip through the body. Capillaries are tiny blood vessels that carry blood to and from every cell in the body. In an adult body, this means the capillaries serve trillions of cells. Capillary walls are very thin and leaky so that oxygen, nutrients, and other substances can pass into cells. Cell waste and carbon dioxide also easily pass out of cells into the capillaries to travel out of the body.
The veins
The veins bring oxygen-poor and carbon dioxide-rich blood from cells back to the heart for pumping into the lungs. Two large veins return dark blue blood to the heart through the right atrium: the superior vena cava returns blood from the upper half of the body, and the inferior vena cava brings blood back from the lower half of the body. The walls of veins are much thinner than artery walls. But vein walls aren't likely to be damaged because blood flows in veins at a much lower pressure than in the arteries.
Source
1. National Heart, Lung, and Blood Institute, National Institutes of Health, The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Express version: NIH Publication No. 13-5233. May 2003. http://www.nhlbi.nih.gov/guidelines/hypertension/express.pdf
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