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The heart is a powerful automatic pump. It's the part of the cardiovascular system we think of most when we think about good health. But healthy blood and blood vessels are also vital for staying well.

 The average adult has between 5 and 6 liters of blood or blood volume. Blood carries oxygen and nutrients to all the living cells in the body. It also carries waste products to systems that eliminate them.

Half the blood consists of a watery, protein-laden fluid called plasma. A little less than half is composed of red and white blood cells and other solid elements called platelets. Platelets cause the blood to coagulate wherever an injury to a blood vessel occurs.

Review Date: 2/2/2023
Reviewed By: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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