Definition of Vein

Vein AnatomyVein – A blood vessel that carries blood to the heart.

All veins except the pulmonary veins carry deoxygenated blood; the pulmonary veins return oxygenated blood to the heart from the lungs.

Because veins lack the muscular structure and contractile capability of arteries, they have valves that keep blood moving only in one direction, toward the heart.

The body’s largest veins are the superior vena cava and the inferior vena cava, which empty blood into the heart’s right atrium.

For further discussion of cardiovascular structure and function please see the overview section “The Cardiovascular System.”

See also ARTERY.

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