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Why can veins hold a large share of the body’s blood volume?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

Veins are able to hold a large share of the body’s blood volume primarily because of their structural characteristics compared to arteries. Specifically, veins possess larger lumens (internal diameters) and thinner, more compliant walls.1

Because the blood within the venous system is under substantially lower pressure than in the arterial system, veins contain less elastic tissue and muscle. These thinner, highly compliant walls allow the vessels to expand readily, enabling them to function effectively as reservoirs that store a significant proportion of the body's total blood volume at any given time.1