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Why do many veins in the arms and legs have valves?

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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.

Many veins in the arms and legs contain one-way valves to ensure the efficient return of blood to the heart. Because these veins are located in the limbs, the blood they carry must often move against the force of gravity.123

These valves function as membranous structures that permit fluid to move in only one direction. By preventing the backflow and pooling of blood, they work in conjunction with other mechanisms—such as the contraction of surrounding skeletal muscles and pressure changes during breathing—to propel blood toward the heart. When these valves fail to function properly, blood can collect in the veins, potentially leading to conditions such as varicose veins.4125