Where are venous valves most numerous and what is their function?

• A. In the arteries of the limbs to prevent backflow
• B. In the veins of the legs (deep and superficial) to prevent backflow and aid venous return
• C. In capillaries to regulate filtration
• D. In the right atrium to prevent backflow of blood into veins

Answer: (C)

Venous valves act as one-way gates in veins to prevent blood from flowing backward and to assist the return of blood to the heart. They are most numerous in the veins of the legs because blood in the lower limbs must move upward against gravity over a long distance and under relatively low pressure. When leg muscles contract, they squeeze the veins and push blood upward through open valves; if any backward flow starts, the valves close to stop it, helping maintain a steady upward return. Capillaries don’t have valves—they’re sites of exchange—while arteries generally lack valves along their length, and the valve in the heart between atrium and ventricle (the tricuspid valve) prevents backflow into the atrium, not into peripheral veins.