What Roles Do Valves Play in Veins?

Venous valves play a critical, single role: to ensure unidirectional (one-way) blood flow back to the heart and prevent the backflow (regurgitation) of blood.

This function is especially important in the limbs, particularly the legs, for two main reasons:

1. Counteracting Gravity: When you are standing, gravity constantly pulls blood downward. Venous valves, which are small flaps of endothelium, act like one-way doors. As blood flows upward, they open. If blood tries to fall back down, it fills the cusps of the valve, forcing them shut.
2. Aiding the Skeletal-Muscle Pump: Veins are often situated between skeletal muscles. When you walk or move, your muscles contract and squeeze the nearby veins. This "pumps" the blood upward. The valves are essential to this process, as they trap the blood in segments, ensuring that when the muscle squeezes, the blood can only move toward the heart, not back down.

Without functional valves, blood would pool in the lower extremities, leading to conditions like varicose veins and chronic venous insufficiency.