Blood flows from the heart through the arterial system, and back to the heart through the venous system.

In the legs, the venous system is composed of three elements:

• Deep veins, which carry ~95% of the blood volume
• Superficial veins, which carry ~5% of the blood volume
• Perforator veins, which connect the superficial veins to the deep veins

While the superficial veins lie directly beneath the skin and are mainly for temperature control, the deep veins lie deep within the legs, acting as the primary channel for the lower body's blood supply. Blood returning to the heart through these veins is impeded by the downward pressure of gravity. To counteract this force, there are a series of one-way valves in every vein that prevent backflow. As muscles around these veins contract during ordinary movement, they squeeze the blood upward through the valves and force the column of blood back to the heart.

Click here to learn more about problems and symptoms arising from venous insufficiency.