Frequently Asked Questions

Normal Venous Circulation
Q:  What is the main function of the deep venous circulation?

A: The deep venous circulation returns blood from the tissues (the extremity) to the heart. To achieve this goal, veins are designed for low pressure, are enclosed within contracting muscle, and contain valves that prevent backflow (reflux).

Q:  What characteristics do veins have that enable them to return blood to the heart?

A:  Veins have (a) valves that prevent backward flow of blood and (b) thin walls capable of expanding to a much larger diameter. The fact that veins are located within contracting muscle is another significant third factor, but is not intrinsic to the vein wall.

Q:  At what three sites does a peripheral pump mechanism contribute to the return flow of blood from the extremity toward the heart? Which is the main contributor?

A:  The thigh, calf, and foot are the three main sites, and the calf is the main contributor.

Q:  How much of the blood contained within the deep veins of the calf is expelled by calf contraction?

A: Sixty percent of the blood is expelled into the popliteal vein (below the knee) with a single, normal calf muscle contraction.

For more information, read Chapter 1: Normal Venous Circulation.