How do veins work?

 

Veins are part of the circulatory system that transports blood throughout the body. With each heart beat oxygen-rich blood is pumped to all of the organs of the body including the legs. Large arteries branch into smaller and smaller arteries until the blood is passed into capillaries that allow the exchange of oxygen with tissues. The capillaries then come back together to form tiny veins that connect into larger and larger veins to return the deoxygenated blood back to the heart.

 

The veins of the legs return the blood from the legs to the heart, but they have a problem that the rest of the body’s veins do not have to overcome: the effect of gravity. In order to overcome the force of gravity, the legs have two special features to propel the blood upward and to prevent it from flowing back down the leg veins.

 

The first special feature of the legs is the propulsive force of the foot and calf pumps. When we step on the foot it squeezes blood out of the foot and up the leg. At the same time the contraction of the calf muscles squeezes blood out of the leg and sends in to the heart. These forces are remarkably effective in returning blood up the leg. This is why people unconsciously shift their weight from side to side when standing.

 

The second special feature of the leg veins is that they have one-way valves spaced every few inches apart that work automatically. The valves open when the blood is going up and close as soon as gravity starts to pull the blood back down. Most vein disease is due to failure of the vein valves.

 

There are three types of veins in the legs: deep, superficial and perforating. Deep inside the leg and within the muscle bundle of the leg are the deep veins. These veins are very well protected and seldom cause problems unless a patient develops a deep vein blood clot (DVT). The deep veins carry 90% of the blood back up the leg and run parallel to the bones.

 

Outside of the muscle bundle and under the skin are the superficial veins that carry only 10% of the blood and also run parallel to the bones. Connecting the superficial and deep veins are about 150 perforating veins that run perpendicular to the bones and have valves directing flow from the superficial veins into the deep veins.

 

The largest superficial veins are called saphenous veins. The longest vein in the leg is the great saphenous vein (GSV) which collects blood from the inside of the foot and travels up the inside of the leg until it joins the deep system at the groin. This is the most common saphenous vein to fail because it is so long. The small saphenous vein (SSV) collects blood from the outer foot and tracks straight up the back of the calf until it empties into the deep veins, usually just above the knee. The anterior great saphenous vein (AGSV) is found in about 30-40% of patients and drains the front of the thigh.

 

Most patients with significant vein disease have failure of one or more of the valves in the saphenous veins or in a perforating vein. These problems can be effectively treated with the modern office-based outpatient treatments at ERVC.

 

Clovis E. Manley, MD

Evansville Regional Vein Center