The heart pumps blood into the arterial system. It travels to the legs under pressure through a system of arteries that becomes smaller and smaller as it progresses towards the smallest arteries called capillaries. There, Oxygen and nutrients are transferred into the cells while wastes are removed. The blood is then returned through tiny veins that become progressively larger as they move away from the tissue and drain towards the heart. The heart does not pump blood out of the legs. Rather, blood is moved through the veins by contraction of the muscles which surround them. As each vein is compressed, the blood moves in one direction towards the heart. This one-way flow is maintained by valves located at intervals along the vein which are designed to only allow the blood to flow one way, back towards the heart.

There are two systems of veins in the legs, the surface or superficial veins and the deep veins. The superficial veins lie just under the skin. The deep veins lie within the large muscles of the leg. The two vein systems are connected by short veins called perforator veins. Perforator veins are called this because they perforate the thick coating or fascia around the large leg muscles to reach the deep veins. The system resembles a ladder with the sides being the superficial and deep vein systems and the wrungs being the perforator veins. All of the veins have valves to maintain one way flow. The superficial veins drain into the deep system both directly and through the perforator veins. Each perforator vein has an important valve that allows blood to flow one way from the skin into the deep veins. When you walk or exercise, the calf muscles squeeze the large, deep veins and pump the blood out of the legs towards the heart. Valves in the deep veins keep the blood flowing in one direction toward the heart. The valves in the perforator veins snap shut when the deep veins are squeezed to prevent back flow of high pressure blood through the perforator veins to the delicate skin veins.

The venous system of the legs is particularly well designed to overcome the effects of gravity and pump blood out of the legs as long as the veins are functioning normally. When the valves in the superficial and deep veins cease to function, gravity can reverse the vein flow and move the blood back towards the feet when the leg is at rest. This restricts venous drainage and results in increased blood pressure in the surface veins of the leg. When valves in the perforator veins become incompetent, high-pressure blood from the deep system flows towards the skin and produces very high blood pressure of the surface veins. Incompetent veins in the superficial and deep veins can produce spider veins, varicose veins, leg swelling, leg ulcers and serious infection. Both of these problems often are present in a patient with advanced venous disease.

One of the first signs of venous disease and the need for varicose treatment is often distention of the most delicate skin veins or “spider veins.” As the disease progresses, larger veins dilate becoming varicose veins. These distended veins often place pressure on nerves resulting in aching pain, night cramps and unusual sensations like "water flowing down the legs" or "crawling feelings on the skin." The dilated veins often leak water into the surrounding tissues resulting in swelling or edema. Blood may leak out as the pressure increases resulting in brownish skin discoloration. The high pressure is also transmitted to the capillary beds. This makes it difficult for blood to flow across the capillaries, disrupting the exchange of nutrients and wastes. The tissues of the leg respond first by thickening of the skin and finally by dying resulting in a venous leg ulcer. Another serious consequence of this type of venous disease is infection of the skin or cellulitis.

There are many reasons why veins dilate, become incompetent and possibly lead to chronic venous insufficiency. Some of these risk factors include advancing age, certain occupations that require standing for prolonged periods and pregnancy.