Overview of Varicose Veins

Varicose veins are enlarged or expanded (dilated) veins that result from defects in the structure and function of valves in the veins. They can be classified as primary or secondary. Primary varicose veins originate in veins that are close to the skin's surface (superficial). Secondary varicose veins originate in deep veins, causing enlargement of veins close to the skin's surface.

Venous System Anatomy

The heart is the hollow, muscular organ that pumps blood throughout the body. Blood is pumped out of the heart via the largest artery (called the aorta) and supplies oxygen to organs and tissues by a network of arteries. The arteries in this network get smaller until they become capillaries, which deliver the oxygen to the cells.

As the blood leaves the capillaries, it enters the venous system. Blood in the veins is much darker in color than arterial blood because it has lost most of its oxygen. The veins start out small, but increase in size as they get closer to the heart, ending in the largest vein (called the vena cava).

There are two venous systems in the legs: the superficial veins, through which blood flows at low pressure, and the deep veins, through which blood flows at higher pressure (but less so than through the arteries).

The normal flow of blood through these systems is from the superficial venous system to the deep venous system. When this flow is reversed, varicose veins form in the superficial venous system. This reversal of blood flow often occurs as a result of a failure in the small veins that connect the two systems (called perforators).

Blood flows through arteries at a high pressure due to the muscular walls of the arteries. Veins lack the same degree of muscle and to compensate for this, the venous system has one-way valves that allow blood to flow only in one direction—toward the heart.

Without these valves, blood would pool in the lower body because of gravity. To help overcome the effects of gravity, the body relies on the leg muscles to pump the blood back to the heart. This is one of the reasons that sedentary people often develop leg swelling (edema).

Varicose veins develop when a valve in a vein leaks or fails, causing the valves below it to fail in turn. Given the lack of muscular walls in the veins, the end result is pooling of blood that causes the veins to enlarge or dilate. This pooling of blood in the veins causes the appearance of a knotted or twisted rope under the skin, usually in the legs.

Incidence and Prevalence of Varicose Veins

Varicose veins are two to three times more common in women than men. Incidence increases with age, and about 50% of people over the age of 50 have varicose veins. They often occur in the legs, but can develop in almost any part of the body. Approximately half of all patients who develop varicose veins have a family history of the condition.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 28 Jun 2007

Last Modified: 27 May 2011