Veins normally function to return blood to the heart. Valves in the veins close after blood travels up the vein, preventing blood from backing up (refluxing) down the vein. Valves can become abnormal, or incompetent for a variety of reasons, including trauma, pregnancy, or hereditary factors.
Once a valve becomes incompetent, the vein below the valve is exposed to higher pressure, and can become larger (dilate). Other valves and veins nearby are exposed to the higher pressure and can also dilate. Varicose veins commonly appear on the legs as raised, often ropy, enlarged veins. They can cause the legs to swell, throb, and in severe cases, can lead to inflammation, ulcers and blood clots.
