Varicose veins

[Greta]

Varicose veins are abnormally enlarged superficial veins in the legs.

Varicose veins may ache or cause itching or a sensation of tiredness.
Doctors can detect varicose veins by examining the skin.
Surgery or injection therapy can remove varicose veins, but new ones often form.

(See also Overview of the Venous System.)
The precise cause of varicose veins is unknown, but the main problem is probably a weakness in the walls of superficial veins (located just under the skin). This weakness may be inherited. Over time, the weakness causes the veins to lose their elasticity. Veins stretch and become longer and wider. To fit in the same space that they occupied before they stretched, the elongated veins become convoluted. They may appear as a snakelike bulge beneath the skin.
Women may be more likely to develop varicose veins than men, and their initial occurrence may be during pregnancy. In addition, the following can contribute to the development of varicose veins in predisposed people:

Prolonged standing
Obesity
Increasing age

More important than the elongation is the widening of the veins, which causes the valve flaps (cusps) to separate. When the person stands, the blood is pulled backward by gravity and is not stopped because the valve cusps are separated. Thus, blood flows backward, rapidly filling the veins and causing the thin-walled, convoluted veins to enlarge even more. Some of the connecting veins, which normally allow blood to flow only from the superficial veins into the deep veins, also enlarge. If they enlarge, their valve cusps also separate. Consequently, blood squirts backward into the superficial veins when the muscles squeeze the deep veins, causing the superficial veins to stretch further.
Many people with varicose veins also have spider veins, which are enlarged capillaries.

[Sarah]

a condition in which the tubes that carry blood, esp. those in the legs, are swollen and can be seen on the skin: