In people with weal venous valves, gravity forces large quantities of blood back down into distal parts of the vein. the resulting back-pressure overloads the vein and pushes its wall outward. After repeated overloading, the walls lose their elasticity and became stretched and flabby.
Such dilated and tortuous veins caused by leaky valves are called varicose veins.
They may be due to heredity, mechanical factors (prolonged standing and pregnancy), or ageing.
Because a varicosed wall is not able to exert a firm resistance against the blood, blood tends to accumulate in the pouched-out area of the vein.
This causes it to bulge and also forces fluid into the surrounding tissue. Veins close to the surface of the legs, especially the saphenous veins , are highly susceptible to varicosities whereas deeper veins are not as vulnerable because surrounding skeletal muscles prevent their walls from excessive stretching.
