How Your Veins Function...

In a properly functioning venous system (below), blood flow to the heart is regulated by a series of valves in the vessel walls that open on the pulse beat and close on the "rest" beat--in effect, stair-stepping blood back to the heart.

Inactivity and certain maladies may cause the legs' venous muscle pumps to malfunction causing improper closure of the venous valves (below left). This allows blood to flow backward and veins to swell; more blood can then pool and coagulate, forming ever-enlarging clots on the vessel wall (below right).

When a clot detaches, blood flow carries it to the lungs where it causes a Pulmonary Thrombosis and quite possibly death. If the clot continues to the heart, Cardiac Thrombosis may occur with death or paralysis as a result.

If the clot does not detach at all--a questionable, best-case scenario--increased swelling may cause Venous Thrombosis or serious ulceration of the tissue surrounding the clot. In either case, medical problems can occur that require extensive surgery to correct.