Blood clotting is a normal process that occurs in the body to prevent bleeding. The body makes blood clots and then breaks them down. Under certain circumstances, the body may be unable to break down a clot, which may result in a serious health condition.
Abnormal blood clotting in the veins is related to a combination of several problems such as "sluggish" blood flow through the veins, an abnormality in clot forming factors or an injury to the blood vessel wall.
Blood clots can form in arteries or veins. Clots formed in veins are called venous clots. Veins of the legs can be classified as superficial veins (close to the surface of the skin) or deep veins (located near the bone and surrounded by muscle). Pooling, or stasis, of blood in the legs and subsequent clotting can result in varicose veins. Clots in the legs may break loose and travel to the lungs, causing pulmonary clots (or pulmonary embolism) that can result in respiratory distress, pain, and in extreme cases, death.
Thrombosis occurs when a blood clot blocks arteries from carrying oxygenated blood from the heart (arterial thrombosis) or veins from carrying oxygen-depleted blood back to the heart (venous thrombosis).
Venous thrombosis can obstruct the veins or damage their one-way valves, allowing blood to pool, which causes chronic pain, swelling, skin discoloration and skin ulcers.
Arterial thrombosis may result from arteriosclerosis, which involves hardening of the arteries where fatty or calcium deposits cause the arterial walls to thicken. This can lead to plaque instability and risk for rupture followed by thrombus.
When arterial thrombosis occurs in the coronary arteries (arteries that branch from the aorta to provide blood to the heart muscle), it can lead to heart attacks. When arterial thrombosis occurs in the brain circulation, it can lead to strokes or lack of oxygen to other organs.