June 24, 2017

Blood Clots

What causes blood clots (blood clots in veins or arteries)?

Blood clots form when there is damage to the lining of a blood vessel, either an artery or a vein. The damage may be obvious, such as a cut or laceration, or may not be visible to the naked eye. Blood also will begin to clot if it stops moving, and becomes stagnant, or in diseases that cause the blood to clot abnormally.

Blood clots in a vein (venous thrombosis) occur when a person becomes immobilized and muscles are not contracting to push blood back to the heart. This stagnant blood begins to form small clots along the walls of the vein. This initial clot can gradually grow to partially or completely occlude or block the vein and prevent blood from returning to the heart.

An analogy to this process is a slow moving river. Over time, weeds and algae start to accumulate along the banks of the river where the water flows more slowly. Gradually, as the weeds start to grow, they begin to invade the center of the river because they can withstand the pressure of the oncoming water flow.

Blood clots in an artery (arterial thrombi) occur by a different mechanism. For those with atherosclerotic disease, plaque deposits form along the lining of the artery and grow, which causes the vessel to narrow. This disease process may cause

If a plaque ruptures, a blood clot can form at the site of that rupture and can completely or partially occlude the blood flow at that point.

What causes blood clots (blood clots in the heart and medical problems)?

Blood clots in the heart: In atrial fibrillation, the upper chamber (atrium) of the heart does not beat in an organized manner. Instead, it jiggles, and blood tends to become stagnant along the walls of the atrium. Over time, this may cause small blood clots to form. Clots also can form in the ventricle after a heart attack when part of the heart muscle is injured and unable to contract normally. Since the damaged area doesn't contract with the rest of the heart, blood can start to pool or stagnate, leading to clot formation.

Blood leaking out of a blood vessel: Blood clots can form when blood leaks out of a blood vessel, and this process can be very beneficial because the clot helps stop further bleeding at the site of injury. A few examples of how bleeding is controlled by the body's clotting mechanism are

Blood clots causing other medical problems: Sometimes, normal blood clotting can cause medical problems because of its location. For example, blood in the urine may occur from any of a variety of reasons (such as infection, trauma, or tumor/cancer), and clots may form over the urethra, the tube that empties the bladder, preventing the bladder from emptying, causing urinary retention.

Clot formation in the uterus may cause pain when the clots are passed through the cervix and can lead to vaginal bleeding, either as part of menstruation or as abnormal vaginal bleeding (menorrhagia, dysmenorrhea).

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Reviewed on 10/28/2016
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