When a blood vessel becomes damaged, the body sets off a chain of events to quickly repair it. The vessel immediately constricts so that the bloodflow slows and clotting can begin. The resulting clot, much like caulk on a pipe, seals the tissue until the vessel is healed.

Clot formation begins when injured collagen fibers in the vessel wall signal blood platelets to adhere to the wound. Before long, a group of platelets forms a temporary bandage and begins to release chemical SOS signals into the bloodstream. As a result, an enzyme called thrombin converts a dissolvable protein, fibrinogen, into long, sticky strands of fibrin. These threads weave together to form a net that holds in blood cells and platelets, sealing off the injured area. At this point, the platelets release other chemicals that aid in tissue repair. Once the injured tissue is undergoing repair, the clot dissolves as part of the healing process.

Although blood clots help heal the body, they can also cause serious harm if the system is interfered with and clotting becomes uncontrolled. Certain diseases can trigger clotting throughout the body, blocking bloodflow. More commonly, arteriosclerosis or inflammation can create a rough spot in a blood vessel where a large clot can develop; if it blocks an artery leading to the heart, a heart attack can occur. If the clot breaks off and clogs a blood vessel in a lung, that’s called a pulmonary embolism, a life-threatening condition, while a clot that affects the brain triggers a stroke. Certain drugs that prevent clotting, called anticoagulants, are often prescribed to keep these large blood clots from forming.

ADDITIONAL FACTS

  1. Some people lack a clotting factor in their blood. As a result, they can bleed profusely from even a minor injury. This condition, called hemophilia, is hereditary and most often affects males.
  2. The female hormone estrogen, often found in birth control pills, can increase the risk of clot formation.
  3. Some people have a genetic defect that increases clotting, giving them a higher risk of phlebitis (an inflamed vein plugged by a clot), heart disease, pulmonary embolism, and stroke. This defect primarily affects females and, during pregnancy, may increase the risk of premature separation of the placenta and obstetrical hemorrhage.
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