blood coagulation

blood coagulation The aggregation of blood platelets and other blood elements to form a semisolid clot. Coagulation occurs under the influence of the clotting factors fibrinogen, prothrombin, and thrombin, which are normally activated in response to injury. Working together, these substances thicken the blood and produce fibrin, a substance that closes off the wound. When blood coagulates abnormally, dangerous blood clots can enter the bloodstream.