blood coagulation

Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel forming a blood clot. The process involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin. Coagulation results in hemostasis, the cessation of blood loss from a damaged vessel, allowing repair.

Coagulation begins almost instantly after an injury to the endothelium that lines a blood vessel. Exposure of blood to the subendothelial space initiates two processes: changes in platelets, and the exposure of subendothelial platelet tissue factor to coagulation factor VII, which ultimately leads to cross-linked fibrin formation. Platelets immediately form a plug at the site of injury; this is called primary hemostasis. Secondary hemostasis occurs simultaneously: additional coagulation factors beyond factor VII (listed below) respond in a cascade to form fibrin strands, which strengthen the platelet plug.