coagulation

the natural process in which BLOOD is converted from a liquid to a semi - solid state to arrest bleeding ( HAEMORRHAGE ). A substance known as prothrombin and calcium are normally present in the blood, and the ENZYME thromboplastin is present in the PLATELETS . When bleeding occurs, thromboplastin is released and prothrombin and calcium are converted by the enzyme into thrombin. A soluble protein called FIBRINOGEN is always present in the blood and is converted by thrombin into FIBRIN , which is the final stage in the coagulation process. A fibrous meshwork or clot is produced, consisting of fibrin and blood cells, which seals off the damaged blood vessel. Normally, thromboplastin is not released and so a clot cannot form. The coagulation or clotting time is the time taken for blood to clot and is normally between three and eight minutes.