Coagulation (clotting) : Coagulation is a complex process by which blood changes from a liquid to gel or clot, It results in the cessation of blood loss from a damaged vessel ( hemostasis), followed by repair. The mechanism of coagulation is initiated by blood platelets. Platelets produce a substance that combines with calcium ions in the blood to form thromboplastin, which in turn converts the protein prothrombin into thrombin in a complex series of reactions, involves activation, adhesion, and aggregation of platelets along with deposition and maturation of fibrin . (Thrombin, a proteolytic enzyme, converts fibrinogen, a protein substance, into fibrin). Disorders of coagulation are disease states which can result in bleeding (hemorrhage or bruising) or obstructive clotting (thrombosis)
Thrombus : A thrombus, is a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus, aggregated platelets that form a platelet plug, and a mesh of cross-linked fibrin protein. A thrombus is a healthy response to injury intended to prevent bleeding, an embolism is a clot that travels from the site where it formed to another location in the body. Thrombi or emboli can lodge in a blood vessel and block the flow of blood in that location depriving tissues of normal blood flow and oxygen. but can be harmful in thrombosis, when clots obstruct blood flow through healthy blood vessels.