in Body Fluids and Circulation (Cardiovascular System, Circulatory system) by

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The process that dissolves blood clot is called thrombolysis (thrombus-blood clot and lysis- to dissolve).

Degradation of fibrin clot is the function of plasmin. – It is a protease that is capable of breaking fibrin molecules/mesh.

Plasmin is produced in inactive form plasminogen in liver.

Tissue plasminogen activator (tPA) and urokinase are the agents that convert plasminogen to the active plasmin, tPA is released in the blood after several days after injury to blood vessels. This occurs because plasminogen became entrapped within the clot when it formed; as it is slowly activated, it breaks down the fibrin mesh. tPA and urokinase are themselves inhibited by Plasminogen activator inhibitor-1 and Plasminogen activator inhibitor-2 (PAI-1 and PAI-2). In contrast, plasmin further stimulates plasmin generation by producing more active forms of both Tissue plasminogen activator (tPA) and urokinase.
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The blood in our body is kept free flowing. It is only clotted when is oozed out of the vascular system. The process, which prevents blood from clotting, is the Fibrinolysis. There are two types of the process involved: the primary fibrinolysis and the secondary fibrinolysis. The Primary fibrinolysis is the normal body process of dissolving clots. The Secondary fibrinolysis is the process of breaking down of clots due to some other reason, like due to medicinal disorder, etc.

The process of fibrinolysis breaks down the coagulated blood or the fibrin clot. The Plasmin is the enzyme, which cuts the fibrin meshwork at different-different places and makes them free in circulation as the fragments. These, fragments are then cleared up the proteases or by liver and the kidney.

The Liver forms the inactive form of enzyme called as Plasminogen, which further gets converted to the active form Plasmin. It is sent into the clot for its breakdown.

The Plasminogen, which is an inactive enzyme, gets converted in to active Plasmin by t-PA (tissue plasminogen activator) and the urokinase and then the fibrinolysis occurs. The broken endothelium of the blood vessels slowly releases the t-PA in to the blood so that after the stoppage of blood from the wound the clot, which is formed, is broken down. The Plasminogen in blood released by the liver cells gets trapped in to the clot and the t-PA releasing from the slowly activates it into the Plasmin and thus the fibrinolysis occurs.

The two enzymes Alpha 2-antiplasmin and alpha 2-macroglobulin inactivates the plasmin. Thus the plasmin activity is also reduced TAFI (thrombin-activatable fibrinolysis inhibitor). This enzyme makes fibrin more resistance to the Tissue plasminogen activator and thus inhibits the fibrinolysis.
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