thrombin

Examples of thrombin in the following topics:

• Coagulation

  • The main role of the extrinsic (tissue factor) pathway is to generate a "thrombin burst," a process by which large amounts of thrombin, the final component that cleaves fibrinogen into fibrin, is released instantly.
  • In the final common pathway, prothrombin is converted to thrombin.
  • Thrombin then  cleaves fibrinogen into fibrin, which forms the mesh that binds to and strengthens the platelet plug, finishing coagulation and thus hemostasis.
  • Antithrombin: a serine protease inhibitor that degrades thrombin, Factor IXa, Factor Xa, Factor XIa, and Factor XIIa.
  • Thrombomodulin: released by the endothelium and converts thrombin into an inactive form.

• Blood Plasma

  • Fibrinogen generates fibrin when activated by the coagulant thrombin, which forms a mesh that clots blood with the assistance of a platelet plug. 
  • Normally, anticoagulants and fibrinolytics in the plasma, such as plasmin and heparin, break up fibrin clots and inactivate thrombin.
  • However, during endothelial injury, damaged cells will release tissue factor, another type of clotting factor that causes a cascade of thrombin production that will overpower the anticoagulants and cause a clotting response.

• Fibrinolysis

  • Plasmin activity is also reduced by thrombin-activatable fibrinolysis inhibitor (TAFI), which modifies fibrin to make it more resistant to the tPA-mediated plasminogen.
  • Heparin is a fast-acting anticoagulant produced by the body and used as a drug which inhibits the activity of thrombin.
  • Warfarin inhibits vitamin K cofactor activation during the coagulation cascade, and citrates chelate calcium to prevent prothrombin activation into thrombin.

• Role of Vitamin K

  • This enzyme is called tenase, and converts prothrombin to thrombin.
  • Calcium mediates the binding of the tenase enzyme complexes (via the terminal gamma-carboxy residues on FXa and FIXa) to the phospholipid surfaces expressed by platelets, which in turn activates prothrombin to produce thrombin, which then produces fibrin from fibrinogen.
  • Blood coagulation pathways in vivo showing the central role played by thrombin.

• Anticoagulants

  • It works by activating antithrombin III, which blocks thrombin from clotting blood.
  • Another type of anticoagulant is the direct thrombin inhibitor.

• Overview of Hemostasis

  • Prothrombin, thrombin, and fibrinogen are the main factors involved in the outcome of the coagulation cascade.
  • When blood vessels are damaged, vessels and nearby platelets are stimulated to release a substance called prothrombin activator, which in turn activates the conversion of prothrombin, a plasma protein, into an enzyme called thrombin.
  • Thrombin facilitates the conversion of a soluble plasma protein called fibrinogen into long, insoluble fibers or threads of the protein, fibrin.

• Tonsillectomy

  • Bleeding is stopped with electrocautery, ligation of sutures, and the topical use of thrombin, a protein that induces blood clotting.

• Platelets

  • During coagulation, they release factors that increase local platelet aggregation (thromboxane A), mediate inflammation (serotonin), and promote blood coagulation through increasing thrombin and fibrin (thromboplastin).