thrombin

(noun)

The end product of the coagulation cascade, which cleaves fibrin from fibrinogen.

Related Terms

  • endothelium
  • fibrin

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).
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