Thrombin





Factor Xa / V complex converts prothrombin (Factor II) into thrombin (Factor IIa)

Actions

Actions of thrombin include:

  1. Clot formation

    • Converts fibrinogen to fibrin
      • Fibrin spontaenously aggregate
    • Activates factor XIII
      • Factor XIIIa in turn stabilise fibrin clot

  2. Positive feedback

    • Activates platelets
      • Platelet activation
      • Platelet aggregation
      • Release of platelet granules
    • More factor activations:
      • Factor V
      • Breaks the factor VIII / vWF complex
        • vWF is released
        • Factor VIII is then activated by thrombin
      • Factor XI

  3. Anti-coagulation

    • Binds to thrombomodulin at intact vessel walls
      • Thrombomodulin-thrombin complex activates protein C
      • Protein C (with co-factor protein S) inactivates factors Va and VIIIa