Fibrin (Factor Ia) (Last Updated - 3/30/2005)

-formed via activation of fibrinogen (Factor I) --> this reaction is catalyzed by calcium (Factor IV) & thrombin (Factor IIa)
-fibrin in turn takes part in the formation of the fibrin plug (clot) --> this reaction is catalyzed by Factor XIIIa

-click here to view an image of the clotting cascade

-also involved in the clot lysis process --> plasmin digests fibrin (Ia)
     -has binding sites for either:
          A) Plasminogen / Plasmin
          B) Alpha-2-Anti-Plasmin
          C) Thrombolytics (Ex.) t-PA)
     -each of these compete for the Fibrin (Ia) binding site
          A) If Plasminogen / Plasmin wins --> clot lysis
          B) If Alpha-2-Anti-Plasmin wins --> clot lysis inhibited
          C) If thrombolytics win --> clot lysis

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References:

Goodman & Gilman's: The Pharmacologic Basis Of Therapeutics - 10th Edition - 2001. Chapter 55.