Factor XIIa (Last Updated - 3/1/2005)

-makes up a step of the intrinsic pathway
-formed via activation of Factor XII --> this reaction is catalyzed by:
     1) Prekallikrein
     2) High Molecular Weight Kininogen (HMWK)
     3) & Kaolin
-Factor XIIa (along with Factor IIa (thrombin)) in turn catalyzes the activation of Factor XI to XIa

-click here to view an image of the clotting cascade

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References:

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