Factor IV (Calcium) (Last Updated - 3/2/2005)

-aka. calcium (2)
-involved in multiple steps of the common pathway:
     1) along with phospholipids and Factors VIIIa, IXa & VIIa catalyzes the activation of Factor X to Xa
     2) along with phospholipids and Factors Va & Xa catalyzes the activation of Factor II (Prothrombin) to IIa (Thrombin)
     3) along with Factor IIa (Thrombin) catalyzes the activation of Factor I (Fibrinogen) to Ia (Fibrin)
     4) along with Factor IIa (Thrombin) catalyzes the activation of Factor XIII to XIIIa

-click here to view an image of the clotting cascade

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References:

1) Goodman & Gilman's: The Pharmacologic Basis Of Therapeutics - 10th Edition - 2001. Chapter 55.
2) Guyton's Textbook of Medical Physiology - 10th Edition - 2000. Pg. 420.