BLOOD COAGULATION CASCADE •. 1 trinsic pathway Blood disturbances and platelet phospholipids activate factor XII to initiate the intrinsic coagulation pathway, which leads to the activation of (factor X). X Extrinsic pathway When a vessel is injured, (tissue factor, or thromboplastin) is released from the endothelium initiating the extrinsic coagulation pathway, which leads to the activation of (factor X). TF X Common pathway (factor II, or prothrombin) is converted by factor Xa into factor IIa, or thrombin. Thrombin cleaves (factor I, or fibrinogen) to form fibrin (factor Ia), a key component of clot formation. II I Adapted from Ansell J. J Thromb Haemost. 2007;5(suppl1):60-64. Guyton AC, Hall JE. Hemostasis and blood coagulation. In: Textbook of Medical Physiology. 10th ed. Philadelphia, PA: WB Saunders Co; 2000:419-429. Moake JL. Hemostasis. In: Porter RS, Kaplan JL, Homeier BP, eds. The Merck Manual Online. http://www.merck.com/mmpe/sec11/ch134/ch134a.html. Accessed March 4, 2008. Fibrin Clot X l l Xl lX VII Ia VII TF Va II I X