Which of the following is the earliest event in the clotting cascade?
The clotting cascade consists of a series of ordered enzymatic steps whose end result is the formation of a clot. There are two limbs of the clotting cascade: the extrinsic pathway and the intrinsic pathway. The extrinsic pathway relies on the exposure of tissue factor by an injury, which then activates Factor VII, the most abundant of the clotting factors. The intrinsic pathway stas when Factor XII, an inactive serine protease encounters exposed collagen from an injured blood vessel. Factor XII is transformed into an activated serine protease. Activated Factor XII cleaves inactive Factor XI into activated Factor XI. This in turn cleaves the inactive form of Factor IX, and the activated Factor IX transforms inactive Factor VII to its active form. Later events in the actual formation of the clot involve platelets, von Willebrand factor, calcium interacting with endothelial surfaces, and formation of D-dimers Ref: Freedman J.E., Loscalzo J. (2012). Chapter 117. Aerial and Venous Thrombosis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.
Binding of platelets to red blood cells
Binding of vitamin K to endothelial cell surfaces
Release of tissue factor by damaged vessels
Secretion of von Willebrand factor by platelets