Blood Clotting Process

The process by which the body prevents blood loss is referred to as coagulation. Coagulation involves the formation of a blood clot (thrombus) that prevents further bloodloss from damaged tissues, blood vessels or organs. This is a complicated process with a cellular system comprised of cells called platelets that circulate in the blood and serve to form a platelet plug over damaged vessels and a second system based upon the actions of multiple proteins (called clotting factors) that act in concert to produce a fibrin clot. These two systems work in concert to form a clot; disorders in either system can yield disorders that cause either too much or too little clotting. Platelets serve three primary functions: 1) sticking to the injured blood vessel (called platelet adherence), 2) attaching to other platelets to enlarge the forming plug (called platelet aggregation), and 3) providing support (molecules on the surface of platelets are required for many of the reactions) for the processes of the coagulation cascade. When a break in a blood vessel occurs, substances are exposed that normally are not in direct contact with the blood flow. These substances (primarily collagen and von Willebrand factor) allow the platelets to adhere to the broken surface. Once a platelet adheres to the surface, it releases chemicals that attract additional platelets to the damaged area, referred to as platelet aggregation. These two processes are the first responses to stop bleeding. The protein based system (the coagulation cascade) serves to stabilize the clot that has formed and further seal up the wound.