The circulatory system must be self-sealing; otherwise continued blood loss from even the smallest injury would be life threatening. Normally, all but the most catastrophic bleeding is rapidly stopped, by a process known as Coagulation, through several sequential processes. Coagulation involves the formation of a blood clot (thrombus) that prevents further blood loss 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 [...]