Hemophilia

The normal mechanism for blood clotting is a complex series of events involving the interaction of the injured blood vessel, blood cells called platelets, and over 20 different proteins which also circulate in the blood.

When a blood vessel is injured in a way to cause bleeding, platelets collect over the injured area, and form a temporary plug to prevent further bleeding. This temporary plug, however, is too disorganized to serve as a long-term solution, so a series of chemical events result in the formation of a more reliable plug. The final plug involves tightly woven fibers of a material called fibrin. The production of fibrin requires the interaction of a variety of chemicals, in particular a series of proteins which are called clotting factors. At least 13 different clotting factors have been identified.

The clotting cascade, as it is usually called, is the series of events required to form the final fibrin clot. The cascade uses a technique called amplification to rapidly produce the proper sized fibrin clot from the small number of molecules initially activated by the injury.