Current concepts of coagulation.

Coagulation is a complex enzymatic process involving the sequential activation of a series of potent proenzymes. The thrombin generated by this cascade serves many functions, including the conversion of fibrinogen to fibrin. This process is closely regulated and normally confined to sites of vascular damage. In subsequent portions of this symposium, we will be dealing with various pathologic states and how they affect the system. In understanding the pathophysiology of these disorders, it is helpful to keep in mind which component(s) of the system is primarily affected. Some disorders, such as von Willebrand's syndrome, are characterized by a defect in only one component, and the clinical manifestations of this disorder are readily understood. Many of the acquired disorders affect multiple components, including both the procoagulant system and the regulatory system. In these conditions, the clinical manifestations can be difficult to predict and can vary from patient to patient. An understanding of how the various components of the hemostatic system interact should help clarify many of these confusing conditions.