Relationships Between Platelets and Coagulation Factors in Hemostasis

In this review the relations between platelets and coagulation factors in hemo­ stasis are considered. The traditional view of hemostasis implies that platelets aggregate to form a hemostatic plug in wounds prior to the coagulation reactions which lead to fibrin formation. In this view the platelet plug merely provides a phospholipid surface on which the coagulation reactions take place. In contrast, we present findings that suggest much closer interactions. between platelets and coagulation factors. For example, thrombin is formed very early in hemostasis; thus a coagulation factor may be involved in early reactions of platelet aggre­ gation. Also, activation of coagulation factors may take place on the platelet surface on specific sites or receptors that direct the coagulation reactions; that is, platelets may provide more than a simple phospholipid surface to the coag­ ulation sequence.