Figure 3.

Platelet and Endothelial Cell Interactions in Hemostasis. (A) Injured endothelial cells elaborate tissue factor (TF) with consequent activation of the coagulation cascade and generation of thrombin (F.IIa). Thrombin activates platelets which subsequently adhere to injured endothelial cells and to subendothelial collagen via specific receptors on endothelial and platelet membrane and via von Willebrand [vWf]. Additional platelets are recruited to the area of injury with subsequent formation of platelet plug. (B) Thrombin generation results in activation of coagulation and fibrinolysis. Thrombin bound to endothelial cell surface thrombomodulin catalyzes the conversion of Protein C bound to endothelial cell protein C receptor (EPCR). Activated Protein C then down regulates further thrombin formation by inactivating activated F.VIII and activated F.V. Additionally, Thrombomodulin bound thrombin catalyzes Thrombin Activatable Fibrinolysis Inhibitor (TAFI) to its active form (TAFIa) which damps the activation of fibrinolysis thereby promoting clot formation and stability.