Schematic representation of blood coagulation and the protein C anticoagulant system. The reactions that are presented in Figures 1 to 3 are here summarized in a schematic form. In addition to the FVIIa/TF-triggered initiation of coagulation, the scheme indicates the activation of FXI by either the contact phase system (CP) or by thrombin. The figure also highlights the dual role of thrombin as both a procoagulant and anticoagulant factor. Illustration by Marie Dauenheimer.