Secondary hemostasis stabilizes the weak platelet plug that is produced by primary hemostasis via the coagulation cascade. The coagulation cascade produces thrombin, which converts fibrinogen in the platelet plug to fibrin. Cross linking of fibrin occurs, which stabilizes the platelet-fibrin thrombus. Factors of the coagulation cascade are produced by the liver in an inactive state. Activation requires exposure to an activating substance, calcium, and platelets.