The formation of fibrin involves three interconnected biochemical pathways; the intrinsic, extrinsic, and common pathways. These pathways allow for the interaction of coagulation factors via a finely tuned sequence of chemical processes, where the factors themselves control the activity of the pathway.
Most coagulation factors are stimulated and activated by the preceding factor, hence the term, "coagulation cascade." Since factor activation requires the activation of a preceding factor, a deficiency in the functionality or availability of any factor would seriously impact the effectiveness of the coagulation process. Factor deficiencies do occur, however, and often lead to impaired vascular repair and depressed hemostatic activity.
The image to the right shows a fibrin clot containing red cells (red) and platelets (blue). The fibrin strands, which are created through the process of secondary hemostasis via the coagulation cascade, are shown in yellow.