When blood vessels are cut or damaged, the loss of blood from the system must be stopped before shock and possible death occur. This is accomplished by solidification of the blood, a process called coagulation or clotting. A blood clot consists of a plug of platelets enmeshed in a network of insoluble fibrin molecules. The Extrinsic Pathway Damaged cells display a surface protein called tissue factor (TF) Tissue factor binds to activated Factor 7. The TF-7 heterodimer is a protease with two substrates: Factor 9 and Factor 10 The Intrinsic Pathway Factor 12 (also called the Hageman factor) circulates in the blood. If blood escapes into tissue spaces (e.g., as a result of an injury), contact with collagens in the tissue space activates Factor 12. Activated Factor 12 is a serine protease that activates Factor 11 which, in turn, activates Factor 9 which, in turn, activates Factor 10.