Coagulation - Intrinsic and Extrinsic Pathways

The key event triggering the extrinsic pathway is the exposure of blood to tissue factor (or thromboplastin), a protein found on the membrane of cells, such as fibroblasts in the sub-endothelial tissue. FVII and tissue factor / FIXa complexes activate both FIX and FX. The remainder of the pathway is common to both extrinsic and intrinsic systems.