**6. The cell-based model**

The five steps of this model are initiation, amplification, propagation, stabilisation and inhibition of further coagulation (7). In health, 1% of circulating FVII is in the active form.

Blue, Red and Purple correspond respectively to Intrinsic, Extrinsic and Common Pathways of the Classic Coagulaton Cascade. Thrombin has a key role throughout, hence is shown in yellow. TF = Tissue Factor. vWF = von Willebrand Factor. TAFI = Thrombin Activated Thrombolysis Inhibitor. TFPI = Tissue Factor Pathway Inhibitor.

Fig. 3. The Cell-Based Model of Coagulation

The intrinsic and extrinsic pathways both lead to activation of FX. FXa, FVa and Ca2+ activate prothrombin (FII) to form thrombin (FIIa). Thrombin has several actions: it activates fibrinogen (FI) to yield fibrin monomers; it amplifies the coagulation process by activating further prothrombin, FV and FVIII; it activates FXIII whose active form promotes cross-linking of fibrin monomers to form stable polymers; (as discussed later in the cell-based model, it also participates in processes that temper coagulation to avoid overwhelming pathological thrombosis.) The common pathway thus yields a mesh of covalently cross-linked fibrin strands and entrapped red blood cells, which form a stable blood clot. Disorders of the common pathway will affect tests of the intrinsic and extrinsic

The five steps of this model are initiation, amplification, propagation, stabilisation and inhibition of further coagulation (7). In health, 1% of circulating FVII is in the active form.

Blue, Red and Purple correspond respectively to Intrinsic, Extrinsic and Common Pathways of the Classic Coagulaton Cascade. Thrombin has a key role throughout, hence is shown in yellow. TF = Tissue Factor. vWF = von Willebrand Factor. TAFI = Thrombin Activated Thrombolysis Inhibitor. TFPI

**5. The common pathway** 

**6. The cell-based model** 

= Tissue Factor Pathway Inhibitor.

Fig. 3. The Cell-Based Model of Coagulation

pathways.

