MICROANATOMY

Detailed explanation-1: -Fibrinogen is a soluble macromolecule, but forms an insoluble clot or gel on conversion to fibrin by the action of the serine protease thrombin, which is activated by a cascade of enzymatic reactions triggered by vessel wall injury, activated blood cells, or a foreign surface (Fig.

Detailed explanation-2: -Once fibrinogen is released into blood, it circulates until thrombin cleaves fibrinopeptides from the A and B chains (FpA and FpB, respectively) to form fibrin monomers.

Detailed explanation-3: -Factor IIa (thrombin) goes on to activate fibrinogen into fibrin. Thrombin also goes on to activate other factors in the intrinsic pathway (factor XI) as well as cofactors V and VIII and factor XIII.

Detailed explanation-4: -Hirudin binds to thrombin and inhibits the conversion of fibrinogen to fibrin.

Detailed explanation-5: -When tissue damage results in bleeding, fibrinogen is converted at the wound into fibrin by the action of thrombin, a clotting enzyme.