What are the phases of coagulation?

Answer 1

These are the three phases:

Phase 1: Formation of prothrombin activator

The prothrombin activator is formed through intrinsic and/or extrinsic pathway. Usually it is formed by both. Its formation is triggered by tissue-damaging events and it involves a series of procoagulants. Each pathway cascades towards Factor X (i.e. the Stuart Factor) that complexes with Ca2+, platelet factor 3 (PF3), and Factor V to form the prothrombin activator.

The intrinsic pathway is triggered by negatively charged surfaces of activated platelets, collagen, and glass and it uses factors present within the blood. As for the extrinsic pathway, it is triggered by exposure to tissue factor (Factor III). The extrinsic pathway bypasses several steps of the intrinsic pathway so it is faster. Once the prothrombin activator is formed, the clot forms in 10-15 seconds.

Phase 2: Prothrombin's conversion to thrombin

The prothrombin activator catalyses the transformation of prothrombin to thrombin.

Phase 3: Fibrinogen conversion to fibrin

Thrombin (Factor II) converts soluble fibrinogen to the solid fibrin. The fibrin formed will cause the plasma to become a gel-like trap for formed elements, forming the structural basis of the clot. The thrombin along with Ca2+ activates Factor XIII to cross-link fibrin. This will strengthen and stabilise the clot.