After its conversion from prothrombin, thrombin catalyzes the conversion of fibrinogen into a fibrin monomer. Additionally, thrombin triggers the conversion of factor XIII into factor XIIIa, forming covalent bonds that crosslink and stabilize the fibrin monomers.
Finally, thrombin feeds back into the intrinsic and common pathways, accelerating the action of factors XI, V, and VIII. As large quantities of thrombin accumulate, it begins to have a down-regulating function by inhibiting several coagulation factors and thus slowing down the cascade.
