Fibrin

Fibrin is an insoluble thread-like molecule. Fibrin is involved in the third and final stage of haemostasis (the stopping of haemorrhage), when the blood forms a solid gel (a clot), from a liquid. During blood coagulation, thrombin converts soluble fibrinogen into fibrin monomers, and then the monomers undergo polymerisation to form the clot. This involves active factor XIII and Calcium ions.