Fibrin (also called Factor Ia) is a fibrous protein involved in the clotting of blood, and is non globular. It is a fibrillar protein that's polymerised to form a "mesh" that forms a hemostatic plug or clot (in conjunction with platelets) over a wound site. Fibrin is made from fibrinogen, a soluble plasma glycoprotein that's synthesised by the liver. Processes in the coagulation cascade activate the zymogen prothrombin to the serine protease thrombin, which is responsible for converting fibrino… (More on Fibrinogen)