Fibrinogen
Fibrinogen is the clotting element present in blood.  When blood comes out of a wound in a vessel, the fibrinogen is activated and forms fibrin, which clots the blood. Although this is fibrinogen's main job, it also forms bridges between platelets. Fibrinogen is a protein made by the liver. It is a dimer (made up of two similar units). Each unit has an alpha, beta, and gamma chain. The alpha and beta chains have a small peptide called fibrinopeptide.