Fibrinogen is a glycoprotein made and secreted into the blood primarily by liver hepatocyte cells. Endothelium cells also make what appears to be small amounts of fibrinogen but this fibrinogen has not been fully characterized; blood platelets and their precursors, bone marrow megakaryocytes, although once thought to make fibrinogen, are now known to take up and store but not make the glycoprotein.[1][10] The final secreted, hepatocyte-derived glycoprotein is made of two trimers each of which is composed of three polypeptide chains, Aα (also termed α) encoded by the FGA gene, Bβ (also termed β) encoded by the FGB gene, and γ encoded by the FGG gene.