sentences:  These clots can block a vein and hinder blood flow.Fibrinogen is a dimeric glycoprotein, which contains two pairs of Aα-, Bβ- peptide chains and y- chains.There are two isoforms of this fibrinogen, one with two yA-chains (yA/yA) and one with a yA-chain and a y’-chain (yA,y’) When fibrinogen is cleaved by thrombin, it releases fibrinopeptide A or B. Thrombin acts on two exosites to fibrinogen.