A glycoprotein synthesized in liver and megakaryocytes which functions in the common pathway of coagulation. Approximately 25% of FV in blood is present in the alpha granules of platelets. When activated by Thrombin, activated Factor V (FVa) serves as a cofactor in the FXa conversion of prothrombin to Thrombin in the presence of phospholipid and calcium (prothrombinase complex). FVa is inhibited by Activated Protein C. The slide show entited Activation of Protein C by Thrombin shows the relationship amongst these components. See also the slide shows entitled Tissue Factor Pathway (Extrinsic) with Common Pathway (PT) and Intrinsic Pathway-APTT.
