Platelet-derived growth factor (PDGF) is one of the numerous growth factors that regulate cell growth and division. It is a potent mitogen for fibroblasts, smooth muscle cells and glial cells. Though PDGF is synthesized, stored, and released by platelets upon activation, it is also produced by a plethora of cells including smooth muscle cells, activated macrophages, and endothelial cells. In both mouse and human, the PDGF signalling network consists of four ligands, PDGF A-D, and two receptors, PDGF Ralpha and PDGFRbeta. All PDGFs function as secreted, disulphide-linked homodimers, but only PDGF A and B can form functional heterodimers. PDGF plays a significant role in blood vessel formation (angiogenesis), the growth of blood vessels from already-existing blood vessel tissue. Recombinant PDGF is used in medicine to help heal chronic ulcers and in orthopedic surgery and periodontistry to treat bone loss.