Fig. (9) Diagram of PTH synthesis and secretion in the parathyroid chief cell. The deactivation of calcium-sensing receptor (CaR) stimulates synthesis of prepro PTH, which is rapidly converted to pro PTH. Pro PTH is transported from endoplasmic reticulum to Golgi complex, where it is converted to active PTH and packaged into secretory granules. Under certain conditions, PTH is released to extracellular space.