| [ Summary ] |
PTH has evolved in terrestrial animals as a defense mechanism against the loss of calcium and the resultant hypocalcemia. To maintain the in-out balance of body calcium, PTH, acting on the kidney, enhances the tubular reabsorption of calcium and stimulates the production of active vitamin D which enhances the intestinal absorption of calcium. The effect exerted by PTH on bone maintains the equilibrium of calcium between bone and the extracellular fluid, thereby preventing diminution of the plasma level of calcium. Over the post several years, the main components involved in the action of PTH have been clarified at the molecular level. The genes encoding PTH, the calcium-sensitive receptor and the PTH/PTHrP receptor have been cloned, and this progress has resulted in clarification of the pathogenesis of many hereditary calcium disorders and bone diseases. |