The Biosynthesis, Intracellular Processing, and Secretion of Parathormone

Publisher Website
Google Scholar
Abstract
EVOLUTIONARY pressures have brought into being a remarkable homeostatic mechanism in higher animals for the control of ionized calcium in the extracellular fluid. This system uses parathormone (PTH), the subject of this review, and two other hormones, calcitonin (1) and active metabolites of vitamin D3 (2–4), which in concert act on bone, kidney, and intestine to maintain the concentration of ionized serum calcium at its physiological set point, about 1.3 mM. This represents about one half of the total (ionized and bound) calcium in serum (5, 6). The parathyroid gland is the principal agent in this system since it responds to the moment to moment fluctuations of calcium in the extracellular fluids. When the concentration of ionized calcium in the blood perfusing the parathyroid drops below its set point, the gland immediately releases more PTH to the circulation (7). The hormone acts directly on osteoclasts to enhance resorption of bone and to bring the calcium and phosphate of the bone mineral into the circulation (8, 9); it acts on osteoblasts to inhibit new bone formation (9); and it acts on the kidney to increase the retention of calcium (8), the excretion of phosphate (10–13), and the formation of 1,25-dihydroxycholecalciferol (2, 14).

This publication has 0 references indexed in Scilit: