once massive quantities of PTH area unit injected, the calcium ion concentration within the blood begins to rise at intervals minutes, long before any new bone cells are often developed. microscopic anatomy and physical studies have shown that PTH causes removal of bone salts from two areas within the bone: (1) from the bone matrix within the vicinity of the osteocytes lying at intervals the bone itself and (2) within the section of the osteoblasts on the bone surface. One doesn’t typically think about either osteoblasts or osteocytes functioning to cause bone salt absorption, because each these varieties of cells area unit osteoblastic in nature and usually related to bone deposition and its calcification. However, studies have shown that the osteoblasts and osteocytes type a system of interconnected cells that spreads at some point of the bone and over all the bone surfaces except the tiny surface areas adjacent to the osteoclasts. In fact, long, filmy processes extend from bone cell to bone cell throughout the bone structure, and these processes additionally connect with the surface osteocytes and osteoblasts.
This intensive system is named the osteocytic membrane system, and it’s believed to produce a membrane that separates the bone itself from the animate thing fluid. Between the osteocytic membrane and therefore the bone is a small quantity of bone fluid. Experiments counsel that the osteocytic membrane pumps metal ions from the bone fluid into the humor, creating a calcium ion concentration within the bone fluid just one third that within the humor. once the osteocytic pump becomes too activated, the bone fluid metal concentration falls even lower, and calcium phosphate salts area unit then absorbed from the bone. This impact is named lysis, and it happens without absorption of the bone’s fibrous and gel matrix. once the pump is inactivated, the bone fluid metal concentration rises to the next level, and phosphate salts area unit redeposited within the matrix. But wherever will PTH work into this picture? 1st, the cell membranes of each the osteoblasts and therefore the osteocytes have receptor proteins for binding PTH. PTH will activate the metal pump powerfully, thereby causing fast removal of phosphate salts from those amorphous bone crystals that lie close to the cells. PTH is believed to stimulate this pump by increasing the metal porosity of the bone fluid facet of the osteocytic membrane, therefore permitting metal ions to diffuse into the membrane cells from the bone fluid. Then the metal pump on the opposite facet of the cell membrane transfers the metal ions the remainder of the way into the humor.