"Osteolysis is a rapid phase of calcium and phosphate removal from bones that increases progressively for several hours. The osteocytes within the bone, as well as the osteocytes and osteoblasts on the bone surface, are interconnected by long filmy processes called the osteocytic membrane system. Parathyroid hormone binds to receptor proteins on the cell membranes of osteocytes and osteoblasts, thereby stimulating calcium pumps in the osteocytic membrane. Calcium diffuses from the bone fluid into the cell membrane, then out of the cells through pumps on the other side of the cells into the extracellular fluid. This is the mechanism by which calcium phosphate salts are removed from amorphous bone crystals 1,2."
"Osteoclast formation and activation is, by contradistinction, a much slower phase that continues for weeks to months. Osteoclast progenitor cells are devoid of receptor proteins for parathyroid hormone; however, they express the RANK (receptor activator of nuclear factor-κ B) cell surface receptor. PTH-activated osteoblasts express the surface protein RANKL (RANK ligand). RANKL ligation to RANK activates a series of downstream signalling pathways that culminate in osteoclast maturation and activation 1,2."
"Osteoclast formation and activation is, by contradistinction, a much slower phase that continues for weeks to months. Osteoclast progenitor cells are devoid of receptor proteins for parathyroid hormone; however, they express the RANK (receptor activator of nuclear factor-κ B) cell surface receptor. PTH-activated osteoblasts express the surface protein RANKL (RANK ligand). RANKL ligation to RANK activates a series of downstream signalling pathways that culminate in osteoclast maturation and activation 1,2."
"Osteoclast formation and activation is, by contradistinction, a much slower phase that continues for weeks to months. Osteoclast progenitor cells are devoid of receptor proteins for parathyroid hormone; however, they express the RANK (receptor activator of nuclear factor-κ B) cell surface receptor. PTH-activated osteoblasts express the surface protein RANKL (RANK ligand). RANKL ligation to RANK activates a series of downstream signalling pathways that culminate in osteoclast maturation and activation 1,2."
"Osteoclast formation and activation is, by contradistinction, a much slower phase that continues for weeks to months. Osteoclast progenitor cells are devoid of receptor proteins for parathyroid hormone; however, they express the RANK (receptor activator of nuclear factor-κ B) cell surface receptor. PTH-activated osteoblasts express the surface protein RANKL (RANK ligand). RANKL ligation to RANK activates a series of downstream signalling pathways that culminate in osteoclast maturation and activation 1,2."
Expected headings
"Physiology"
"Calcium and phosphate absorption from bone"
"Calcium excretion and phosphate excretion"
"Stimulation of 1,25-cholecalciferol synthesis"
"Osteoclast formation and activation is, by contradistinction, a much slower phase that continues for weeks to months. Osteoclast progenitor cells are devoid of receptor proteins for parathyroid hormone; however, they express the RANK (receptor activator of nuclear factor-κ B) cell surface receptor. PTH-activated osteoblasts express the surface protein RANKL (RANK ligand). RANKL ligation to RANK activates a series of downstream signalling pathways that culminate in osteoclast maturation and activation 1,2."
"Cholecalciferol (vitamin D3) is synthesised in the skin. It is converted to 25-hydroxycholecalciferol in the liver. In the kidneys, parathyroid hormone stimulates its conversion to 1,25-dihydroxycholecalciferol, which, in turn, promotes intestinal absorption of calcium and phosphate 1,2."