title: Vitamin D endocrinology.
abstract: Current status of our understanding of the metabolism of vitamin D and its implications in metabolic bone disease is reviewed. The details of metabolism of vitamin D3 to 25-hydroxyvitamin D3 in the liver and its further conversion in the kidneys to either 1,25-dihydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 are presented. The latter conversions are regulated by the vitamin D status, serum calcium through the parathyroid gland system, and serum inorganic phosphorus concentration. The 1,25-dihydroxyvitamin D3 can now be regarded as a calcium- and a phosphate-mobilizing hormone and must be considered as one of the most important serum calcium-regulating hormones. Disruption of the vitamin D metabolic sequence or the signal system for 1,25-dihydroxyvitamin D3 results in several bone and calcium metabolism disorders such as renal osteodystrophy, hypoparathyroidism, pseudohypoparathyroidism, and vitamin D-dependency rickets. The use of the synthetic analogs of 1,25-dihydroxyvitamin D3 as well as 1,25-dihydroxyvitamin D3 itself in the management of these disease states is discussed.
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood / Q000378:metabolism; D002762:Cholecalciferol / Q000378:metabolism / Q000502:physiology / Q000627:therapeutic use; D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000503:physiopathology; D004702:Endocrine Glands / Q000503:physiopathology*; D004872:Ergocalciferols / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D006962:Hyperparathyroidism, Secondary / Q000503:physiopathology; D007408:Intestinal Absorption; D007668:Kidney / Q000201:enzymology; D010710:Phosphates / Q000097:blood; D014807:Vitamin D / Q000378:metabolism / Q000502:physiology*
chemical_list: D004872:Ergocalciferols; D010710:Phosphates; D014807:Vitamin D; D002762:Cholecalciferol; D002118:Calcium