The Endocrine System, Parathyroid Hormone, Calcitonin, Calcium and Phosphate Metabolism, Vitamin D, Bone, and Teeth
There are 2 regulatory hormones, Parathyroid Hormone and calcitonin. CALCIUM AND PHOSPHATE IN THE EXTRACELLULAR FLUID AND THE PLASMA FUNCTION OF VITAMIN D. CONTROL OF VITAMIN D FORMATION The active form of Vitamin D 1,25-dihydroxycholecalceferol is regulated via the following steps In the skin: 7-dehyrocholesterol is conveted by UV light to Vitamin D3 In the liver: Vitamin D3 is converted to 25-hydroxycholecalciferol In the cortex of the kidney: 25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalceferol in reaction stimulated and controlled by PTH. PTH formation is stimulated by a reduction in ECF Calcium concentration, formation of 1,25-dihyroxycholecalcepherol also increases when Calium concentration in the ECF drops GASTROINTESTINAL CALCIUM ABSORPTION - 1,25-DIHYDROXYCHOLECALCIFEROL stimulates the intestinal epithelium of the small intestine to form calcium binding protein, calcium stimulated ATPase and Alkaline phosphatase, all which promote absor