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. Author manuscript; available in PMC: 2010 Sep 1.
Published in final edited form as: Curr Clin Pharmacol. 2009 Sep 1;4(3):172–190. doi: 10.2174/157488409789375320

Fig. 1.

Fig. 1

Regulation of Plasma Ca2+. Vitamin D cholecalciferol is formed in the skin as a result of UV irradiation or absorbed from the gut, then hydroxylated to 25(OH)D in liver. Under the influence of parathyroid hormone (PTH), 25(OH)D is further hydroxylated in kidney to 1,25(OH)2D3, the most active form of vitamin D. PTH stimulates 1,25(OH)2D3 formation. 1,25(OH)2D3 stimulates Ca2+ transport from intestine, reabsorption in renal tubules and release from bone. Calcitonin inhibits Ca2+ mobilization from bone.