True about calcium reabsorption in kidney ?

Ans. is 'b i.e., Major regulating factor is parathormone Calcium excretion by kidney Calcium is both filtered and reabsorbed in kidneys but not secreted. Thus renal excretion of kidney is - Renal calcium excretion = Filtered calcium - Calcium reabsorbed Normally, 99% of filtered calcium is reabsorbed in kidney. 1) PCT : Maximum calcium is reabsorbed in PCT. About 65% of filtered calcium is absorbed here. 2) Loop of Henle : About 25-30% of calcium is reabsorbed in loop of Henle (only from thick ascending limb). 3) DCT and collecting tubules : About 4-9% of calcium is reabsorbed in DCT and collecting tubules. Primary controller of renal tubular reabsroption is parathormone. It increases calcium reabsorption in Loop of Henle (thick ascending limb) and distal tubules. Vitamin D (calcitriol) and calcitonin also stimulate calcium absorption in thick ascending limb of loop of Henle and distal tubule, although these hormones are not as impoant quantitatively as PTH in reducing renal excretion.