Translations:Calcitriol/17/en

Calcitriol acts in concert with parathyroid hormone (PTH) in all three of these roles. For instance, PTH also indirectly stimulates osteoclasts. However, the main effect of PTH is to increase the rate at which the kidneys excrete inorganic phosphate (P_i), the counterion of Ca²⁺
. The resulting decrease in serum phosphate causes hydroxyapatite (Ca₅(PO₄)₃OH) to dissolve out of bone, thus increasing serum calcium. PTH also stimulates the production of calcitriol (see below).