The function of which of the following is increased by an elevated parathyroid hormone concentration:

PTH increases phosphate excretion in the urine and thereby depresses plasma phosphate levels. This phosphaturic action is due to a decrease in reabsorption of phosphate effects on NaPi-IIa in the proximal tubules PTH acts directly on bone to increase bone resorption and mobilize Ca2+. PTH also increases the formation of 1,25-dihydroxycholecalciferol, and this increases Ca2+ absorption from the intestine. On a longer time scale, PTH stimulates both osteoblasts and osteoclasts.