The function of which of the following is increased by an elevated parathyroid hormone concentration:
Osteoclasts
Hepatic formation of 25-hydroxycholecalciferol
Phosphate reabsorptive pathways in the renal tubules
Action of osteoblasts only
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.
Endocrine System