Answer:
(C). calcitriol.
Explanation:
PTH (parathyroid hormone) is a peptide hormone, synthesized and secreted by parathyroid glands. It helps in regulation of calcium level in blood by affecting intestine, bones, and kidneys.
PTH increases blood calcium by promoting synthesis of calcitriol hormone, which represents an active form of vitamin D.
Calcitriol increases calcium level in blood by increasing calcium absorption in intestine, increasing calcium reabsorption in kidneys, decreasing calcium, and by activating osteoclats (bone cells) to release calcium.
Thus, the correct answer is option (c).
