PTH and 1,25(OH)2D are the principal hormones involved in the normal physiologic regulation of calcium homeostasis.

PTH and 1,25(OH)2D are the principal hormones involved in the normal physiologic regulation of calcium homeostasis.

• A. True
• B. False
• C. Not established
• D. Unknown

Answer: (A)

Calcium levels in the body are controlled mainly by two hormones that coordinate bone, kidney, and gut handling of calcium. Parathyroid hormone (PTH) is released when calcium drops and acts to raise calcium by promoting bone breakdown, increasing kidney reabsorption of calcium, and stimulating the production of the active vitamin D. The active form of vitamin D, 1,25-dihydroxyvitamin D, then enhances calcium absorption from the gut and, together with PTH, supports bone calcium mobilization. This combination keeps serum calcium within a narrow range under normal conditions. Calcitonin can oppose PTH, but in healthy individuals its role is not essential for daily calcium homeostasis, making PTH and calcitriol the primary regulators. Therefore the statement is true.

Calcium levels in the body are controlled mainly by two hormones that coordinate bone, kidney, and gut handling of calcium. Parathyroid hormone (PTH) is released when calcium drops and acts to raise calcium by promoting bone breakdown, increasing kidney reabsorption of calcium, and stimulating the production of the active vitamin D. The active form of vitamin D, 1,25-dihydroxyvitamin D, then enhances calcium absorption from the gut and, together with PTH, supports bone calcium mobilization. This combination keeps serum calcium within a narrow range under normal conditions. Calcitonin can oppose PTH, but in healthy individuals its role is not essential for daily calcium homeostasis, making PTH and calcitriol the primary regulators. Therefore the statement is true.