[Campbell Biology P.1066] Parathyroid hormone PTH and calcitonin play crucial roles in calciu... | Practice Question

Parathyroid hormone PTH and calcitonin play crucial roles in calcium homeostasis. Which of the following statements accurately describes their antagonistic actions?

  • A: PTH increases blood Ca2+ by promoting bone breakdown and kidney reabsorption, while calcitonin decreases blood Ca2+ by inhibiting bone breakdown.
  • B: PTH decreases blood Ca2+ by promoting bone formation, while calcitonin increases blood Ca2+ by stimulating intestinal absorption.
  • C: Both PTH and calcitonin work together to increase blood Ca2+ levels.
  • D: Calcitonin stimulates vitamin D activation in the kidneys, whereas PTH inhibits it.

Explanation

The text states that 'Parathyroid hormone PTH , secreted by the parathyroid glands, causes bone to release Ca2+ into the blood and stimulates reabsorption of Ca2+ in the kidneys. PTH also stimulates the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food. Calcitonin, secreted by the thyroid, has the opposite effects in bones and kidneys as PTH.' Therefore, PTH increases blood Ca2+, while calcitonin decreases it.