Which hormone released by the thyroid decreases blood calcium levels via negative feedback?

Which hormone released by the thyroid decreases blood calcium levels via negative feedback?

• A. Calcitonin
• B. Thyroxine
• C. Epinephrine
• D. Progesterone

Answer: (A)

Calcium homeostasis relies on opposing hormonal actions, and calcitonin from the thyroid lowers blood calcium when levels rise. It does this mainly by inhibiting osteoclasts, which reduces bone resorption, and by promoting calcium deposition into bone. It also promotes calcium excretion by the kidneys, nudging blood calcium back down. This creates a negative feedback loop: high calcium stimulates calcitonin release, which then lowers calcium toward normal. The other substances listed do not regulate calcium in this way. Thyroxine primarily controls metabolic rate, epinephrine handles acute stress responses, and progesterone governs reproductive processes. Calcitonin is the thyroid hormone that decreases blood calcium through this feedback mechanism.

Calcium homeostasis relies on opposing hormonal actions, and calcitonin from the thyroid lowers blood calcium when levels rise. It does this mainly by inhibiting osteoclasts, which reduces bone resorption, and by promoting calcium deposition into bone. It also promotes calcium excretion by the kidneys, nudging blood calcium back down. This creates a negative feedback loop: high calcium stimulates calcitonin release, which then lowers calcium toward normal.

The other substances listed do not regulate calcium in this way. Thyroxine primarily controls metabolic rate, epinephrine handles acute stress responses, and progesterone governs reproductive processes. Calcitonin is the thyroid hormone that decreases blood calcium through this feedback mechanism.