Which hormone has the opposite function of calcitonin in regulating blood calcium levels?

• A. Insulin
• B. Parathyroid hormone (PTH)
• C. Thyroxine (T4)
• D. Aldosterone

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the role of calcitonin in regulating blood calcium levels. Calcitonin is a hormone produced by the thyroid gland that lowers blood calcium levels by inhibiting osteoclast activity (cells that break down bone tissue) and promoting calcium storage in bones.
2. Step 2: Identify the hormone that has the opposite function of calcitonin. This hormone should increase blood calcium levels by stimulating processes that release calcium into the bloodstream.
3. Step 3: Learn about parathyroid hormone (PTH). PTH is produced by the parathyroid glands and increases blood calcium levels by stimulating osteoclast activity, enhancing calcium reabsorption in the kidneys, and promoting calcium absorption in the intestines via activation of vitamin D.
4. Step 4: Compare the functions of calcitonin and PTH. Calcitonin decreases blood calcium levels, while PTH increases them, making PTH the hormone with the opposite function of calcitonin.
5. Step 5: Review the other options provided (Insulin, Thyroxine (T4), and Aldosterone) to confirm that none of them regulate blood calcium levels in the same way as PTH or calcitonin. Insulin regulates blood glucose, Thyroxine (T4) regulates metabolism, and Aldosterone regulates sodium and potassium balance.