Which of the following is not a function of parathyroid hormone (PTH)?

Which of the following is not a function of parathyroid hormone (PTH)?

• A. Raising blood calcium
• B. Inhibiting osteoclast activity
• C. Stimulating kidney reabsorption of calcium
• D. Increasing intestinal absorption of calcium

Answer: (B)

Parathyroid hormone (PTH) is primarily involved in regulating calcium levels in the blood. Its main functions include raising blood calcium levels, stimulating the kidneys to reabsorb calcium, and increasing intestinal calcium absorption indirectly through its action on vitamin D metabolism.

The correct choice highlights that PTH does not inhibit osteoclast activity; rather, it stimulates osteoclasts. By doing so, PTH promotes bone resorption, which releases calcium ions into the bloodstream, thereby increasing blood calcium levels. This is crucial because osteoclasts are the cells responsible for breaking down bone tissue, leading to the release of calcium when PTH levels are elevated.

In contrast, osteoblasts are the cells that build bone, and an inhibition of osteoclast activity would not align with the main role of PTH in elevating blood calcium levels. Instead, PTH acts to increase osteoclast activity to mobilize calcium from bone when needed. This distinction is key to understanding PTH's role in calcium homeostasis in the body.