What feedback mechanism regulates PTH secretion when calcium levels are elevated?

When calcium levels in the blood are elevated, the body employs a feedback mechanism to maintain homeostasis. In this case, high calcium levels lead to the suppression of parathyroid hormone (PTH) secretion from the parathyroid glands.

PTH is primarily responsible for increasing blood calcium levels by promoting calcium release from bones, increasing renal reabsorption of calcium, and stimulating the activation of vitamin D, which enhances intestinal absorption of calcium. However, when there is an excess of calcium in the bloodstream, the parathyroid glands detect this through calcium-sensing receptors. As a result, the secretion of PTH is decreased, thus reducing its effects on increasing calcium levels further. This negative feedback loop ensures that calcium levels do not rise excessively, which is crucial for maintaining overall physiological balance and preventing potential complications associated with hypercalcemia.

In this context, the correct choice accurately describes the regulatory mechanism of PTH secretion in response to elevated calcium levels.