When plasma calcium levels drop, what happens to the secretion of parathyroid hormone?

When plasma calcium levels drop, it stimulates the parathyroid glands to increase the secretion of parathyroid hormone (PTH). The main role of PTH is to help regulate calcium levels in the bloodstream. When calcium levels are low, the body responds by releasing more PTH, which works to increase calcium levels in several ways: it promotes the release of calcium from bones, enhances calcium reabsorption in the kidneys, and increases the activation of vitamin D, which in turn increases intestinal absorption of calcium.

The increase in PTH is a crucial part of the feedback mechanism that helps maintain calcium homeostasis in the body. Therefore, the correct understanding is that a decrease in plasma calcium directly leads to an increase in PTH secretion to counteract the low calcium levels and restore balance.