What triggers the release of parathyroid hormone?

The release of parathyroid hormone (PTH) is triggered primarily by low blood calcium levels. When calcium levels drop below the normal range, the parathyroid glands, which are located on the posterior aspect of the thyroid gland, detect this decrease and respond by secreting PTH. This hormone plays a crucial role in maintaining calcium homeostasis in the body.

PTH effectively increases blood calcium levels through several mechanisms: it stimulates the release of calcium from bones into the bloodstream, enhances the reabsorption of calcium in the kidneys, and promotes the activation of vitamin D, which increases intestinal absorption of calcium. This feedback loop ensures that calcium levels are restored to their normal range, thus highlighting the importance of PTH in calcium regulation.

Other options do not elicit the same response. High blood calcium levels would actually inhibit the secretion of PTH, while excess potassium and low magnesium levels do not directly stimulate PTH release in the same manner as low blood calcium levels do. Therefore, the correct trigger for PTH release is indeed low blood calcium levels.