Secretion of the parathyroid hormone is regulated by blood levels of:

The secretion of parathyroid hormone (PTH) is primarily regulated by the levels of calcium in the blood. When blood calcium levels drop, the parathyroid glands are stimulated to release PTH, which in turn acts to increase blood calcium levels through several mechanisms: it promotes the release of calcium from bones, increases calcium reabsorption in the kidneys, and enhances the activation of vitamin D, which increases intestinal absorption of calcium.

In contrast, phosphorus, potassium, and sodium do not have a direct regulatory effect on the secretion of PTH. While phosphorus can influence calcium balance indirectly, it is not the primary regulator of PTH secretion. PTH itself also plays a role in regulating phosphorus levels by promoting its excretion in the urine. Therefore, understanding the specific role of calcium is essential for grasping how calcium homeostasis is maintained in the body and how PTH functions as a critical part of this process.