What is the primary function of the parathyroid gland?

The primary function of the parathyroid gland is to detect serum calcium concentration and regulate calcium levels. The parathyroid glands, typically four small glands located near the thyroid gland in the neck, are crucial in maintaining calcium homeostasis in the body. They achieve this primarily through the secretion of parathyroid hormone (PTH), which is released in response to low blood calcium levels.

When serum calcium levels drop, PTH is secreted to stimulate several physiological responses: it increases calcium reabsorption in the kidneys, promotes the release of calcium from bones, and enhances the intestinal absorption of calcium by activating vitamin D. This coordinated response ensures that calcium levels are restored to their normal range, essential for numerous bodily functions, including muscle contraction, nerve transmission, and bone health.

In contrast, other glands mentioned in the choices have specific and distinct functions that do not relate to calcium regulation. Insulin production and glucose regulation is a function of the pancreas; metabolism is controlled primarily by thyroid hormones produced by the thyroid gland; and cortisol, which helps regulate stress responses, is produced by the adrenal glands. Thus, these organs have different roles that do not pertain to calcium metabolism, highlighting the unique function of the parathyroid gland in maintaining calcium balance.