What is the primary function of the parathyroid glands?

The primary function of the parathyroid glands is indeed to regulate blood calcium levels. These small glands, located on the posterior side of the thyroid gland, are crucial for maintaining calcium homeostasis in the body. They secrete parathyroid hormone (PTH), which plays a significant role in increasing blood calcium levels when they fall too low.

PTH accomplishes this through several mechanisms: it stimulates the release of calcium from bones, enhances the reabsorption of calcium in the kidneys, and promotes the activation of vitamin D in the kidneys, which in turn increases intestinal absorption of calcium. This regulation is critical, as calcium is vital for various physiological processes, including muscle contraction, blood clotting, and nerve signaling.

The other options refer to functions that are not associated with the parathyroid glands. For instance, blood glucose regulation is primarily managed by the pancreas through the secretion of insulin and glucagon, rather than by the parathyroid glands. Similarly, metabolic hormones are mainly produced by the thyroid gland and other endocrine organs, while the adrenal response involves hormones produced by the adrenal glands, such as adrenaline, which is unrelated to calcium regulation.