Which glands are responsible for regulating calcium levels in the blood?

The parathyroid glands are primarily responsible for regulating calcium levels in the blood. These small glands, located on the rear surface of the thyroid gland, produce parathyroid hormone (PTH). PTH plays a crucial role in maintaining calcium homeostasis by increasing blood calcium levels when they drop too low. It achieves this by stimulating the release of calcium from bones, enhancing calcium reabsorption in the kidneys, and promoting the activation of vitamin D, which helps increase intestinal absorption of calcium.

While the thyroid gland does have a role in calcium regulation through the secretion of calcitonin, which lowers blood calcium levels, its influence is more about keeping calcium levels from becoming too high. The adrenal glands and pineal glands do not directly control calcium levels; the adrenal glands produce hormones related to stress and metabolism, while the pineal gland regulates sleep cycles through the secretion of melatonin. Therefore, the parathyroid glands are the key players in calcium level regulation in the bloodstream.