Which gland is responsible for regulating calcium levels in the blood?

The parathyroid gland plays a crucial role in regulating calcium levels in the blood. It achieves this through the secretion of parathyroid hormone (PTH), which is essential for maintaining calcium homeostasis. When blood calcium levels drop, PTH is released into the bloodstream, leading to several physiological effects. These include stimulating the release of calcium from bones, increasing the reabsorption of calcium in the kidneys, and promoting the activation of vitamin D in the kidneys, which enhances calcium absorption in the intestines. This coordinated response helps to elevate calcium levels back to a normal range.

In contrast, the thyroid gland primarily regulates metabolism and calcium levels indirectly through the secretion of calcitonin, which helps lower blood calcium levels when they are too high, but it does not regulate calcium levels in the same direct manner as the parathyroid gland. The adrenal gland is involved in regulating stress responses and metabolism, primarily through the release of hormones like cortisol and adrenaline, rather than calcium levels. The pituitary gland controls a variety of other endocrine functions, such as growth and reproduction, but does not directly regulate calcium levels as the parathyroid gland does.