What hormone regulates the metabolism of calcium in the body?

The regulation of calcium metabolism in the body is primarily controlled by parathyroid hormone (PTH). This hormone is secreted by the parathyroid glands and has a crucial role in maintaining calcium homeostasis. When blood calcium levels drop, PTH is released, which acts to increase these levels through several mechanisms. It promotes the release of calcium from bones into the bloodstream, increases the absorption of calcium in the intestines by enhancing the activation of vitamin D, and decreases the loss of calcium through the kidneys by promoting renal tubular reabsorption of calcium.

In contrast, insulin is primarily involved in glucose metabolism, thyroxine (produced by the thyroid gland) plays a significant role in regulating metabolic rate and energy expenditure but is not directly involved in calcium regulation, and estrogen influences calcium metabolism by affecting bone density and promoting retention of calcium, but it does not regulate calcium balance in the same direct way as parathyroid hormone. Thus, parathyroid hormone is the key hormone that specifically regulates calcium metabolism in the body.