In Paget's disease, when serum calcium levels are lowered, which hormone increases to release calcium into the blood?

In Paget's disease, when serum calcium levels are lowered, which hormone increases to release calcium into the blood?

• A. Antidiuretic hormone (ADH)
• B. Parathyroid hormone (PTH)
• C. Calcitonin
• D. Growth hormone

Answer: (A)

When calcium in the blood falls, the parathyroid glands release parathyroid hormone to raise it. PTH acts in three coordinated ways: it stimulates bone to release calcium into the bloodstream, it increases calcium reabsorption in the kidneys to reduce loss in urine, and it promotes production of active vitamin D (calcitriol) in the kidneys, which raises intestinal calcium absorption. Calcitonin lowers calcium levels and acts in opposition to PTH, but it is not the responder when calcium drops. ADH governs water balance, not calcium regulation, and growth hormone’s effects on bone are more about growth and turnover than direct, acute control of blood calcium. So the hormone that increases to release calcium into the blood when levels are low is parathyroid hormone.

When calcium in the blood falls, the parathyroid glands release parathyroid hormone to raise it. PTH acts in three coordinated ways: it stimulates bone to release calcium into the bloodstream, it increases calcium reabsorption in the kidneys to reduce loss in urine, and it promotes production of active vitamin D (calcitriol) in the kidneys, which raises intestinal calcium absorption. Calcitonin lowers calcium levels and acts in opposition to PTH, but it is not the responder when calcium drops. ADH governs water balance, not calcium regulation, and growth hormone’s effects on bone are more about growth and turnover than direct, acute control of blood calcium. So the hormone that increases to release calcium into the blood when levels are low is parathyroid hormone.