Parathyroid hormone increases calcium levels in the blood. It is produced by which gland?

• A. Pituitary gland
• B. Parathyroid gland
• C. Pineal gland
• D. Thyroid gland

Answer: (B)

Calcium homeostasis is regulated mainly by parathyroid hormone, calcitriol, and calcitonin, with PTH being the key hormone that raises blood calcium when it’s low. It is produced by the parathyroid glands, small glands located on the back of the thyroid. When calcium levels drop, PTH is released and acts on bone to stimulate osteoclast activity and bone resorption, releasing calcium into the bloodstream. It also increases calcium reabsorption in the kidney’s distal tubules and promotes formation of calcitriol, the active form of vitamin D, in the kidneys, which enhances intestinal calcium absorption. Feedback from rising calcium levels then reduces PTH release. The other glands listed do not produce PTH: the thyroid makes calcitonin (which lowers calcium), while the pituitary and pineal glands do not regulate calcium through PTH.