Which organ produces parathormone?

• A. Adrenal cortex
• B. Parathyroid glands
• C. Thyroid
• D. Pancreas

Answer: (B)

Calcium homeostasis is controlled by parathyroid hormone produced by the parathyroid glands. These tiny glands sit behind the thyroid and secrete PTH when serum calcium drops. PTH raises calcium levels through three main actions: it stimulates osteoclasts to release calcium from bone, increases calcium reabsorption in the kidneys, and promotes formation of active vitamin D (calcitriol) in the kidneys, which boosts intestinal calcium absorption. PTH also lowers phosphate reabsorption in the kidneys to prevent phosphate from binding calcium.

Understanding the other organs helps reinforce the idea that this hormone isn’t produced elsewhere: the adrenal cortex makes steroid hormones, not PTH; the thyroid makes thyroid hormones and calcitonin (the latter lowers calcium, not raises it); and the pancreas makes insulin and glucagon, which regulate glucose, not calcium. So the organ responsible for parathormone production is the parathyroid glands.