Which organ dysfunction predominantly drives secondary hyperparathyroidism?

• A. Parathyroid glands
• B. Kidneys
• C. Liver
• D. Intestines

Answer: (B)

The driving problem in secondary hyperparathyroidism is the dysfunction of an important mineral-regulating organ: the kidneys. When kidney function declines, the ability to excrete phosphate is impaired and the production of active vitamin D (calcitriol) is reduced. Hyperphosphatemia increases calcium-phosphate deposition and lowers ionized calcium, while less calcitriol means less calcium absorption from the gut. The resulting hypocalcemia triggers the parathyroid glands to secrete more parathyroid hormone to try to normalize calcium levels. Over time this chronic stimulation causes parathyroid hyperplasia and sustained elevation of PTH. The liver and intestines participate in vitamin D metabolism, but the initiating driver is kidney dysfunction.