Which effect is produced by increased parathyroid hormone secretion?

Which effect is produced by increased parathyroid hormone secretion?

• A. Decreased blood calcium levels
• B. Increased renal reabsorption of phosphate
• C. Decreased bone resorption
• D. Increased intestinal absorption of calcium

Answer: (D)

Rising parathyroid hormone levels raise serum calcium through three main routes: stimulating bone resorption, increasing renal calcium reabsorption, and boosting intestinal calcium absorption via increased production of calcitriol (1,25-dihydroxyvitamin D3). The statement that describes increased intestinal absorption of calcium fits this last mechanism, since PTH promotes calcitriol synthesis in the kidney, which enhances calcium uptake from the gut. The other ideas don’t fit PTH’s actions: it does not lower blood calcium, it does not increase renal phosphate reabsorption (it actually reduces phosphate reabsorption, promoting excretion), and it does not decrease bone resorption (it promotes bone breakdown to release calcium).

Rising parathyroid hormone levels raise serum calcium through three main routes: stimulating bone resorption, increasing renal calcium reabsorption, and boosting intestinal calcium absorption via increased production of calcitriol (1,25-dihydroxyvitamin D3). The statement that describes increased intestinal absorption of calcium fits this last mechanism, since PTH promotes calcitriol synthesis in the kidney, which enhances calcium uptake from the gut. The other ideas don’t fit PTH’s actions: it does not lower blood calcium, it does not increase renal phosphate reabsorption (it actually reduces phosphate reabsorption, promoting excretion), and it does not decrease bone resorption (it promotes bone breakdown to release calcium).