What is the main effect of parathyroid hormone?

• A. Increase blood glucose levels
• B. Regulate sleep patterns
• C. Increase calcium levels in the blood
• D. Stimulate digestion

Answer: (C)

Parathyroid hormone (PTH) primarily functions to regulate calcium levels in the bloodstream. When calcium levels drop, the parathyroid glands release PTH, which then acts to increase blood calcium levels through several mechanisms.

Firstly, PTH promotes the release of calcium from bones. It stimulates osteoclasts, which are cells that break down bone tissue, releasing stored calcium into the bloodstream. Secondly, PTH enhances the reabsorption of calcium in the kidneys, reducing the amount of calcium excreted in urine. Lastly, PTH also promotes the activation of vitamin D in the kidneys, which increases intestinal absorption of calcium from dietary sources.

This regulation is vital for maintaining proper calcium balance in the body, as calcium is crucial for various bodily functions, including muscle contractions, nerve function, and blood clotting. In contrast, the other options presented do not align with the primary role of PTH, as they pertain to different physiological processes unrelated to calcium homeostasis.