What is the primary effect of calcitonin?

• A. Increase calcium absorption
• B. Decrease calcium levels in the blood
• C. Stimulate red blood cell production
• D. Increase blood pressure

Answer: (B)

The primary effect of calcitonin is to decrease calcium levels in the blood. Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland and plays a crucial role in calcium homeostasis. It acts primarily by inhibiting the activity of osteoclasts, the cells responsible for bone resorption, which leads to a reduction in the release of calcium from the bones into the bloodstream.

Additionally, calcitonin promotes the deposition of calcium into the bones by stimulating osteoblasts, contributing to the overall lowering of calcium levels in the circulating blood. By effectively lowering blood calcium levels, calcitonin helps counterbalance the effects of parathyroid hormone, which increases blood calcium levels when needed. This regulation is essential in maintaining the delicate balance of calcium, which is vital for various bodily functions, including bone health, muscle function, and nerve signaling.