What is the role of calcitonin in the body?

• A. To increase blood calcium levels.
• B. To lower blood calcium levels.
• C. To stimulate the release of parathyroid hormone.
• D. To enhance vitamin D absorption.

Answer: (B)

Calcitonin's primary role in the body is to lower blood calcium levels. This hormone is produced by the parafollicular cells (C cells) of the thyroid gland and is released in response to elevated levels of calcium in the bloodstream. When calcitonin is secreted, it acts to decrease the concentration of calcium by promoting bone formation and inhibiting bone resorption. By stimulating osteoblast activity (cells that build bone) and limiting the activity of osteoclasts (cells that break down bone), calcitonin effectively helps to reduce calcium release from the bone into the bloodstream. Additionally, it decreases calcium reabsorption in the kidneys, further contributing to lower blood calcium levels.

Understanding this role is crucial in distinguishing calcitonin from other hormones, such as parathyroid hormone, which functions to increase blood calcium levels, or vitamin D, that enhances calcium absorption from the diet.