The thyroid gland contains specialized cells called parafollicular cells (C cells) responsible for secreting calcitonin. Calcitonin plays a key role in lowering blood calcium levels by inhibiting osteoclast activity, thus reducing bone resorption. This hormone complements parathyroid hormone (PTH), which raises blood calcium levels. The parathyroid glands secrete PTH, not calcitonin. Recognizing the thyroid as the source of calcitonin is crucial in surgical procedures involving the neck to avoid inadvertent damage to the parafollicular cells affecting calcium homeostasis.

Reference: Gray’s Anatomy, Standring S, 42nd Edition.