an endocrine gland forming a shieldlike structure on the front and sides of the throat, just below the thyroid cartilage. It produces the iodine-containing thyroid hormones (thyroxine and triiodothyronine) in response to thyroid-stimulating hormone from the anterior pituitary gland. C cells (parafollicular cells) in the thyroid produce the hormone calcitonin, which controls levels of calcium and phosphate in the blood.