The thyroid gland is composed of two lobes that are joined together by a central mass called the isthmus. The gland is inferior to the larynx. The thyroid gland produces these hormones:
(1) "thyroid_metabolic hormones" and
(2) calcitonin, which is also known as thyrocalcitonin.
The "thyroid metabolic hormones" are two separate substances
(1) T3, known as triiodothyronine and
(2) T4, known as thyroxine or tetraiodothyronine.
Both T3 and T4 help regulate metabolism. Calcitonin decreases blood calcium levels by stimulating calcium deposits in bones.
The thyroid is composed of structures called follicles, which contain colloid. Colloid contains thyroglobin. This substance the precursor for T3 and T4 . The cells that make up the follicle border are called follicular cells. Scattered among, but external to, the follicles are parafollicular (C-cells) cells. These cells produce calcitonin.