Which hormones are produced by the thyroid gland?

• A. Thyroxine (T4), Triiodothyronine (T3), Reverse T3 (rT3), Calcitonin
• B. Thyroxine (T4) and Triiodothyronine (T3)
• C. Reverse T3 (rT3) and Calcitonin
• D. Calcitonin and Parathyroid Hormone

Answer: (A)

The thyroid gland secretes a trio of hormones: the main metabolic drivers thyroxine (T4) and triiodothyronine (T3) from the follicular cells, and calcitonin from the parafollicular (C) cells, which helps regulate calcium levels. Reverse T3 (rT3) is not released directly by the thyroid gland; it’s produced in peripheral tissues by deiodination of T4 and serves more as a metabolite indicator rather than a primary thyroid hormone. Parathyroid hormone, on the other hand, is produced by the parathyroid glands, not the thyroid. So, the thyroid’s hormonal output includes T4, T3, and calcitonin, while rT3 is formed elsewhere in the body.