Question: what is the difference between the two types of thyroid hormone secreted by the thyroid gland?
Answer: The highly active hormone is triiodothyronine (referred to as T3). Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. The thyroid gland produces just 20% of the high active T3, but it produces 80% of the prohormone T4.