Thyroid Stimulating Hormone (TSH) stimulates the thyroid gland to secrete the hormones Thyroxine (T4) and Triiodothyronine (T3) exhibits greater activity and is produced in smaller quantity. It is the most powerful thyroid hormone, and affects almost every process in the body, including body temperature, growth and heart rate. Thyroxine (T4) is the major thyroid hormone.