What are the thyroid hormones?
There are two major hormones secreted by the thyroid gland – thyroxine (T4) and triiodothyronine (T3). The thyroid gland secretes more thyroxine (T4) than triiodothyronine (T3) but most T4 is eventually converted into T3. Although T3 is secreted in significantly smaller quantities, it is about four times as potent as T4.
The thyroid hormones are best known for regulating the metabolism of the body although it has several other effects on the different tissues of the body which become evident when there is an excess or deficiency of these hormones. Most of the secretion of the thyroid hormones are regulated by another hormone known as the thyroid-stimulating hormone (TSH), which is secreted from the pituitary gland, particularly the anterior pituitary.