What hormone is secreted by the thyroid and converted to its active form T3?

The hormone that is secreted by the thyroid and converted to its active form T3 is thyroxine, also known as T4. In the body, T4 is produced by the thyroid gland and serves primarily as a precursor to the more active form of the hormone, triiodothyronine (T3). Once released into the bloodstream, T4 is converted into T3 through various tissues, such as the liver and kidneys, where it gains biological activity.

Thyroxine plays a crucial role in regulating metabolism, heart rate, and overall growth and development. The thyroid's ability to produce and secrete T4 is essential for maintaining normal physiological functions, including metabolism regulation and thermogenesis. Consequently, understanding the relationship between T4 and T3 is fundamental in the context of thyroid health and hormonal balance.