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Triiodothyronine. Picture credit: Wikipedia
One of two tyrosine-based hormones secreted by the thyroid gland, the other being thyroxine (T4). Triiodothyronine (T3), as its name suggests, has three iodine atoms within its molecular structure. Although the thyroid gland produces about 20 times less triiodothyronine than thyroxine, triiodothyronine is the more powerful hormone by a factor of three or four. It affects almost every process in the body, including body temperature, growth, and heart rate.

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