CLINICAL MEDICINE

Detailed explanation-1: -Your thyroid gland makes T4 and a tiny bit of T3. However, most conversion of T4 to T3 occurs outside of the thyroid gland, particularly in the liver (2). Impaired liver function, therefore, may negatively affect this conversion even if liver enzymes appear to be within normal limits.

Detailed explanation-2: -The liver does most of the conversion of T4 to T3, but it also happens in the heart, muscle, gut, and nerves. About 20 percent of T4 can be converted to T3 by healthy gut bacteria. Also, not all T4 converts. Only about 60 percent of T4 is converted into T3.

Detailed explanation-3: -T4 is converted into T3, the active form of thyroid hormone, by two enzymes called deiodinases. People with hypothyroidism are treated with a synthetic T4 hormone, which the enzymes convert to T3. This treatment is usually effective, but some people continue to have symptoms even after treatment.

Detailed explanation-4: -T4 is converted to the active T3 form by deiodination, removal of an iodide from the outer phenolic benzene ring by selenium-containing enzymes, deiodinase enzymes D1 or D2.