The thyroid gland, or simply the thyroid, in vertebrate anatomy, is one of the largest endocrine glands and consists of two connected lobes. The thyroid gland is found in the neck, below the thyroid cartilage. The thyroid gland controls how quickly the body uses energy, makes proteins, and controls how sensitive the body is to other hormones.
T3 and T4 are not equal in strength; T3 is the more active hormone of the two. While T3 is stronger, taking synthetic T4 hormone is considered the standard treatment for hypothyroidism. The reason for this is because most of the T3 in our bodies actually used to be T4. When T4 hormones come into contact with other cells in the bloodstream, they give up an iodine atom to interact with those cells. When T4 loses an iodine atom, it becomes T3. When this T4 into T3 conversion occurs, T3 then conveys the metabolic "message" to the other cells throughout the body. The benefit of taking only T4 therapy is that you're allowing your body to perform some of the actions it is meant to do, which is taking T4 and changing it into T3. The half life of T4 is also longer compared to T3 (7 days versus 24 hours), that means that it will stay for a longer time in your body after ingestion.
Last date updated on June, 2014