This video from our Thyroid Disease Masterclass is a fast-paced refresher on how T3 and T4 are produced. Find out how they differ from each other and the exact steps taken by the thryoid follicles to convert iodine into these two essential hormones.
This video was taken from our hands-on and CME accredited Thyroid Essentials course.
[00:00:00] Thyroid hormone is produced in two forms: T3, which is the active form of thyroid hormone and T4, which is an inactive precursor to T3. Most of the thyroid hormone that's produced by the thyroid, about 80% is present as T4 and only 20% is secreted as T3. T4 travels to the target tissues through the bloodstream, where it's converted to active T3. Thyroid hormone requires iodine for its production, as iodine is a key structural component of the
[00:00:30] thyroid hormone. T3 consists of three iodines, whereas T4 consists of four iodines. Thyroid hormone synthesis occurs at the follicular cell, in the colloid in the follicles of the thyroid. This involves several steps, which we will review in the next few slides. The first step of thyroid hormone synthesis is iodine uptake. Iodine from the bloodstream is transported into the cells, via sodium iodine symporter and the iodine is then transported into the colloid. In the colloid,
[00:01:00] an enzyme called thyroid peroxidase or TPO, oxidizes the iodine and then catalyzes its binding to a protein called thyroglobulin. Upon binding to thyroglobulin, the iodine forms thyroid hormone precursors: DIT and MIT. These precursors are coupled together to form T4 and T3. T3 and T4 are then taken up by the cell, dissociated from the thyroglobulin molecule, and secreted into the bloodstream,
[00:01:30] where they travel to the target tissue.