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What Are Thyroid Hormones T3 And T4? - Dr. Ladenson (VIDEO)

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Listen as Dr. Ladenson discusses thyroid hormones T3 and T4.

Dr. Ladenson:
The thyroid gland in the front of the neck makes these two chemicals, the thyroid hormones that in tissues of the body regulate our metabolism and other functions. The main hormone made in human beings by the thyroid gland is a molecule called T4 or thyroxine. That "4" refers to the number of iodine molecules that are attached to each thyroxine or T4 molecule.

And so the thyroid gland has become specialized to concentrate the iodine that we consume in our diet, to concentrate that iodine within itself to use the iodine as a building block for T4, the major thyroid hormone that then gets shipped out to all of the other tissues in the body through the blood.

Now although thyroid hormone is mainly T4 in terms of what’s produced by the thyroid gland, outermost target tissues of the body T4 gets converted into the second thyroid hormone T3, and as the name "3" implies, that conversion is the result of removing one of those 4 iodines.

So, T4 is really what we call our pro hormone. It’s the precursor of the real business thyroid hormone in most tissues which is T3 that then enters cells and the nucleus of cells to affect the expression of DNA or genetic blueprint.

About Dr. Ladenson:
Dr. Ladenson is Director of the Division of Endocrinology and Metabolism Johns Hopkins in Baltimore, where he is the John Eager Howard Professor of Endocrinology and Professor of Medicine, Pathology, Oncology, and International Health. Dr. Ladenson was raised in Missouri and educated at Dartmouth College, Oxford University, and Harvard Medical School before training in Internal Medicine and in endocrinology and metabolism at Massachusetts General Hospital in Boston. He is also the past-president for the American Thyroid Association. Dr. Ladenson’s research interests include the effects of thyroid hormone on the cardiovascular system, applications of thyroid hormone analogs, novel approaches to thyroid cancer diagnosis and management, and health economic analyses related to thyroid patient care.

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