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thyroxine(T4)
(thi-rok´sin)
a thyroid hormone that contains iodine and is a derivative of the amino acid tyrosine; its chemical name is tetraiodothyronine. It is formed and stored in the thyroid follicles as thyroglobulin and released from the gland by the action of a proteolytic enzyme. It is deiodinated in peripheral tissues to form triiodothyronine (T3), which has a greater biological activity. Thyroxine acts as a catalyst in the body and influences many different processes,
including metabolic rate (oxygen consumption); growth and development; metabolism of carbohydrates, fats, proteins, electrolytes,
and water; vitamin requirements; reproduction; and resistance to infection. Pharmaceutical preparations of thyroxine, extracted
from animals or made synthetically, are called levothyroxine.
free thyroxine
the fraction of thyroxine in the serum that is not bound to a binding protein.
Copyright 2007. An Elsevier publication. All rights reserved.
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