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Molecular Mechanisms of Thyroid Hormone Synthesis and Secretion

Part of the Endocrinology book series (ENDOCR)


Thyroxine (T4) and triiodothyronine (T3), collectively called as thyroid hormones, are synthesized in the thyroid gland. Another molecule called reverse T3 (rT3), whose function is unknown, is also secreted from the thyroid gland. T4 is the major molecule synthesized and secreted from the thyroid gland, whereas other molecules are mainly generated in extrathyroidal tissues by deiodination of T4. The thyroid hormone synthetic pathway comprises the following steps: (1) thyroglobulin synthesis and secretion into the follicular lumen; (2) iodine uptake into the follicular epithelial cells; (3) iodine transport and efflux into the follicular lumen; (4) oxidation of iodine, iodination of thyroglobulin tyrosine residues, and coupling of iodotyrosines; (5) endocytosis of the thyroglobulin-thyroid hormone complex into follicular epithelial cells; (6) hydrolysis of the complex; and (7) secretion of thyroid hormone. Thyroid-stimulating hormone (thyrotropin) stimulates thyroid hormone synthesis. In this chapter, the outline of the thyroid hormone synthetic pathway is discussed. The mechanisms regulating thyroid hormone synthesis is briefly described. Furthermore, the clinical aspects of altered thyroid hormone synthesis and secretion induced by immunological or genetic abnormalities are also discussed.


  • Thyroxine
  • Triiodothyronine
  • Thyroid gland
  • Follicle
  • Iodine
  • Na+/I symporter
  • Thyroglobulin
  • Thyroid peroxidase
  • Dual oxidase

Conflict of Interest

The author does not have any conflict of interest.

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Koibuchi, N. (2018). Molecular Mechanisms of Thyroid Hormone Synthesis and Secretion. In: Belfiore, A., LeRoith, D. (eds) Principles of Endocrinology and Hormone Action. Endocrinology. Springer, Cham.

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  • Print ISBN: 978-3-319-44674-5

  • Online ISBN: 978-3-319-44675-2

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