TY - CHAP M1 - Book, Section TI - Chapter 7. The Thyroid Gland A1 - Cooper, David S. A1 - Ladenson, Paul W. A2 - Gardner, David G. A2 - Shoback, Dolores PY - 2011 T2 - Greenspan’s Basic & Clinical Endocrinology, 9e AB - The thyroid gland is the body's largest single organ specialized for endocrine hormone production. Its function is to secrete an appropriate amount of the thyroid hormones, primarily 3,5,3′,5′-l-tetraiodothyronine (thyroxine, T4), and a lesser quantity of 3,5,3′-l-triiodothyronine (T3), which arises mainly from the subsequent extrathyroidal deiodination of T4. In target tissues, T3 interacts with nuclear T3 receptors that are, in turn, bound to special nucleotide sequences in the promoter regions of genes that are positively or negatively regulated by thyroid hormone. Among their life-sustaining actions, the thyroid hormones promote normal fetal and childhood growth and central nervous system development; regulate heart rate and myocardial contraction and relaxation; affect gastrointestinal motility and renal water clearance; and modulate the body's energy expenditure, heat generation, weight, and lipid metabolism. In addition, the thyroid contains parafollicular or C cells that produce calcitonin, a 32-amino-acid polypeptide that inhibits bone resorption, but has no apparent physiologic role in humans. However, calcitonin is clinically important as a tumor marker produced by medullary thyroid cancers that arise from these cells (Chapter 8). SN - PB - The McGraw-Hill Companies CY - New York, NY Y2 - 2024/03/28 UR - accessbiomedicalscience.mhmedical.com/content.aspx?aid=8401830 ER -