Kent, George C., Jr. Louisiana State University; Author's Services, Inc., Baton Rouge, Louisiana.
Lynn, W. Gardner Department of Biology, Catholic University of America, Washington, DC..
Burrow, Gerard N. School of Medicine, University of California, San Diego, California.
Woeber, Kenneth A. Department of Medicine, Mount Zion Hospital and Medical Center, San Francisco, California.
Li, Choh Hao Formerly, Laboratory of Molecular Endocrinology, University of California, San Francisco, California.
- Comparative Anatomy
- Embryonic Origin
- Development, Differentiation, and Morphogenesis
- Thyroid hormones and retinoic acid
- Development in homeotherms
- Metabolism of hormones
- Regulation of thyroid function
- Physiological actions
- Links to Primary Literature
- Additional Readings
An endocrine gland found in all vertebrates that produces, stores, and secretes the thyroid hormones. The primary function of the thyroid, in warm-blooded vertebrates at least, is to regulate the rate of metabolism. In humans, the gland is located in front of, and on either side of, the trachea (Fig. 1). Thyrocalcitonin, a hormone of the thyroid gland, assists in regulating serum calcium by reducing its levels. The thyroid gland is capable of accumulating inorganic iodides and uniting them with the amino acid tyrosine to produce iodinated proteins. This activity is regulated by thyrotropic hormone from the anterior lobe of the pituitary gland. Microscopically (Fig. 2), the tissue consists of thyroid follicles composed of a single layer of secretory cuboidal epithelium which secretes hormone as a colloid into a blind lumen. The height of the secretory cells and the amount of colloid vary with the functional state of the gland. A main site of action of thyroid may be in the mitochondria, where energy-rich phosphate bonds are formed.
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