Anatomy of the thyroid gland

The thyroid gland is located in the front of the neck, below the larynx (voice box). The small, two-inch gland consists of two lobes, one on each side of the windpipe, connected by tissue called the isthmus.

The thyroid tissue is made up of two types of cells: follicular cells and parafollicular cells. Most of the thyroid tissue consists of the follicular cells, which secrete iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3). The parafollicular cells (also called C cells) secrete the hormone calcitonin. The thyroid needs iodine to produce the hormones.

Functions of the thyroid gland

The thyroid plays an important role in regulating the body's metabolism and calcium balance. The T4 and T3 hormones stimulate every tissue in the body to produce proteins and increase the amount of oxygen used by cells. The harder the cells work, the harder the organs work. The calcitonin hormone works together with the parathyroid hormone to regulate calcium levels in the body.

Levels of hormones secreted by the thyroid are controlled by the pituitary gland's thyroid-stimulating hormone, which in turn is controlled by the hypothalamus.

Medical Reviewer: [ Daphne Pierce-Smith MSN FNP RN CCRC, Joy Fincannon RN MN, Kelley Gaskin RN MN, Louise Akin RN BSN, Nancy Bowers RN MPH RN MPH, Sara Foster RN MPH, Lee Jenkins] Copyright: Copyright © 2007 Staywell Content Services, Inc. except where otherwise noted.


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