Thyroid Gland

The **thyroid gland** is located in the neck, just below the larynx and in front of the trachea. It is a butterfly-shaped gland with two lobes that are connected by the isthmus. When the thyroid swells due to dysfunction, it can be felt under the skin of the neck. The thyroid gland is made up of many spherical thyroid follicles, which are lined with a simple cuboidal epithelium. These follicles contain a viscous fluid, called colloid, which stores the glycoprotein thyroglobulin, the precursor to the thyroid hormones. The follicles produce hormones that can be stored in the colloid or released into the surrounding capillary network for transport to the rest of the body via the circulatory system. Thyroid follicle cells synthesize the hormone thyroxine (T4) and triiodothyronine (T3). Follicle cells are stimulated to release stored T3 and T4 by thyroid stimulating hormone, which is produced by the anterior pituitary. These thyroid hormones increase the rates of mitochondrial ATP production. A third hormone, calcitonin, is produced by parafollicular cells of the thyroid either releasing hormones or inhibiting hormones.



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## Keywords
thyroid gland hormone thyroxine metabolism goitre