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 connected by a thin bridge of tissue called the isthmus. When the thyroid becomes enlarged due to dysfunction, it can be felt beneath the skin of the neck. The thyroid gland consists of numerous spherical structures called thyroid follicles, each lined with a simple cuboidal epithelium. These follicles contain a viscous fluid known as colloid, which stores the glycoprotein thyroglobulin, a precursor to thyroid hormones. The follicles produce thyroid hormones, which can either be stored in the colloid or released into a surrounding network of capillaries for distribution throughout the body via the circulatory system. Thyroid follicle cells synthesize the hormones thyroxine (T4) and triiodothyronine (T3). The release of T3 and T4 from stored reserves is stimulated by thyroid-stimulating hormone (TSH), produced by the anterior pituitary gland. These thyroid hormones increase the rates of mitochondrial ATP production. In addition, the thyroid’s parafollicular cells produce calcitonin, a hormone that helps regulate calcium levels in the blood according to the body's needs. *LICENSES AND ATTRIBUTIONS CC licensed content, Shared previously, 3.5.6 Endocrine Glands, Authored by: OpenStax College. License: CC BY: Attribution. License Terms: Download for free at:http://cnx.org/contents/41UfyQJ1@1.10:pwjTy-w3@6/Endocrine-Glands* ## Keywords thyroid gland hormone thyroxine metabolism goitre