Located in the throat just below the Adam’s apple is the small, lobed gland known as the thyroid. The hormones secreted by the thyroid are active in a variety of bodily functions, but are most important to metabolism regulation.

View a second image of a thyroid gland.

View a third image of a thyroid gland.

The thyroid is composed of follicles, which are filled with colloid, a viscous fluid. Each individual follicle produces hormones, which are bound to the protein thyroglobulin and stored within the colloid. The casing of each follicle is composed of tightly packed cells and is sheathed in a membrane covered with a dense network of capillaries, which provide a ready supply of plasma to the cells.

Essential to proper growth, thyroid hormone deficiency is sometimes a cause of dwarfism and mental retardation. Other problems related to a shortage of thyroid hormone include sluggish metabolism, inflammation, goiters, and nodules. Although less common, the thyroid sometimes produces an overabundance of hormones, causing the body to burn calories too quickly. If thyroid disorders go untreated, they can have adverse affects on reproduction, the heart, and other vital organs and bodily functions.