Thyroid follicles. Computer artwork of cells of thyroid follicles (pink, purple) superimposed on an artwork of the thyroid gland (red, centre). A thyroid follicle consists of a layer of epithelial cells (purple) around a central storage chamber (spaces). The cells produce the thyroid hormones tri-iodothyronin (T3) and thyroxine (T4) and secrete them into the central chamber where they are stored as the glycoprotein thyroid colloid (red). Thyroid hormones regulate the body's metabolism.