STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Thyroid gland. Coloured scanning electron micrograph (SEM) of a fracture through the thyroid gland revealing several follicles (yellow). Between the follicles is connective tissue (purple). A follicle consists of a layer of epithelial cells (grey) around a central storage chamber. 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 (yellow). Thyroid hormones regulate the body's metabolism.
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