STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Thyroid gland follicle. Coloured transmission electron micrograph (TEM) of a follicle from the thyroid gland. The follicle consists of a layer of epithelial cells (pink) around a central storage chamber. The cells produce the thyroid hormones tri-iodothyronine (T3) and thyroxine (T4) and secrete them into the central chamber where they are store as the glycoprotein thyroid colloid (brown). The follicle is surrounded by blood vessels (red), which transport the hormones around the body. Thyroid hormones regulate the body's metabolism.
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