BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Thyroid gland. Light micrograph of a section through a healthy thyroid gland showing the follicles (large cells). The follicles are lined by a single layer of cuboidal epithelial cells (purple, dark nuclei), which synthesise and secrete the iodine-containing hormones T3 (tri-iodothyronine) and T4 (thyroxine). The thyroid follicle is filled with a glycoprotein substance called thyroglobulin, or thyroid colloid (pink), which is a storage form of the thyroid hormones.
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