ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY
Light micrograph of normal human thyroid gland. The parenchyma of the gland consists of closed vesicles surrounded by a network of blood vessels (deep blue meshwork). Each vesicle is bounded by a layer of cubical epithelial cells with pink nuclei. These cells secrete the precursors of the hormones tri-iodothyronine and thyroxine into the central space of the vesicle, in the form of a homogenous colloid, seen as bright red masses. In life this colloid fills the vesicle: the clear space around each mass here is an artefact due to shrinkage during preparation of the specimen. Magnification: x50 at 35mm size.
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