STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Tonsil. Light micrograph of a section through the surface of a tonsil, showing a lymphoid nodule (purple). Tonsils are lymph nodes, which filter pathogens from tissue fluid. The lymphoid nodules house the immune system's B cells (B lymphocytes, a type of white blood cell) and antibodies. At top is the upper surface of the tonsil, which consists of stratified squamous epithelial cells (yellow), which are flat and scale-like in structure.
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