PROF. ARNOLD BRODY / SCIENCE PHOTO LIBRARY PROF. ARNOLD BRODY / SCIENCE PHOTO LIBRARY
Lung alveolar cells. Coloured Scanning Electron Micrograph (SEM) of epithelial cells lining an alveolus (air sac) of the human lung. At lower frame are smooth alveolar cells type I which cover 90% of the air sac surface, and function in gas exchange. Oxygen and carbon dioxide pass through these cells, to and from the bloodstream. At centre left & top are two alveolar cells type II. They are covered in fine microvilli and secrete surfactant, a substance that reduces surface tension in the air sac and prevents it from collapsing. At centre right is a brush cell with thick microvilli, whose function is unknown. Magnification: x5,100 at 6x4.5cm size.
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