STEFAN DILLER / SCIENCE PHOTO LIBRARY STEFAN DILLER / SCIENCE PHOTO LIBRARY
Lung tissue, coloured scanning electron micrograph (SEM). At upper centre is a capillary filled with red blood cells (erythrocytes) and surrounding it are alveolar ducts. Alveolar ducts are the narrowed endings of bronchioles that open into clusters of alveoli (air sacs, not seen). Magnification: x555 when printed 10 centimetres high.
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