SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Lung bronchiole and alveoli. Coloured scanning electron micrograph (SEM) of a bronchiole (yellow) and alveoli (air sacs, pink) in a healthy human lung. The large holes are capillaries running through the alveoli and bronchiole. The bronchiole carries inhaled air from the upper airway to the alveoli in the lung. The alveoli are the sites of gaseous exchange; oxygen enters the blood and carbon dioxide leaves.
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