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This image shows a section of inflated lung containing a respiratory bronchiole. Although the walls of respiratory bronchioles contain respiratory epithelium (which prevents gas exchange), note that there are also sections that contain thin-walled alveoli (air sacs) through which gas exchange can take place. The distal ends of respiratory bronchioles open into alveolar ducts whose walls are formed by a series of alveoli lying adjacent to one another. Coming off the alveolar ducts are groups or clusters of alveoli that form alveolar sacs. |