uwl-280-145
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  Respiratory bronchiole section

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Unit_14-07a

 1. Proximal end of bronchiole

 2. Alveolar sac

 3. Respiratory epithelium

 4. Alveolar duct

 5. Simple squamous epithelium

 6. Blood vessel

 7. Alveolus

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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. 

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