#alveolus__air_sac__air_cell__aircell  a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways
  supertype:  sac  a structure resembling a bag in an animal
  part of:  lung  either of two saclike respiratory organs in the chest of vertebrates; serves to remove carbon dioxide and provide oxygen to the blood
     part of:  lower_respiratory_tract__lowerrespiratorytract  the bronchi and lungs

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