Alveoli alveolar ducts

Buds of granulation tissue filling the distal airspaces (alveoli, alveolar ducts, respiratory bronchioles, bronchioles) constitute the histological hallmark of OP, with associated features including mild interstitial inflammatory infiltrate, type 11 cell hyperplasia, and intra-alveolar foamy macrophages (Pig. 3) (2,3,14,33). However, this elementary lesion is in no way specific and may be seen as a minor feature in other disorders such as infections, NSIP, hypersensitivity pneumonitis. 

Alveolar cavities are the lowest portion of the lung airways where gas exchange with blood takes place. Alveoli are formed in clusters and each alveolus consists of a tubular alveolar duct leading into a terminal alveolar cavity. Before they terminate, the alveolar ducts branch several times. If all the alveoli in both lungs were laid out flat, the total surface area available for gas exchange would be about 75 m. ... 

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