Lung Structure- Relation to Response to Particulate

Abstract

One of the main anatomical differences between the lung of the dog and rat is in the terminal portions of the bronchial tree. Exposure of dogs and rats for long periods to oil mist and calcined diatomaceous earth revealed that the histopathologic response in the dog was limited to accumulation of particulates and macrophages around the respiratory bronchioles; the alveolar spaces of the air sacs were free of any changes. In the rat the histopathologic changes showed accumulation of particulate-laden macrophages in the alveolar spaces and around the blood vessels. Phagocytosis of the particulates by macrophages was seen in both species of animals. Accumulation sites differed between the rat and dog. This probably was due to lack of lymphatics and a long respiratory bronchiole in the terminal portions of the bronchial tree of the rat lung. Bronchoconstriction in the dog may be an important factor for the accumulation of particulates in this area. That the human lung accumulates particulates around the respiratory bronchioles has been shown by numerous researchers.