The Lung as an Embattled Domain Against Inanimate Pollutants

The embattlements of the lung against inanimate pollutants have 3 primary functions: to prevent inhaled pollutants from reaching the alveolar membrane, to remove those that settle on the alveolar surface, and to sequester those that cannot be removed. Although the mechanisms responsible for each of these functions are separate and different, they constitute a combined defense that is 98 to 99 per cent efficient. Yet, it is the 1 to 2 per cent inefficiency that accounts for the pneumoconioses. The respiratory bronchiole is the most vulnerable structure in the lung because functionally it is the bottleneck through which inhaled pollutants are cleared. Mobilization of sequestered dust by edema fluid may result in new sequestration reactions and thereby cause progression of a pneumoconiosis in the absence of further dust exposure.