Lung disease defense mechanisms

As discussed above, absorption to the systemic circulation from the lungs is also a route of exposure of occupational concern. Pulmonary absorption is influenced by the diffusion factors just described, by the degree of hydration at various levels of the respiratory tract and the water solubility and water reactivity of the chemical, and by the integrity of the respiratory system s defense mechanisms. The mucociliary escalator, for example, provides an efficient capture and removal system for inhaled contaminants unless overwhelmed by the magnitude or frequency of exposure or otherwise compromised (e.g., by disease). 

The mineral asbestos possesses some unique properties that cause lung injury and necessitate microscopic methods for evaluating its hazard. The characteristic fibrous shape of asbestos particles [see Fig. 1.4(b)] enables them to get past respiratory defense mechanisms and cause asbestosis (scarring of lung tissue), mesothelioma (cancer of the lining of the lung), and lung cancer. Microscopy is used to identify those asbestos fibers whose size and shape enable them to cause these diseases. 

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