The architectural arrangement of the small airways and distal gas exchange region in the lungs is obviously critical in determining the sites of deposition of gases and particles as well as in subsequent tissue responses due to injury. In the chapter, the results of quantitative determination of the structure of the small airways and gas exchange regions of the lungs will be covered. Because extrapolation of experimental studies in laboratory animals to the adverse health effect in man is a central interest, the authors are particularly interested in comparing the structure of the gas exchange region of different species and the implications that these differences in structure have on dosimetry. The complex architecture of the pulmonary airway system has made the calculation of dose of inhaled pollutants delivered to specific sites in different species a difficult process. This difficulty is particularly apparent in the lack of structural data describing the gas exchange regions of the lungs where low level, chronic exposures to reactive gases and aerosols have their most significant effects.

"EPA 600/D-90/164."