Cross-sectional physiology of the lung.

It is well known that gravity influences the physiology of the lung and thereby affects the intrapulmonary localization of disease processes. Less well known are the anatomic and physiologic differences in the axial or cross-sectional plane, which also affect the distribution of disease. Physiologic gradients in ventilation, perfusion, and lymph flow and stresses in the lung are present in the axial plane. Anatomic difference in branching patterns, interstitial design, and development of the secondary pulmonary lobules are also found. These regional disparities in anatomy and physiology can be applied to an old concept--the corticomedullary organization of the lung--and are used to consider why some diseases exhibit a propensity for the central or peripheral portions of the lung. The same analysis is applied to the anatomy and physiology in the secondary pulmonary lobule.