Regional differences in the intercellular junctions of the alveolar-capillary membrane in the human lung.

There are regional differences in the human lung concerning ventilation, perfusion, and hydrostatic pressure. Structural differences corresponding to these physiologic differences have not been documented. In this study the intercellular junctions of the alveolar-capillary membrane in 3 human lungs were examined by the freeze-fracture technique. The intercellular junctions of the alveolar epithelium revealed neither qualitative nor significant quantitative differences from the upper zone to the lower zone of the lung. There were definite regional differences in the intercellular junctions of the capillary endothelium in the 3 zones of the lungs examined. The number of strands that comprise the tight junctions of the capillary endothelium increases from the upper zone (2.80) to the lower zone (4.99) of the lung.