Morphometric Study of Rat Lung Cells

Abstract

Four normal rat lungs were positive-pressure inflated (7 mm Hg downslope) and perfusion-fixed for electron microscopy. Morphometric analysis yielded estimates for compart-mental volume densities in alveolar septal lung tissue excluding capillaries: type I cells, 0.126; type II cells, 0.097; endothelium, 0.264; interstitial cells, 0.358; interstitial space, 0.116; macrophages, 0.039. Numerically, the largest cell population of the parenchymal tissue was the endothelial cells (43%) followed by interstitial (31.8%), type II (14.5%), and type I (7.5%) epithelial cells; 3.2% were macrophages. Individual type I cells possessed the largest cell volume (915μm3) as well as the largest luminal surface (4,518 μ3), covering 97.5% of the alveolar surface. Type II cells (volume, 366 μ3; surface, 62 μ2) line only 2.5% of the alveolus. Total endothelial surface is 16% larger than the alveolar surface, although individual endothelial cells are much smaller (volume, 336 μ3; luminal surface, 946 μ2) than type I cells. Macro...