The air-blood barrier in the lung (rat)

Electron microscopy (high magnification). The alveolar space (1) and the capillary space (2) (with part of an erythrocyte, 3) are separated from each other respectively by cytoplasm of endothelial cell (5), the common basal lamina (6) with a lamina densa (6a) and the type I alveolar cell (4, pneumocyte I). Note numerous transport vesicles (pinocytosis, diacytosis) in (4) and (6). The air-blood barrier consists of the layers (4)+(6)+(5). Thin-alled areas are most favourable to gas exchange and alternate with thick-walled areas (not shown here) consisting of supporting fibers, extracellular matrix and cells of the alveolar framework that separate the alveolar epithelium from the capillaries.