Type II and type I alveolar cells in the lung (human, adult)

Electron microscopy. At the top the alveolar space (1) is lined by a thin cytoplasm (2) of type I alveolar cell (pneumocyte I). At the left side part of a type II alveolar cell (3, pneumocyte II) with electron-dense remnants of two characteristic multilamellar bodies (4) as well as many organelles. Note at (*) junction between these two epithelial cells. Below a capillary with some erythrocytes (5). The arrows (↓) indicate junctions between the endothelial cell processes. (6) points to an extension of an interstitial cell squeezed between capillary (5) and the pneumocytes (2,3). Thin-walled areas (not shown here) are most favourable to gas exchange and alternate with thick-walled areas (thick line, ▬) consisting of supporting fibers, extracellular matrix and cells of the alveolar framework that separate the alveolar epithelium from the capillaries.