Air-blood barrier in the lung (mammals)

Scheme electron microscopy. (1, ↓) Represents type I pneumocytes lining alveolar spaces (A). Cell (2) represents a free alveolar macrophage. The type II pneumocyte (3) is adherent to type I pneumocyte extensions (note junctional connection), and contains multilamellar bodies (surfactant). A myofibroblast (4) is located in the interstitium (note surrounding cross-sectioned collagen fiber dots), and (*) indicate elastin. (5, ↓) Indicate endothelial cells within the capillaries. (6↔) Indicates the thin-walled area of the air-blood barrier.