Title: Alveolar cell type II (pneumocyte II) in an alveolus
Electron microscopy, dog. At (X) the alveolar space, the bulging alveolar cell type II shows the characteristic multilamellar bodies
(*, cytosomes) that contain precusor material of surfactant. The lamellar bodies are responsible for the vacuolated appearance of these cells, and they give rise to surfactant (phospholipids, glycosaminoglycans, proteins). The free surface of the cell is provided with microvilli (↓).
Title: Lamellar body of a type II alveolar cell in the lung
Electron microscopy, dog. Extrusion of surfactant material out of a type II alveolar cell (pneumocyte II, great alveolar cell). After fusion of a multilamellar body (1) (cytosome) with the apical cell membrane (note microvilli 2) the electron-dense lamellar content or surfactant (consisting of phosphatidylcholine, phosphoglycerol, cholesterol and SP-proteins) will be discharged. After release the secretion spreads over the alveolar surface and forms an extracellular coating. This detergent reduces the surface tension at the air-fluid interface, it also contributes to stabilize alveolar diameters. At (* ) remnants of surfactant the so-called tubular myelin (after adequate fixation). Several packed lamellae resemble stacks of the crystalline phase of a polar lipid-water system.
Title: Detail of lamellar body (surfactant) and type I alveolar cell in lung
Electron microscopy, rat. After fixation the extracellular lining of surfactant (phosphatidylcholine, phosphoglycerol, cholesterol and proteins) will often be present as free packed lamellae in the alveolar space (4). This so-called tubular myelin is observed as stacks (5) of lipid crystals and aqueous layers of proteins and proteoglycans (crystalline phase of a polar lipid-water system). (1) is type I alveolar cell, (2) indicates common basal lamina of alveolar cell and endothelium (3) of capillary (C). Note the transport vesicles (*) in both (1) and (3). (↔) is the Air-Blood barrier is the so-called thin-walled area. Thin-walled 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.
Title: Free surfactant (tubular myelin) in alveolar space of the lung
Electron microscopy, rat. After fixation the extracellular lining of surfactant (phosphatidylcholine, phosphoglycerol, cholesterol and proteins) will often be present as free packed lamellae in the alveolar space. This so-called tubular myelin (partly cross-sectioned), (1) is observed as stacks of lipid crystals and aqueous layers of proteins and proteoglycans (crystalline phase of a polar lipid-water system).
Keywords/Mesh: respiratory tract, lung, alveolus, pneumocyte I, pneumocyte II, alveolar cell type II, multilamellar bodies, cytosomes, surfactant, tubular myelin, capillary, Air-Blood barrier, histology, electron microsccopy, POJA collection