Brush alveolar

The ultrastructure of the respiratory membrane is unique by virtue of its function. A diagrammatic representation of the respiratory membrane is shown in Figure 1. The respiratory membrane basically comprises two main layers. The first layer is the alveolar epithelium, which consists of at least three different cell types alveolar types I, II, and III or brush cells and migratory alveolar macrophages. 

Alveolar epithelium consists of three types of cells. Roughly 98 % of the alveolar surface is covered by squamous (type I) epithelial cells, from which thin sheets of cytoplasm extend to cover large areas of surface of even several alveoli (Haies et al. 1981). Type II epithelial cells, though more numerous but compact, occupy only 2 % of the alveolar surface. Type III cells, also called alveolar brush cells, are rare. 

Alveolar brush cells are selectively decorated with cytokeratin 18- and villin-specific antibodies (HOfer and Drenckhahn 1992, Kasper et al. 1994). 

Figure 4.2 Lung morphology from pig lung 24 hours post air exposure. A and B alveolar spaces. C and D bronchiolar conducting airways. Alveolar spaces (B) were free of inflammatory cell infiltrate and oedema ( ). The lumen of conducting airways (C) were free of mucus and cellular debris ( ) with normal pseudo-stratified columnar epithelium with a brush cell border (D 4). Dark scales are 200 pm and white scales are 50 pm. Stippled boxes show the area expanded in the adjacent image.

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