The respiratory membrane consists of the alveolar and capillary walls

The respiratory membrane consists of the alveolar and capillary walls

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The respiratory membrane consists of the alveolar and capillary walls. Gas  exchange occurs across this membrane. Characteristics of this membrane follow: Type I cells are thin, squamous epithelial cells that constitute the primary  cell type of the alveolar wall. Oxygen diffusion occurs across these cells. Type II cells are cuboidal epithelial cells that are interspersed among the  type I cells. Type II cells secrete pulmonary surfactant (a phospholipid bound  to a protein) that reduces the surface tension of the moisture that covers the  alveolar walls. A reduction in surface tension permits oxygen to diffuse more  easily into the moisture. A lower surface tension also prevents the moisture 
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Unformatted text preview: on opposite walls of an alveolus or alveolar duct from cohering and causing the minute airway to collapse. • Alveolar macrophage cells (dust cells) wander among the other cells of the alveolar wall, removing debris and microorganisms. • A thin epithelial basement membrane forms the outer layer of the alveolar wall. • A dense network of capillaries surrounds each alveolus. The capillary walls consist of endothelial cells surrounded by a thin basement membrane. The basement membranes of the alveolus and the capillary are often so close that they fuse....
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