Thursday, May 5, 2011

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Microscopic structure of alveolar wall

From blood to air we have the following structures:
1) The capillary endothelium
2) A basement membrane and surrounding interstitial tissue 
3) The pulmonary interstitium is most prominent in thicker portions of the alveolar septum.
4) Alveolar epithelium.

The latter contains a continuous layer of two principal cell types: flattened, platelike type I pneumocytes covering 95% of the alveolar surface and rounded type II pneumocytes which produce pulmonary surfactant and are the main cell type involved in repair of alveolar epithelium in the wake of damage to type I pneumocytes. 

The alveolar walls are not solid but are perforated by numerous pores of Kohn, which permit passage of bacteria and exudates between adjacent alveoli.
Alveolar macrophages, mononuclear cells of phagocytic lineage, usually lie free within the alveolar space.  

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