- Pneumocyte
Two types of cells contribute to the maintenance of the
alveoli of the lungs: Type I and Type II pneumocytes. These cells function to aid in gas exchange, secretion of pulmonarysurfactant , and self-regeneration.Type I
Type I pneumocytes are responsible for
gas exchange in the alveoli and cover a majority of the alveolar surface area (>95%). While type I pneumocytes account for most of the surface area, they are approximately half as numerous as type II cells, due to differences in size. Type I pneumocytes are large, thin cells stretched across a large surface area, while type II pneumocytes are smaller cells.Type I pneumocytes are unable to replicate and are susceptible to toxic insults. In the event of damage, Type II cells can proliferate and/or differentiate into type I cells to compensate.
Type II
Type II pneumocytes are granular and roughly cuboidal in shape. Type II pneumocytes are typically found at the alveolar-septal junction and cover a much smaller surface area than type I cells (<5%), but are much more numerous. Type II cells are responsible for the production and secretion of
surfactant (dipalmitoylphosphatidylcholine ), aphospholipid that reduces the alveolar surface tension. Surfactant phospholipids are stored in Type II pneumocytes in lamellar bodies, which are specialized vesicles. Release of surfactant in lamellar bodies occurs from an infant's first breath onwards.Type II pneumocytes can replicate in the alveoli and will replicate to replace damaged Type I pneumocytes.
ee also
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Dust cell External links
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* [http://www.meddean.luc.edu/lumen/bbs/p/ppi10.html Electron micrograph at luc.edu]
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