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Type II pneumocyte: Wikis

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Type II pneumocytes (great alveolar cells) 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.

Development

Type II cells start to develop at about 24 weeks of gestation, secreting small amounts of surfactant. However, adequate amounts of surfactant are not secreted until about 35 weeks of gestation - this is the main reason for increased incidence rates of Infant respiratory distress syndrome, which drastically reduces at ages above 35 weeks gestation.

Function

Type II cells are responsible for the production and secretion of surfactant (the majority of which are dipalmitoylphosphatidylcholine), a group of phospholipids that reduce 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.

MUC1, a human gene associated with type II pneumocytes, has been identified as a marker in lung cancer.[1]

References

  1. ^ Jarrard JA, Linnoila RI, Lee H, Steinberg SM, Witschi H, Szabo E (December 1998). "MUC1 is a novel marker for the type II pneumocyte lineage during lung carcinogenesis". Cancer Res. 58 (23): 5582–9. PMID 9850098. http://cancerres.aacrjournals.org/cgi/pmidlookup?view=long&pmid=9850098.  
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