Two cell types predominate in mammalian alveolar epithelium: Type I cells (membranous pneumonocytes), which have a small, nucleated cell body with attenuated peripheral cytoplasm containing a relative paucity of intracytoplasmic organelles, and which cover most of the alveolar surface; and Type II cells (granular pneumonocytes), which are nearly cuboidal with abundant cytoplasmic organelles, including moderate amounts of endoplasmic reticulum, ribosomes, and lamellar inclusions, and which cover areas of the alveolar surface not lined by type I cells. The lamellar inclusions of the type II cells represent sites of synthesis of pulmonary surfactant, the phospholipid rich substance primarily responsible for alveolar stability. The past few years have witnessed the ascendency of 3 other related concepts concerning the type II pneumonocyte: it participates in the injury and repair processes of pulmonary parenchymal tissue: it may be the progenitor of the more numerous type I alveolar epithelial cells; and the reparative adaptive response determines, to some extent, the susceptibility of lung parenchyma to oxidant stress. This editorial summarizes the 3 mutually complementary concepts.
|Original language||English (US)|
|Number of pages||3|
|Journal||Annals of Internal Medicine|
|State||Published - 1974|
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