Pneumocyte

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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 pulmonary surfactant, and self-regeneration.

1 Type I
2 Type II
3 See also
4 External links

[edit] 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.

[edit] Type II

Alveolar type II cell, the lamellar bodies can be seen leaving the surface of the cell.

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), a phospholipid that reduces the alveolar surface tension.

Type II pneumocytes can replicate in the alveoli and will replicate to replace damaged Type I pneumocytes.