Type II pneumocytes are specialised cells within the alveoli of the lungs. There are as many type II as type I pneumocytes within the alveoli, but type II cells only constitute 1-5% of the alveolar surface area as they are cuboidal rather than squamous in shape.
Type II pneumocytes are adapted to produce surfactant. Their cytoplasm exhibits apical secretory granules termed lamellar bodies. These are released continuously by exocytosis onto the epithelial cell surface. The lamellar bodies contain the phospholipid component of surfactant.
Type II cells also retain the ability to differentiate into type I cells. They occupy the thick portion of the alveolar-capillary complex.
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