IIpneumocyten

Type II pneumocytes, sometimes referred to as IIpneumocyten in certain languages, are specialized cells lining the alveoli of the lungs. They are one of the two major types of alveolar epithelial cells, the other being type I pneumocytes. Type II cells are typically cuboidal in shape and sit at the corners of the alveoli, where they contribute to the integrity of the alveolar epithelium by forming tight junctions with neighboring cells. They contain cytoplasmic lamellar bodies, which store surfactant components.

A primary function of type II pneumocytes is the production and secretion of pulmonary surfactant, a lipoprotein complex essential for reducing surface tension at the air–liquid interface in the alveoli. Surfactant lowers the work of breathing and prevents alveolar collapse during exhalation. The surfactant includes phospholipids, notably dipalmitoylphosphatidylcholine (DPPC), and specific proteins: SP-A, SP-B, SP-C, and SP-D. Lamellar bodies store these components and release them by exocytosis into the alveolar space.

Beyond surfactant production, type II pneumocytes play a crucial role in alveolar repair and homeostasis. They can proliferate in response to injury and differentiate into type I pneumocytes to restore the thin alveolar epithelium after damage. They also contribute to innate immunity through secreted surfactant proteins that participate in pathogen recognition and clearance.

Developmentally, type II cells begin surfactant production late in gestation, which is vital for fetal lung function. Clinically, insufficient surfactant in premature infants can cause respiratory distress syndrome, a condition that often requires exogenous surfactant therapy. In adults, type II cells participate in fluid regulation and barrier maintenance during lung injury.