Pulmonary Alveolar Epithelial Cells (PAEC)

Alveolar cells are cells lining the alveoli of the lungs. Two types of alveolar cell exist: type I alveolar cells and type II alveolar cells. Type I alveolar cells are squamous and cover approximately 90~95% of the alveolar surface. Type I cells are involved in the process of gas exchange between the alveoli and blood. It was proved that all alveoli are covered with an epithelial lining. Pulmonary alveolar epithelial cells (PAEC) need to be so thin to be readily permeable for enabling an easy gas exchange between the alveoli and the blood. Type II alveolar cells cover a small fraction of the alveolar surface area. Their function is of major importance in the secretion of pulmonary surfactant, which decreases the surface tension within the alveoli. They are also capable of cellular division, giving rise to more type I alveolar cells when the lung tissue is damaged.