Alveolar type 1 cells

Alveolar type 1 (AT1) cells are thin, squamous epithelial cells that cover approximately 95% of the gas exchange surface in the lung alveoli. Their extremely flattened morphology (extending over large areas) is ideal for the passive diffusion of oxygen and carbon dioxide between the airspace and the underlying pulmonary capillaries. They are terminally differentiated and crucial for maintaining the delicate blood-air barrier.