Alveolar type I cells are thin, flat epithelial cells that line the alveoli, the tiny air sacs in the lungs where gas exchange occurs. These cells cover about 95% of the alveolar surface area and are crucial for facilitating the exchange of oxygen and carbon dioxide between the air and the bloodstream. Their thin structure allows for efficient diffusion of gases. In addition to their role in gas exchange, alveolar type I cells also contribute to the maintenance of the alveolar structure. They are involved in the production of substances that help keep the alveoli open and prevent collapse, ensuring proper lung function. Their health is vital for overall respiratory efficiency and is affected by various factors, including exposure to pollutants and diseases like chronic obstructive pulmonary disease (COPD).