Alveolar Type I Cells are thin, flat cells that line the alveoli, the tiny air sacs in the lungs where gas exchange occurs. They cover about 95% of the alveolar surface area and are crucial for facilitating the exchange of oxygen and carbon dioxide between the air and blood. Their thin structure allows for efficient diffusion of gases. These cells are part of the respiratory epithelium and play a vital role in maintaining the integrity of the alveolar barrier. They are supported by Alveolar Type II Cells, which produce surfactant to reduce surface tension and prevent alveolar collapse.