Type I alveolar cells, also known as type I pneumocytes, are thin, flat cells that line the alveoli in the lungs. They cover about 95% of the alveolar surface area and play a crucial role in gas exchange. Their thin structure allows for efficient diffusion of oxygen and carbon dioxide between the air in the alveoli and the blood in the surrounding capillaries. These cells are supported by type II alveolar cells, which produce surfactant, a substance that reduces surface tension in the alveoli. This helps keep the alveoli open and prevents collapse during exhalation. Together, type I and type II alveolar cells are essential for maintaining healthy lung function and effective respiration.