Alveolus is the structural and functional unit of the lung. The alveoli are the chambers in the lungs that are composed of squamous cells and filled with capillary networks that carry out gaseous exchange. Its diameter is 200-300 micrometers. Human lungs have about 480 million (48 crore) alveoli. These create 525 square feet, the equivalent of a tennis court, and about 11,800 square centimeters of breathing space.
