Alveoli have thin walls. Oxygen passes through the wall and into the blood through the alveoli's capillaries. Alveoli are moist. Oxygen in the air dissolves into water before it is carried into the blood. Carbon dioxide, which is released by the blood, passes in the opposite direction. The total area of the alveoli in your lungs is larger than a tennis court. Alveoli are located at the ends of the tubes which lead from the windpipe into the lungs.
