Healthy alveoli in the lung. Cutaway computer artwork showing the interior of healthy alveoli (spheres), and bronchioles (tubes) and blood vessels (red and purple) of the lungs. Alveoli are the tiny air sacs of the lungs where gases are exchanged between the air in the lungs and the blood in the blood vessels that surround them. Bronchioles are small airways that carry inhaled air to the alveoli, and used air from them.