The Human Lungs

Human Lungs Air travels to the lungs though a series of tubes and airways. The two branches of the trachea, called bronchi, subdivide within the lobes into smaller and smaller air vessels. They terminate in alveoli, tiny air sacs surrounded by capillaries. When the alveoli inflate with inhaled air, oxygen diffuses into the blood in the capillaries to be pumped by the heart to the tissues of the body, and carbon dioxide diffuses out of the blood into the lungs, where it is exhaled.