These are little air sacs in the lungs where “air exchange” takes place. When you breathe, air goes in through your breathing tube, or trachea, which splits into smaller tubes called bronchi. These split into yet smaller tubes, called bronchioles. Finally, the smallest tubes lead into the alveoli. The alveoli are lined by only a few layers of cells. It is here that blood in capillaries is exposed to oxygen that you breathe. The blood goes back to the heart and then out to the rest of your body.
Dr. Kaplan
