3. Normal Bronchial Tubes
When we inhale, air passes into our windpipe (trachea), our diaphragm contracts and moves downward creating air space in our chest cavity. The air enters the lungs, passing through the bronchial tubes and finally to the air sacs (alveoli). Oxygen from the air passes from the alveoli and into the bloodstream through the tiny blood vessels called capillaries. The capillaries deliver this oxygen-rich blood to your pulmonary vein, which goes to the left side of the heart. Your heart then pumps the oxygen-rich blood to the rest of the body. When you exhale, air that is rich in carbon dioxide (CO2) passes out of your lungs, through the windpipe, and out your nose or mouth.