Let's take a journey through the air passageways of the lungs. Within the lungs, you can see a network of tubes called the bronchial tree, through which air enters and leaves your body.
Upon inhalation, the air you breathe in passes through the trachea (windpipe) and follows the network of bronchial tubes into each lung. The winding passageways branch into smaller and smaller sections, which end at tiny air sacs called alveoli. In each alveolus, the oxygen you inhale is exchanged for the carbon dioxide released from the cells in your body. The carbon dioxide is expelled in the reverse direction during exhalation.