The trachea (windpipe) divides to form the right and left main bronchi. These divide to form smaller and smaller tubes called bronchioles. Eventually the bronchioles end in the alveoli (small air sacs). At the alveoli, oxygen from the air we breathe into our lungs is moved into the blood. The blood then carries oxygen around to the rest of the body, which needs oxygen to survive. Without the bronchi, air would never get into the lungs, and oxygen would never get into our bodies.