Color enhanced Bronchogram of right lung. Colored bronchogram (X-ray) of the bronchial tree of a healthy human lung. At upper right is the trachea (windpipe, red) which branches into the right bronchus (center right). A network of smaller branches called bronchioles divide from the bronchus, and these supply air to alveoli (air sacs, not seen) where gaseous exchange takes place. The healthy lung tissue is colored yellow. Bronchography renders the airways visible on X-ray film by prior injection of a radio-opaque contrast medium into the windpipe. This technique is used to locate such lung disorders as an abscess or a lung tumor.