Each lung is subdivided by connective tissue into ten independently functioning compartments called bronchopulmonary segments. Every bronchopulmonary segment is supplied by its own set of blood vessels and tertiary bronchus (or segmental bronchus). Thus, if one becomes infected or is damaged, other bronhcopulmonary segments in the same lobe may not be affected. Connective tissue in each lung partitions the bronchopulmonary segments into approximately 130,000 lung lobules (= pulmonary or primary lobules). The tiny lobules each measure about 3.5 millimeters in diameter and contain many alveoli. These thin-walled air sacs are the regions where respiratory gases are exchanged with nearby blood vessels.