bronchopulmonary segment

A bronchopulmonary segment is a smaller, self-contained district within a lobe — a wedge of lung with its own dedicated air supply and artery. If a lobe is a city, segments are its neighbourhoods, each plumbed independently.

Each segment is ventilated by its own segmental bronchus and fed by its own branch of the pulmonary artery, while the veins run between segments rather than within them. There are roughly ten such segments in the right lung and eight to ten in the left, and because each is relatively independent, it can be removed on its own.

This independence is surgically valuable: a segmentectomy can take out a small tumour while sparing more healthy lung than removing a whole lobe would. The vein-free planes between segments give surgeons natural lines along which to divide the tissue.