The bronchopulmonary segments are the anatomic, functional, and surgical units of the lungs. Each lobar (secondary) bronchus, which passes to a lobe of the lung, gives off branches called segmental (tertiary) bronchi.
Each segmental bronchus passes to a structurally and functionally independent unit of a lung lobe called a bronchopulmonary segment, which is surrounded by connective tissue. The segmental bronchus is accompanied by a branch of the pulmonary artery, but the tributaries of the pulmonary veins run in the connective tissue between adjacent bronchopulmonary segments.