EXTRAPULMONARY & INTRAPULMONARY BRONCHUS

1. PRINCIPAL (Primary) BRONCHUS

• Trachea bifurcates at Carina (at lower border of T4 vertebra at T4-T5 disc space) into right and left principal (primary) bronchi.
• Right principal bronchus is wider, shorter (2.5 cm long), and more vertical in the line of trachea (25 degree with median plane).
• Therefore a foreign body is most likely to lodge in the right bronchus.
• Right bronchus divides into epiarterial and hyparterial bronchi, passing respectively above & below the pulmonary artery, before entering the hilum.
• Left principal bronchus is narrower, longer (5 cm long) & more horizontal (45 degree with median plane).
• Left bronchus crosses in front of the esophagus producing a slight constriction.

2) SECONDARY (lobar) BRONCHUS

• Right lung has three lobar bronchi.
• Right lower lobar (secondary) bronchus is most vertical, nearly continues in the direction trachea.
• On left side there are two lobar bronchi upper & lower lobe of left lung, respectively.

3. TERTIARY (segmental) BRONCHI

• Lobar or secondary bronchi divides into tertiary bronchi.
• The part of lung tissue aereated by a tertiary bronchus is called as bronchopulmonary segment which is the antomical, functional & surgical unit of lung.
• There are 10 bronchopulmonary segments in each lung, thus each lung has 10 tertiary bronchi.
• Each tertiary bronchus undergoes about 13 more divisions & ends as lobular bronchiole.
• Lobular bronchiole further divides into terminal bronchioles, which emnate into respiratory bronchioles.
• Respiratory bronchioles proceed into alveolar duct, which immediately branch into alveolar sacs (alveoli).