Bronchi

Two principal or main bronchi, singular bronchus, diverge from the trachea at the level of the tracheal bifurcation level with the sternal angle, the lower border of the fourth thoracic vertebra. They pass laterally to form the respiratory passages on each side of the thorax within the mass of lung parenchyma. In order to do this, they undertake many orders of subdivision:

• the main bronchus on each side divides into
• lobar bronchi, two on the left, three on the right; the lobar bronchi divide the lung into lobes; each lobar bronchus divides into
• 2-5 segmental bronchi; each segmental bronchus supplies a bronchopulmonary segment; there are usually ten bronchopulmonary segments in each lung; within each bronchopulmonary segment, the segmental bronchi ramify into
• subsegmental bronchi; ultimately, the subsegmental bronchi ramify into ever smaller bronchioles

The adjective for items related to the bronchi is bronchial.