Bronchi are larger air passageways that conduct air from the trachea into each lung. All bronchi are held open by hyaline cartilage, although the amount of hyaline cartilage gradually decreases as the distance from the trachea increases. Bronchi are categorized into 3 types:

  1. Main bronchi result from the bifurcation of the distal portion of the trachea into two passageways. These passageways are the right and left main, or primary, bronchi. Each main bronchus penetrates the medial surface of the lung in a region called the hilum prior to branching into lobar bronchi.

  2. Lobar bronchi branch from the main bronchi and penetrate the lobes of each lung. Lobar bronchi are also known as secondary bronchi. There are three lobar bronchi on the right that penetrate the three lobes of the right lung. Two lobar bronchi on the left penetrate the two lobes of the left lung.

  3. Segmental bronchi branch from the lobar bronchi and penetrate into individual segments of the lung lobes. Segmental bronchi are also known as tertiary bronchi.

Figure 1: The bronchi of the bronchial tree and a cross-section of a bronchus.