Corpus: Bronchus

The bronchi are part of the respiratory system. These tubular structures in the lungs originate from the trachea and carry air into the alveoli. Together, they form the bronchial tree.

The trachea splits at its lower end (bifurcation) into two main bronchi, one for each lung. These branches further divide into smaller branches that spread throughout the lungs, supplying air to both the right and left lungs.

Two lobar bronchi arise from the main bronchus on the left side and three on the right side, corresponding to the lung lobes. These lobar bronchi then branch further into segmental and subsegmental bronchi.

The hierarchy of the bronchial tree is organised as follows:

• Right and left main bronchi
• Lobar bronchi: upper, middle (right side only), and lower
• Segmental bronchi: 10 on the right, 9 on the left
• Subsegmental bronchi
• Bronchioles
  • Lobular bronchioles
  • Terminal bronchioles
  • Respiratory bronchioles

Histologically, the walls of the bronchi are lined with a multi-layered ciliated respiratory epithelium, which includes bronchial glands and goblet cells. Other features include endocrine cells, cartilage rings (in the main bronchi), cartilage plates, and smooth muscle.

Cellular composition of the respiratory epithelium

On a chest X-ray, only the larger, mostly single bigger bronchi are visible. In a computed tomography (CT) scan, the bronchial walls appear as tubular structures that narrow toward the outer areas of the lungs.