The bronchi are classified as the lower airways that conduct air from the trachea to the lungs. They form a bronchial tree as the large bronchi branch into smaller bronchi and bronchioles. The bronchial tree has two parts - extrapulmonary part and intrapulmonary part.

The largest part of the bronchial tree extends into the lungs, and the bronchi located within the lungs are called the intrapulmonary bronchi. However, the intrapulmonary bronchi do NOT form the lung parenchyma. The bronchial tree is only the conducting part that transmits the air from the external environment to the site of the gas exchange.

The bronchial tree starts at the tracheal bifurcation with the right main bronchus and left main (principal) bronchus that branch into smaller bronchi. The bronchial tree is composed of the following bronchi (from the largest to the smallest):

Main (principal) bronchi
Lobar bronchi
Segmental bronchi
Subsegmental bronchi
Bronchioles
Terminal bronchioles

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Bronchial tree