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Lobar Bronchi, Tertiary (Segmental) Bronchi and Pulmonary Units

Lobar Bronchi

The right principal bronchus splits (produces) 3 lobar bronchi, 1 for every lobe of the right lung on going into the lung. On going into the lung lung splits into 2 lobar bronchi, 1 for every lobe of the left lung on going into the lung.

Tertiary (Segmental) Bronchi

Every lobar bronchus divides into segmental (tertiary) bronchi, 1 for every bronchopulmonary section.

The segmental bronchi divide repeatedly to create quite small bronchi termed terminal bronchioles. The terminal bronchioles give off respiratory bronchioles, which lack cartilage in their own walls.

Every respiratory bronchioel aerates a small portion of lung termed pulmonary units, that is concerned with gaseous exchange inside the lung.

Pulmonary Units

Every pulmonary unit is composed of.

  • Alveolar ducts
  • Atria
  • Air saccules
  • Alveoli

Points to be noted

A. The respiratory bronchiole represents the transitional zone/part between the running and respiratory portions of the respiratory system.

B. The alveoli are specialized sac like structures which create greater part of the lungs. They’re the principal sites for the gaseous exchange of oxygen and carbon dioxide between the divine air and blood.

Clinical Significance


In this state, alveoli of lungs are damaged by compounds discharged by pollutants. Medically it presents as shortness of breath and the chest appears barrel shaped in chest radiograph.

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