Lobar bronchi

Lobar bronchi are the secondary ramifications of the main bronchi, specifically dedicated to ventilating the different lung lobes.

Lobar bronchi are air-conducting tubes that branch off from the main bronchi (or, in some cases, directly from the trachea for the right cranial lobe) and extend towards a specific pulmonary lobe. Each pulmonary lobe generally receives its own lobar bronchus. These bronchi are smaller in diameter than the main bronchi, but their wall still contains cartilage (in the form of irregular plates rather than complete rings), smooth muscle, and a ciliated respiratory mucous membrane. They then branch into segmental bronchi.

The nomenclature and number of lobar bronchi are directly related to the pulmonary lobation of each species, with a notable variation for the right cranial lobe:

• Ruminants (Cattle, Sheep):

  • Right Cranial Lobe: The lobar bronchus for this lobe is a major peculiarity. It branches directly from the trachea and is called the tracheal bronchus or right apical lobar bronchus.

  • The other lobar bronchi (for the middle, caudal, and accessory lobes of the right lung, and the cranial and caudal lobes of the left lung) branch off from the corresponding main bronchi.

• Cat, Dog and Horse:

  • Right Cranial Lobe: The lobar bronchus for this lobe branches off the right main bronchus, after the tracheal bifurcation. There is no tracheal bronchus.

  • The other lobar bronchi branch off from the main bronchi in a similar manner. Pulmonary lobation is less pronounced in horses, which can influence the branching of the lobar bronchi.

In humans, there is no tracheal bronchus. All lobar bronchi branch off from the main bronchi.