Bronchi and Bronchioles - Anatomy & Physiology
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Introduction
The trachea bifurcates at the levels of the 4th-6th intercostal space, approximatley halfway between the thoracic inlet and the diaphrgam, dividing into two Principle 'Bronchi', tubes which conduct air into the lngs. These further divide into smaller bronchi and bronchioles. The initial division after entry to the lung, the Principle Bronchi divide into two Lobar Bronchi' for the left lung, and into four Lobar Bronchi for the right lung.
Structure
- The structure of the larger bronchi is identical to that of the trachea. On the smaller bronchi the cartilage rings are gradually replaced by plaques. Bronchioles have no cartilage at all.
- The bronchioles are less than 1mm in diameter, and these go through further divisions, the last of which is characterised by the loss of goblet cells.
Function
- The bronchi and bronchioles are parts of the 'Conduction' part of the respiratory system - allowing the passage of air from the external environment into the lungs where gaseous exchange can take place.
Histology
- The histology of the bronchi is almost identical to that of the trachea. The bronchioles have no cartilage rings but have muscular walls to enclose the lumen.
- The lumen is lined by a pseudostratified epithelium, including goblet cells and serous cells.
Species Differences
- The diameter of the bronchi and bronchioles vary greatly and more significantly than the variations of the trachea.
- The number of bronchial divisions before bronchioles are present varies by species - small mammals such as mice may have only 4/5 generations, whereas 12+ may be necessary in larger animals.