The Bronchioles

• • Each segmental bronchus branches several times, ultimately ending in terminal bronchioles. The walls of terminal bronchioles lack cartilage, and their epithelium is not the typical respiratory epithelium.
• Each segmental bronchus branches several times within the bronchopulmonary segment, forming many bronchioles
• Bronchioles then branch into the smallest diameter conducting branches, called terminal bronchioles
• Walls of the terminal bronchioles are continuous and lack cartilage and mucous cells
• Proximal segments are lined by a pseudostratified ciliated columnar epithelium
• More distal segments of terminal bronchioles are lined with a simple columnar ciliated epithelium
• Terminal bronchiole walls contain a significant amount of smooth muscle which the autonomic nervous system regulates
• Sympathetic activation and the release of epinephrine by the adrenal medullae cause bronchodilation, which increases the luminal diamter of the airways, reducing resistance to airflow
• Parasympathetic stimulation causes bronchoconstriction, a reduction on the lumninal diameter of the airways, increasing resistance to airflow
• Within the lobule, the terminal bronchiole branches int several respiratory bronchioles