Last reviewed 01/2018

Bronchioles are fine airways which constitute the passages produced by the 11th to 17th divisions of the bronchi within the lung parenchyma. The adjective for things related to bronchioles is bronchiolar.

Bronchioles are characterised by:

  • luminal diameters from 0.5mm to 0.2mm
  • within their walls:
    • no hyaline cartilage
    • no submucosal glands
  • prominent outer wall layer of smooth muscle cells capable of constricting the bronchiolar lumen in response to parasympathetic (vagal) inputs; sympathetic fibres dilate the bronchioles

In addition, there are further specialisations of the bronchiole according to its relative position within the respiratory tree:

  • conducting bronchioles
  • terminal bronchioles
  • respiratory bronchioles