Mucociliary clearance in health and disease
Generations of the airway
The airways consist of a series of branching tubes, becoming narrower and shorter the further they extend into the lungs. There are 23 divisions of the adult airway which eventually terminate at the alveoli, the principle sites for gaseous exchange.
The larger airways up until the level of the segmental bronchi are composed of smooth muscle and cartilage which supports the structure of the airway. Below the level of the segmental bronchi cartilage is absent, with the patency of the smaller airways depending on the relationship between the elastic and smooth muscle fibres in the airway walls.
The epithelium is present throughout each generation of the airways, lining the airways and extending all the way down to the alveoli. However cilia and mucus secreting goblet cells only extend as far as the level of the respiratory bronchioles. This means the defence mechanisms provided by these cells are absent in the lower most airways, meaning dust and debris reaching the distal most lung regions have no mechanism of natural clearance.
