Module 4: Lung Defences Against The Environment - The Mucous Layer And The Muco-Ciliary Escalator.

The Mucous Layer And The Muco-Ciliary Escalator:

The nasal and tracheo-bronchial clearance mechanisms are most efficient with larger particles (> 7 microns).

The figure below shows the relationship between particle size and its lung deposition. Particles trapped in the nose or by the muco-ciliary escalator in the tracheo-bronchial tree will not be retained by the lung.

At particle size < 7 microns particles may be deposited in alveoli as the airway defences become increasingly less efficient. Maximal pulmonary deposition occurs with particles 1 - 3 microns, and with ultrafine particles < 0.1 microns.

Deposition in the respiratory system as a function of particle size for 15 respirations/min (1450 ml tidal volume)

The illustrations below show particle size relative to cellular structures, the Mucous Layer and the Muco-ciliary escalator.