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Pulmonary clearance

How does pulmonary elimination work?

Apart from specific cases, deposited particles are eliminated from the lungs by natural clearance mechanisms:

  • physical: insoluble particles deposed in the trachea-bronchial tree and the upper airways are in majority eliminated by Muco-ciliary transport towards the noise and the mouth. They are swallow or release toward outside (sneeze,…). At the level of pulmonary alveoli, macrophages take charge of the elimination of insoluble particles by phagocytosis,
  • chemicals: dissolving (for those that are soluble) or fixing to the components of the liquid lining the airways permit their transfer in the blood and excretion in the urine. The chemical elimination processes occur in all regions of the respiratory system.

When is a pulmonary elimination not working?

macrophage

Alveolar macrophages.

Less well phagocyted by the macrophages, some nanoparticles, in particular individual particles (nonaggregate or nonagglomerate), could reside longer in the lung, which would facilitate their entry into the cells of the respiratory epithelium and their transfer to deeper layers (interstitial spaces, bloodstream) [C. Buzea et al., Biointerphases 2 (2007) 17-172 / G. OberdÖrster et al., Journal of Nanoscience and Nanotechnology 9 (2009) 4996-5007 / H.M. Braakhuis et al., Particle and Fibre Toxicology 11 (2014) ].

Some articles focus on mesothelioma observation via MWNTC absorption, geometrically rigid nano-objects, the nearest of asbestos fibers [A. Takagi et al., The Journal of Toxicological Sciences 33 (2008) 105-116 / K. Donaldsonet al., Particle and Fibre Toxicology 7 (2010)].

Other nanoparticles, particularly Mn oxide, could go back up the olfactory nerve endings of the nasal passages and directly reach the brain [J. Wang et al., Toxicology 254 (2008) 82-90 / H. Shiet al., Particle and Fibre Toxicology 10 (2013)].