The Respiratory System and the Lungs - Pollution control-filters, cleaners, and traps

Air pollution being what it is these days, it is fortunate that we have several natural devices that serve to filter out and wash away most of the impurities in the air we inhale.

Air gets into the lungs from outside about equally well via the nose or mouth. The mouth offers the advantage of getting more air in at a faster rate—absolutely a must if we have to push our body physically. But the nose has more and better equipment for cleaning air before it reaches the trachea. Via the mouth, air must only pass over a few mucous membranes and the tonsils, which can collect only so many germs and impurities.

Nose Filter System

Air taken in through the nose, however, first meets the “guard hairs” ( vibrissae ) of the nostrils, and then must circulate through the nasal cavity, a kind of cavern framed by elaborate scroll-shaped bones called turbinates , and lined with mucus-secreting membranes and waving, hair-like fibers called cilia . Foreign particles are caught by the cilia and carried away by the mucus, which drains slowly down the back of the throat.

It would be nice to be able to ascribe an important function to the eight paranasal sinuses , four on either side of the nose: the headache and discomfort of sinusitis might then be more bearable. But these “holes in the head” seem to exist simply to cause us trouble; for example—swelling to close the nasal air passages, making it impossible to breathe, as recommended, through the nose.

Filter System beyond the Nose

The cleansing and filtering action started in the nose and mouth does not stop there, but is repeated wherever air travels along the air passages of the lungs. Cilia project inward from the walls of even the tiniest bronchioles of the lungs, and impurities are carried from the alveoli on films of mucus that move ever back toward the trachea for expulsion—as when we cough. See also Ch. 12, Diseases of the Respiratory System and Ch. 13, Lung Disease .