Which of the following help(s) comprise the defense system of the nose?
1. Clearance of foreign matter by ciliary action
2. Gross filtration by the large hairs of the nasal vestibule
3. Impaction of particulate foreign matter on the nasal mucosa
4. Laminar flow through the concha
a. 1, 2, and 3 only
b. 2 and 4 only
c. 3 only
d. 1, 2, 3, and 4
ANS: A
Filtration of inhaled air is carried out by the hair in the anterior portion of the cavity and the sticky mucous membrane that covers the complex surface of the cavity. Filtration is enhanced by the flow pattern through the nasal cavity. Inspired gas is accelerated to a high velocity through the anterior nares. It then changes direction sharply as it enters the internal nasal cavity. This pat-tern causes particles larger than 10 µm in diameter to impact on the nasal mucosa. Ciliary action or nose blowing then clears these particles. Past the external nares, the cross-sectional area in-creases. This results in a decrease in gas velocity. Turbulence increases because of the narrow convolutions of the passages. Low velocity and turbulence combine to remove any remaining particles.
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