Question

Cilia lining the nasal cavity and nasopharynx beat in unison to propel mucus and debris inferiorly. Cilia lining the respiratory tract inferior to the true vocal cords beat in unison to propel mucus and debris superiorly. Explain the reason for this functional difference.

Answer 1

The basic function of cilia is to keep us free from irritation and to propel the foreign/toxic substances outwards from the body.

Keeping this in mind, consider the location of the cilia mentioned in the question.

The nearest opening near the nasal cavity and nasopharynx is the nares. The propulsion of cilia here makes the debris exit our body through the nares if in the nasal cavity or via the mouth in case of nasopharynx.

In the respiratory tract the cilia beat superiorly so as to expel the debris outwards via the mouth or nasal cavity.