Individuals that are heavy smokers may eventually have trouble clearing the mucous from their lungs because the structures that move fluid along the epithelial lining of the lung become damaged over time. What are these structures called?

Cilia

Explanation:

The respiratory system is the system of organs which allows the inhalation and exhalation of the gases especially oxygen and carbon dioxide. The respiratory system begins from the nose or nasal passage and end at the  lungs.  

The histology of the respiratory passages reveals that the epithelium layer of these is made of the columnar, cuboidal and the simple squamous epithelium along with ciliated structures.  These ciliated structures allow the movement of the mucus secretions and the other cell by whiplash movement.

In the given question, since the epithelium of the person is not able to move the fluid therefore the structure that is involved in the cilia.

Thus, cilia is the correct answer.

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