Chapter 13, Problem 1MC

Summary Introduction

Introduction:

The respiratory system comprises of lungs, nose, trachea, pharynx, larynx, bronchi, and alveoli. Alveoli are the sac-like structures present in the lungs. These are the actual sites of gaseous exchange in the entire respiratory system. The kind of cells that are present in the alveoli depends on the function they perform.

Answer to Problem 1MC

Correct answer:

The cells present in the alveoli of the lungs are squamous and cuboidal epithelia and macrophages.

Explanation of Solution

Justification/Explanation for the correct answers:

Option (a) is given that squamous epithelia are present in the alveoli. The alveolar wall is made up of a single layer of these cells. The thinness of the sacs allow air to pass in between the adjoining air sacs and at the same time, allow expansion. Hence, option (a) is correct.

Option (b) is given that macrophages are present in the alveoli. Macrophages are the defensive cells, which trap the bacterial particles that manage to pass through the nasal hairs and other air passageways. Hence, option (b) is correct.

Option (d) is given that cuboidal epithelia are present in the alveoli. These cells are present in between the other epithelial cells inside the alveolar sac. They produce a lipid molecule, that lubricates the alveoli. This surfactant reduces the surface tension during each contraction and expansion of the alveolar sac and thus, prevent the alveoli from collapsing. Hence, option (d) is correct.

Explanation for the incorrect answer:

Option (c) is given that columnar epithelia are present in the alveoli. These cells are either ciliated or non-ciliated. These cells are present in regions, where movement of particles is required. The ciliated ones are present in the upper respiratory tract and the non-ciliated ones are mostly secretive and/or protective in nature. The alveoli are free of any kind of particles. As the secretion is carried out by the cuboidal epithelial cells, these cells have no use here. So, it is an incorrect option.

Hence, option (c) is incorrect.

Conclusion

Thus, the alveoli are made up of simple squamous cells that line the alveolar surface, cuboidal epithelia that is present inside the sac, and macrophages that serve as the third line of defense in the respiratory system.