FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

What type of epithelium lines the alveoli of the lungs?

1. Cuboidal epithelium

2. Squamous epithelium

3. Columnar epithelium

4. Transitional epithelium

The correct answer is: Squamous epithelium

The alveoli of the lungs are lined with squamous epithelium, specifically a type known as simple squamous epithelium. This type of epithelium is composed of a single layer of flat cells, which allows for efficient gas exchange between the air in the alveoli and the blood in the surrounding capillaries. The thinness of the squamous epithelium minimizes the distance that oxygen and carbon dioxide must diffuse, facilitating the rapid transfer of these gases during respiration. Additionally, the vast surface area provided by the numerous alveoli enhances the lungs' capacity for gas exchange, making this epithelium particularly suited for their function. Other types of epithelium, such as cuboidal and columnar, are not ideal for the specific needs of the alveoli because they would introduce additional thickness and potentially hinder the efficient passage of gases. Transitional epithelium, primarily found in the urinary bladder, is specialized for areas that stretch and contract, which is not relevant to the structure and function of the alveoli. Thus, the presence of simple squamous epithelium in the lungs is essential for their role in respiratory physiology.