Which of the following statements about squamous alveolar cells is true?

Squamous alveolar cells, also known as type I alveolar cells or type I pneumocytes, are the primary cells that make up the alveolar walls in the lungs. Their major function is to facilitate rapid gas diffusion between the alveoli and the blood in the surrounding capillaries. The thin, flat structure of these cells minimizes the distance that oxygen and carbon dioxide need to travel, making gas exchange efficient and effective.

In contrast, type II alveolar cells are responsible for secreting surfactant, which reduces surface tension in the alveoli and helps keep them open. Immune defense in the alveoli is primarily carried out by immune cells known as macrophages rather than the squamous alveolar cells. Additionally, mucus production in the lungs is typically associated with goblet cells found in the airways, not in the alveoli, where squamous cells are found.

Therefore, understanding the primary role of squamous alveolar cells in gas exchange helps clarify why this statement is considered true.