Final answer:
The question pertains to type II alveolar cells in the lungs that secrete pulmonary surfactant, which is vital for keeping the alveoli open by reducing surface tension, unlike type I alveolar cells which primarily aid in gas permeability.
Step-by-step explanation:
Type II alveolar cells are cuboidal epithelial cells located in the alveolar walls of the lungs and serve a critical function by secreting pulmonary surfactant. This substance is crucial for reducing the surface tension within the alveoli, preventing their collapse during exhalation and facilitating gas exchange. While type I alveolar cells, being squamous epithelial cells, make up the majority of the alveolar surface and are highly permeable to gases, they do not secrete surfactant.
In contrast, the surfactant produced by type II cells is composed of phospholipids and proteins, which facilitates breathing by decreasing the surface tension and thereby helping the alveoli to remain open. This is particularly important in premature infants, who may be born before sufficient surfactant is produced, leading to respiratory distress due to difficulty in inflating the lungs.