Final answer:
A squamous pulmonary epithelial cell is a type I pneumocyte, which is the major cell type on the alveolar surface and facilitates gas exchange due to its thinness and high permeability.
Step-by-step explanation:
The squamous pulmonary epithelial cell is a type I pneumocyte. This cell is a squamous epithelial cell found in the alveoli of the lungs, making up to 97 percent of the alveolar surface area. These cells are known for being extremely thin, approximately 25 nm, which allows for high permeability to gases, facilitating efficient gas exchange. Type I pneumocytes differ from type II pneumocytes, which are cuboidal epithelial cells that secrete pulmonary surfactant to reduce surface tension within the alveoli, and other cell types such as Clara cells, dust cells, and brush cells, which have different functions in the lung.