What type of epithelial cell is primarily involved in diffusion?

The epithelial cell type primarily involved in diffusion is squamous epithelium. Squamous cells have a flat and thin structure, which facilitates the rapid exchange of substances across the cell layer. This characteristic is essential in locations where diffusion needs to occur efficiently, such as in the alveoli of the lungs, where gas exchange takes place, and in the lining of blood vessels (endothelium), where nutrients and wastes are exchanged between the blood and tissues.

The thinness of the squamous cells minimizes the distance that molecules must travel, thus increasing the rate of diffusion. In contrast, cuboidal and columnar epithelial cells, which have more volume and a greater height, are less suited for diffusion as they may hinder the rapid passage of materials. Transitional epithelium, found in the urinary bladder, is specialized for stretch rather than diffusion, making squamous epithelium the clear choice for this function.