The respiratory (diffusion membrane) across which exchange of gases occurs in the lungs consists of all the following, except

The diffusion membrane is made up of three major layers:1. the thin squamous epithelium of alveoli2. the endothelium of alveolar capillaries3. the basement substanceThe basement substance is composed of a thin basement membrane supporting the squamous epithelium and the basement membrane surrounding the single layer endothelial cells of capillaries) in between them.