Explanation

The diffusion membrane is made up of three major layers (figure) namely, the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and the basement substance in between them. However, its total thickness is much less than a millimeter. Therefore, all the factors in our body are favourable for the diffusion of $O_{2}$ from alveoli to tissues and that of $CO_{2}$ from the tissues to alveoli