How do the alveoli within the lungs create an efficient gas exchange surface?

The epithelial cells in the lungs are arranged into structures called alveoli which are found at the end of bronchioles and are adapted for efficient gas exchange.
Firstly, there are millions of alveoli within the lungs and this provides a very large surface area, increasing the rate of diffusion. The alveoli are very small and this provides a larger surface area to volume ratio. Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium- so the wall is one cell thick, providing a short diffusion distance, thus increasing the rate of diffusion. The walls of the alveoli contain elastic fibres so they recoil and this helps with ventilation. Also, the alveoli have a rich blood supply, constantly taking away oxygen and bringing in carbon dioxide, helping to maintain a steep concentration gradient.