How are the lungs adapted for gas exchange?

The alveoli are the site of gas exchange in the lungs. Oxygen diffuses into the blood down a concentration gradient while carbon dioxide exits the lung by diffusion. Alveoli have a very large surface area as there are millions inside each lung. Squamous cells present in the alveoli are moist. This ensures the cells are more permeable to the gases.There are only two layers of cells between the alveoli and the blood which decreases diffusion distance. The vast network of capillaries and the constant breathing maintains large concentration gradients.