What specialised structures do the lungs have to allow diffusion of gases?

The lungs are highly specialised. They have alveoli which are small air sacs. Alveoli give the lungs a big surface area, meaning that more oxygen can diffuse from the lungs into the blood stream, and more waste gases from the blood into the lungs. Further, they are moist, covered in surfactant which reduces surface tension throughout the lung. This prevents the alveoli collapsing, hence reducing gas exchange. Alveoli have thin walls which are one cell thick - this allows a small diffusion distance from the blood stream to the lungs. Surrounding the alveoli is a network of capillaries. These allow effective gas exchange between the blood and the lungs. Specialised areas allow effective gas exchange within the lungs.