Explain how are the lungs adapted for fast gas exchange?

The lungs are specifically adapted for gas exchange (diffusion) - meaning the lungs allow oxygen into the blood stream and carbon dioxide out. To ensure our cells can respire properly, we want fast and efficient gas exchange. The lungs contain many 'tubes' or airways that carry air in and out of our lungs. The end of these tubes are called alveoli, which are tiny sacs where the gas exchange occurs. Before we go through how the alveoli are adapted for this, it may be useful to remember Ficks Law: the rate of diffusion = (surface area x concentration gradient)/distance of diffusion pathway. Faster diffusion = larger surface area, steeper concentration gradient, and shorter diffusion pathway. With this in mind, you can see how the alveoli are well adapted for fast diffusion/gas exchange: There are many many alveoli (around 500 million!)- meaning there is a large surface area for diffusion to occur. The alveoli walls (or alveoli epithelium) are one cell thick - therefore there is a short diffusion pathway (short distance). The concentration of gases inside the alveoli and in the capillary is hugely different - meaning a steep concentration gradient. This gradient is maintained by the flow of blood in the vessels and constantly inspiring/expiring.