[Music] the alveoli are the site of gas exchange in the lungs and they're located here at the very end of the bronchioles they have a structure that's something like this we often describe it as having a sort of cauliflower ship but basically they're just tiny little air sacs at the end of the bronchioles if we see it here represented in more of a diagram format we can see what's going on first of all oxygen and carbon dioxide are constantly being supplied and removed through breathing let's look a little bit closer at the lining here notice there's only one cell thick oxygen can diffuse across the cell membrane of the cell that lines the alveolus from there can obviously diffuse across to outside of that cell the same thing applies for the lining of the blood capillary until eventually it diffuses into the red blood cell where it can bind with hemoglobin to form oxyhemoglobin similarly carbon dioxide can also diffuse across these cell membranes and reach the RV or a sac to then exit the body now then oxygen as we've already said is constantly being supplied through breathing but it's also being taken away from this area because of the blood flow what this means is that we are constantly maintaining a concentration gradient which is what allows this transfer of gas this gas exchange to continue there is important features of the gas exchange surface that you need to know first of all it's got a large surface area which is provided by this particular shape of the alveoli and also by the fact that there are lots and lots and lots of them inside of the lungs it's very thin which provides a short diffusion pathway notice that the lining is only one cell thick it's also got a moist lining the inside of each alveolar sac is is moist which allows gases to dissolve which then allows them to diffuse across the lining it's got a very good blood supply each one of the alveoli has lots and lots of blood capillaries surrounding it if we have a little look at what lung tissue looks like under a microscope we can see this sort of zigzag crisscross sort of mesh of little almost streams this is the capillary network and we can tell that because if we look at one of these individual little red splotches here those are individual red blood cells finally there is very good ventilation then our basic list means there's a really good supply of air which is supplied through breathing a little bit of exam help on this you might get asked to describe the features of the lungs that make gas exchange efficient well the exchange surface has a large surface area and that's provided by the large number of alveoli and the surface is only one cell thick remember that that provides a very short diffusion pathway and it is supplied with blood by a very dense capillary network so there you're easily going to get those three marks [Music]