[Music] hi and welcome back to three sighs lessons cold okay by the end of this video you should be able to describe how the lungs are adapted for gas exchange in the last few videos we've been looking at the circulatory system we saw that the heart pumps blood to the lungs where the blood collects oxygen the blood then returns to the heart unders come true on the whole body where it delivers the oxygen to the body cells so in this video were looking at how the lungs are adapted for gas exchange I'm showing you a picture of the lungs here as you can see humans have got two lungs air passes into the lungs through a tube called the truck ear now one key feature of the truck here is that a contains wings of cartilage these prevent the trachea from collapsing when we inhale the trachea now splits into two smaller tubes called bronchioles the bronchus subdivide into many smaller tubes called bronchioles and finally the bronchioles end in tiny air sacs called alveoli now the lungs contain a huge number of alveoli and each one's microscopic in this diagram I'm showing them bigger than they actually are the alveoli are where gases diffuse in and out of the bloodstream in other words they're the sites of gas exchange so now we're going to take a look at how alveoli are adapted for gas exchange and it's really important that you learn these adaptations I'm showing you a close-up of a single alveolus here oxygen in the air diffuses into the bloodstream like this and carbon dioxide diffuses out of the blood stream back into the air like this now the alveoli have several adaptations to make the rate of gas exchange as fast as possible first the millions of alveoli mean that the lungs have a huge surface area secondly the alveoli have very thin walls so the diffusion path is very short and lastly the alveoli have a very good blood supply once the oxygen diffuses into the blood it's rapidly removed this ensures that the concentration gradient is as steep as possible these adaptations mean that oxygen diffuses rapidly into the blood stream and carbon dioxide diffuses rapidly out now there is one final point which is really important by breathing we also increase the rate of diffusion breathing brings fresh oxygen into the alveoli arm takes away the carbon dioxide this makes the concentration gradients high for these gases and again that increases the rate of diffusion remember you'll find plenty of questions on the adaptations of the lungs in my revision work book and you can get that by clicking on the link above ok so hopefully now you should be able to describe how the lungs are adapted for gas exchange [Music]