hello and welcome to learn a level biology for free with mr. ik this video is going to be about the human gas exchange system and ventilation so just to go over some key terms sometimes where there's misconceptions breathing and respiration are completely different breathing is the movement of air into and out of the lungs respiration is the chemical reaction that happens in every cell to release energy in form of ATP ventilation is the same thing as breathing it's the scientific term for breathing and gaseous exchange or gas exchange that is the diffusion of oxygen from the air in the alveoli into the blood and calm dark side in the other direction so from the blood into the air in the alveoli so the human structure for the gas exchange system then these are the key parts that you need to be aware of so these are key organs in this organ system the lungs you have to up so there are two large structures the left and the right lung and your trachea is the windpipe so just here we have our two here which is the windpipe and that has cartilage rings within it C shaped rings and those cartilage rings are really tough and that helps to support the tube that you care to keep your windpipe which is what the cheek here is open the trachea then branches into two brawn key and the bronchial bronchi will then branch into several smaller tubes in each lung and those are called the bronchioles and at the end of the bronchioles are these air sacs with very very thin epithelial cells which we call alveoli so first of all look at then is ventilation so how is it that air is drawn into the lungs and then out of the lungs and the two key structures involved are two muscles the diaphragm which is underneath the lungs and that is a muscle and then you have antagonistic pairs of muscles working together in the ribs and antagonistic means when one of the muscles contracts the other does the opposite it relaxes so you always have one muscle relaxing while the other is contracting and that's we're going to have a look at a bit more detail these antagonistic muscles so the external intercostal muscles and these are the muscles between the ribs so inter is between when the outside muscles the external ones when they contract that pulls the ribcage up and outwards and that provides a much bigger volume in the thorax so in that area and that leads to inspiration or inhaling or breathing in and while the external ones are contracting the internal intercostal muscles will be relaxing now because they're antagonistic to X Phi or exploration or exhale breathe out the internal intercostal muscles which you can just see it's certain angles in this rotating image they will then contract and the external ones will relaxed and that will pull the ribcage back in and down to decrease the volume in the thoracic cavity and therefore you'd have a high pressure forcing out the air so just to summarize those two key processes Lincoln it T's we said the structures involved and the effect it has on air pressure and the lung volume so first of all when you are inspiring or inhaling we said that external intercostal muscles will contract and because their antagonists ik pairs that internal ones will relax the diaphragm will contract at this point and when the diaphragm contracts that causes it to pull downwards so instead of it being in a domed up position it flattens and it pulls down so the impact this has is it's going to cause a decrease in the pressure in the lungs and that's because we have a bigger volume so whenever you have a bigger volume that causes the pressure to drop and therefore the air moves into the lungs because from the atmosphere which I've just some Bri v8 adair to atm from the atmospheric pressure compared to the pressure in the lungs there's a higher pressure outside compared to in so the air is always moving down it's pressure gradient meaning from a high pressure to a low pressure and in this scenario there is a higher pressure in the atmosphere compared to in the lungs so that causes the air to flow into the lungs and that is what inhaling is more inspiration expiration or exhaling is the exact opposite the external intercostal muscles will now relax and the antagonistic pair the internal intercostal muscles will contract and that pulls the rib cage back inwards and down at the same time the diaphragm muscle will relax and that causes it to pop back up into a domed position so we now have a much smaller volume in the thorax and that will call us the pressure inside of the lungs to increase and it increases to a higher pressure compared to the atmosphere and therefore this time the pressure gradient is you have a higher pressure in the lungs compared to the atmosphere and therefore the air is forced out of the lungs and into the atmosphere and that's what exhaling is so if we just get back to this diagram again so we can see all of that we can see the diaphragm here when you're inhaling Contracting and it's pulled down so it is flatter compared to when you're exhaling and the diaphragm relaxes and it domes much much higher up the ribcage is pulled out and upwards when you inhale because they're external intercostal muscles are contracting and when you are expiring the ribcage moves back down and in because the external intercostal muscles are relaxing and instead the internal intercostal muscles are contracting so Ranieri have a question linked to describing and explaining ventilation in humans you will always have to refer to whether the external and internal intercostal muscles are contracting and relaxing whether the diaphragm is contracting and relaxing and then what that does to the body therefore what it does to the pressure and therefore which direction will the air move so this table splits it up into the marking points for you the last thing then is the gas exchange in the alveoli and these are right at the end the air sacs at the end of the bronchioles so you have lots and lots of these air sacs and they are surrounded by capillaries we can see here zoomed in just on one single alveoli this air sac that is a very short diffusion distance because the alveoli are just made up of a single layer of cells and the capillary is also made up of a single layer of cells which you can just click here to see the video in more detail to learn about the blood vessels so we can see we've got diffusion because there's a high concentration of carbon dioxide compared to loads so carbon dioxide will diffuse out and we've got the blooms representing dilated Bloods but that alveoli will be full of highly oxygenated air so oxygen will be diffusing from the alveoli across the epithelium and into the blood and that's the last thing on the specification is known about the adaptations of the alveoli epithelium which is this layer that I'm just indicating all the way around here so the gases in alveoli we just said are diffusing from the alveoli into the blood becomes outside actually diffuses the opposite way around alveoli are the tiny air sacs and there are about 300 million in the left lung and the right lung so in terms of how does this gas exchange surface provide the three conditions that you always have to have the large surface area short diffusion distance and concentration gradients the fact that there are so many of these alveoli is what provides the large surface area the short diffusion distance this is maintained or created by the fact that alveoli are just made up of the walls are just one layer of epithelial cells and those epithelial cells are very very thin they're flattened cells so they're incredibly thin so that provides a very short distance for diffusion into the capillaries and finally because the alveoli are surrounded by this network of capillaries that is what provides a constant concentration gradient because the blood will be flowing in at a low concentration of oxygen and as soon as it picks up the oxygen that is diffusing in it's transported away again so you're constantly maintaining that concentration gradients so that is it for gas exchange in humans if you found helpful please give it a thumbs up and click subscribe to keep updated with all the latest videos [Music] [Music]