hi everyone and welcome to miss estc biology in this video I'm going to be going through everything you need to know for topic 9 gas exchange for Cambridge International a level this is your perfect video for revision or even for learning it for the first time if you happen to miss a lesson or maybe you are self teing it and if you do need any more help and revision resources then check the link below CU I've got a whole range of things there that are going to help you to get the grades that you need but for now let's get into gas exchange cie topic 9 and in this one we're going through gas exchange so the Maman gas exchange system then you need to know the key structures the trachea or trocha Brony bronchos and the Alvi and the root that air takes during ventilation is it will be inhaled through the nasal cavity or mouth then it passes down the trachea which is the wind pipe it then is split between these two tubes which are the Brony it then branches into multiple smaller tubes which are the bronchioles and then we get to these air sacks at the end which are the alvioli so let's have a look at these structures in more detail now you could be asked to identify these structures on a photo micrograph or an electron micrograph so we're going to go through these structures what the function is but first i'm just going to talk you through what to look for to be able to identify them so for the trachea you're looking for a large tubular structure which is lined with ciliated epithelium which we might be able to see on an electron micrograph so there hairlike structures coming out of the Cent cells you might also see goblet cells which are interspersed amongst epithelial cells which would be this big almost like um indent into the cell where you have mucus being produced The traal Wall should contain cartilage as well and you get these c-shaped rings of cartilage the Brony are similar to the trachea but smaller diameter so the bronchia also lined with ciliated epithelium they contain these cartilagenous plates instead of complete rings and the plates may appear as irregular shaped segments along the Broncho wall the bronchioles are smaller less structured Airways compared to the tracha and Brony the bronchos is aligned with simple ciliated epithelium without the presence of cartilage you have smooth muscle fibers which may be visible in the bronchol wall heing as irregular bands or layers now the alvioli there's lots of round structures with an airs space in the middle and they've got very very thin walls they only one cell thick so if we go through these structures in more detail than just what they would look like on a microscope so we're starting with the tra which is the air pipe or windpipe and you have these c-shaped rings of cartilage which is what you can see here in this beige color and that cartilage provides structural support so the airway is constantly open and it doesn't get flattened or stuck together and it's c-shaped rather than the whole way round because your esophagus would be here and you don't want that hard cartilage against the esophagus because as the esophagus is Contracting and relaxing with peristalsis that could be interfered by that cartilage you also have ciliated epithelium with goblet cells the cyia those hairlike structures are there to sweep mucus up and out of the lungs to prevent infection of the lungs and then it's the goblet cells that produce that mucus so goblet cells upper section swells with mucin droplets mucus comprises mucin and it's this viscous solution of glycoproteins with multiple carbohydrate chains making it really sticky and capable of trapping inhaled particles which could be dust or it could be pathogens mucous glands beneath the epithelium produce the mucus certain chemical pollutants like sulfur dioxide and nitrogen dioxide can dissolve a mucus creating an acidic solution that irritates the airway lining so that's not a good thing smooth muscles is within the walls of the tra so smooth muscles are within the walls of the tra the muscle contracts if there are harmful substances detected in the airway and this results in the Lumin of the traa constricting and reducing air flow to the lungs as a way to try and protect the lungs when the smooth muscle relaxes the Lumin dilates this stretch and recoil of the Lumin is possible due to the elastic fibers within the tra wall next in the Brony and the bronchos the trachea splits into two tubes the Brony so you have a left and a right one and that leads to the left lung and the right lung and those Bronies split into the bronchioles which are these smaller tubes and both the Brony and the bronchioles have cartilage within their walls for structural supports to keep the tubes open now you will have noticed in that previous slide we said that the bronchioles don't have cartilage they will have cartilage at the very top Parts but as they Branch further and further those smaller tubules in the bronchioles don't have cartilage then the bronchioles end at the alvioli which are these air sacks and they're located at the end it's the site of gas exchange oxygen diffuses from the alvioli where you have a high concentration of oxygen or partial pressure into the blood where there is this lower partial pressure of oxygen and carbon dioxide does the opposite it's Al moving down its concentration gradients the blood that is entering the capillaries at this point is a high concentration of carbon dioxide so it diffuses from the blood into the alvioli where it'll be exhaled so in terms of adaptations then first of all the fact that there are so many Alvi in both lungs is what provides a large surface area one individual alveoli doesn't produce a large surface area it's the fact that there are millions in both lungs the short diffusion distance so that is created by the fact that the alvioli wall is made up of just one thin layer of cells and those thin layer are called squamous epithelial cells which I love that word squamous is such a cool word basically it's like the idea it's squashed it's a squashed flat cell and that reduces the diffusion distance also the endothelium of the capillary is just one layer of cells as well so you've got a very short diffusion distance the gases only have to diffuse through two cells which are both flat the maintaining of the concentration gradient that's done through ventilation but also the fact that the blood is constantly being transported away so as soon as the oxygen diffuses into the blood it's being transported away so a bit more then about this gas exchange in the Alvi we said that oxygen is inhaled into the alvioli and diffuses across the layers of those two um structures but we haven't said yet that the fact that the moist lining of the alvioli is there so you have this moist layer on that layer of cells and that's so the gases can dissolve in that liquid and then they diffuse across that way we did talk about that single layer of cells which is squamous epithelial cells they're flat they've got that really short diffusion distance the oxygen then diffuses through the endothelial cells lining the capillaries simultaneously carbon dioxide which is the waste product of respiration or arobic respiration diffuses from the blood in the pulmonary capillaries into the alvioli and carbon dioxide diffuses in the opposite direction of the oxygen moving in the efficiency of gas exchange is due to those three factors that we talked about the large surface area because there's so many Alvi the short diffusion distance because of these squamous epithelial cells and the fact that both the alv wall and the capillary endothelium is only made up of one single layer of cells and the concentration gradient is maintained by ventilation and that blood flow in the capillaries next then you need to know about the distribution of tissue and cells in the gas exchange system we've talked about this throughout but we've got a summary here for you so you can just create a summary sheet of information so the cartilage is distributed in the walls of the trachea and those larger Brony providing structural supports so that it doesn't collapse those tubes don't flatten and collapse the ciliated epithelium that's in your nasal cavity trachea and Brony and it's to move the mucus to sweep that mucus up and out of the lungs goblet cells you have lots of them in the respiratory epithelium secret a mucus to trap and remove inhaled particles the walls of the alvioli we said consist of a single layer of squamous epithelial cells and that allows for the efficient gas exchange between the alvioli and the capillaries smooth muscle is found in the bronchioles that helps to regulate air flow by controlling the diameter of the Airways and the capillaries form a dense Network surrounding the Alvi in the lungs which helps to facilitate rapid gas exchange because it maintains that concentration gradient so that is it for gas exchange make sure you do 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