now if you remember one of the function of the gas exchange system is to filter the dust and pathogens when you breathe air into the lungs the reason why it has to do that is because well the air depending on where you live all right if you live in a big busy City full of cars and such um cars will release a lot of pollutants then there may be dust of fine particles in the air or even pathogens for that matter which if they go into our lungs may damage the lung tissue so it is imperative that the air that is full of dust and pathogens when it passes through the trachea and also the broni um it the air has to be filtered so as you can see the air going into the traa at the top is full of dust and pathogens but as it passes through the airway system there will be lesser dust and pathogen entering our lungs um the reason is because we want to mitigate any damage that can be exerted onto our lung tissues so the question here is this how does our gas exchange system actually filter the dust and pathogens in the air one way it does so is by the presence of goblet cells in our trachea and broncus where it's located along the epithelial layer which we discussed in the previous video so what exactly do goblet cells do well I'm just drawing out one goblet cell here and the function of the Goblet cell is actually to release something called mucin or mucus if you look at your textbook they'll use these two words interchangeably there are some slight differences in the terms mucin and mucus but for the exam purposes using mu mucin or mucus is fine do not worry so much about that so how does the Goblet cell actually release this mucus so we have to talk about the steps a little bit because it involves a few different Chapters at the same time you see in the Goblet cell they have a nucleus and inside the nucleus they have chromosomes which contain genes and very specific genes will undergo transcription where it produces the MRNA the MRNA will then move to the rough ER where it under goes translation and after that polypeptide chains are produced so this step that I'm showing you here is transcription and transl ation which is part of protein synthesis so you might be thinking what does protein synthesis have to do with mucus well what might happen to those specific polypeptide chains up they will go to the GGI apparatus where the GGI apparatus will modify this polypeptide chains by adding them together with some carbohydrate or sugar molecules and by adding them together with some sugar chains or sugar molecules they will produce something called glyco protein a glyco protein is just a particular type of molecule where it's made up of a protein where it's that green color blob that I'm showing you there and they also have these carbohydrate chains extending out of its main body those branch-like structures are the carbohydrate portion that's why it's called glycoprotein so what does this have to do with anything that glycoprotein is referred to as muin you see you've learned about a few types of glycoproteins by the way you saw gly proteins on the cell surface membrane in chapter 4 where they act as receptors and then in chapter 11 you learned about a very specific type of glycoprotein called antibodies and um now you're learning about a particular type of glycoprotein called mucin or mucus and the interesting thing about this particular type of glycoprotein mucin or mucus is they will then be packaged into vesicles that's what the G geop Paratus does uh it will modify the polypeptide chain to produce glycoproteins and then they will also package the glycoprotein into vesicles once it is packaged into vesicles that's when those glycoproteins I'm just zooming in over here what's Happening Here those vesicles are fusing with the cell surface membrane and those greenish structures which I'm representing as mucus mucus is not naturally green in color by the way it's usually clear um but what happens to the mucus is the mucus will be released by exocytosis please do not say the the vesicles are released by exocytosis that is wrong it is the mucus that is released by exocytosis what the vesicles only have to fuse with the cell surface membrane and of course in chapter 4 we studied uh exocytosis before this process also requires ATP so this is how the goblet cells actually produce the mucin or mucus and they release it out of the cell so that the mucus will remain on the surface of the epithelium so once it remains on the surface of the epithelium as I'm just representing it here the pathogen and dust will stick the glycoprotein branches form these kind of armik projections and the arms can capture the pathogen and dust and that's what causes the pathogen and dust to stick to the mucus because the mucus has that very sticky attackyoutube has to be pushed upwards and how is it pushed upwards that is done by the cated epithelium where they have the Celia and the Celia produces an upward beating to move the mucus upwards they move it upwards towards your throat and then automatically you'll swallow it so it goes into your stomach and then your stomach acid and enzymes can digest whatever you have swallowed if there's too much dust and pathogen inside your tra and broncus it sends a signal to your brain which produces sneezing or coughing so you can forcefully expel it as well so this is how filtration of the air for dust and pathogens happen simple stuff now another very important thing that we also have to talk about is the response of the bronchioles during exercise just a little bit of revision the bronchioles usually have a ciliated epithelium no goblet cells the Lumen is quite small underneath the epithelium they actually have smooth muscle cells so why is it important that they have the smooth muscle cells the reason is because well let's look at a situation first imagine that you're running when you're running your muscles need more oxygen well that's kind of logical because when you're running you need more energy so your muscles need more oxygen to carry out aerobic respiration to produce more ATP that's all in chapter 12 but the point here is I just want you to look at the Lumen of the bronchial when you're standing and when you are running the slight difference is when you look at the Lumen when you're running the Lumen of the bronchos are slightly larger right and when you're standing the Lumen is slightly smaller now why is that so the reason is because when you're standing the smooth muscles in your bronchos are Contracting so it kind of squeezes to make the Lumen smaller but when you're running the smooth muscles in your bronchol are relaxed which makes the Lumen larger again why does this happen remember question asks you what are the adaptations of the bronchioles for exercise you just have to say that in the bronchioles the cartilage are absent so it allows the Lumen size to change so when the smooth muscle relaxes the Lumen gets larger this allows more air to go into the alveoli so that more oxygen can diffuse into the blood it is as simple as that and this usually happens more when we are exercising so that you know because more exercise when we exercise more if we exercise more sorry if we exercise more not when because some of my students do not exercise uh so if we exercise more oxygen can actually diffuse into the blood because that is quite important to happen