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跟随氧分子的足迹从口而入,直达肺泡!里希(Dr.RIshi Desai)是儿童传染病医师,他是可汗学院的成员之一. Rishi Desai 创建




so here's a little person and I've drawn their face and you can see in blue at the bottom I've drawn their voice box and I'm gonna show you exactly what happens when you draw a little molecule like this of oxygen and follow it along its journey so it's gonna be breathed in either through the nose or through the mouth and you know it's gonna kind of end up in the same place or so we think right we said that basically kind of the back of the throat is where it's gonna end up and this is my nose kind of going to the back of the throat and the mouth kind of empties into the same spot but already there are going to be some differences so for example you have in your nose these little yellow nose hairs and the first question of course people think of with nose hairs is what the heck is their purpose what do they do and nose hairs are part of our filter system so we have this great filter system and there's nose hair and their job is to make sure that all the kind of large particles of dirt and dust are kind of picked up so they're good for getting all the large particles out of the air so it's cleaned up then you also have this kind of green slime right this kind of green mucus that we all kind of make and this mucus sometimes you think of it as snot this snot or mucus is good for small particles because it's really sticky and the small particles of dust and dirt are gonna glom onto it and so that is our way of kind of cleaning up the air so that when we breathe in through our nose the air is basically clean or at least cleaner then then it would be otherwise and so of course if you compared nose air or the air that you breathe in through your nose to air you breathe in through your mouth the mouth air will be of course a little dirtier because they didn't have that nice filter system and and kind of thinking along the same route if you if you think about picking your nose that would be basically kind of cleaning the filter right so that's kind of a new way maybe of thinking about that habit so air is gonna end up going to the back of the throat so air is gonna kind of go in this way and a little molecule of oxygen is gonna kind of end up at the back of the throat and another kind of interesting difference is that already that oxygen molecule and the air around it is gonna be slightly different in other ways it's gonna be cleaner if I went through the nose but either way nose or mouth it's going to be warmer and also more moist so that's another change in comparison on the outside the air is a little colder and drier so these are some key differences in terms of what's happening to the air these are two major differences right so now the air or our little molecule of oxygen has got a choice it can either go kind of down one of two paths one I'm gonna draw is gonna be into the larynx this is our larynx right here and we also call our larynx our voice box so you might remember that was the name I had mentioned previously a voice box or larynx is kind of the more medical word I guess and sitting over the larynx is the epiglottis the epiglottis and the epiglottis is basically like a lid kind of protecting the larynx from making sure that food and water don't go into it now there's another tube I just alluded to and it's sitting right here and this purple tube is our esophagus so the esophagus is basically it's fantastic for things like food and water you want food and water to go down the esophagus because it's going to lead to the stomach so you want food and water to go that way but you don't want food and water to go into the larynx and so you want to make sure that the epiglottis that lid is working really well in a food and water if you're swallowing food and water this epiglottis will literally just kind of close up and protect your larynx but in this case that's not that's not happening right we're not we're not actually food and water we're a little molecule of oxygen so let's follow that molecule a little bit further down let's see what happens to it I'm gonna drag up the canvas a little bit just make a little bit of space and I want to just stop it right there because I want to show you that the air molecule or the oxygen molecule has already kind of made an interesting crossroads is actually kind of broken an important boundary and that's this boundary right here and on the on the top of this boundary I've included the larynx and of course all the other stuff we just talked about the mouth and the nose and this is considered our upper respiratory tract so anything above this dashed line is our upper restaurant right and then of course you can then guess that anything below the line must then be our lower restaurant right so this is an important boundary because people will talk about the upper and lower tract and I want to make sure you know what is on which side so on the top of it is the larynx and everything above that and below it is the trachea let me label that here the trachea is right here the windpipe or the trachea and everything below that which of course mainly includes things like the lungs but as we'll see a few other structures that we're going to name so I'm gonna keep moving down but now you know that important boundary exists so now let me just make a little bit more space so you can see the entire lungs you can see the molecule is gonna go through the trachea and actually I have my left lung in completely drawn let me just draw finish it off right there so we have our right and left lung right these are the two lungs and our air is gonna just kind of slowly pass down our molecule of oxygen is going to pass down and it's going to go either into the right lung or the left lung now here I want to make sure I just take a quick pause and show you the naming structure and the important word of the day is the bronchi which alludes to one or sorry I screw it up already the bronchi which alludes to more than one sorry about that and bronchus which alludes to one so bronchi means more than one and bronchus bronchus means one so just keep track of these letters I and us okay so if we say that for example we are going into this area right here let me just choose a new color so it's really clear this will be our main if we go into this spot let's say our air molecule oxygen molecule goes this way then we would say it's in our left main I'm just gonna underline as I go left main bronchus that's what we would call that and then if it went further let's say went down here then instead of calling it main I would call it the low bar that's the word here so it's it's my left lobar bronchus and then if I want to go a little bit further I could say well now this is my segmental segmental so these are the words that we use and this final one would be then my left segmental bronchus and of course if you want to talk about two of them let's say I want to talk about you know both this guy and this guy then I would say those are my right segmental bronchi because now I have to use the top word because it's plural so that's the naming structure and another kind of important naming structure you'll sometimes see is primary bronchus secondary bronchus and segmental they call tertiary bronchus so you'll see either one of those but I'm gonna stick to main lobe are in segmental because I think it's a little bit easier and more intuitive to remember it that way now there are a couple important interesting things happening already so right here this not sure this point right here this is our Carina this is our Carina so at the Carina you have your break between the right and left main bronchus and what I want to point out to you is that this is a little bit more vertical this right-sided one is a little bit more vertical and the left-sided one is a little bit more lateral this is a little bit more flat or lateral so it's kind of a cool thing to know which is that if something was to slide down the throat let's say penny or a peanut or something was to slide down here it's more likely to go down this way simply because of gravity so gravity's gonna push things towards the right main bronchus more than the left main bronchus because the right main bronchus is a little bit more vertical that's kind of a fun fact that you now know and we should actually I guess I didn't do this already but we should take a break and make sure we name some of these things remember this is called our cardiac notch cardiac notch and remember that there are and there's that's one clue to kind of telling the part they left and right lung and the other clue we said was the lobes so of course the right one has the upper lobe the middle lobe and the lower lobe and the left lung only has the upper and lower so that's an important clue I just want to make sure we don't forget our little tricks that we've learned for telling apart the lungs so I'm gonna take a little pause there and now I'm going to show you in a sped up version all of the different branch points so for example here we have just a couple branch points right one two and getting into the segmental bronchi would be the third branch point but I'm gonna speed things along and show you how many more branch points that actually are before we get to the final part of our lung where the gas exchange actually happens so so enjoy [Music] [Applause] [Music] going back to the very point where we left off we we start with kind of a bronchi right and we said that there is a naming structure for how to name the bronchi but that's really just the first three branches and then after the first three branches all the orange stuff all those branches going from branch point four all the way down to about branch point 20 those are the conducting bronchioles so that's the name we give them they're no longer bronchi they're bronchioles and so if you see that word just keep that in mind that we're a little bit further along in the lungs and then after the conducting bronchioles you get into a few more branch points and we call them the respiratory bronchioles and actually the final I should mention this the final conducting bronchial sometimes you'll see this called the terminal bronchial it's that kind of a bad name because terminal sounds like we're done but actually we're just done with the conducting bronchioles and we're still kind of going into the restaurant gills I guess if I'm only pointing to one I should just probably make a singular and then finally get into the alveolar ducts and the alveolar sac which is kind of a few alveoli put together and if it's plural as alveoli then singular just talking about one little part of that sac would be alveolus so that's where our little molecule of oxygen ends up and this is kind of where it ends up before it's going to participate in gas exchange now this entire area going from respiratory bronchioles on downwards this is all called the respiratory zone the respiratory zone and anything above that is considered the conducting zone so anything above that and that really includes not just the connecting bronchioles but conducting bronchioles and then all the stuff above it so all the bronchi and even the larynx and the mouth and the throat that's all considered part of the conducting zone so basically oxygen is going to come in through the entire conducting zone everything we just talked about and is going to go down into the respiratory zone and finally our little molecule of oxygen is going to be very happy to finally made it to the very end of the bronchial tree and is ready for gas exchange now