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肺部系统包括肺、喉、气管、支气管、细支气管、肺泡和胸膈膜. Sal Khan 创建




I've done a bunch of videos already on respiration and I think even before those videos you had a sense that we need oxygen that we need oxygen and that we release co2 and if you watched the videos on respiration you know that we need the oxygen in order to metabolize our food in order to turn our food into ATP's that can then drive other types of cellular functions or anything that we have to do move or breathe or think or everything that we have to do and that through the process of respiration we break down those sugars and we release carbon dioxide so in this video what I want to do is kind of take a big step back and think about how we actually get our oxygen into our body and how we release it back out into the atmosphere or another way to think about is how we ventilate ourselves ventilation how do we get the oxygen in and how do we get the carbon dioxide out and I think any of us could at least start off this video and it starts off and either our nose or our mouth I always have a a clogged sinus so I often have to deal with my mouth I sleep with my mouth open often but always starts in our nose or our mouths let me draw someone with the nose and a mouth so let's say that this is my person maybe his his mouth will be open so that he can breathe so this is let me his eyes aren't important but just so that you know it's a person so this is my test subject or the person I'm going to use to diagram that's his ear maybe he has maybe he has a bit of a I mean just give him some hair oh maybe some sideburn anyway I'm most at all of that is irrelevant but this is our guy this is the guy that's gonna show us how we take air in and how we take air out of the body so let's go inside of this guy let me like and draw his outside first now let me see how well I can do this so this is outside the guy that'll look great so let's say the guy looks something like this and then you know he's got this is his shoulders just like that that's our guy all right so in our mouth we have our oral cavity right there which is just the space that our mouth creates we have our oral cavity I could draw our tongue in all of that and maybe I will maybe I'll draw our the tongue you know maybe the tongue looks something like that but you have this space inside of the mouth I'll call that the oral cavity so this space inside of our mouth just like that this is the oral cavity oral cavity oral for mouth cavity for space or hole or opening and then also you have your nostrils and they open up into a nasal cavity so they open up into a nasal cavity so that's another big space just like this and we know that they connect they connect at the back of our nose or the back of our mouth and this passage right here this passage right here where they connect is called the pharynx this is the pharynx and that's you know when your air goes through your nose they say breathing through your nose is better probably because it get filtered by your nose hairs and it gets warmed up and and whatnot but you can breathe through either side the air goes in through either your nasal cavity or your oral cavity and then comes back through your pharynx and then it's the flat pharynx splits into two pipes one for well one air can go down either one but the other one is for food so your pharynx gets split in the back you have your esophagus in the back and we'll talk more about the esophagus in a future video in the back you have your esophagus and in the front let me draw a little dividing line there in the front maybe this is let me make it connect like that actually maybe I do it I should I was using yellow I'm gonna use yellow to continue and I'm gonna use green for the air so it divides just like that so this is the dividing line so in the back or the back of your you know behind your air pipe you have your esophagus you have your esophagus let me make that in another color so this right here is your esophagus oesophagus and then right here is your larynx this is your larynx and I'm going to concern ourselves with the larynx esophagus is where your food goes down we know that we eat food with our mouth as well so this is where we want our food to go down the esophagus that's for food but the focus of this video is our ventilation what do we do with our air so I'm gonna focus as the air goes through our larynx our larynx and the larynx is also our voice box so as you hear me talking right now they're these these little things right about here that are vibrating at just the right frequencies and I'm able to shape the sound with my mouth to make this video so that's also your voice box but I won't focus on that right now it's called a voice box cuz of this whole anatomical structure that looks something like that but then after the air passes through the larynx this is on the way in it goes to the trachea so then the air goes into the trachea just like that which is a you essentially just the pipe for air the esophagus is the pipe for food let me write this down right here so this right here is our trachea and then from the trachea the trachea is actually a reasonably rigid structure it has cartilage around it and it makes sense that it has cartilage you you don't want you can imagine like a hose if it bent a lot you wouldn't be able to get a lot of water through it or a lot of air through it so you don't want this thing to bend a lot so that's why it needs to have some rigidity so that's why it has cartilage around it and then it splits it splits into two tubes and I think you know where these two tubes are going to and I'm not drawing this in super detail I just want you to get the idea of them but these two tubes are the bronchi or each one is a bronchus let me see these are the bronchi these are the bronchi and they also have cartilage so they're fairly rigid but the bronchi keep splitting they keep splitting into smaller and smaller tubes just like that at some point they stopped having cartilage so they stopped being reasonably rigid but they keep splitting off so I'll just draw them as these little lines at some point they become such thin they just keep splitting off so the the air just gets keep splitting off and spread and goes down to the different paths and when the bronchi no longer have cartilage around them they're no longer rigid the first of those are called or actually all the tubes after that point are called bronchioles these are bronchioles so for example that we could call a bronchial and I you know there's nothing fancy here it's just a pipe that just gets thinner and thinner and thinner we've labeled the different parts of the pipes different things but the idea is let's take it through our mouth or our nose and we just keep dividing and keep dividing this main division into two different paths that takes us into each of our lungs so let me draw the sky's lungs here so the lungs so that's one of this guy's lungs and that's the other of this guy's lungs and these bronchi or the bronchi split into the lungs the bronchioles are in the lungs and eventually the bronchioles terminate and this is where it gets interesting or they keep dividing smaller and smaller thinner and thinner thinner into these little air sacs these little air sacs just like that at the end of every super small bronchial are these little air sacs super small air sacs I'm going to talk about these air sacs in a second and these are called alveoli alveoli so I've used a lot of fancy words but the general idea is simple air comes into a pipe the pipe gets thinner and thinner and thinner and they end up at these little air sacs and you're saying well you know what how does that get the oxygen into my system well the key here is that these air sacs are super small and have a very very very thin walls or I guess thin membrane so let me zoom in so if I were to zoom in on one of these alveoli and just to give you an idea these are super duper duper small I've drawn them fairly large here but each áliveá alveoli let me draw a little bit bigger so let me draw these air sacs so you have these air sacs like this these air sacs and then you have a bronchial that's terminating in that air sac maybe a bronchioles terminating in another air sac just like that another set of air sacs just like that each of these are only two to three hundred microns in diameter so that distance right there you switch colors that's distance right there is 200 to 300 microns and if in case you don't know what a micron is a micron is a millionth of a meter or you can view it as a thousandth of a millimeter so this is 200 thousandths of a millimeter or you can think of them as and this is actually a very easy way to visualize it this is about 1/5 of a millimeter of a millimeter so if I actually try to draw on the screen if you made this fullscreen a millimeter is about that far maybe a little farther than that maybe about that far so imagine 1/5 of that and that's how what we're talking about the diameter of one of these things and just to put it in the whole scheme relative to cells the average cell in the human body is about 10 microns so this is only about 20 or 30 cells in diameter or relative to the average cell in the human body so these have a super thin membrane these have a super thin membrane around so this this you know if you view them as balloons the balloon is very thin pretty much one cell thick and they're connected to the blood Sulli a better way to think about is that our circulatory system passes right next to each of these things so you have blood vessels that come from the heart that come from the heart and they want to be oxygenated and in general we want things that the blood vessels that don't have oxygen and I'm gonna do this in a lot more detail when I make the videos about the heart and our circulation system with the blood vessels that don't have oxygen deoxygenated blood is a little bit darker it looks a little bit of purplish so I'll draw it as blue so this is these are vessels that are coming from the heart so this is blue so that this this blood right here has no oxygen in it or it's been deoxygenated or it's very little oxygen in it and the word for the blood that come from the heart our arteries let me write that down I'll review that again when we go covered in the heart so arteries arteries are vessels our vessels blood vessels from the heart from the heart and you've probably heard of arteries and vessels that go to the heart are called veins veins go to the heart and this is really important to keep in mind because later on you're gonna see that the arteries don't always carry oxygen or they're always not deoxygenated and veins always aren't one way or the other we're gonna go into a lot more detail when we actually cover the heart and the circulatory system but just remember arteries go away veins go to the heart so here these are arteries these are arteries going away from the heart to the lungs to the alveoli because they want the they want the blood that's traveling in them to get oxygen so that what's going to happen is that the air the oxygen is flowing through the bronchioles I need to get new colors it's flowing through the bronchioles and circulating around the alveoli filling the alveoli and as they fill the alveoli the little molecules of oxygen the little molecules of oxygen are allowed to across the membrane of the alveoli and essentially be absorbed into the blood and I'll do a lot more on that when we talk about hemoglobin and red blood cells but you just have to realize that there's just a lot of of capillaries capillaries are just super small blood vessels that allow air to pass essentially oxygen and carbon dioxide molecules to pass between them these have a lot of capillaries on that allow the get the the exchange of gases so the oxygen can go into this blood and so once the oxygen so this is the vessel that's coming from the heart and then it's just a tube so then once it gets the oxygen it's gonna go back to the heart so once again once it gets the oxygen it'll go back to the heart once it gets the oxygen goes back to the heart and so essentially this is the point where this vessel this pipe part of our circulatory system goes from being an artery because it's coming the heart to a vein because going back to the heart and there's a special word for these arteries and veins they're called pulmonary arteries and veins so this is a going away from the heart to the lungs to the alveoli these are the pulmonary pulmonary arteries and going back to the heart are the pulmonary veins pulmonary veins now you're saying Sal what does pulmonary mean well pulmo comes from the Latin for of the lungs it literally means the arteries that are of the lungs or that go to the lungs and the veins that come from the lung so anytime people talk about pulmonary anything they're talking about our lungs they're talking about their or maybe something related to how we breathe so it's a it's a good word to know so anyway you have your oxygen coming in through your your let me go back to this guy I drew through your mouth through your nose through the pharynx they you know it could fill your stomach we can blow up our stomach like a balloon but that doesn't help us actually get oxygen into our bloodstream but they the oxygen will come through our larynx it into our tract here through the bronchi eventually in bronchioles ending up in alveoli and being able to be absorbed into what were the arteries but then we're gonna go back and then essentially oxygenate the blood the the red blood cells become red once the hemoglobin has actually more specifically the hemoglobin becomes very red or scarlet once it actually has the oxygen and then we go back but at the same time this isn't just about getting oxygen into our arteries or int onto the haemoglobin it's also about releasing carbon dioxide so these these blue arteries coming from the lungs are also going to release carbon dioxide into the alveoli and these will be exhaled so we have oxygen coming in so we have Oh two coming in when we inhale other things will be coming in but the o2 is what gets absorbed in the alveoli and then when we breathe out when we breathe out we're going to have carbon dioxide that was in our blood but then it gets absorbed into the alveoli and they get squeezed out I'm gonna tell you in a second how it gets squeezed and then it gets squeezed back out co the carbon dioxide it's actually that's squeezing out that actually when the air goes back out it can vibrate my vocal cords and it'll allow me to talk but I'm not gonna go into too much detail of that so the last thing to consider about this whole pulmonary system or about our lungs is is well you know how does it how does it force the air in and how does it force the air out and the way it's done is really kind of like a like a a you could imagine it it's kind of a pump or a balloon is that we have this huge layer flat muscles let me pick a good color here so if these are my lungs I have a huge layer flat muscles right here right here let me color it in right below the lungs and this is called a thoracic diaphragm thoracic thoracic diaphragm diaphragm and so when it's relaxed it kind of has this arch shaped and so the lungs are kind of squeezed in they don't have a lot of volume but when I essentially breathe in what's happening is this thoracic diaphragm is contracted and what's contracted it gets shorter but more importantly it opens up it opens up the space in where my lungs are and so my lungs can fill up that space so what it does is it essentially you can imagine it's like pulling a balloon larger making the volume of my lungs larger and when you make the volume of something larger so the lungs will become larger as my thoracic diaphragm is contracted and it kind of arches down create some more space and as the volume of something becomes larger the pressure inside of them goes down if you remember from physics the pressure times volume is a constant so your volume let me write this down so when we breathe in breathe in our brain is essentially telling our diaphragm to contract so diaphragm contracts we have more space around our lungs our lungs expand lungs expand to fill the space we have less pressure here than we have outside we already commute as negative pressure so air always wants to go from high pressure to low pressure so air is going to flow into our lungs and hopefully there will be some oxygen there that can then essentially go into our alveoli and then end up in our arteries and then go back in the veins is oxygen attached to hemoglobin I'll talk more about that in detail and then when we stop contracting the diaphragm it goes back to this arched position it contracts it's kind of like a rubber band it contracts back the lungs and it essentially expels the air back and now that air is going to have a lot more carbon dioxide and just to give a sense of you know our lungs you know I can look at my lung I can't look at them but they don't seem too large you know how do I get enough oxygen in them and what the key is is that because of this branching process because of this branching process the insulin and the alveoli the inside surface area of the lungs are actually much larger than you could imagine or actually then I could have imagined had someone not told me so it actually turns out I looked it up the internal surface area of your alveoli so the the total surface area that where the oxygen can be absorbed in or the carbon dioxide can be absorbed out from the blood it's actually 75 square meters 75 that's meters not feet square meters if you think about it that's like a imagine some type of a tarp or or a field that's you know that's that's almost nine by nine nine meters by nine meters that's almost 20 maybe 27 20 you know roughly 27 by 27 square feet that's the size of some people's backyards that's how much surface area you have inside of your lungs it's all folded up that's how it you know gets jammed into what looked like relatively small lungs but that's what gives us enough surface area for enough of the air enough of the oxygen to cross the alveoli membrane into our blood system and enough of the carbon dioxide to go back in and just to have a sense of how many alveoli we had i sell-- told you that they're very small we actually have 300 million in each lung in each lung we have 300 million alveoli so anyway hopefully that gives you a decent sense of how we at least get air or oxygen into our blood system and carbon dioxide out of it in the next video I'll talk more about our actual circulatory system and how we get how we get the blood how we get the oxygen from the lungs to the rest of the body and how do we get the carbon dioxide from the rest of the body into the lungs