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Current time:0:00Total duration:16:30

Video transcript

in the last video on the lungs or the gas exchange in our bodies or on the pulmonary system we left off with the alveolar sacs let me draw one right here so we have these alveolar sacs that I talked about and they're kind of in these little clumps like this let me draw a couple of them just you get the idea and if you remember from the last video these are kind of where you know air goes in through our trachea then that splits up into our bronchi and then those put into the bronchioles and then the bronchioles terminate at these alveoli let me so that's the alveoli these are these super small sacs that we talked about in the last video on the pulmonary system you might want to watch that video if none of this sounds familiar and then of course we have our bronchial that feeds into this and then that might have branched off from another one that feeds into another set of alveolar sacs but I don't want to get too focused on that I cover that in the last video let me label it bronchial bronchial and then these are alveoli these are al viola in the last video we saw that air when we breathe in when our diaphragm contracts and makes our lungs expand and fill up that space air comes in air comes in and in that air that comes in is going to be as we're breathing atmospheric air it's going to be 20 21% oxygen oxygen and it's going to be 78% nitrogen 78% nitrogen and actually in our atmosphere carbon dioxide is actually almost a trace gas it's less than 1% so it's less you make that it's less than 1% carbon dioxide so anytime you breathe in on earth this is what you're going to get and we said that in the last video that you have these capillaries these pulmonary capillaries that are running all along the side of these alveoli so let me draw those pulmonary capillaries and so when they are deoxygenated so they come here to be oxygenated so when they're deoxygenated they might look a little purplish so when they're deoxygenated they might look a little purplish and they're running along the side of these alveoli and then they pick up the oxygen from inside the alveolar the oxygen diffuses across the membrane of the alveoli into these capillaries into these super small tubes and then once they do that makes the blood red I'm going to talk in a little bit about why it becomes red so then it becomes red and now that the blood is red it has its oxygen the whole point is get your oxygen it's ready to go back to the heart it's ready to go back to the heart so that's just one little part of it and we learned in the last video that something that goes away from the heart so this is going away from the heart that is an artery a 4-way artery and something that's going towards the heart is a vein so this right here is is a vein now one question and this is this actually came up in the last video someone asked which I think is a very good question is gee you know when we breathe in we most of the air is nitrogen only 21% is oxygen what happens to all that nitrogen there how come that doesn't go into our blood and that's actually an excellent question so the answer that I think that actually helps explain what's going on here let's draw a little bit bigger so let me draw let me draw the alveolar membrane a little bit bigger like that so this is the inside of my of an alveolus this is its membrane right here super-thin maybe one almost one cell thick and then you have a capillary you have a capillary running right next to it so let me do that in a neutral color so you have a capillary that's maybe running right along this surface so this is its capital the capillary that's running right along the surface just like that just like that and this is poorest to gases like oxygen nitrogen carbon dioxide and what we have here let's say that this is so the heart is over here the heart is over here so this is blood coming from the heart and then this is going to go back to the heart well the hearts on both sides so let me write it this way from the heart from the heart and to the heart and what you have here is when we're coming from the heart this is deoxygenated blood and it's actually going to have a high concentration of carbon dioxide so let me draw a carbon dioxide well let me draw a carbon dioxide is green one already to nitrogen screen let me do carbon dioxide it's orange so these are little these there's a lot of carbon dioxide and actually carbon dioxide actually gets diffused in the blood it actually is carried in the plasma of the blood it's not carried by red blood cells that we're going to talk about in a second so that's a bunch of carbon dioxide here and the concentration of carbon dioxide in the deoxygenated blood is going to be higher than the concentration of carbon dioxide in the alveolus so if this is porous to carbon dioxide this membrane and it is these carbon dioxide molecules are going to diffuse they are going to diffuse into into the alveolus now on the other side of that we have oxygen we have oxygen here we're breathing it in the air is 21% oxygen so you're actually gonna have a lot more oxygen than carbon dioxide and this is deoxygenated blood we used all of the oxygen in our body and we'll talk more about that either at the end of this video or in a future video on how we use it but or where it goes in our body but there's no oxygen here so the oxygen is going to be taken it's going to diffuse across this membrane it's going to diffuse across this membrane because the concentration of oxygen is low now the question is so immediately you see that as the oxygen diffuses across this membrane often this is oxygenated blood ready to go back to the heart this is so you know this transition between artery and vein is a very subtle thing you know very clearly here you say that okay this is going from the heart this is this is our vein this is going to the heart a second live I always get confused this is going away from the heart and as I was looking for an A and I looked from this is away from the heart so this is an artery and this is going to the heart so this is a vein so you can make the division you could say okay once it's oxygenated maybe we're going back to the heart but it's kind of an arbitrary sorry I spelled artery wrong these are these are my flaws artery spelling was never my strong suit so it's hard to say where the artery ends and the vein begins a good demarcation is when the carbon dioxide concentration goes low and that the oxygen concentration goes high that's a good time where we start from the pulmonary artery and I want to in a probably in the next video I will make a very you'll see why the pulmonary arteries are special because pulmonary arteries coming away from the heart have no oxy or very little oxygen and they have a lot of carbon dioxide while pulmonary veins so pulmonary pulmonary veins which is you know we could it's it's arbitrary where the artery turns into a vein but we can say once it gets oxygenated it's ready to go back to the heart it's a vein it's a pulmonary vein and it is oxygenated so it has oxygenated oxygenated and we could write D oxygenated oxygenated now the reason why I say it's special besides the fact that pulmonary arteries and veins go to and from the lungs is that they're kind of the opposite because in the rest of the body when we're going away from the heart or we're talking about arteries you're going to see that that's oxygenated blood while when we're going away from the heart to the lungs that's deoxygenated blood similarly in the rest of the body when we're going to the heart where you're going to see that that's deoxygenated blood but in the pulmonary vein when we're going to the heart it's oxygenated because the the lungs are what take up the carbon dioxide and give us the oxygen now I still haven't answered that that interesting question that rose on the on the message board on the last on the last video what happens to the 78% of nitrogen that's sitting here so there's just a ton of nitrogen over here there's just a ton more than more than the oxygen a lot more than the carbon dioxide what happens to all of these nitrogen molecules and the answer is nitrogen can diffuse and does diffuse into the blood but the Bloods ability to take in nitrogen isn't that high and you might say well you know why isn't why is oxygen special why why can the blood take up oxygen so much easier than nitrogen and that's where the red blood cells come into play let me write this down write it in red red blood cells which are fascinating on a whole set of levels red blood cells so what red blood cells these are these cells that are sitting in that they're flowing through our flowing through our circulatory system and they look kind of like lozenges if I were to draw one so they kind of have the kind of like a like a flattened sphere with a little divot on either side of it a lot like a like a lozenge so if I were to draw it from the side it might look something like well for the side it would look like that and if you could see through it there'd be a little divot on each side if I were to draw it in an angle it would look something like this it would look something to me it would look like that and there be a little divot on that side and they're very similar divot on the other side and red blood cells and I could do a whole set of videos just on red blood cells they contain hemoglobin they contain hemoglobin maybe we'll do a whole video on hemoglobin hemoglobin are these small proteins actually they actually are immune that that contained for heme groups so hemoglobin let me draw it this way so inside of red blood cells you have millions of hemoglobin proteins and the hemoglobin proteins I'll just draw them is this they have these four heme groups and heme groups the main component is iron and that's why iron is so important if you don't have enough iron you're going to have trouble processing oxygen in your blood and you your emo globin won't be functional left but it has iron on it has four of these heme groups and each of these heme groups can bond to oxygen molecules and very good bonders of oxygen and we're going to see in a little bit probably the next video wow they release the oxygen but this has tons it has millions of heme groups in it and the oxygen the oxygen diffuses across the membrane of the red blood cells and bonds to these little to the heme groups on your hemoglobin so because the red blood cells have the hemoglobin inside of them they are like the sponges for oxygen because hemoglobin is so good at taking in oxygen so the red blood cells are able to essentially suck up all of the oxygen out of the plasma the plasma we can view is just the general fluid of the blood not including the red blood cells so the red blood cell here the red blood cell here isn't so red and the reason and this is the key point the reason why it's not so red so maybe we had a red blood cell over here and we make it clear carbon dioxide for the most part is traveling within the plasma it gets it gets absorbed into the actual fluid and I'll talk about in the future video it's actually in a slightly different form it's as carbonic acid and that's extra key point for how the plasma knows where to dump the oxygen but I'll talk about that in a future video but over here this red blood cell has a bunch of hemoglobin proteins in it but those hemoglobin proteins have dumped their oxygen and it actually turns out is the hemoglobin that so with oxygen hemoglobin looks red with oxygen hemoglobin looks red it reflects red light when it doesn't have oxygen when it doesn't have oxygen hemoglobin does not look red it looks kind of purplish bluish darkish you know something and that's why that's why in most of your body your veins that have deoxygenated red blood cells look kind of bluish so this is and the reason why it changes color is that when the oxygen bonds to the heme sites on the hemoglobin it actually changes the entire conformation the entire structure of the protein we've seen that multiple times the whole protein folds in such a way that all of a sudden instead of you know purplish or dark light being reflected now red light is reflected and that's why red blood cells will become red once they take the oxygen but I'm going on a tangent the whole point here is saying why are we taking up so much more oxygen than nitrogen given that there's less oxygen in the atmosphere than nitrogen and the key is these red blood cells these red blood cells have these millions of hemoglobin proteins inside of them and they take them up and they saw up all of the oxygen out of the plasma actually they stopped up about 98.5 percent of the oxygen so 98.5 percent of the oxygen gets chopped up by the red blood cell so these red blood cells are just traveling and they're going to go back to the heart that they are what make our blood red so you have this thing hemoglobin that's sitting in red blood cells that's sopping up all of the oxygen so it keeps the oxygen concentration in the actual plasma low you have nothing like that for nitrogen there is no cell that's sopping up the nitrogen nitrogen does not bond to hemoglobin so that's why oxygen is taken up so much better than nitrogen this is a very interesting question because you know it's it's it's it's a you know it's a if you just think about how much the nitrogen is it's kind of a very natural idea now I want to focus a little bit on the red blood cell itself because it's fascinating it's almost you know in the video on the structure of the cell I I started off saying oh well you know all cells have a membrane and they all have DNA now the fascinating thing about a red blood cell let me zoom in I just keep drawing the same drawing has a little divot here it has a little divot here the fascinating thing about the red bus I already said it has a bunch of it has millions of hemoglobin molecules or proteins inside of it the fascinating thing about a red blood cell it has no nucleus no nucleus and no DNA no DNA this is this is mind boggling when I first found it I was like well why is it a cell is it really even a living thing and it turns out when it's growing it does have a nucleus we all you know all cells need a nucleus with DNA in order to generate the proteins that build it up in order to kind of exist and and structurally make itself the way it needs to be made but the whole point of a red blood cell is to contain as much hemoglobin as possible and so you can imagine this is this was actually a favorable evolutionary trait that as red blood cells are ready to kind of go into the into bin you've built the whole structure they actually get rid of their nucleus they actually push their nucleus out of the cell and the whole reason why that's beneficial is that's more space more space for hemoglobin more space for hemoglobin hemoglobin because the more hemoglobin you have the more oxygen you can take up and I can do a ton of videos on on on hemoglobin and all of that and actually I want to do a lot more on the circulatory system so don't worry about that but I want to go over one other really interesting thing about hemoglobin and we already talked about red blood cells I think it's fascinating that they actually don't have a nucleus in their mature form and next we have very short lives they live maybe 80 120 days so they're not like these long list cells that so you know it's almost a philosophical question or are they still alive once they've lost their DNA or are these are they just vessels for oxygen that aren't really alive because they aren't kind of regenerating and producing their own DNA so actually instead of going into the hemoglobin discussion right now I'll leave you there in this video I realize I've been making 20 minute videos where my goal is really to make 10 one so I'll leave you here and in the next video we'll talk more about hemoglobin and the circulatory system