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进一步了解血红蛋白之间的良性竞争何以更有效的帮助氧气和二氧化碳输送.里希(Dr.Rishi Desai)是儿科传染病医师,在可汗学院工作. Rishi Desai 创建




so we've talked a little bit about the lungs and the tissue and how there's a kind of an interesting relationship between the two where they're trying to send little molecules back and forth the lungs are trying to send of course oxygen out to the tissues right and the tissues are trying to figure out a way to efficiently send back carbon dioxide so these are the the kind of core things that are going on between the two and remember in terms of getting oxygen across are two major ways we said the the first one kind of the easy one is just dissolved oxygen dissolved oxygen in the blood itself but that's not the major way the major way is when oxygen actually binds hemoglobin in fact we call that HBO 2 and the name of that molecule is oxy hemoglobin so this is kind of how the majority of the oxygen is going to get delivered to the tissues and on the other side coming back from the tissue to the lungs you've got dissolved carbon dioxide a little bit of carbon dioxide actually literally comes just right in the plasma but that's not the majority of how carbon dioxide gets back the the more effective ways of getting carbon dioxide back remember we have this protonated hemoglobin and actually remember when when I say there's a proton on the hemoglobin there's got to be some bicarb floating around in the plasma and the reason that that works is because when they get back to the lungs the proton that bicarb actually kind of meet up again and they form co2 and water and this happens because there's an enzyme called carbonic anhydrase inside of the red blood cells so this is where the carbon dioxide actually gets back and of course there's a third way remember there's also some hemoglobin that actually binds directly to carbon dioxide and in the process you know it forms a little proton as well and that proton can go do this business right it can bind to hemoglobin as well so there's a little interplay there but the important ones I want you to really kind of focus in on are the fact that hemoglobin can bind to oxygen and also on this side that hemoglobin actually can bind to protons now the fun about all this is that there's a little competition right a little game going on here because you've got on the one side you've got haemoglobin binding oxygen and let me draw it twice and let's say this top one interacts with a proton well that proton is gonna want to snatch away the haemoglobin and so there's a little competition for hemoglobin and here the oxygen kind of gets left out in the cold and the carbon dioxide does kind of the same thing we said we now we have little hemoglobin bound to carbon dioxide and it makes a proton in the process but again it leaves oxygen out in the cold so depending on whether you have a lot of oxygen around if that's the kind of key thing going on or whether you have a lot of these kinds of products the proton or the carbon dioxide depending on which one you have more of floating around in the in the tissue in the cell will determine which way that reaction goes so keeping this concept in mind then I could actually step back and say well you know I think that oxygen is affected by carbon dioxide and protons I could say well these two contacts and protons are actually affecting let's say are affecting the let's say the affinity the affinis or the the willingness of hemoglobin to bind of hemoglobin for oxygen right that's one kind of statement you could make by looking at that kind of competition another person come along and they say well I think oxygen actually is affecting you know depending on which one which perspective you take you could say oxygen is affecting maybe the affinity of hemoglobin for the carbon dioxide and proton of hemoglobin for co2 and protons so you could say it from either perspective and what I want to point out is that actually in a sense both of these are true and a lot of times we think well maybe it's just saying the same thing twice but actually these are two separate effects and they have two separate names so the first one talking about carbon oxide protons their effect is called the Bohr effect so you might see that word or this description this is the Bohr effect and the other one kind of looking at it from the other perspective located from oxygens perspective this would be the holiday in effect that's just the name of it Haldane effect so what is the Bohr effect in the Haldane effect other than simply saying that the things compete for hemoglobin well let me actually bring up a little bit of the canvas and let's see if I can't diagram this out because sometimes I think a little diagram would really go a long way in explaining these things so let's see if I can do that let's use a little graph and see if we can illustrate the Bohr effect on this graph this is the partial pressure of oxygen how much is dissolved in the plasma and this is oxygen content which is to say how much total oxygen is there in the blood and this of course takes an account mostly the amount of oxygen that's bound to hemoglobin so as I slowly increase the partial pressure of oxygen see how initially not too much is going to be binding to the hemoglobin but eventually as a few of the molecules bind you get cooperativity and so then slowly the slope starts to rise and becomes more steep and this is all because the cooperativity oxygen likes to bind where other oxygens have already bound and then it's gonna kind of level off and the leveling off is because hemoglobin is starting to get saturated so there aren't too many extra spots available so you need a lots and lots of oxygen dissolved in the plasma to be able to seek out and find those extra remaining spots on hemoglobin so let's say we choose two spots one spot let's say as a high amount of oxygen dissolved in the blood and this let's say is a low amount of oxygen dissolved in the blood I'm just kind of choosing them arbitrarily and don't don't worry about the unit's and if you were to think of where in the body would be a high location that could be something like the lungs where you have a lot of oxygen dissolved in blood and lo would be let's say the thigh muscle where there's a lot of co2 but not so much oxygen dissolved in the blood so this could be two parts of our body and you can see that now if I want to figure out looking at this curve how much oxygen is being delivered to the thigh then that's actually pretty easy I could just say well how much oxygen was there in the lungs or in the blood vessels that were leaving the lungs and there's this much oxygen in the blood vessels leaving the lungs and there's this much oxygen in the blood vessels leaving the thigh so the difference whatever oxygen is between these two points that's the amount of oxygen that got delivered so if you want to figure out how much oxygen got delivered to any any tissue you can simply subtract these two values so that's the oxygen delivery but looking at this you can see it a kind of an interesting point which is that if you wanted to increase the oxygen delivery let's say you wanted for some reason to increase it become more efficient then really the the only way to do that is to have the thigh kind of become more hypoxic as you move to the left on here that's really becoming hypoxic or having less oxygen so if you become more hypoxic then yes you'll you'll have you know maybe a lower point here maybe a point like this and that would mean a larger oxygen delivery but that's not ideal you don't want your size to become hypoxic you know that that could start aching and hurting so is there another way to have a large oxygen delivery without having any hypoxic tissue or tissue that has a low amount of oxygen in it and this is where the Bohr effect comes into play so remember the Bohr effect said that co2 and protons affect the hemoglobins affinity for oxygen so let's think of a situation I'll do it in green and in this situation where you have a lot of carbon oxide and protons the Bohr effect tells us that it's going to be harder for oxygen to bind hemoglobin so for us to sketch out another curve initially it's going to be even less impressive with less oxygen bound to hemoglobin and eventually once the once the concentration of oxygen Rises enough it will start going up up up and it does bind hemoglobin eventually so it's not like it'll never bind hemoglobin in the presence of carbon dioxide and protons but it takes longer and so the entire curve looks shifted over these conditions of kind of high co2 and high protons that's not really relevant to the lungs the lungs were thinking well for for us you know who cares we don't really have these conditions but for the thigh it is relevant because the thigh has a lot of co2 and the thigh has a lot of protons again remember high protons means low pH so you can think of it either way so in the thigh you're gonna get then a different point right it's gonna be on the green curve not the blue curve so we can draw it at the same level actually being down here so what is the o2 content in the blood that's leaving the thigh well then to do it properly I would say well it would be actually you'd be over here this is the actual amount and so Oh to delivery is actually much more impressive look at that so OH - delivery is increased because of the Bohr effect and if you want to know exactly how much that's increased I could even show you I could say well this amount from here down to here literally the vertical distance between the green and the blue lines so this is the extra oxygen delivered because of the Bohr effect so this is how the Bohr effect is so important and actually helping us deliver oxygen to our tissues so let's do the same thing now but for the Haldane effect and to do this we actually have to switch things around so our units and our axes are going to be different so we're gonna have the amount of carbon dioxide there and here we'll do carbon dioxide content in the blood so let's think through this kind of carefully let's first start out with increasing the amount of carbon oxide slowly but surely and see how the content goes up and here as you increase the amount of carbon dioxide the content this kind of goes up as a straight line and the reason it doesn't take that s shape that we had with the oxygen is that there's no cooperativity and binding the hemoglobin it just kind of goes up straight so that's easy enough now let's take two points like we did let's take a point let's say up here this will be a high amount of co2 in the blood and this will be a low amount of co2 in the blood so you'd have a low amount let's say right here in what part of the tissue well low co2 that sounds like the lungs there's not too much co2 there but high co2 it probably is the thighs because the thighs are like little co2 factories right so the thigh has a high amount and the lungs have a low amount so if I want to look at the amount of co2 delivered we do it the same way we say okay well the size had a high amount this is the amount of co2 in the blood remember and this is the amount of co2 in the blood when it gets to the lungs so the amount of co2 that was delivered from the thigh to the lungs is the difference and so this is how much co2 delivery we're actually getting so just like we had Oh to delivery we have this much co2 delivery now read over the howling effect and let's see if we can actually sketch out another line in the presence of high oxygen what's going to happen well if there's a lot of oxygen around then it's gonna change the affinity of hemoglobin for carbon dioxide and protons so it's gonna allow less binding of protons and carbon dioxide directly to the hemoglobin and that means that you're gonna have less co2 content for any given amount of dissolved co2 in the blood so that line still is a straight line but it's actually you notice it's kind of sloped downwards so where is this relevant where do you have a lot of oxygen well it's not really relevant for the thighs because the thighs don't have a lot of oxygen but it is relevant for the lungs it is very relevant there so now you can actually say well let's see what happens now that you have high o2 how much co2 delivery are you getting and then you can already kind of see it it's gonna be more right because now you've got this much you've got going all the way over here so this is the new amount of co2 delivery and it's gone up and in fact you can even show exactly how much it's gone up by by simply taking this difference so this difference right here between the two this is the Haldane effect this is the kind of visual way that you can actually see the Haldane effect so the Bohr effect in the Haldane effect these are two important kind of strategies our body has for increasing the amount of o2 delivery and co2 delivery going back and forth between the lungs and the tissues