- Hematologic system questions
- Mini MCAT passage: Symptoms of low platelet counts
- What's inside of blood?
- Hemoglobin moves O2 and CO2
- Bohr effect vs. Haldane effect
- Blood types
- How do we make blood clots?
- Coagulation cascade
- Life and times of RBCs and platelets
- Blood cell lineages
Explore the intriguing interplay between oxygen, carbon dioxide, and protons in our body's hemoglobin transport system. Understand the Bohr and Haldane effects, two crucial strategies that increase oxygen delivery and carbon dioxide removal. Take a close look at how some friendly competition for Hemoglobin allows the body to more efficiently move oxygen and carbon Dioxide around. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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- All cells of the body need oxygen, right? Well, here is my question. Do the red blood cells that carry the oxygen need some of it? After all, they are red blood CELLS! Also, for that matter, capillaries, veins, and arteries are made of tissue, right? And tissue is made of cells. What supplies them with oxygen?(44 votes)
- That's a great question! Red blood cells are somewhat unique compared to other cells in the human body, in that they do not have any mitochondria (and thus do not need any oxygen!). As a matter of fact, they have hardly any organelles at all -- not even a nucleus in their mature state. For this reason, many people debate whether they should be considered cells at all!
They instead derive all of their energy from anaerobic means -- specifically, glycolysis and lactate production from pyruvate. So they don't have to take any oxygen from the supply that they carry. As for blood vessels, the larger ones have tiny feeder vessels that supply them with oxygen and nutrients directly, while the smaller vessels are able to scavenge enough oxygen from blood as it passes by and diffuses into the tissues near the capillary beds.
Hope that helps :)(147 votes)
- Do these reactions have a net effect on the pH of the blood?(5 votes)
- The net effect should be to maintain a constant pH, by the haemoglobin "mopping up" the H+ ions, acting as a pH buffer (pH is a measure of H+ ions in solution). The blood has to remain at a fairly constant pH, otherwise it would be an acid bath, which cause any protein based structures to denature, including the haemoglobin in red blood cells.(12 votes)
- I have two Questions:
Does the production of lactic acid in skeletal muscle contribute to lowering the pH and thus increase O2 delivery?
Also, because there is low CO2 in the lungs and therefore less HCO3- and H2CO3 because of Le'Chatelier's principle, does that mean that the lungs have a more basic environment than the rest of the body?
Thanks for any info on this!(8 votes)
- I think that you raise a good point for #2. In the lungs HCO3- and H2CO3 are converted back into CO2 and H2O, which removes protons from the blood, which should raise the pH of the blood. So I guess yes, the blood in the lungs will be more alkali than the blood in the muscles. Great question!(4 votes)
- Hey, how is O2 different than just O? If it's the same element, why should it matter how many there are in a bond?(4 votes)
- What is partial pressure ??(3 votes)
- It is the hypothetical pressure of that gas if it was by itself in the recipient. You can see it as the total pressure (let's say the atmosferic pressure, which is760 mmHg) times the concentration of this gas in the mixture (let's pick up oxigen, for example. Taking note that oxygen forms around 21% of the atmosphere) So, to find oxigen's partial pressure: 760 mmHg * 0,21 = around 160 mmHg :)(11 votes)
- At which point does the body use the Bohr/Haldane effect? Is it some sort of a compensatory mechanism?(3 votes)
- It is both homeostatic and compensatory. When the blood is in the lungs surrounded by a lot of oxygen, the blood is more likely to pick up oxygen and release H+ so that CO2 can be made and released into the alveoli. Conversely, the acidity in the tissues causes the hemoglobin to drop off the oxygen and pick up H+ to give the tissues what they need. During exercise, the acidity in the tissues is even greater so even more oxygen is likely to be dropped off where it is needed the most.(10 votes)
- At2:52, how does CO2 binding to oxyhaemoglobin produce an extra proton? ie it looks like the equation isn't balanced...(6 votes)
- One hemoglobin molecule can bind to 4 O2 molecules. When Rishi mentions that the hemoglobin drops off its 4 O2 molecules in the thigh that got me wondering if it were possible for it to drop one or two O2's along the way. Does a full hemoglobin unload all its O2's at once - in one tissue - or does it make pit-stops along the way - unloading an O2 here and an O2 there, in various tissues?(6 votes)
- I think the hemoglobin makes pit stops along the way. The affinity of hemoglobin for oxygen is reduced in the tissue compared to the lungs. due to cooperativity. Once the first oxygen binds to hemoglobin, the molecule undergoes a conformation change (tense state to relaxed state) that allows other oxygen molecules to bind to hemoglobin more readily. The reverse process occurs in the tissues, as more oxygen molecules depart the hemoglobin, , the hemoglobin's affinity is reduced.
There are two models for how affinity change occurs in molecules such as hemoglobin. The concerted model suggests that all the cooperative binding sites change at the same time. The sequential model is that change in one binding site causes the neighboring binding site to change. My best guess is that the concerted model would cause more oxygen to be dropped off "all at once" in one local area whereas the sequential model would favor a more distributed "pit stop" delivery of oxygen.
Source: Lehninger, A., Nelson, David L., & Cox, Michael M. (2005). Lehninger principles of biochemistry (4th ed.). New York: W.H. Freeman.(1 vote)
- I know this is off subject but what is the difference's between red and white blood cell's?(1 vote)
- Red blood cells carry oxygen (which is attached to hemoglobin) to different parts of your body and white blood cells fight diseases by eliminating germs and other foreign bodies(6 votes)
- why redblood cell has no nucleus?(0 votes)
- The nucleus is ejected after it finishes maturing to maximize the amount of hemoglobin that can be contained within the cell. The nucleus is only needed to create new proteins, however since an mature RBCs only goal is to transport oxygen (( and co2 XD )) the cell after matures no longer requires the need to synthesize proteins!(5 votes)
So we've talked a little bit about the lungs and the tissue, and how there's 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. And the tissues are trying to figure out a way to efficiently send back carbon dioxide. So these are the core things that are going on between the two. And remember, in terms of getting oxygen across, there are two major ways, we said. The first one, 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 HbO2. And the name of that molecule is oxyhemoglobin. So this is 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 more effective ways of getting carbon dioxide back, remember, we have this protonated hemoglobin. And actually remember, 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 works is because when they get back to the lungs, the proton, that bicarb, actually 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, it forms a little proton as well. And that proton can go do this business. It can bind to a 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 part about all this is that there's a little competition, a little game going on here. Because you've got, on the one side, you've got hemoglobin binding oxygen. And let me draw it twice. And let's say this top one interacts with a proton. Well, that protons going to want to snatch away the hemoglobin. And so there's a little competition for hemoglobin. And here, the oxygen gets left out in the cold. And the carbon dioxide does the same thing, we said. Now, we have little hemoglobin bound to carbon dioxide. And it makes a proton in the process. But again, it leave 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 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, I think that oxygen is affected by carbon dioxide and protons. I could say, well, these two, carbon dioxide and protons, are actually affecting, let's say, are affecting the, let's say, the affinity or the willingness of hemoglobin to bind, of hemoglobin for oxygen. That's one kind of statement you could make by looking at that kind of competition. And another person come along and they say, well, I think oxygen actually is affecting, 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 dioxide and 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, looking at it from the other prospective, looking at it from oxygen's perspective, this would be the Haldane effect. That's just the name of it, Haldane effect. So what is the Bohr effect and 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. So 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 into 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 it becomes more steep. And this is all because of cooperativity. Oxygen likes to bind where other oxygens have already bound. , And then it's going to 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 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, is 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 worry about the units. 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 low 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 are 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, whenever 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 tissue you can simply subtract these two values. So that's the oxygen delivery. But looking at this, you can see 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 only way to do that is to have the thigh 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 have 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 thighs to become hypoxic. 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 hemoglobin's 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 dioxide and protons, the Bohr effect tells us that it's going to be harder for oxygen to bind hemoglobin. So if I was to sketch out another curve, initially, it's going to be even less impressive, with less oxygen bound to hemoglobin. And eventually, 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 high CO2 and high protons, that's not really relevant to the lungs. The lungs are thinking, well, for us, 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 going to get, then, a different point. It's going to be on the green curve not the blue curve. So we can draw it at the same O2 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 actually be over here. This is the actual amount. And so O2 deliver is actually much more impressive. Look at that. So O2 delivery is increased because of the Bohr effect. And if you want to know exactly how much it'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 at 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 going to have the amount of carbon dioxide there. And here, we'll do carbon dioxide content in the blood. So let's think through this carefully. Let's first start out with increasing the amount of carbon dioxide slowly but surely. And see how the content goes up. And here, as you increase the amount of carbon dioxide, the content is 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 in binding the hemoglobin. It just goes up straight. So that's easy enough. Now, let's take two points like we did before. 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 because there's not too much CO2 there. But high CO2, it probably is the thighs because the thighs like little CO2 factories. 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'd do it the same way. We say, OK, well, the thighs had a high amount. And 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 O2 delivery, we have this much CO2 delivery. Now, read over the Haldane 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 going to change the affinity of hemoglobin for carbon dioxide and protons. So it's going to allow less binding of protons and carbon dioxide directly to the hemoglobin. And that means that you're going to have less CO2 content for any given amount of dissolved CO2 in the blood. So the line still is a straight line, but it's actually, you notice, it's kind of slope 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 you can already see it. It's going to be more 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 visual way that you can actually see that Haldane effect. So the Bohr effect and the Haldane effect, these are two important strategies our body has for increasing the amount of O2 delivery and CO2 delivery going back and forth between the lungs and the tissues.