Oxygen Dissociation Curve and the Bohr Shift

by Jason Amores Sumpter
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This sigmoid aled graph of oxygen saturation has a bunch of different names, and they're all correct. So use whichever one you like. It could be called the oxygen dissociation curve. Sometimes it's the oxygen, hemoglobin, equilibrium curve. Or sometimes people call it the Oxy hemoglobin saturation curve. Ah, these air. Not the best names, you know. But they get the job done. And either way, it's just a sigmoid curve that is just trying. Thio illustrate the oxygen saturation of hemoglobin, a different partial pressures of oxygen. So here on the Y axis, we have our, uh, saturation of oxygen. And on the X axis we have our partial pressures of oxygen. So what you hopefully will notice is that as partial pressure of oxygen increases, oxygen saturation increases. Hopefully, you also notice that this is not a straight line, meaning that the rate of oxygen saturation or ox, the rate of oxygen saturation in hemoglobin is not, you know, doesn't correspond linear Lee to the partial pressure of oxygen. That's why it's that you know, the that's that's why we say that this has a sigmoid. It'll shape right. It has that curve to it, and the reason for that is because of the cooperative binding, right? Uh, when oxy hemoglobin, you know, on Lee has ah little bit of oxygen bound. It's or I'm sorry. When it doesn't have any oxygen bound, it's going thio, uh, you know, take a little bit for it. Thio find some oxygen. But once it has some oxygen bound, that's why the rate of saturation kind of shoots up in this middle region. Right? That's that's the important thing to take note of is that the rate here is a two rate at low partial pressure and really high partial pressure is less then in the middle. Because essentially that is, you know as, uh, you know, let's say like one oxygen is bound here, it's going to make it really easy to bind those next oxygen's. And then, you know, as one Oxygen is released here, it's gonna make it really easy to release those other oxygen's here. So that Z, that cooperative binding is what gives Thesiger boy, it'll shape of this graph. So with all that, let's make it even more confusing. That curve can actually move to the right into the left. Now we're only going to really talk about the right shift. But the left shift is basically just gonna be due to, uh, the opposite reasons of a right shift. So that right shift we call the boar shift. Sometimes it's the boar effect named after Thebe guy who theorized it, and it's essentially a shift of the curve to the right. So, you know, that drew that direction. And, uh, it's going to be due to a number of factors we're only gonna look at to really, And those two factors are decreasing pH. So lower ph things getting mawr acidic and also increasing the partial pressure of CO two. So hemoglobin also, uh, can you, uh, can also bind co two? However, all you really need to worry about is the fact that increasing partial pressure of co two will lower hemoglobin affinity for oxygen mawr Higher Co two concentration makes hemoglobin have a lower affinity for oxygen, which is going thio cause it thio unload oxygen right, which makes sense because tissues that air consuming a lot of oxygen are going to generate ah lot of CO two, which is going to cause an increase in the partial pressure of co two So essentially, the idea there is that tissues that are performing a lot of cellular respiration, they're consuming lots of oxygen are going to have a higher Ah, a higher partial pressure of co two. And this is going to cause hemoglobin to unload its oxygen more efficiently. And we can visualize that on our graph by having our curve, you know, shift over to the right. So here's my new curve. Sorry, it's so ugly. Not an artist. Um, but essentially, the idea is that now hemoglobin has a lower affinity for oxygen, right? Because at, uh, it will take higher partial pressures to achieve the same level of saturation. That's essentially all, uh, all that boils down to. And and it's just a mechanism that makes hemoglobin mawr efficient at unloading oxygen, uh, in in tissues that really need it. Now, the other thing we're gonna look at, as I said was ph how pH effects it so lowering ph, which could also be thought of as increasing the acid concentration. So lowering pH or increasing asset however you want to think of it will result in lowering hemoglobin affinity for oxygen? No, the way I like to think about this is that CO two when it gets into the blood is going to combine with water and form carbonic acid. Acid means lower pH. So basically, the more co two the Mawr carbonic acid, which means thelancet lower the pH and that lower pH is going to cause a right shift in the curve. And remember that a right shift in the curve is going. Thio allow hemoglobin to unload its oxygen more easily. So this is just another way of sort of detecting those co two concentrations, right? Uh, not only is it affected by the partial pressure of CO two, but it's also affected by Ph. And that pH is in a large or that pH fluctuation isn't going to be in a large part, do you two carbonic acid, which comes from CO. Two. So these air just ways of making hemoglobin better at doing its job. Basically. And you know, as I said, there's other stuff that can affect this curve. Uh, I don't want you to worry about any of that. I just want you to worry about increasing acid, right? That's the same Azaz lowering the pH and, of course, increasing the partial pressure of CO two, and that causes a right shift or a reduced affinity of hemoglobin for oxygen, which makes it better at unloading its oxygen. Now there's actually an enzyme called carbonic and hydrates that catalyze is the formation of carbonic acid from CO two and water. And essentially, that is going to help ensure that co two that makes it into the blood will, you know, basically, uh, very rapidly be converted into carbonic acid. This has, ah few effects. First, it's going to lower the partial pressure of CO two in the blood. If you're taking CO two and converting it into a different model molecule, that means that you don't have the CO two anymore. So this is going to ensure that the partial pressure of CO two is lower in the blood than, for example, tissues, which will ensure that the diffusion of CO two goes from the tissues into the blood. So it's just another way in which, you know the body has mechanisms to ensure that gas is diffused in the right direction. Now, in addition to lowering the partial pressure of CO two in the blood, you know, by turning the CO two into something else. It's turning that co two into acid, which lowers the pH. And again. This will induce the board shift and make hemoglobin better at unloading oxygen, which will be important. You know, in terms of hemoglobin being able, thio unload oxygen most effectively in the tissues that have the highest demand, which are gonna be the tissues that air giving off the most co two Now, lastly, it's worth noting that in terms of home, yo Stasis of gas is our body isn't actually detecting those gasses directly. Right? It actually uses ph detectors in the respiratory center, which is part of the medulla oblong gotta brain region in the brain stem. Uh, those PH detectors air what are going to regulate ventilation. So, uh, kind of cool. Now, you, you know, hopefully can understand why, uh, using pH detectors is, you know, a NIF effective method of monitoring the gas is in our blood and monitoring ventilation. Right? Because of how co two will, uh, you know, turn into acid in the blood. So kind of a cool way that our body indirectly monitors this system. Now, that's all I have for this lesson. I'll see you guys next time