Hemoglobin Binding in Tissues & Lungs - Video Tutorials & Practice Problems
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Hemoglobin Binding in Lungs & Tissues
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In this video we're going to begin our discussion on hemoglobin binding in the tissues and in the lungs. And so at this point in our course, we already know that hemoglobin can bind to oxygen. However, what you may not have known is that hemoglobin can also bind to carbon dioxide and protons. And so this leads us directly into what's known as the Bohr effect, which we're actually going to talk about in a lot more detail later in our course. But for now, I can tell you that the Bohr effect just describes the effect of the concentration of carbon dioxide or c o 2, and it describes the effect of pH or in other words, it describes the effect of hydrogen ion concentration on hemoglobin's binding and release of oxygen. And so it's important to note that under low oxygen conditions, hemoglobin is actually going to release its oxygen. But, when hemoglobin releases its oxygen, it's actually capable of binding and transporting both carbon dioxide and protons. And so when hemoglobin binds carbon dioxide, dioxide, we're going to refer to it as just HBCO 2. And when hemoglobin binds protons, we're going to refer to it as HHB plus. And so, c o two and hydrogen ions are both going to act as heterotrophic allosteric inhibitors to hemoglobin's oxygen binding activity. And so recall from our previous lesson videos, hetero is just referring to the fact that carbon dioxide and protons are different than oxygen. And so these are the allosteric effectors and the allosteric effectors are different than the ligand and that's why it's hetero. And, of course, we know that inhibitors are going to decrease the activity and so both c o two and protons are going to decrease hemoglobins protonation of hemoglobin are going to stabilize hemoglobin's t state, which is the 10th state. And of course, the t state binds ligand inefficiently. So hemoglobin, when it's, when hemoglobin's t state is being stabilized, it's going to cause hemoglobin to release its oxygen and so essentially what we're saying here is that both carbon dioxide and protons are going to cause hemoglobin to release its oxygen. And so if we take a look at our image down below, notice over here on the left hand side, what we have is hemoglobin's t state. And when hemoglobin is in the t state like this, essentially, it can be bound to carbon dioxide as well as protons. Now depending on whether we're specifically focusing on carbon dioxide or protons being bound, we're going to refer to this form of Hemoglobin as either HbCO 2 or Hb h h b plus. And so notice that when hemoglobin is in its t state, it's going to be releasing its oxygen. Now, specifically, these conditions here as we can see are going to exist in the tissues. And so, in the lungs, it turns out that, the opposite is a reaction here is going to occur. And so in the lungs, hemoglobin is going to be present mostly in its R state. And so here we have the R state hemoglobin which we know has a high affinity for its ligand and so when it's in its R state, it's going to be binding to oxygen as, h b o 2. And then, of course, when it's in its r state, it's going to have to release hydrogen ions or c 02. So you can pretty much think of this as hemoglobin has an option. It can either bind carbon dioxide and protons but release oxygen or it can bind oxygen and release protons and c 02. And so, as we move forward in our course, we're going to talk about the exact conditions, in the tissues that allow for the t state to be stabilized, as we see here. And we'll talk about the exact conditions in the lungs that allow for the r state of hemoglobin to be stabilized like we see over here. And so this concludes our introduction to hemoglobins binding to carbon dioxide and protons and later in our course we'll be able to focus even more on this particular binding. So I'll see you guys in our next video.
2
concept
Hemoglobin Binding in Lungs & Tissues
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11m
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Video transcript
In this video, we're going to talk about the exact conditions in our muscle tissues that allows for hemoglobin to release oxygen in our tissues. And so first we need to note that our muscle tissues are constantly contracting and respiring, and recall from your previous biology courses that cellular respiration allows our muscle tissues to acquire the energy that they need for a muscle contraction. However, cellular respiration also consumes a lot of oxygen, and so what we're saying here is that in our muscle tissues, oxygen is constantly being consumed and depleted through cellular respiration leading to a relatively low partial partial pressure of oxygen in the tissues right around a value of about 20 tors, which is very low, especially in comparison to the partial pressure of oxygen in our lungs, which is 5 times greater at a value of about 100 tors. And so again, what we're saying here is that in our muscle tissues, oxygen is relatively low. Now, of course, in our respiring muscle tissues, cellular respiration is going to lead to lots of c o two production, carbon dioxide production produced by metabolism. And so in our muscle tissues, we're going to have quite a high concentration of c o 2. And so really, this these are the conditions in our muscle tissues that allow for us to get the background that we need to understand the next five steps that we have down below that lead to hemoglobin's release of oxygen in the tissues. And so, with step number 1 here, we're going to start off with the high concentration of c o two in our muscle tissues. And so the concentrations of c o two are so high in our muscle tissues that these high amounts of c o 2 produced by our respiring tissues is going to diffuse out of our muscle tissues into the capillaries and into our red blood cells or our RBCs for short. And so down below in our image right here, notice on the far left, what we have is our muscle tissues here. You can see we have a image of a bicep and notice that the number one right here also corresponds with the number 1 up above. So, in our muscle tissues, there's quite a high concentration of c o 2, like we said up above. And the high amounts of c o 2 is going to, diffuse into the capillaries and into our red blood cells. So all of this c o two here is gonna diffuse out of the muscle tissues and into the red blood cell, which is actually represented by this red box right here. Now, way down below over here, we also have another representation the steps up above that lead to hemoglobin's release of oxygen in the tissue. So if we take a look at this image, down below, notice that we're zooming in specifically on the area of the blood by the tissues. And in this image, over here on the far left, what we have are our muscle tissues. And then over here, the rest of the image is representing our blood capillary. And, of course, this red circle right here represents the exact red blood cell. And so, what you'll notice is that in our muscle tissues, there's quite a high concentration of c o 2 indicated by number 1 right here, which corresponds with the number 1 up above as well. And so there's so much c o two being produced by our muscle tissues that it's going to diffuse out of our muscle tissues into the blood capillary and then ultimately make its way into the red blood cell. So that leads us directly to step number 2 here. And so inside of our red blood cells, there's actually an enzyme known as carbonic anhydrase. And so carbonic anhydrase catalyzes a reaction, where c o two can react with water to form carbonic acid, which is relatively acidic and breaks up into bicarbonate and a proton. And so you can see that the number 2 right here corresponds with the number 2. And you can see that the carbonic anhydrase enzyme inside of the red blood cell here is catalyzing a reaction where c o two can react with water to produce carbonic acid, h two c o three, which has a p k a of 6.35 and is relatively acidic. So it's going to break up into its conjugate base, bicarbonate, and a proton right here. And so if we take a look down below at our image over here, notice that the number 2 right here, carbonic anhydrase, is showing the same, reaction being catalyzed where the CO2 is, reacting with water to form carbonic acid, which is going to break up into its conjugate base, bicarbonate, and a proton. And so, there is so much, c o two being produced in the tissues that when it diffuses into the red blood cell, there's also going to be quite a high concentration of c o two in the red blood cell. And, of course, the high concentration of c o two is gonna cause this equilibrium right here by Le Chatlier's principle to compensate for the high c o two by shifting to the right towards the production of hydrogen ions. And so notice that with step number 3, what we're saying is that this equilibrium shift towards hydrogen ion production due to the high concentrations of c 02 in the muscle tissues, along with the fact that muscle tissues produce lactic acid, an idea that we'll talk more about later in our course. Together, this lactic acid production and the equilibrium shift towards h plus leads to an increased concentration of h plus in our tissues. And of course, an increased concentration of h plus, we know corresponds with a decrease in the pH. From a pH of about 7 point 4 down to a pH of about 7.2 in the tissues, which is actually relatively acidic in comparison to the blood pH of 7.4, which is where, the blood pH is normally at when it's not near the lungs or near the tissues. And so, we have the number 3 right here to correspond with the number 3 down below to show that there is indeed a PH decrease down to 7.2. And we have that same number 3 down below right here showing the equilibrium shift to the right towards hydrogen ion production due to the high concentrations of c 02. And so because h plus is being increased, the blood pH in the tissues is being decreased down to a value of about 7.2. And so, moving on to our step number 4 here, what we need to recall, is that, near the tissues, hemoglobin is actually going to bind carbon dioxide and bind protons. And the reason for this is because in the tissues, again, there's a high concentration of c o two, lots and lots of c o two, and there's an equilibrium shift towards h plus. So h+ is being increased. So we have lots of h+ and lots of c 02 in the tissues and there's so much c 02 and h+ in the tissues that hemoglobin is just bound to bind to all of this c o two and h plus when it's near the tissues. And of course, we know from our last lesson video that c o two and h plus act as heterotrophic allosteric inhibitors to hemoglobin's oxygen binding. So when hemoglobin binds to c o two and h plus in the tissues, it's going to cause hemoglobin to release, its oxygen. And so essentially what we're saying here is that in the tissues, hemoglobin is going to go from being in its r state when it's bound to lots of oxygen and it's going to shift into its t state in the tissues. And so when it's in its T shape, T state, it's going to bind CO2 and hydrogen ions while releasing oxygen. And so if we take a look down below at our step number 4, you'll see our step number 4 is right, here. And so what you can see is that upon arrival to the tissues, hemoglobin is bound to oxygen in its R state. And so we have the r state hemoglobin here bound to oxygen but as soon as hemoglobin encounters the high concentration of hydrogen ion and the high concentrations of c02, again, there's so much c o two and so much h plus that it's bound to react with the hemoglobin here, and it's bound to bind to the Hemoglobin. All of the c o two and h plus is bound to bind to the Hemoglobin which is going to stabilize the t state of the hemoglobin. And of course, the t state of the hemoglobin has a lowered affinity for oxygen so it's going to release the oxygen and that's exactly what we have here is released oxygen. Now, in step number 5, what we need to recall from our previous lesson videos is that myoglobin, abbreviated as MB, is, its function is, in the tissue. So notice that myoglobin is over here in brown and it's correlating with step number 5 here. And so, myoglobin, recall from our previous lesson videos, has a smaller k d and therefore a stronger oxygen affinity than hemoglobin. And so this means that myoglobin, when it's present in the tissues like this, it's going to facilitate oxygen diffusion into the tissues. And so, essentially, what we're saying is hemoglobin is going to release this oxygen, and then this oxygen diffusion into the tissues here like this is being facilitated by myoglobin's high affinity for oxygen. And so, again over here on the left, we have this circulatory system where we can see that the blood pH in the tissues is 7.2, and the blood pH at normal levels is around 7.4, and then the blood pH in the lungs is around 7.6. And so, now that we can understand better how exactly, these 5 steps right here lead to hemoglobin's release of oxygen in the tissues. In our next video, we'll be able to talk about how hemoglobin is able to bind oxygen in the lungs. So I'll see you guys in our next video.
3
concept
Hemoglobin Binding in Lungs & Tissues
Video duration:
8m
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Video transcript
So now that we know that hemoglobin releases oxygen in our muscle tissues, in this video we're going to talk about the exact conditions in our lungs that allows hemoglobin to bind oxygen in our lungs. And so really these conditions in our lungs are going to be pretty much the exact opposite of the conditions in our tissues. And so, what we need to realize about our lungs is that we are constantly and repetitively breathing in and out. And so we are constantly inhaling lots and lots and lots of oxygen. Meaning that in our lungs, we're going to have a relatively high partial pressure of oxygen right around a value of about a 100 tors, which is again fairly high considering that the partial pressure of oxygen in our muscle tissues is only about 20 tors. And so we also need to realize that in our lungs with every breath that we breathe out, we are exhaling lots and lots of carbon dioxide or c 02, meaning that we're going to have a relatively low concentration of c02 in our lungs. And so what you'll note is that these here are the conditions that are required in our lungs to understand the next five steps that allows hemoglobin to bind oxygen in the lungs. And so just like we started our last story with the concentration of CO 2, in this video, we're also going to start with the concentration of CO 2. And of course, in our lungs, we know that there's a low of CO 2 due to exhalation. And so if we take a look at our image down below, we can better understand these steps that we have. And so notice that we're zooming in on the bloodstream by the lungs. And so over here on the far right, what we have is our lungs. And then, of course, we have our bloodstream, our blood capillary over here on the left with our red blood cell here in this circle. And so one thing to note is that this equation that we talked about in our last lesson video right here is actually being flipped and that's actually okay because we have these equilibrium arrows and it's totally possible for these reactions to go in the forward and reverse direction And so we did flip this reaction here. So keep that in mind. And so, what's important to note is that in our lungs, we are constantly exhaling c02. So there's going to be a very, very low concentration of c02. And this low concentration of c02 is going to translate backwards here into our red blood cells. So we're going to have a very low concentration of c o two here in our red blood cell. And so if we have a low concentration of c o two, of course, by Le Chatelier's principle, this equilibrium here controlled by carbonic anhydrase is going to compensate for this decrease in c02 by shifting to the right. And so it's going to be shifting towards the production of c02. And so that is exactly our number 1 up above. So the number 1 corresponds with this equilibrium shift. And, of course, the low c o 2 in our lungs is going to cause the reaction equilibrium to shift towards c o two production. And, of course, if it's it's shifting towards c 02 production, that means that the concentration of hydrogen ions is going to decrease. And so, if we decrease our concentration of hydrogen ions, of course, that's going to correspond with an increase in the PH up to about a value of 7.6 in the lungs. And so notice over here, what we're saying is that the pH in the lungs, the blood pH in the lungs is going to be right around a value of 7.6, which is slightly basic in comparison to the blood pH, the normal blood pH of 7.4, as well as the blood pH in the tissues, which we already know is slightly acidic at 7.2. And so, again, what we need to realize here is that in our second step, this low concentration of c02 in our lungs, again, via exhalation is going to cause the c02 diffusion into the lungs. And so if we take a look at our image down below, again, we have a very, very low concentration of c02 here. And so, recall that the way that diffusion works is that it goes from high to low concentration. And so if we have a low concentration here, that must mean that we must have a higher concentration of c o two out here, and so that is gonna cause c o two to diffuse into the lungs. And that is exactly how we have, step number 2 right here, which corresponds with, again, step number 2 here, diffusion of CO2 into the lungs and that allows us to breathe out all of the CO2 in our lungs which is going to leave our bodies and go into the atmosphere. And so this leads us to our 3rd step right here and in our 3rd step, what we need to realize is that in our lungs, we're also constantly inhaling lots and lots of oxygen. So we have a very high concentration of oxygen in our lungs. And so here what we can say is that we have high oxygen in our lungs via inhalation, and this is going to cause oxygen diffusion into the capillaries and into our red blood cells or our RBCs for short. And so, again, the the way that diffusion works is it goes from a high concentration to a low concentration. And upon arrival to the lungs, hemoglobin is going to be in its deoxygenated t state. And so that means that it's not going to be bound to oxygen, and so it's gonna be have relatively low relatively low oxygen in the red blood cell. And again, high oxygen in our lungs with every inhalation. And so it diffuses from high to low and so, you can see that the number 3 right here corresponds with oxygen being, diffused, into the capillaries and into our red blood cells. And so that leads us to step number 4, which of course we know that when hemoglobin is near the lungs, hemoglobin is going to bind all of that oxygen that's present and available pretty much endlessly with every single breath that we take. And, of course, if it binds onto the oxygen, that means that the r state is going to dominate and when hemoglobin is in the r state, it's going to release carbon dioxide and hydrogen ions. So, essentially, what we're saying is that near the lungs, hemoglobin is going to transition from its t state to its r state. And, of course, in its r state, it's going to have a high affinity for oxygen, and it's going to be bound to oxygen. And so in step number 5, all of this oxygenated hemoglobin is ready to deliver oxygen to the tissues. And so you can see that in the lungs, hemoglobin becomes oxygenated and then eventually, it will make its way down to the tissues where it can deliver that oxygen and then go back to the lungs to acquire oxygen again and then go back to deliver oxygen and this is a constant cycle that allows hemoglobin to be an excellent oxygen deliverer and transporter. And so one thing to note here about, the lungs is that myoglobin does not come into play because myoglobin is really only going to be significant in the tissues and not in the lungs. And so this here concludes our lesson as to, why exactly hemoglobin binds oxygen in the lungs. And we'll be able to get some practice utilizing all of these concepts as we move forward in our course. So I'll see you guys in our next video.
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Problem
Problem
In the lungs, the _________ pressure of CO2 causes hemoglobin to _________ CO2 and H+. The _________ pressure of O2 causes O2 to _________ hemoglobin, allowing for its transportation to the tissues.
A
Low; Bind; Low; Release.
B
High; Bind; Low; Release.
C
High; Bind; High; Release.
D
Low; Release; High; Bind.
E
High; Release; Low; Bind.
F
Low; Release; Low; Bind. Blood pH in Tissues ≈ 7.2 Blood pH in Lungs ≈ 7.6 Blood pH ≈ 7.4
5
Problem
Problem
Which of the following explains why hemoglobin in RBCs binds to O 2 in the lungs but releases O2 in muscle tissues? (Select all that apply).
A
pH is lower in the lungs than in the tissues.
B
pCO2 is lower in the lungs than in the tissues.
C
BPG is produced at higher levels in tissues compared to the lungs.
D
The temperature of the lungs is generally higher than the temperature in actively contracting muscle tissues.
E
None of the above are true.
6
Problem
Problem
How is the vast majority of carbon dioxide transported in the blood from the tissues to the lungs?
A
As diffused gas bubbles of CO2, just as in carbonated soft drinks.
B
As bicarbonate ions (HCO3-).
C
As carbamate groups bound directly to deoxyhemoglobin.