Respiration - Online Tutor, Practice Problems & Exam Prep

Respiration involves the exchange of oxygen (O₂) and carbon dioxide (CO₂) between the blood and tissues, relying on pressure gradients. External respiration occurs in the alveoli, where O₂ moves into the blood and CO₂ exits. Internal respiration involves the transfer of O₂ from blood to tissues and CO₂ from tissues to blood. The total amount of O₂ exchanged equals the amount of CO₂ exchanged, reflecting cellular respiration's balance. Key principles include Dalton's law of partial pressure and Henry's law regarding gas solubility.

Respiration

Alright, everybody. We now want to spend some time really diving into some of those details of respiration. But before we get into all the nitty gritty, I want to sort of step back, kind of reset the table here, and give an overview of this whole thing. So when we get into those, you know, fine details, we remember how all these puzzle pieces fit together. Alright. So remember that respiration is the exchange of oxygen and carbon dioxide with the blood. And we said that respiration relies on pressure gradients. And remember, that's why we spent so much time talking about Dalton's law of partial pressure, because oxygen and carbon dioxide are always going to be moving from areas of high pressure to areas of low pressure. But importantly, when we're talking about that, we're always talking about those gases' individual partial pressures that they're moving in response to. Alright. When we talked about respiration, we broke it up into sort of 2 steps. We have external respiration and internal respiration. External respiration happens in the alveoli, and that's going to be exchanging these gases between the air and the blood. And just knowing that, and you probably already know the basic direction that these gases move in, we should be able to figure out generally what these pressure gradients are. So for oxygen, well, oxygen, there's going to be a net movement from the air into the blood in the alveoli. So knowing that, we now know that the partial pressure of oxygen in the air must be greater than the partial pressure of oxygen in the blood because that oxygen is going to move down its pressure gradient into the blood. Well, in contrast, that carbon dioxide well, the partial pressure of carbon dioxide in the air, well, it must be less than the partial pressure of carbon dioxide in the blood. Because in the alveoli, carbon dioxide moves down its pressure gradient from the blood and into the air so we can breathe it out of our body. Alright. Now we can look at internal respiration. Well, internal respiration, after those gases have exchanged with the blood in the alveoli, that blood travels to the tissues of the body. So this happens in the tissues. And again, just knowing which way these gases move, we can figure out just generally what these pressure gradients are going to be. Well, in the tissues, there's going to be a net movement of this oxygen from the blood into the tissues where it's used as part of cellular respiration. So that means that the partial pressure of oxygen in the blood must be greater than the partial pressure of oxygen in the tissues because it's going to move down its pressure gradient. Now in contrast, well, the partial pressure of carbon dioxide in the blood must be less than the partial pressure of carbon dioxide in the tissues. Because carbon dioxide is made in the tissues as a waste product of cellular respiration, it's going to be there's going to be a lot of it there. It's going to move down its pressure gradient into the blood, and then it's carried by the blood back to the alveoli where it moves down its pressure gradient again, so it connects to the body. Alright. Quick note here, we've been talking about partial pressures, but here we've been talking about partial pressures of these gases, both in a gas in the alveoli and in liquids either dissolved in the blood or dissolved in the cytoplasm of cells in the tissues. Well, that's because remember Henry's law. Henry's law allows us to convert from that partial pressure in a gas into how much of that molecule is going to dissolve into a liquid. So we're going to say here, Henry's law allows us to use the same unit. We can use that unit of partial pressure for both gases and gases dissolved in a liquid. So from here on out, we're always going to be using that unit, partial pressure. Alright. As I said, we're going to get into a lot more details coming up. I'm looking forward to it, and I will see you there.

When determining the directions that molecules will move in external and internal respiration:

• A. Molecules will always move down the pressure gradient according to their individual partial pressures.
• B. Molecules will move up the pressure gradient for internal respiration and down the pressure gradient for external respiration.
• C. CO₂ will always move up the pressure gradient, while O₂ will always move down the pressure gradient.
• D. Molecules will always move from the area of greatest total pressure to the area of lowest total pressure.

Internal and External Respiration

When we previously introduced respiration, we said that carbon dioxide and oxygen are always moving down their pressure gradients between the air and the blood and between the blood and the tissues. Well, now we want to look at this in a little bit more detail. We're going to put some values on those gradients, and we're going to look at the nitty gritty. Before we really get into it, though, we need to note that the composition of atmospheric air is actually different than the air in the alveoli. So previously, we've been talking about atmospheric air and you can see those numbers here. You'll note they may be a little different than what we've seen before. It's okay. They're close enough. The one major difference here, we pulled argon out because we don't really care about that physiologically and we put water vapor in instead because that is going to be a little important. Alright. But these numbers, that's not actually part of the gradient that we're talking about. The gradient is between the air and the alveoli in the blood, and the composition of the air in the alveoli well, you can see here you can look at those numbers. They're pretty much different across the board. Now importantly, one number that is not different is going to be that total pressure. In both the alveoli and the atmospheric air, the total pressure is at 760 millimeters of mercury because remember that intrapulmonary pressure always equalizes to atmospheric pressure during ventilation. Alright. But we can go through this, and the first thing that we'll see here is that that water vapor there's way more water vapor in the lungs than in the atmospheric air. And that means that sort of more of that total pressure in the lungs is going to be taken up by that water vapor. And that's just because, right, it's wet inside your body. So in your lungs, that air is just very humid. Alright. But we can go now to carbon dioxide and oxygen. Those are the molecules we really care about, and you can see here look at that percent composition for carbon dioxide. There's over 100 times the percentage of carbon dioxide in your lungs than in the air around you and that converts to over 100 times the partial pressure in that alveoli. Now that's because during ventilation, right, your tidal volume is only 500 milliliters, but the residual capacity, the amount of air that doesn't move out of your lungs with every breath, is something like closer to 2 liters. So you're only replenishing a bit of that air with each breath, and that carbon dioxide is just always moving from the blood into the alveoli, so that partial pressure is much higher than in the atmosphere here. Well, the opposite is going to be true for the oxygen. You can see here there's much less oxygen in the alveoli compared to the atmospheric air, and that converts to significantly lower partial pressure due to oxygen in the alveoli than in the atmospheric air. You'll note the difference is relatively not nearly as great compared to the difference for carbon dioxide, but it is significant. Alright. Finally, there's nitrogen. Nitrogen is not that interesting physiologically. You'll note that it's a little bit different there, but we don't worry about that. The big thing here though is that I'm just going to gray out this atmospheric air, those columns there, because we don't care about them. What's important is those partial pressures in the alveoli and specifically the partial pressures for oxygen and carbon dioxide. These are numbers you might want to remember. Partial pressure for oxygen is going to be 104. Partial pressure for carbon dioxide is going to be 40 millimeters of mercury in the alveoli. Alright. Let's take a look at this now. Alright. We are going to be talking about 2 gradients that determine the movement of the gases in the body, and that's going to

Respiration Example 1

Alright. For this example, it says, place the following areas in order from highest to lowest according to their expected partial pressure of oxygen, or that \( p_{{O}_2} \) there that we see. Then do the same for partial pressure of carbon dioxide. In some cases, the values are the same. If that is the case, circle the equal sign between the two values. If the values are not the same between locations, circle the greater than sign between each value. Alright. So here we have, where we need to fill in for partial pressure of oxygen and then partial pressure of carbon dioxide. And the places that we need to fill in are the body tissues, arterial blood, venous blood, the external air, and the air in the alveoli. Alright. So let's start with partial pressure of oxygen. As you look at those five areas, which one do you expect the partial pressure of oxygen to be the greatest? Well, I expect it to be the greatest in d, the external air. Right? The air around us has the most oxygen, the highest partial pressure of oxygen. Alright. Where do we go from there? Well, remember, the air comes into our alveoli, and there's a lower partial pressure of oxygen in the alveoli than in the external air. So air in the alveoli is going to come next, and that external air definitely has a greater partial pressure. So I'm going to circle that greater than sign there and I'll cross out the equal sign. Alright. Well, where do we go next? Alright. Well, the blood comes through those capillaries in the alveoli, and the partial pressure of oxygen is going to equalize to that air in the alveoli, and then that blood goes from those capillaries into the arterial blood. So that's going to come next. I'm going to put b here for the arterial blood. Now we got to think do we circle the greater than sign or the equal to sign? Well, I just said it equalizes too, but remember as it leaves, the partial pressure just goes down just a little bit as some of that oxygen gets picked up by the hemoglobin. So it's technically just a little bit different. The partial pressure of oxygen in the alveoli is just a little bit greater than in the arterial blood. Alright. From the arterial blood, where do we go next? Alright. Well, from there, the arterial blood goes to the capillaries through the tissues, and that partial pressure in the tissues is definitely lower than in the arterial blood. So I'm going to put that one next. Body tissues, that is a. And so, the arterial blood is greater than, so I'll circle the greater than sign, I'll cross out the equals to sign, and that leaves us with the venous blood is left. So remember that blood goes through the tissues, it equalizes to the tissues, and then it leaves, and now it's in the venous blood. So venous blood comes last, but that is going to be equal to the partial pressure in the tissues. Alright. That's our \( c \). I'm sorry. That's our oxygen. Now let's do our \( CO_2 \), our carbon dioxide. So carbon dioxide, where do you expect the partial pressure of carbon dioxide to be the greatest? Well, that's going to sort of be the opposite of the oxygen. It's going to be the greatest in the body tissues where cellular respiration is happening and that carbon dioxide is being produced. Alright. So high partial pressure in the body tissues. Well, what's next after that? Well, the blood goes through the capillaries, through those tissues, and the partial pressure of carbon dioxide is going to equalize to the partial pressure in those tissues, and then that blood leaves and then it's in the venous blood. So venous blood is going to come next. That's c. And we said it's going to equalize to that, so I'm going to circle the equal sign here and cross out the greater side. Alright. Where do we go next? Well next, that blood goes through the capillaries through the alveoli, And so that partial pressure in the alveoli is definitely lower than the partial pressure in the venous blood. So I'm going to put air in the alveoli next, and I said it's lower there. So I'm going to circle this greater than sign that's sort of pointing out that venous blood, and I'll cross out the equal sign. Alright. From there, that blood leaves the alveoli, and it enters into the arterial blood. So I'm going to put arterial blood next. And again, here as it goes through the alveoli, that blood equalizes to the partial pressure in the alveoli. So I'm going to circle equal to here and cross out the greater than, and that leaves us with one more thing to put in here. The external air needs to come last and, well, external air, do you remember, is that partial pressure going to be equal to or much less than the partial pressure in the arterial blood? Well, for carbon dioxide, remember, the partial pressure of carbon dioxide in the external air is really, really low. There's not much carbon dioxide in the air around us. So I'm definitely circling this greater than sign here that's sort of pointing toward that arterial blood. There's not much carbon dioxide, not much partial pressure of carbon dioxide in that external air. Alright. That felt a little complicated, but we straightened it out. We put them all in order. Practice problems after this. Give them a try.

What is the approximate partial pressure of oxygen in the blood as it enters and leaves the capillaries of the alveoli?

• A. Enters: 40 mm Hg, Leaves: 46 mm Hg.
• B. Enters: 46 mm Hg, Leaves: 40 mm Hg.
• C. Enters: 100 mm Hg, Leaves: 46 mm Hg.
• D. Enters: 40 mm Hg, Leaves: 100 mm Hg.

What is one difference between air in the alveoli compared to air in the atmosphere?

• A. The total pressure of air in the alveoli will be greater than the total pressure of air in the atmosphere.
• B. The partial pressure due to water vapor is much greater in the alveoli than in the atmosphere.
• C. The partial pressure due to carbon dioxide is greater in the atmosphere than in the alveoli.
• D. The partial pressure of oxygen is equal to the partial pressure of carbon dioxide in the alveoli, but not in the atmosphere.

External Respiration

Now that we've taken a look at the entire process of respiration, we want to look at the processes of external respiration and internal respiration in a little bit more detail. We're going to start with external respiration here. Alright. Remember, the way I remember external respiration, I say it's the exchange of gases between the blood and the external air, but I actually want to restate that here because, remember, the external air, that atmospheric air, is actually different than the air in the alveoli. So I want to say here the external respiration is the exchange of gases between the blood and that alveolar air because those are the partial pressures that we really care about. And between the blood and the air in the alveoli, there's going to be a net movement of oxygen (O₂) into the blood and carbon dioxide (CO₂) into the air. Alright. We need to add another wrinkle to this though because as we're thinking about partial pressures, partial pressures tell us how these molecules dissolve into the blood or specifically dissolve into the liquid of the blood, the blood plasma. But you're going to remember from the blood chapter, we have hemoglobin. And hemoglobin is this protein in red blood cells that carries oxygen. It binds to oxygen, and it carries a lot of oxygen in those red blood cells. Now it also binds to CO₂, but it's going to be a little less important for CO₂. We really want to focus on it for oxygen. Alright. Now as we look at this, the last thing that I want to note is that when we're thinking about these molecules crossing between the blood and the air, we want to remember that the total amount of carbon dioxide exchanged is going to equal the amount of oxygen exchanged. If we're going to count the total number of molecules that cross there, for oxygen and carbon dioxide, it should be equal, and that is because for cellular respiration, the same number of oxygen molecules are used as carbon dioxide molecules are produced, and that's where all these molecules are going to or coming from. So because it's equal in cellular respiration, we're going to be exchanging the same number of molecules in both internal and external respiration here. Alright. Well, to talk about this, we're going to bring back this analogy that you may remember from the blood chapter here. We have the lung lounge that represents the air in the alveoli there, And then we have a street going by there, and that represents a capillary going by that alveoli there. Now at the street in the sidewalk there, that's going to sort of represent the space in the blood, the liquid of the blood, the blood plasma. Well, we have these buses on that street, and those buses represent the hemoglobin. Alright. So we're going to start on the left. We have this bus rolling up. This bus has carbon dioxide on it. It's deoxyhemoglobin, and w

Respiration Example 2

Alright, we've got a big, long example here, so let's start reading. It says hyperventilation occurs when the rate and or tidal volume of ventilation increases to a point where the composition of alveolar air more closely resembles atmospheric air. Alright, so just starting off, remember we said that there's actually a big difference between the composition of the air in the alveoli and the air in the atmosphere around us, because when you ventilate your lungs, you only replace a portion of that air in the alveoli with each breath. Alright, here we go, we're going to keep reading. It says, based on the above description, when hyperventilating, would you expect the relative change in partial pressure of carbon dioxide or the partial pressure of oxygen to be greater? Alright, what do you think? You're breathing really, really hard, so that air in the alveoli resembles more of the atmospheric air. Relatively, which is that going to affect more, the partial pressure of carbon dioxide or the partial pressure of oxygen? Well, we looked at these values in a table, and while you probably don't need to remember the exact values, you should be relatively familiar with what they are. And so I'm just going to write this out again. We had the partial pressure of oxygen and the partial pressure of CO₂ in both the atmosphere and the alveoli. And we said the partial pressure for oxygen in the atmosphere was about 159 millimeters of mercury, and in the alveoli, it was about 104 millimeters of mercury. And for carbon dioxide, we said it was 0.3 millimeters of mercury in the atmosphere, really, really low, and it was 40 millimeters of mercury in the alveoli. So as I look at these, I think if I'm breathing really, really hard, my alveoli is going to have a composition more like atmospheric air. Which one does it affect more? Well, relatively, as I look at these, well, 104 is about two-thirds the amount of the atmospheric air. So they're pretty close. Whereas the difference for the pressures in carbon dioxide goes from 0.3 to 40, That's a more than 100 fold change. So relatively, that's a huge change in carbon dioxide, but that's not that much of a change for oxygen. So which one is it going to affect more? I'm going to say the partial pressure of CO₂. Alright, we're going to keep reading here. It says the normal partial pressure of oxygen and carbon dioxide in arterial blood is listed below. Next to each, write an up arrow or down arrow based on whether you expect that value to increase or decrease during hyperventilation. Alright, well, now we're talking in the blood. So here it says the partial pressure of carbon dioxide in that arterial blood, that blood leaving the alveoli and headed to the tissues, is 40 millimeters of mercury, and the partial pressure of oxygen is 100 millimeters of mercury. So now, if we change that alveolar air to be more like atmospheric air, how do we expect these to change? Well, first up, what do you think about carbon dioxide? Well, Henry's law, right? It tells us that whatever that partial pressure is is going to tell us how much of that gas can dissolve into the liquid, in this case, the blood. So if we take that alveolar air and we make it more like atmospheric air, here, we are really reducing the partial pressure of carbon dioxide in the alveoli. And so that should really reduce, or a down arrow, the amount of carbon dioxide that will dissolve into that blood. Alright, we can do the same thing for oxygen here. So oxygen, 100 millimeters of mercury is what it normally is, leaving, the alveoli in that arterial blood. Well, we look here if we make this alveoli more like atmospheric air, well, we're increasing that partial pressure. So I would expect more, or I'll draw an up arrow, to dissolve into the blood. Alright, one more here. It says hemoglobin leaving the alveoli is usually 98% saturated, meaning 98% of the hemoglobin molecules are carrying the maximum amount of oxygen molecules. Knowing this and based on your previous answers, would you expect hyperventilation to affect the amount of oxygen molecules carried by the blood or carbon dioxide molecules more? Alright, so let's think this through. Which of these in the blood is going to be affected more, especially now that we're thinking of hemoglobin? Alright, so what it says there is that most of the oxygen in the blood right? Remember, oxygen isn't as soluble in blood, and so it's being carried by those hemoglobin molecules. But at our normal partial pressure, the hemoglobin is 98% saturated, meaning it's carrying about all the oxygen it can. Well, remember carbon dioxide, especially in our arterial blood, it's really just traveling around dissolved in the plasma because carbon dioxide is much more soluble. So if we change those partial pressures, which is going to be affected more? Well, if we raise the partial pressure of oxygen, we're not raising it relatively that much, and most of the oxygen is being carried by the hemoglobin anyway, and it can't carry that much more. So it's probably not going to affect how much oxygen is in the blood very much at all, but the carbon dioxide again, most of that carbon dioxide is in solution, and so if we really change the partial pressure, that is going to really change how much can get dissolved into the blood. So for that reason, I think that carbon dioxide is going to be affected much more when we're talking about how much of those molecules are actually in the blood when you're hyperventilated. Alright, that was a big long problem, but we worked through it. Hopefully, you were there with me. More practice to follow. See you there.

Which gradient most directly determines the direction that oxygen and carbon dioxide molecules will move between the air in the alveoli and the blood:

• A. The pressure gradient between alveolar air and the blood plasma.
• B. The concentration gradient between the hemoglobin and the blood plasma.
• C. The concentration gradient between carbon dioxide and oxygen.
• D. The pressure gradient between the hemoglobin and alveolar air.

Choose which of the following statements is correct.

• A. The pressure gradient for O₂ is much less than the pressure gradient for CO₂, but because of hemoglobin, more O₂ can be carried in the blood.
• B. Because the pressure gradient for O₂ is greater than the pressure gradient for CO₂, more molecules of O₂ will be exchanged in the alveoli than molecules of CO₂.
• C. Most molecules of O₂ are carried by hemoglobin, but it is the gradient between the plasma and the alveoli that determines the movement of O₂ in and out of the blood.
• D. O₂ is 20 times more soluble than CO₂, meaning that much more O₂ can be carried in the blood plasma than CO₂.

Internal Respiration

Alright, everybody. It is now time to talk about internal respiration. Remember, internal respiration, we said, is the exchange of gases, including oxygen and carbon dioxide, between blood and the internal tissues of the body. Here in internal respiration, we are going to have a net movement of carbon dioxide or CO₂ into the blood and oxygen or O₂ into the tissue. Also, we want to remember that in any tissue, just like in the alveoli, the total amount of carbon dioxide exchanged is going to equal the amount of oxygen exchange. If we were to count the total number of molecules crossing here, these two would be equal. And again, that's because of cellular respiration. Cellular respiration occurs in the tissues, and it uses the same amount of oxygen as carbon dioxide it produces.

Alright. So to look at this more closely, we're going to bring back this analogy of the tissue tower. The tissue tower, from the blood chapter, represents the tissues where all these molecules are either going to or coming from. Going by the tissue tower here, we have the street, and the street represents the capillary. Inside the capillary, so the space in the capillary, the space on the street or on the sidewalk there, represents the liquid portion of the blood or the blood plasma. And then we also have these buses coming through, and those buses represent the hemoglobin molecules.

Alright. So we'll start over on the left there. You see that hemoglobin molecule coming in. It's loaded up with oxygen. There's also oxygen dissolved in the blood plasma there, and we can look at the gradients here. Well, the partial pressure of oxygen on the street there is 100 millimeters of mercury. Well, in the tissue tower, it's less than or equal to 40 millimeters of mercury. Remember that less than or equal to depends on just how metabolically active that tissue is. Alright. So we have this big gradient. It's just way more crowded on the street, so there's a lot more pressure on the street that's going to be pushing these oxygen molecules off the street and into the tissue tower where there's less pressure. So these molecules move into the tissue tower, and as there becomes more room on the street, well, some of those molecules are going to hop off the bus. Those oxygen molecules hop off the bus, onto the street. It's more crowded now as they're getting off. That pushes more molecules into the tissue tower, and that process just continues until the partial pressure of the blood plasma well, on the street, equalizes to the partial pressure in the tissue tower. So here now it equals 40 millimeters mercury in both places, so no more oxygen molecules are going to cross.

Alright. But then that bus turns around. Well, actually, we just want to note we showed here this bus emptying, but really remember in every red blood cell, there's 250,000,000 of these buses, 250,000,000 hemoglobin molecules. We just want to note most of those actually don't drop off all their oxygens. There's actually a huge reservoir of oxygen still bound to hemoglobin even after this exchange happens. So that's just to say if you really need a lot of oxygen, don't worry. There's a lot of it in your blood. That hemoglobin carries a lot of oxygen around all the time.

Alright. But some of those hemoglobins do drop off their oxygen. We can follow that one along. So now it's this deoxyhemoglobin over here, and we can look at these gradients for the carbon dioxide. Well, you can see it's greater in the tissue tower, 46 millimeters of mercury in the tissue tower compared to 40 millimeters of mercury out here on the street. So it's crowded in the tissue tower. There's a lot of pressure. Those molecules get pushed out of the tissue tower. They come out. They come out onto the street. Now the street's getting more crowded. Some of those molecules hop on the bus. As they hop on the bus, you know, they're sort of riding on the outside of the bus here. Remember, that's because carbon dioxide binds to a different place on the hemoglobin than the oxygen does. But these molecules hop on the bus. This continues. That creates a little bit more room on the street. More molecules are pushed out until, right, that partial pressure on the street equalizes to the partial pressure in that tissue tower, and now they are both equal to 46 millimeters of mercury.

Alright. From here, this blood rolls on, and it's going to go through the veins back up to the alveoli, and it's going to continue this entire process again. Alright. But let's look at these gradients. So that oxygen gradient here, well, that gradient again was 60 millimeters of mercury. It's 60 millimeters of mercury greater in the street, in the plasma, than it is in the tissue tower than in the tissues, and that's why that oxygen moves into the tissues. Well, the CO₂ gradient was 6 millimeters of mercury. Again, greater in the tissue tower than on the street. That's why those molecules move out of the tissue and into the blood plasma.

Alright. Those should look familiar. That's the same gradients that we had for external respiration. So, hopefully, those are easy to remember. It's always 60 and 6. Alright. Again, quick note, those gradients do depend on metabolic activity. If this is a really metabolically active tissue, like skeletal muscle when you're exercising, those gradients will be larger. Alright. So now we've followed along how these molecules move in and out of blood, both external respiration and internal respiration. We're going to review this all some more and some examples and practice problems to follow. I will see you there.

Respiration Example 3

Alright, let's take a look at this example. It says, for the statements below, identify whether it applies to respiration in the alveoli, the tissues, or neither by writing the letter on the correct line. If the statement applies to respiration in both the alveoli and the tissues, write the letter on both lines. Alright, so we have 9 statements there, and then we have alveoli, tissues, and neither, and we got to write those letters down there. So let's start going through them one by one. Alright, first off, a says the site of internal respiration. Remember what that is. Now the site of internal respiration, respiration, the exchange of those gases, internal is down in the tissues. So I'm gonna put a there on tissues, exchanging the oxygen and carbon dioxide between those capillaries and blood and the tissues. Alright, so crossing out a. Next, we have b, the site of external respiration. Well, the site of external respiration. Yeah, it's in your body, but it's exchanging the blood with the external air in the alveoli. Alright, so b goes on the line oh, b for alveoli. Alright, next, we have the partial pressure of oxygen is about 6 millimeters of mercury greater than in the blood. Where does that happen? Partial pressure of oxygen, about 6 millimeters of mercury greater than in the blood. Nowhere. That oxygen gradient, remember, is always about 60 millimeters of mercury, not 6. It's a really big gradient and that 60 is both in the tissues between the blood and the tissues, and in the alveoli between the blood and the alveoli, just in opposite directions. Alright, so c, I'm gonna write that on neither. Alright, next, we have the partial pressure of carbon dioxide is about 6 millimeters mercury less than in the blood. Alright, well, now we're talking about the partial pressure of carbon dioxide, and here again it says 6 millimeters mercury less than in the blood. Where is that? Alright, well, that means carbon dioxide is gonna be moving down its pressure gradient from the blood to this space. So carbon dioxide leaves the blood in the alveoli. So I'm gonna write d on the line here. The partial pressure of carbon dioxide is 6 millimeters mercury less in the alveoli than in the blood. Alright, next, we have the partial pressure of oxygen is more than twice the partial pressure of carbon dioxide. Alright, where does that happen? That happens in the alveoli. Alright, remember, partial pressure of oxygen in the alveoli was like 104 millimeters of mercury, and partial pressure of carbon dioxide in the alveoli was about 40. That is more than twice the partial pressure, so I am putting e on the line for alveoli. Alright, next, we have f. The partial pressure of carbon dioxide is more than twice the partial pressure of oxygen. Where does that happen? Nowhere. Alright, so I'm putting that f on neither. Right? Where the partial pressure of carbon dioxide is greater than oxygen is in the tissues, but there the partial pressure of carbon dioxide, we said, is about 46 millimeters of mercury and the partial pressure of oxygen is about 40. So it's definitely not twice. Alright, so crossing out f, that brings us to g. We said g, there is a net release of oxygen from the hemoglobin. Alright, where does that happen? Where does hemoglobin release its oxygen? That's gonna happen in the tissues. In the tissues, right, the oxygen gets released from the hemoglobin, enters into the plasma, and then from the plasma, it goes into those tissues. Alright, we have h. There's a net movement of carbon dioxide into the blood. Where does that happen? Alright, well, carbon dioxide moves down its pressure gradient from the tissues into the blood. So again, we're gonna put tissues here. h is where there is a net movement of carbon dioxide into the blood. Alright, and then finally, we have the net movement of total oxygen and carbon dioxide molecules will be approximately equal. Where does that happen? Right, well, we said that both in the alveoli, so I'll put an I here, and in the tissues, you expect the total number of oxygen and carbon dioxide molecules exchanged should be about equal. And we said that's really just a factor of cellular respiration, what we use to break down our food molecules and capture ATP, because that equation uses 6 oxygen molecules and produces 6 CO2 molecules. That's an equal number, and so that's where all these molecules are going to or coming from. So in the end, the exchange should be roughly equal in all places. Alright, hopefully, you were able to straighten all that out. We have a few more practice problems after this. I'll see you there.

For internal respiration, which of the following must be true:

I. The total amount of CO₂ exchanged equals the amount of O₂ exchanged.

II. Carbon dioxide will move down its concentration gradient to enter the blood.

III. The partial pressure of O₂ in the tissue before gas exchange is ≥ 40 mm Hg.

• A. I only.
• B. I and II.
• C. III only.
• D. I, II, and III are true.

Here’s what students ask on this topic:

What is the difference between external and internal respiration?

External respiration occurs in the alveoli of the lungs, where oxygen (O₂) moves from the air into the blood, and carbon dioxide (CO₂) moves from the blood into the air. This process relies on pressure gradients, with O₂ moving down its gradient from high partial pressure in the alveoli to lower partial pressure in the blood, and CO₂ moving from high partial pressure in the blood to lower partial pressure in the alveoli. Internal respiration, on the other hand, occurs in the tissues of the body. Here, O₂ moves from the blood into the tissues, where it is used for cellular respiration, and CO₂, a waste product of cellular respiration, moves from the tissues into the blood. Both processes ensure that the body receives the necessary O₂ and expels CO₂.

How do Dalton's law of partial pressure and Henry's law apply to respiration?

Dalton's law of partial pressure states that the total pressure of a gas mixture is the sum of the partial pressures of each individual gas. In respiration, this means that O₂ and CO₂ move according to their own partial pressures. For example, O₂ moves from areas of high partial pressure in the alveoli to areas of lower partial pressure in the blood. Henry's law states that the amount of gas that dissolves in a liquid is proportional to its partial pressure and its solubility. This is crucial in respiration because it explains how gases like O₂ and CO₂ dissolve in blood plasma. O₂ has a lower solubility than CO₂, requiring hemoglobin to carry most of the O₂ in the blood.

What are the partial pressures of oxygen and carbon dioxide in the alveoli and blood during respiration?

In the alveoli, the partial pressure of oxygen (P_O2) is approximately 104 mmHg, while the partial pressure of carbon dioxide (P_CO2) is about 40 mmHg. In the venous blood returning to the lungs, P_O2 is around 40 mmHg, and P_CO2 is about 46 mmHg. As blood passes through the alveolar capillaries, O₂ moves into the blood, raising its P_O2 to about 100 mmHg in arterial blood, while CO₂ moves into the alveoli, lowering its P_CO2 to 40 mmHg. These gradients drive the exchange of gases during both external and internal respiration.

Why is the composition of alveolar air different from atmospheric air?

The composition of alveolar air differs from atmospheric air due to several factors. First, alveolar air contains more water vapor because the respiratory tract humidifies the air as it is inhaled. Second, alveolar air has a higher concentration of carbon dioxide (CO₂) and a lower concentration of oxygen (O₂) compared to atmospheric air. This is because CO₂ is constantly being transferred from the blood to the alveoli, while O₂ is being absorbed into the blood. Additionally, the residual volume of air in the lungs, which does not get fully exchanged with each breath, contributes to these differences in gas composition.

How does hemoglobin facilitate the transport of oxygen and carbon dioxide in the blood?

Hemoglobin, a protein in red blood cells, plays a crucial role in transporting oxygen (O₂) and carbon dioxide (CO₂) in the blood. Each hemoglobin molecule can bind up to four O₂ molecules, significantly increasing the blood's oxygen-carrying capacity. This binding occurs in the lungs, where O₂ partial pressure is high. Hemoglobin also helps transport CO₂ from tissues to the lungs. CO₂ binds to hemoglobin at a different site than O₂, forming carbaminohemoglobin. Additionally, CO₂ is converted to bicarbonate (HCO₃^-) in red blood cells, which is then transported in the plasma. This dual role of hemoglobin ensures efficient gas exchange and transport in the body.