The Science of Everything Podcast - Episode 123: Respiratory and Circulatory Systems Part 2

Episode Date: November 30, 2021

Concluding the two-part series on the circulatory and respiratory systems, I discuss the biochemical mechanisms by which red blood cells and hemoglobin molecules deliver oxygen to the tissues and carbon dioxide to the lungs, and the mechanisms which regulate these processes. I then consider the respiratory system, giving an overview of the structure and function of the lungs, the process of breathing, control of breathing, and adaptations to high altitudes. Recommended pre-listening is Episode 122: Respiratory and Circulatory Systems Part 2. If you enjoyed the podcast please consider supporting the show by making a PayPal donation or becoming a Patreon supporter. https://www.patreon.com/jamesfodor https://www.paypal.me/ScienceofEverything

you're listening to The Science of Everything podcast episode 123 respiratory and circulatory systems part two. I'm your host, James Fodor. This episode is, unsurprisingly, a direct continuation of the previous episode, 122 respiratory and circulatory systems part one, which is a prerequisite. And in this episode, we're going to pick up from where we left off there and talk about the role of blood and how it transports oxygen and other nutrients and wastes around the body. We're going to look at blood pressure, oxygen dissociation curves, blood types, and a bit about the lymphatic system. We're then going to talk about the respiratory system and talk about where blood gets its oxygen from

and how oxygen and carbon dioxide are exchanged in the lungs and the process of breathing, as well as control of respiration and a little bit about adaptations to breathing in high altitudes. Before we get into that, however, there are a couple of announcements about the show. So some of you may have noticed previous episodes appearing in the feed. And I mentioned this in the end of the past episode, but for those of you may have missed that or forgotten, the reason for this is because certain aggregator sites do not allow MP4, sorry, do not our M4A files to be played or distributed. And some of my early episodes are in M4A format for some strange reason that I don't understand.

So the only way that I've figured out around that is to re-upload them as MP3s, and unfortunately, I can't put them earlier in the feed, so they just appear, you know, as most recent items in the feed. So that's why you're seeing those there. Feel free to have a listen to those if maybe you haven't listened to them yet or for a long time, but otherwise they're just the same as they were previously. The numbering is still consistent, so don't worry about that. The prerex, you'll be able to find them. I should have finished uploading all of those just before uploading this one. I think it's mostly episodes 4 through 20-ish that have been re-uploaded.

So that's why those are sitting there in the feed. Henceforth, the numbering should continue, and hopefully that issue won't reoccur. all right so having said that now let's get started and talk about blood so at the end of the previous episode i talked about blood vessels and distinguished arteries veins and capillaries and i just want to make a few remarks about capillaries that are important for understanding how blood actually transports oxygen around the body so remember the capillary wall is only a single cell thick and they're basically thin cells that surround the capillary and allow blood to pass through. But critically, the blood obviously has to exchange oxygen,

as well as other nutrients, with the intercellular fluid that surrounds the tissue that is needing delivery of oxygen. And the way this occurs is that the capillary wall basically functions as a semi-permeable membrane, or the surrounding tissue of the capillaries, because there are gaps between the capillary cells, which small molecules, such as water and glucose, as well as gases, like oxygen and carbon dioxide, can squeeze through between gaps in the cells, which is called paraccellular transport. So they can squeeze through the gaps, essentially, whereas larger molecules like proteins can't, and those have to be transported across the cell membrane and then across the other side of the cell membrane to get out of the capillary. So that's not the focus here,

but the key thing to understand is that you can think of the wall surrounding a capillary as kind of a leaky barrier because gases and also glucose, which is important that blood carries glucose as an energy source for cells, those can sneak through the sides and squeeze through. And then from there they enter the tissue fluid or the interstitial fluid, the fluid that bathes most cells in the body. And from there, then they're taken up into cells. So again, oxygen and carbon dioxide can pass through the cellular membrane. and glucose is taken up by particular proteins that allow that to happen. I'll talk more about that when I get around to doing nutrition and the digestive system.

And this is all mediated as well by changes in pressure. So I've mentioned before that the partial pressure of oxygen is highest in cells that are near the sort of artery end of the capillaries. Remember, capillaries go from the arterial end to the venous end. So from arteries to the veins, right? and the partial pressure of oxygen will be highest near the artery end, obviously because the oxygen-ended blood is coming and has its supply of oxygen to deliver. In those areas, oxygen pressure is highest, and so in the blood, and therefore it tends to be released and enter the surrounding tissues.

Whereas at the venous end, the oxygen pressure in the blood is quite low because it's lost all this oxygen, right? And so in that case, actually what you have is the opposite. You have reabsorption, so it tends to absorb gases, particularly. of the carbon dioxide from the tissues at the venous end. So what's happening is the fluid is exiting the capillary at the arterial end because of the higher pressure there and then re-entering being reabsorbed at the venous end because of the lower pressure there. That's a combination of hydrostatic pressure, so the fluid pressure as well as the gas pressure. Now I'll talk more about that

in a moment, but the important point there is that the blood kind of knows when to give up and when to retake on the basis of the pressure differences from the arterial to the venous end of the capillaries. So water, oxygen, glucose and other nutrients go out. They sneak through the gaps around between the capillary cells and enter the interstitial fluid in the arterial end, and carbon dioxide, waste products, as well as water, sneak through and enter the capillary bed from the interstitial fluid at the venous end. And that's mediated by pressure differences. as well as concentration gradients and partial pressures of the gases. So that's how that's all mediated.

Now, there is one exception to what I've said here, which is something called the blood-brain barrier. This is effectively a series of mechanisms that prevents the normal processes of exchange occurring between the capillaries in the brain and the actual brain tissue. So the blood-brain barrier is something that I may talk more about in the future. I may have mentioned it in the past when I've talked about the nervous system. I can't remember. it's very important because it helps protect the brain from toxins and many infections and

also psychoactive substances. There are obviously certain substances that can cross the blood brain barrier, such as alcohol, but many substances can't. And so it's a protective mechanism. The blood brain barrier, though, is not really like a wall. It doesn't separate the brain from the rest of the body in a physical sense. Like it's not like there's a barrier across the top of the neck. Rather, the blood band barrier is a series of mechanisms including basically seals called gap junctions between the epithelial cells that surround the capillary, link the cells directly together and kind of seal them so that the space between the cells that normally is what allows water and other molecules to sneak past, that's sealed and so it can't happen. Gases such as oxygen

and carbon dioxide and hormones can get across the blood band barrier, but many solutes and pathogens can't. All right, so having now introduced that general idea of how nutrients and gases are exchanged from the blood through the tissues in the surrounding capillary. So let's now talk about some of the details. And I'm going to start with talking about blood pressure. Obviously, this is a very important characteristic of blood that people are probably familiar with. Blood pressure refers to the pressure of the circulating blood against the walls of blood vessels. And as you should be aware, that depends on the place in the body that it's measured, because pressure varies right across the circulatory system. It's typically measured in the

brachial artery, so in the arm, using a device called a sphigmo monometer. And that is one of the harder words to say. That is the inflated cuff that they put around your arm with the tubes attached to it. And so essentially what they do is they inflate it to a certain point, a cutoff where it effectively closes off the artery and so the pressure that they need to inflate it to to close off the artery is then the upper value of blood pressure as you probably know blood pressure is always measured as two numbers not a single number because the heart is constantly beating right so you want to measure the pressure over the course of the heartbeat cycle so to speak so the way

it's done is that you measure the maximum and the minimum pressure and the maximum pressure it's called the systolic pressure and that's the pressure generally that's going to occur when the left ventricle is contracting because that's generating the most the most force and pushing the blood around you know through the arteries so that's going to increase the pressure and then the diastolic pressure is the minimum pressure which is between two heartbeats so the period when the ventricles are relaxing and refer back to the previous episode when i talked about the process of moves through through a series of contractions and relaxations during the heartbeat so yeah you've got your maximum systolic and your minimum diastolic pressure and the way that this is

measured as i said is that you place the the inflatable cuff on the arm and uh inflate that until it occludes the artery there uh in the break a artery and then you make a note of the pressure that allows that which is then the systolic pressure the maximum pressure and then you deflate it until the minimum pressure which which allows the um artery to to reopen during the period when there's lowest pressure and so that is the diastolic pressure and the typical sort of average, roughly, it's slightly different between men and women, is 120 over 80, which you may have heard of before. That's measured in millimeters of mercury. If you have high blood pressure, that's called hypertension, and if you have low blood pressure, that's called hypotension,

from the prefixes that just mean high and low, or above and below. And there are many reasons why you can have higher, low blood pressure. We won't get into that here. That will probably be a discussion for maybe an episode on nutrition or something. But the blood pressure is very important because it indicates the health of the respiratory and particularly circulatory systems. So moving from blood pressure, let's talk a little bit more about some of the properties and key characteristics of blood in humans. So an average adult contains about five litres of blood, which is about 7% of total body weight, you know, for an average healthy adult. And that's kind of freaky if you think about it. Five liters is a lot

of blood. But obviously that's spread around your entire body. Now, blood consists of 55% what's called plasma and 45% of what's called formed elements. So roughly we can call that 50-50. So blood plasma is mostly water. It's a fluid that contains waste, gases, and nutrients. So like dissolved glucose, for example, and some dissolved gases, various solutes, ions, things like that. There's also proteins in it, so it's about 7% protein. But it's 92% water.

So blood plasma is essentially a fairly concentrated solution in terms of that there's quite a lot of proteins and other things in it. But, you know, it's mostly water. Now, the other part of blood, which is, I think what people more think about when to think about blood is the formed elements. So this is the other half of it. And when we say formed elements, it's basically like cells and cell remnants. So the main formed elements that you find in blood are red blood cells, white blood cells, and the platelets. So red blood cells are the cells that. are responsible for carrying oxygen around the body. And those are the main ones that we're going to be

talking about today. They are the cells that give rise to the red color of blood when it's oxygenated. And they form the majority of the volume and mass of the formed elements. In addition to that, there's also white blood cells, which are a variety of white blood cells, which are part of the immune system. I've talked about those in previous episode when I talked about the immune system. So I'm not going to go over those here. And then platelets. So these are cell remnants that are also involved in the immune system as well as in blood clotting. And again, I won't go over those now because I've talked about those in the past. So, but those are your three components of your formed elements. You've got your red blood cells, your white blood cells, and your platelets. And the red blood cells form

the majority of that. Red blood cells are also called erythracites, but I'll probably just call them red blood cells because it's sort of easier. Okay, so at this point we've got blood, which is circulating around the body, half of it's the plasma, which is essentially a concentrated solution, and then the other half of the formed elements, most of which are your red blood cells, and those are the ones that are actually carrying the oxygen around the body. But how do the erythrocytes or the red blood cells actually carry the oxygen and how do they deposit in the tissues when it's needed? Also, how do they pick up oxygen from the lungs when they need to? It's very important that that all works properly, right? The red blood cells need to pick up oxygen in the lungs

and deliver it to the tissues in the capillaries. Suppose they did that in reverse. If they dropped off oxygen in the lungs and then picked it up in the tissues, well, then you would be constantly starved of oxygen and you would die very quickly. So obviously that wouldn't work very well. So there needs to be a careful regulation

of the way that oxygen is absorbed and delivered by red blood cells. And that also has to be responsive to the amount that's needed in different tissues. So it all has to be carefully controlled. And there are a range of different. essentially biochemical mechanisms that have been evolved over, I don't know, hundreds of millions of of years to achieve this. And this leads us to one sort of way to describe this, which are oxygen dissociation curves. So this is a little bit technical, and I know you can't see the graph here,

but I'll try to explain the basic idea here. I mentioned before that the partial pressure of oxygen, this is just the pressure of oxygen in the blood or in the interstitial tissue. Essentially, it's the concentration of it, right? You can think of it as that. The pressure of oxygen is one of the key factors that determines whether oxygen is released or taken up by the blood. And it's similar for other things as well, like glucose and carbon dioxide. If there's a lot of it in the surrounding tissues, then it's typically to be taken up by the blood. Conversely, if there's not much compared to the blood in the surrounding tissues, then it's going to be delivered by the blood. That's just your concentration gradients. Pretty much all molecules or substances in chemistry

are going to move from where there's a lot of it to where there's not a lot of it, just by diffusion. And so that's sort of fairly easy enough to understand. But there's a lot more to it than that. So when we're thinking about the oxygen dissociation curves, we can think about a graph that shows how much of oxygen is bound to, or taken up by the red blood cells. That's on the vertical axis. And the x-axis shows the partial pressure of oxygen in the surrounding tissue. So what you expect to see is that the curve is going to slope upwards, right? It's going to go from the lower left to the upper right.

It's going to be an increasing curve because as the partial pressure of oxygen increases, more oxygen is going to be bound to the red blood cells. The red blood cells are going to tape up oxygen, the more of it is in the surrounding tissues, because there's more of it around, and so the red blood cells become saturated with it. Conversely, the less oxygen there is in surrounding tissues, the more the red blood cells are going to release that oxygen, and so there's going to be less of a saturation. The vertical axis will go down, and it will deliver that oxygen to the tissues. Now, it's not a perfectly straight line. It's actually a bit of a curve. It kind of has a decreasing slope. So it like slopes up and then sort of asymptotes up at one. Obviously you can't

have more than 100% saturation where all of the all of the red blood cells have as much oxygen as they can hold. So it's sort of an upward sloping but flattening out curve is the shape that this looks like. And so this is one important mechanism that helps with the delivery of oxygen because basically oxygen will be delivered to tissues that don't have very much of it and then it will be taken up from tissues that have a lot of it, such as the lungs. But there's more to it. than that because carbon dioxide also plays an important role here because, I mean, there are various reasons for this, but one way to think about this is it's not just the amount of oxygen that matters, it's also the amount of carbon dioxide. In fact, if you can't breathe, typically you're going to

experience difficulties from the fact that there's too much carbon dioxide before you're going to experience difficulties from the fact that you don't have enough oxygen. Or in other words, carbon dioxide toxicity is a bigger or a more immediate problem than lack of oxygen. I mean, they're both problems, right, but in terms of which will typically cure you first. So the point there is that it's not just the partial pressure of oxygen, it's also the partial pressure of carbon dioxide that plays a role in the uptake and delivery of oxygen. And the way that works is through something called the bore effect, or bore shift, it's sometimes called. And what this refers to is a shift in that oxygen dissociation curve. So remember this is an upward curve that says that the more

the higher the partial pressure of oxygen in the surrounding tissue, the more saturated the red blood cells become with oxygen. So that means they're going to take it up in the lungs and deliver it to the tissues when needed. But this curve can shift, move to the left or the right, based on the amount of carbon dioxide that is present. When there is more carbon dioxide present, the curve shifts to the right or shifts down, which is probably an easy way to think about it. I mean, it's sort of equivalent, right? But let's talk about it shifting down just for simplicity. What does it mean? What does it if the curve shifts downwards. Well, that means that at a given partial pressure of oxygen, right, so at a given location in the tissue, because the tissue has a tissue in particular

location in the body will have a particular partial pressure of oxygen depending on where it's located and its usage of oxygen, so forth. So at a given tissue, the red blood cells are less saturated with oxygen than they are before. That's what it means to be down on this graph, right? Because remember, the vertical axis is the saturation of red blood cells with oxygen, specifically hemoglobin, but we'll get to that in a moment. So, if you're a little, If we're lower on the vertical axis, that means that red blood cells are holding less oxygen than they were before, which means they've given up more to the tissues. And that makes sense, right?

Because if there's more carbon dioxide in the tissues, there's more of a need for oxygen. There's also more of a need to take up that carbon dioxide, which red blood cells also help with, but we'll get to that in a moment. So the long and the short of this is, the less oxygen there is in the tissues, the more oxygen is delivered by red blood cells. Conversely, the more oxygen there is in the tissues, particularly here with the tissue, we're talking about the lungs with very high partial pressures of oxygen, the more oxygen is taken up by the red blood cells. Also, the more carbon dioxide there is in the tissues, the more oxygen is delivered

to those tissues. The less carbon dioxide there is in the tissues, such as again in the lungs, the less oxygen is delivered to those tissues, or conversely, the more is taken up from those tissues. So these two mechanisms of the partial pressure of oxygen and carbon dioxide together help to ensure that in the lungs, where there's high partial pressures of oxygen and the lower of carbon dioxide, we're taking up oxygen and delivering carbon dioxide from the red blood cells. Conversely, in the tissues, we're giving up oxygen and taking up carbon dioxide. So these mechanisms ensure that you have a flow of carbon dioxide from the tissues to the lungs and a flow of oxygen from the lungs to the tissues and it all works as it should.

If the degree of saturation didn't change with the pressures, then this wouldn't work, right? And basically, the red blood cells would grab onto oxygen in the lungs and they never let it go, right? So it would never actually deliver it to the tissues, and that wouldn't work so well. Likewise, carbon dioxide would just build up in the tissues and wouldn't have any way of getting to the lungs to be exhaled. So again, that wouldn't work so well. So these mechanisms are critical here. The effect of the partial pressure of oxygen and the bore effect, which relates to the concentration of carbon dioxide. Now, I've been talking here about red blood cells, just, again, for sort of simplicity,

but it's not really the red blood cell per se that's actually responsible for carrying the oxygen. It's actually the molecules of hemoglobin that are located in the red blood cells. Red blood cells are quite interesting. They are cells, right? So they have a cell membrane and all that, but they don't actually have a nucleus, right? They're anucleate. And that means that they don't synthesize their own proteins. They're kind of born with what they have, and they'll live for a time and then die, and they're turned over regularly. So red blood cells are produced by tissue in the bone marrow, and they circulate for a few months before they are destroyed and their components recycled. So they can't replenish themselves because they lack the nucleus and therefore can't produce new

proteins and so forth. Each red blood cell contains something like 200, 300 million hemoglobin molecules, so they're packed with these hemoglobin molecules. And it's the hemoglobin molecules that actually carry the oxygen. Hemoglobin is a complex protein. I won't try to describe the full structure here, but it's what's called a tetramer, which means that there are four subunits in it. And two of the subunits are identical, and then two of the others are identical, right? So there's two subunits, two of one type of subunit, two with the other type of subunit called hemoglobin A and hemoglobin B. And each of these subunits contains a heem group. So a hem group is just a particular chemical structure. And the critical part of it is that there's an iron molecule coordinated in the middle,

so surrounded by carbon chains and so forth. Again, I'm not trying to describe the structure fully here. The important point is that each hemoglobin molecule has four subunits, and each of those subunits has a single heem group with one iron molecule, kind of in the center. of a ring that surrounds it. And these heem groups are critical because they are the bits that actually carry the oxygen molecules. So the iron is used because it's a transition metal. Transition metals can change oxidation states very readily.

The iron is held in place by five nitrogen atoms that surround it and kind of keep it stuck in place. That's the coordination. But then there's one bond free. It can form six bonds because of the coordination chemistry there. I need to do an episode on coordination chemistry. I'll get to that and I'll talk. talk about this in more detail, but suffice it to say that the way that this iron works is that it

can form six bonds. Five of those are from nitrogens that are surrounded in a ring and sort of keep it in place, but there's one spare site, and that spare site is where the oxygen can bind, but it reversibly binds, right? It depends on these factors that I mentioned, the concentration of oxygen in the surrounding tissues as well as concentration of carbon dioxide, as well as the confirmation of the hemiburban molecule itself. So each of these four heme groups in the the hemoglobin molecule can bind or not bind oxygen depending on those factors. And when I say bind, the oxygen just becomes coordinated to the iron. The ion is positively charged.

It has an oxidation state of 2 plus when it's coordinated with the oxygen. And so basically that the positive charge is going to attract the negatively charged lone pairs in the oxygen, so keeping it coordinated there. And that's how it carries the oxygen. It's coordinated to the iron. So each hemoglobin molecule with its four subunits can carry four oxygen molecules at maximum. So that's what the saturation refers to, the fractional saturation that I talked about, is how many of these hemgroups have an oxygen molecule carried along with them, an O2 molecule.

It can be anywhere from zero when none of them have it, and that tends to occur when there's very low partial pressures of oxygen in surrounding tissues, because basically the oxygen is given up by the hemoglobin and it diffuses into the surrounding tissues. Or it can be a maximum of one, which occurs in the lungs where there's very high partial pressures of oxygen, and therefore the oxygen is kind of pushed in and binds into the heen group. Now there's quite a lot of complex chemistry involved in this. I mentioned that there's two different confirmations of hemoglobin. There's a kind of a tense form and a relaxed form and they they look different like physically. It's a physical rearrangement. And the different forms basically allow the hemoglobin to be in a

state where it's ready to grab oxygen or in a state where it's less ready to grab oxygen. So at high partial pressures of oxygen, again, like in the lungs, the relaxed state is favored, and the relaxed state is a state where it's easier for the hemgroups to bind oxygen. Conversely, when there's a low partial pressure of oxygen, the tenth state is favored, and the tenth state tends to disfavor binding of oxygen. So these different confirmations are a part of what helps the curve that I mentioned exist, right? The dissociation curve. It's because of the different confirmations of the hemoglobin, and therefore the effect on the heemgroups,

hem in each hemoglobin, that allow different degrees of saturation of hemoglobin depending on the partial pressure of oxygen. So it's a complicated set of mechanisms. It's the amount of surrounding oxygen and the effect that that has on the actual shape of the hemoglobin molecule, allowing it to favor or disfavoring binding to oxygen, so that it favors, it adopts a confirmation favorable to binding of oxygen in the lungs, and then disfavorable in the tissues when it needs to give up that oxygen. Now, I mentioned that hemoglobin doesn't just carry oxygen, it also carries carbon dioxide. Carmodyoxide is carried through tissue in a variety of ways. So some of it binds to hemoglobin directly.

Now, it's important to note that it doesn't bind on the hemoglobin, right? The heem group is where the oxygen binds, not the carbon dioxide. However, carbon dioxide can bind to hemoglobin at other sites. This is called allosteric binding, right? There are different sites that it can bind at on the hemoglobin molecule. So some carbon dioxide is carried directly on hemoglobin in the red blood cells. However, a lot of carbon dioxide is also carried just dissolved in the blood plasma. But it's more complicated than that even because carbon dioxide doesn't typically just dissolve

as a gas in the plasma. Some proportion of it will, but most of it actually reacts with water in the plasma to form bicarbonate. So that's effectively where carbon dioxide gains an oxygen and a proton to form HCO3 minus instead of CO2. And that bicarbonate then exists a dissolved in solution. So carbon dioxide is there, but it's in a form where it's not in carbon dioxide form, it can convert back from carbon dioxide to bicarbonate, back and forth. And that, of course, depends on various factors, including the pH of the pH of the pH. And this is an important reason why blood pH matter pH matter of carbon dioxide that your blood's going to hold, and vice versa. The amount of carbon dioxide in your blood affects the pH. When carbon dioxide is

converted into bicarbonate, it releases a proton. That proton is released from the protein. That proton is released from the water, actually, not from the carbon dioxide, obviously. Carbon dioxide doesn't have protons, but it's released from the water that carbon dioxide is interacting with. And we know that when you release protons into solution, that makes it more acidic. It lowers the pH. So, blood that has a high amount of carbon dioxide, then that carbon dioxide tends to react to form bicarbonate, releasing protons, which lowers the pH. So low pH tends to go along with higher amounts of carbon dioxide. And so that's one of the reasons is so important to maintain blood pH, is because if blood pH is off, then that, that's, you know,

that's going to affect the amount of carbon dioxide that your blood holds. And if that's off, then that's going to affect the amount of carbon dioxide that's taken up from the tissues, as well as the amount of oxygen that's taken up from the tissues. Because remember, carbon dioxide and oxygen interact with each other through the bore effect that shifts the dissociation curves. So all of this means that it's very important to maintain blood pH. And that's part of homeostasis, which I'll talk more about in other episodes, but that's an important connection there. Now, carbon dioxide isn't just affected by the blood pH and affect the blood pH. It also affects oxygen.

So remember I said that there are two confirmations or forms, shapes of hemoglobin. There's the relaxed form and the tense form. The relaxed form favours oxygen binding, whereas the tense form disfavours it. Whether the hemoglobin is in relaxed or tense form depends on the partial pressure of oxygen. However, it also depends on the amount of carbon dioxide present. Basically, because carmodoxy can bind to hemoglobin, as I mentioned before, it can change the confirmation. So when the CO2 binds to hemoglobin, it favours the tenth state. And if you recall, the 10th state disfavors oxygen binding. So basically CO2 binding to hemoglobin causes the hemoglobin to release

oxygen. And this is the reason for the bore shift, where those oxygen association curves shift downwards or to the right, whichever you want to think about it, meaning that when there's more carbon dioxide, for a given partial pressure of oxygen, hemoglobin holds less oxygen. And so all of this means is that the presence of carbon dioxide contributes to and favors oxygen being released, which is as it should be, right? If there's more carbon dioxide in the tissues, they need more oxygen because their metabolism has produced the carbon dioxide as a waste. It needs more oxygen to keep that going. So that all makes sense. The converse happens as well. In areas where you don't have very much carbon dioxide, such as in the lungs, the hemoglobin holds onto more

of its oxygen because the curve is shifted upwards or stays upwards. Not only does carbon dioxide affect oxygen, but oxygen affects carbon dioxide. So when oxygen concentration is high, like in the lungs, binding of oxygen to hemoglobin causes protons to be released. Remember I said that hemoglobin can bind protons at various parts of the molecule, again, not the part on the iron where the oxygen binds at different parts of the molecule. So those protons are typically there to some extent, right? But when oxygen binds, that tends to cause these protons to be released because the molecule changes shape and releases some of these protons, which enters solution in the blood plasma, Now, an increase in the number of protons in solution pushes the reaction with bicarbonate backwards.

This is called the Le Chateer principle, which I would have talked about in one of the previous chemistry episodes. Basically, if you have a reaction that can go both ways, if you introduce something on one side of the reaction, it pushes the reaction to the other way. So if I have carbon dioxide reacting with water to produce protons plus bicarbonate, if I add in some protons, that's going to push the reaction back towards carbon dioxide and water. So the long and the short of that is, when you have more oxygen binding to hemoglobin, that results in a release of protons, which results in the reaction with of bicarbonate and carbon dioxide going backwards, producing carbon dioxide gas. So that means that in the lungs, when there's lots of oxygen binding to hemoglobin, carbon dioxide is released from solution, like it's converted back from bicarbonate to carbon dioxide, and then can be respired out during exhalation. So there's this nice process where carbon dioxide tends to get converted into bicarbonate in the tissues and then get converted back in the lungs so that it can be released. So all of these processes interact with each other, right? You've got your partial pressures of oxygen. Higher partial pressures of oxygen lead to more oxygen binding because there's more of it around, whereas lower partial pressures of oxygen lead to oxygen being released because there's less of it around and it tends to diffuse to where it's needed.

This is also facilitated by changes in the confirmation. that I mentioned, low affinity versus high affinity, which further facilitates that effect. There's also the bore effect, which is essentially the effect of carbon dioxide and blood pH, so that when there's more carbon dioxide, that binds to the hemoglobin, causing it to change confirmation and into the confirmation where it tends to release more oxygen. Conversely, when there's less carbon dioxide and more oxygen, it tends to adopt the confirmation where it holds onto its oxygen. And finally, more oxygen also tends to release protons from the hemoglobin, which promotes bicarbonate going back to carbon dioxide and then being released.

So all of these combinations, pressure of carbon dioxide, pressure of oxygen, amount of carbon dioxide, like dissolved in the blood, a pH of the blood, and the confirmation of the hemoglobin. All of these things go into the complex mechanisms that allow the oxygen to be delivered to tissues when it's needed and taken up from the lungs where it's needed. Conversely, oxygen to be taking up from tissues and then delivered back to the lungs where it's needed. And not just in an absolute sense, right? So this is, so these things are all graded. So basically when there's tissues that are really oxygen starved, they'll be, they'll have a lot of oxygen dumped to them. And if they only need a little bit of oxygen, they'll have less oxygen delivered to

them. So it's all kind of graded and aligned in proportion. There's other things that can adjust as well, such as heart rate, for example. But in combination, all of these things allow for delivery of oxygen when it's needed and then uptake of carbon dioxide when that's needed. So it's all very, really cool. think how this works and how the mechanism sort of precisely tuned again obviously by evolution now moving on from the delivery of oxygen and the oxygen dissociation curves let's talk a little bit about some other aspects of the blood system that I just want to touch on fairly quickly and one is blood type so this is something that many people know about blood you know that there's such a thing as a blood type and you probably know about a b and type o negative and positive and so forth so let's break down all of what

those things refer to so basically what blood type refers to are the antidepresses that are present on erythrocytes, so red blood cells. All cells have antigens on their surfaces. I've talked about that in previous episodes, such as the immune system, and when I talked about cell signaling, there's many, many different of these antigens, which are just like proteins, or bits of proteins that are being displayed on the surface of the cell. Again, all cells have these antigens being displayed of all sorts of types. But because of genetic differences, some people have this particular antigen. I don't really know what its origin is. It doesn't matter for our purposes that's called A. There's another type of antigen that some people have

which is called B. So some people because of genetic differences will have A and some people won't. Some people will have B and some people won't. You can have both A and B or you can have neither of them. So there's four possibilities. You can be A but not B, B but not A, A and B or neither A nor B. So four possibilities there. It's just averse to the fact that do your red blood cells display or like have on their surface displayed this particular bit of approach? in this antigen. Now, the reason this is so important is because if you have that antigen displayed by your own blood cells, your immune system won't attack anything that has that antigen on it. It won't be sensitive to that antigen. Basically, because your immune system goes through a process of sensitization in the thymus during development, where basically all of the

antigens that are presented by self, so your own cells, the antibodies to those are destroyed. So basically so that you don't attack your own cells. Now, when this doesn't work properly, you get autoimmune diseases. But the critical point is that someone who is type A-B, so that they have A and B antigens on their red blood cells, won't have antibodies to either A or B, because the self-ex expects to see those antigens, so it won't attack them. Antibodies are the things that detect and attack antigens. So if you're A-B, you won't have antibodies to A or B. Conversely, if you're type O, if you don't have either A or B antigens, you will have those antibodies because your body is like, well, I don't recognize these things, so I better attack them if I do see them.

So that means, conversely, if you have only A, then you won't have A antigen, antibodies, but you will have B antibodies. And if you are B, if you have B antigens, you won't have B antibodies, but you will have A antibodies. So antibodies and antigens are kind of like opposites. If you have the antigen, you won't have the corresponding antibody, because that would attack your own cells, and that would be bad, right? So if you're type A, B, you have all the antigens, but none of the antibodies. If you're type O, you have all the antibodies, but none of the antigenes. Hopefully that's sort of clear. Now, there is another type of antigen, which is called the resus factor, and this is often represented as plus or minus, so you have it

or you don't. So that's why you have like A positive and B and B, and things like that. So I've been talking about A and B just to make it simple because there's like the two main ones, but then there's the recess factor as well, which is plus or minus. So then that kind of adds a third factor in. But anyway, it's all the same thing. It's all about do you have the antigen or don't have the corresponding antigen? And the reason this is really, important is Liza because of blood transfusions. So there's two types of transfusions or two aspects to you can donate or receive either the red blood cells themselves, like the formed elements, or the plasma. Now the plasma is where the antibodies are present, right? So if you have type A, B,

if you're type A, B, then you don't have any antibodies. That means everyone can receive your plasma. Why? Because there's no antibodies in it. Well, no, there are antibodies in, but no A or B antibodies, right? and so that wouldn't cause a problem for anyone. Antibodies will attack the corresponding antigen. But if you don't have any antibodies in the plasma, then it's not going to be a problem, right? So that means that group AB are universal plasma donors. However, the formed elements,

their red blood cells contain antigens for A and B. So they can't donate to anyone except for other A.Bs. Because suppose that you had, suppose that you received a donation of red blood cells from someone who has AB and you're in group A, right? That means you have anti-B antibodies. So that's going to attack the B antigens in the blood that you've just received. And that's going to be a problem.

You're going to have a reaction to that. So it's a little confusing. Type A-B people are universal donors of plasma, but they can't donate to anyone, except for other AB's, formed elements. So the actual cells themselves. Type O is the opposite. Type O can donate red blood cells to anyone because they don't have antigens on them. but they can't donate the plasma to anyone except other type O, because their plasma has anti-B

antigens and anti-A antigens. So it's a problem for everyone unless you're also type O and you don't have any of the antigens. So essentially, when you're dealing with blood donation, as well as organs, where this is an issue too, you need to make sure that blood type is matched so that there's not going to be a problem, it's not going to be an incompatibility. Different people will be compatible or incompatible with different types of blood, depending on which antigens and which antibodies they have. I suppose ideally what you'd want to have is none of the antibodies and none of the antigens,

because then you could get anything from anyone. It wouldn't matter. I don't know if these particular antigens are actually present on any pathogens. So I don't know if any of these blood types have an effect on immunity. I suppose that that could possibly be a factor. But in general, I think that they just cause a nuisance. Anyway, so that's a little bit about blood typing and kind of what all that's about. It's about the antigens and antibodies. All right, moving on, then let's talk a little bit about the lymphatic system. Now, this is not a podcast on the lymphatic system, so I don't want to talk about it too much, but there are just a few little points that I wanted to touch on here.

So the lymphatic system consists of a series of capillaries and vessels that collect water and solutes from the interstitial fluid and deliver them to the circulatory system. So it's kind of like a parallel circulatory system in that it circulates stuff, but it doesn't circulate blood. It circulates lymph, which is similar to the interstitial fluid. So one of the important purposes of the lymphatic system is to control the amount of fluid that's present in the body. So you don't want to have too much fluid because then you'll swell, but you don't want to have too little, because then you might dehydrate and you may have not enough protection around organs and things like that.

So the lymphatic system plays a role in that. Remember that the fluid that is contained, or some of the fluid that's contained in the blood, in blood plasma specifically leaks out of the capillaries. So some of the water leaks out and some solutes and other. things leak out as well when they're passing through the capillaries. So that needs to be returned. Otherwise, there'd be a net leakage of fluid from the blood to institutional fluid. That fluid is ultimately returned by the lymphatic system. Lymphatic system also delivers fat that's absorbed from the small intestine to the bloodstream. We'll talk more about that when we

talk about nutrition. It also transports cellular debris and pathogens and other things to the lymph nodes. So that's basically a component of the immune system. Lymph nodes are special organs located around the body that help filter the lymph before it enters the bloodstream. And so they help to identify target pathogens. So again, they're part of the immune system effectively. Important lymph nodes include the tonsils, which help to defend against inhaled pathogens, the spleen, which filters pathogens and as well as worn out red blood cells from the blood. And the thymus gland, that's the side of T-cell maturation that I mentioned before. The thymus gland is located kind of around the throat.

So that's just a little bit on the lymphatic system. It's kind of a parallel circulatory system, but it plays roles in control of fluid, control of some nutrients, as well as in the immune system. You don't hear about it so often. I'm entirely sure why that is, because it's is very important. Anyway, so that's, that concludes what I wanted to talk about with respect to blood. So we mostly talked about how blood picks up and then releases oxygen carbon dioxide when it's needed and how it delivers it to the relevant tissues. Now we're going to move on and talk about the respiratory system. And this is mostly the lungs and the process of breathing. So obviously you need to actually get the oxygen into your body in order for it to be,

to be carried around by erythrocytes and to take into your cells. Also, you need to remove carbon dioxide from your body. It's got to be, you know, released in some way. And that's what the lung is for. The purpose of the lung is to exchange gases between the air and your body, or specifically, you know, the bloodstream. That's what the lungs do. They're gas exchanges. And breathing is just the process of exchanging air between your, the lungs and, you know, the environment so that you can constantly shift that out, because otherwise it would just to equilibrate and there'd be a little point in taking blood to the lungs because, you know, the gases there would just be the same as ever else. So obviously, you have to continually

exchange that out. And some people, well, I think people have a misconception that we breathe in oxygen and breathe out carbon dioxide. That's not really correct. There's a kernel of truth to it, right? In that the air that we breathe in has something like 20% oxygen and a fraction of percent carbon dioxide. The air that we breathe out has slightly less oxygen and slightly more carbon dioxide. It doesn't actually change the percentage very much. It depends on, you know, like how much exercise you're doing and other things like that and how deeply you breathe in in terms of what the exact pressures are. But the point is that we breathe in mostly nitrogen and breathe out mostly nitrogen. That's, you know, like 70, sorry, 80-something percent. And we, the next most common

gas is oxygen. What happens is that the concentration of oxygen goes down a little bit. I think it's a couple of percent on exhale there compared to inhale there. And the concentration of carbon oxide goes up a few times in exhale there compared to inhale there. That's why, you know, if you are breathing into a plastic bag or something that doesn't exchange air with the environment, you can do that, right? There's still oxygen in there. It's not like that there's no oxygen. The problem is that eventually you're going to get to a point where there's too much carbon dioxide in that air, that you're not going to be able to remove the carbon dioxide that you need to, and that's going to lead to problems, as we kind of talked about before.

Acidosis of the blood is something that's going to happen very quickly because of the carbonic acid that's produced and releasing those protons. So the issue is not so much that when we breathe out, that there's no oxygen in the air. It's actually that there's too much carbon dioxide there. And if carbon dioxide builds up too much in the surrounding air that we're breathing in, then we're not able to remove carbon dioxide rapidly enough, and we experience very rapid problems. All right, so let's talk about the lungs. Obviously, we have two lungs. Each lung branches out from the trachea, which is essentially the airpipe. The treki then branches into two bronchae, so one leading into each of the lungs. And each of the bronchi then branches, in turn, into a bronchial tree. So basically what we've got here is a series of progressively smaller and narrower but more numerous air passages. And you can think of it as kind of like an inverted tree, where the branches and leaves of the tree are inside each lung, and then the branches progressively come together. and fuse to form the trunk, which then leads up into the connecting up to the trachea.

That's not exactly obviously how it is, but I think it's a useful analogy to help sort of picture what happens here. So you've got the trachea, the bronchi, bronchial tree, and at the end of the different branches of the bronchial tree are air sacs, which are called elvoli. So the alveoli are bundled together in sacks that are called alveola sacks, and they share a common opening to a particular branch of the bronchial tree. So basically you've got a tree here, but instead of leaves, they've got these basically little circular sacks, which are the alveoli or the air sacks. And each of these alveoli consists of a thin layer of endothelial cells. This is important because they are covered by capillaries, which of course is necessary to allow rapid exchange of gases.

Interestingly, the blood pressure in the alveolar is quite low, and that is important to maintain water, to minimize water loss to the air, because if the blood pressure was high, you'd have very rapid evaporation of liquid in the lungs, and you'd lose too much water. Now, as I said before, the concentration of oxygen is highest in inhaled air and lowest in expired air. Conversely, the concentration of carbon dioxide is lowest in inhaled air and highest in exhale there. So the point is to basically dump out excess carbon dioxide and breathe it out and breathe in oxygen that's needed to pass around the body. So that's the overall structure of the lung. You've got the bronchial tree terminating in these alveolar sacs, which is as thin layers of tissues covered in capillaries around which you have the exchange of gases. So you've got the gas in the middle and then the capillary surrounding the sacs and the gas can exchange across the thin layer of tissue between them. So that's all simple enough.

Let's now talk about the process of breathing. It's sort of a bit of an odd thing to think about because we sort of do this automatically all the time. It's actually slightly disturbing if you think about it, that breathing is something that we have to do constantly, or almost constantly, for our entire lives. And if you stop football at a few minutes at a time, you will die. So breathing consists of two phases, inhalation and exhalation. Breathing is something that is modulated by the diaphragm and the intercoastal muscles. So intercostal muscles are muscles between the ribs and the ribs and the, rib cage. And the diaphragm is a big muscle that sits just below your rib cage and it separates

the thoracic from the abdominal cavities. Now surrounding the lungs are two layers of tissue, or two layers of membrane, which are called the pulmonary plurier. I hope I pronounced that correctly, pulmonary plurier. So these two thin layers of tissue, which sort of oppose each other so they sit like one on top of the other. These surround and overlay the lungs and fit inside the thoracic cavity. And the purpose of these is to modulate the pressure so that breathing can occur. So what happens is that when the diaphragm and intercoastal muscles contract, that pulls the lungs downwards and outwards. And that lowers the pressure in the interplural space. That's the space between the two pulmonary plurier, so the space between these two laser tissue, which surround

the lungs. So basically expanding that space by contracting the diaphragm and the intercostal muscles, it increases the space, thereby reduces the pressure, and that causes air to be drawn into the lungs through the trachea and ultimately through the nose and the mouth. So it's interesting, we sometimes think about breathing as sort of sucking in air, and of course you can do that if you're panting if you're breathing heavily, that increases the rate at which you can move air into and out of the lungs. But you don't need to do that in order to breathe. Typically during passive breathing, the air is drawn into the lungs by a decrease in pressure in the interplural space. When you exhale, the opposite happens. So the diaphragm and the intercoastal muscles relax, that causes the ribcage

and the thoracic cavity to move downwards and inwards. That increases pressure. in the interplural space, thereby forcing air out of the lungs. So it's a constant in and out a rhythm of increasing and reducing pressure brought about by the diaphragm and the intercostal muscles. So it's quite an elegant system there. Now let's talk a bit about the lung capacities, which is important when thinking about the rate at which we breathe and the sort of spare capacity of the lungs. So the tidal volume is a phrase used to refer to the amount of air that is moved or inspired or exhaled in each breath when you're breathing normally. And these volumes are typically measured in cubic centimeters.

So the tidal volume is about 500 cubic centimeters. Obviously, it is going to depend on things like age and sex. The total lung volume, which is the maximum possible volume of the lungs at maximum inspiration, is about 6 litres or 6,000 cubic centimeters. So of that, the tidal volume is only less than a 10th, 500 cubic centimeters. So the point there is that with normal breathing in and breathing out, we don't actually change the volume of the lungs by very much. The overall capacity is not utilized in most breathing, which if you think about it makes sense, because we need a lot of reserve capacity for times when we need extra oxygen. So we don't want to be using the entire capacity every time.

So the tidal volume is only a small fraction of that. If you imagine the tidal volume is sort of a small oscillation about the standard lung volume, which is around two and a half to three liters, we're sort of constantly fluctuating between two and a half to three liters as we breathe in and out, there's sort of two extremes. You could either inspire more than the standard amount or exhale more than the standard amount, right? And if you breathe in normally, that brings you up to the top of the tidal volume, about three liters. If you then try to breathe in as much as you can, inhale as much air as possible, going from there up to the maximum possible inspiration, the total long volume,

that's the inspiratory reserve volume. And that's the total amount of extra breathing and you can do above them. normal amount. And that's about an additional three liters, so, or 3,000 cubic centimeters, which is substantially more than, you know, we ordinarily breathe in and out. Now, if we go the other way, if we breathe out forced exhalation as much as possible, that difference between the bottom of the tidal volume and breathing out as much as you possibly can is called the expiratory reserve volume. So inspiratory is breathing in as much as you can, the volume of breathing in as much as you can, and expiratory is breathing out as much as you can,

the difference between that and the bottom of tidal volume. So that is about 1.3 litres or 1,300 cubic centimeters. So it's a lot less than the inspiratory reserve volume, which again, I guess is sort of intuitive, at least to me, that you can breathe in a lot more beyond normal than you can breathe out a lot more than normal. It's just apparently how it works. The vital capacity of the lung is the sum of the inspiratory and expiratory reserve volumes plus the tidal volume, plus the tidal volume on top of that. The vital capacity of the lung is the sum of the inspiratory and expiratory and expertory plus the that. So that is the vital capacity. That's essentially the total amount of usable lung volume that you can vary if you would exhale that much air if you first exhaled as much as you could, and then from there breathed in as much as you could. That would be the vital capacity. And that is usually about five litres, a bit less than females. Now I said that the total volume of the lungs is about six litres or six thousand cubic centimetres. And so that means that compared to the 5,000 cubic centimeter vital capacity, there's about a liter or so, about 1,000 cubic centimeters, of residual volume, which is what called dead space. And that is volume that cannot be emptied.

So that's just volume of the lungs that you can breathe out, essentially. There's a limit to how much you can breathe out. So that is your residual volume. So basically, you've got the total lung volume is divided into residual and vital capacity. Vidal capacity is about five liters compared to residual of about one. And vital capacity is divided into the expiratory reserve, the tidal volume, which is only about half a liter, and then the inspiratory reserve, which is about three liters. So there's a lot of reserve capacity there to breathe in more if needed, and that obviously happens when you're needing to breathe in more oxygen for very rapid, very intense exercise, and likewise the expiratory reserve volume is needed for breathing out a lot of carbon dioxide if you're building that

up very quickly. And you can also use that, of course, for holding your breath. Now, in terms of control of respiration, I mentioned before that respiration is automatic, just like the heartbeat, you don't need to think about it in order to do it. So that is governed by the Medulla-Ablong which, as I said before, is part of the brain stem, the most primitive lower part of the brain, that sends signals every few seconds to the diaphragm and the intercostal muscles to contract, which initiates inspiration in the way that I said. Now, during heavy breathing, there is an additional area of the medulla that becomes active, which sends signals to the abdominal muscles to contract for forceful exhalation.

So remember, the intercostal muscles are in the thoracic cavity, but abdominal muscles are used if you want to forcefully eat. inhale or exhale. And so those are only activated when we need a lot of extra oxygen and carbon oxide to be exchanged. Now in terms of how that's how that's controlled within the medulla, there are chemoreceptors that detect the concentration of carbon dioxide in the blood, as well as in the, so those are located in the medulla itself, but also in various arteries throughout the body. And those receptors send signals that help to tell the medulla basically whether we need to breathe more or less, like whether to activate the heavy breathing or

or whether normal breathing is sufficient. There are also sensors in some of the arteries, such as the carotid arteries near the brain, that detect changes in oxygen levels, and similarly send signals to the medulla that tell it to change the breathing rates, particularly if oxygen levels get too low, there'll be signals to increase the breathing rate.

pH sensors also can detect the pH of the blood, which is a direct signal of the amount of carbon dioxide. Remember, because of the conversion of carbon dioxide to carbonic acid, which increases pH by releasing the protons. So if the blood becomes too acidic, we need to breathe out more chlamidoxide. So that also will send signals to the medulla. So the medulla is actually integrating a large number of signals. This is the respiratory center of the medulla, which integrates these signals from across the body,

particularly muscles and blood vessels, and then sends those signals to the diaphragm, their intercostal muscles, as well as abdominal muscles to tell them to contract in at what rates. Now, we do have conscious control over the rate at which we breathe. So we can, if we want to, send signals down from the cortex to the medulla, which then sends further signals to alter the rate of breathing. So breathing is under conscious control, but we don't need to exercise conscious control in order for it to occur. So we can bring it under, but it's not essential. So that's different from heart rate, which we can't, at least most people cannot voluntarily control. There is something called biofeedback where people are able to train themselves

to be able to vary their heart rate, although I don't entirely know how this works, But I don't think it's an exercise of conscious voluntary control in the way that you move your arm or decide to breathe in or breathe out. I think it's a bit more indirect than that. They basically train themselves to be able to, to be able to activate their or modify the behavior of non-conscious automatic bodily functions. But I don't fully understand how that works. But for most people, you can't decide to change your heart rate, but you can decide to change your breathing rate, which is interesting. I guess that probably relates to the need to hold your breath underwater and things like that, which we don't have for, like, there's never a time you want to stop your heart, but there are times when you want to. stop breathing, essentially. Plus, there's also the fact that we need to control our red breathing

for talking, for language, and also because we, for interesting evolution and reasons, use the same initial passageways for eating as well as breathing, which can obviously lead to choking if we're not careful to control our breathing during eating, although, you know, that happens automatically as well, but there's an element of conscious decision there. So I think that these are some of the reasons why we have more control over breathing than heart rate. Now, a few final comments about adaptions to high altitude, because this is something. that is important for the respiratory system. So hypoxia is a lack of oxygen in the blood specifically and it's a grave risk at high altitudes because the partial pressure of oxygen is lower

at higher altitudes, basically because the atmosphere gets thinner, the high you go up. So this can lead to lightheadedness around 4,000 meters up, dizziness around 6,000 meters and unconsciousness by around 7,000 meters. So there is a height or an altitude around the very highest mountains, which I think is around 7,000 meters, which is called the dead zone, where if you go above that, you have a very high risk. A lot of people die, right, because you can go unconscious unless you're acclimatized to those conditions or unless you have artificial oxygen. And that's one of the reasons why, one of the many reasons why climbing very high mountains is dangerous, in addition to the cold, in addition to falling, in addition to being remote and hard to get to. So the death rate of Mount

Everest climbers is actually quite high, high than I would like to contemplate anyway. But The point is that this happens because the partial pressure of oxygen in the air that we're breathing in is a lot lower. And remember I said that it's the partial pressure of oxygen that's responsible for loading oxygen onto hemoglobin and transporting around the body. So if that's too low, you're just not going to load enough hemoglobin. You're not going to load enough oxygen on your hemoglobin, and therefore you're not going to transport it around the body enough. So therefore, your brain doesn't get enough oxygen, you become lightheaded, eventually become dizzy and go unconscious if you don't do something about that pretty soon. Now, the human body can adapt to high altitude in the both immediately, like in the short term and through longer term acclimatization.

There's a complex series of processes that happen, especially in the longer term. So in the short term, the lack of oxygen is sensed by the receptors in the carotid arteries and elsewhere that I mentioned before, and that can increase the breathing rate. So that is a sort of short-term way of dealing with this. The problem with that is that it also leads to breathing out more carbon dioxide, which results in, remember if too much carbon dioxide results in an acidic blood? but too little carbon dioxide results in alkaline blood. And that's a problem as well,

because we need to keep the blood pH in a very small range for normal metabolic functions to continue. So that prevents us from breathing in too much. That's one of the reasons why hyperventilation is dangerous. It's not so much that you get too much oxygen. It's that you remove too much carbon dioxide, so you have respiratory alkalosis or alkaline blood. So that's only a limited short-term solution to this problem.

Over a number of weeks and months, however, you can increase or the body can learn to increase cardiac output permanently, as well as increasing the rate of production of erythrocytes, so that overall we're able to pump more blood and hold more oxygen in the blood. And that's certainly the case for populations that live in high altitudes, as well as people who spend significant amounts of time there. So that can be a way, acclimatizing over a long period of time to these higher altitudes is a way of reducing the risk of this. And I think that that is what many of the climbers do these days. But it is a significant risk that you should bear in mind if you're ever going to a higher altitude. It's also a reason why,

for example, aircraft are pressurized, like commercial jet aircraft that fly at high altitudes are pressurized, because if they weren't, people would go unconscious throughout the flight quite quickly because of the low pressure there. All right, and that brings me to an end of what I wanted to talk about today. So just as a quick recap, we talked about the blood, blood pressure, how blood, what particularly arethrocytes, how they transport oxygen and carbon dioxide around the body and the various mechanisms that ensure that oxygen is taken up when it's needed and then delivered when it's needed and vice versa of carbon dioxide in terms of oxygen dissociation curves, partial pressures, hemoglobin binding and the bore effect and so forth. I also talked about

blood types, a little bit about the lymphatic system. We then moved on to the respiratory system, and I talked about the structure of the lung, control of breathing and lung capacities and control over respiration through the medulla. And then a little bit about adaptations to high altitudes. So hopefully you found this episode interesting. If you did, you can support the show by going to a podcast aggregator of your choice and leaving a positive review, which helps to spread word about the show. You can also email me. My address is Fods12 at gm.com.

That's FODS12 at gmail.com. Feel free to send feedback or suggestions or just let me know that you've been listening. If you'd like to support the show financially, you can become a Patreon. You can Google my podcast Patreon to make a pledge there, or you can make a one-off PayPal donation, which some people prefer to do, and I really appreciate everyone who contributes to the podcast. In terms of what's happening next,

so I've got a few ideas for future episodes, so one that I will do, so the next episode will be volcanoes and earthquakes, so stay tuned for that one. That's going to be exciting. That's been one I've been wanting to do for a while. Some other topics that are on my radar are sleep. I've been wanting to do an episode on that for a while,

so that is something that will happen soon, as well as probably some more geology, probably some more biology episodes. So stay tuned for those. Hopefully you enjoyed today. Thanks for listening. I'll talk you next time.