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0:01
So as we continue our study of respiratory physiology ... there are two key pieces we need to go over. We talked about pulmonary ventilation which is breathing, moving air in and out of the lungs, we discussed how those volume and pressure ... changes are going to allow that to occur. We now need to focus on external respiration which ... remember is gas exchange. Between your blood in the pulmonary capillaries and your lungs. And then in the next lecture we will focus on internal ...
0:35
respiration and that's the gas exchange between your ... systemic capillaries and your tissues. And so as we explore these topics we will look at factors ... that affect it and also how the gases are transported.
0:50
But first we need to cover two gas laws. If you look at room air, if I were to run around my ... room with a jar and collect a sample of air and look at ... what's inside, notice that we're surrounded ... mostly by nitrogen, N2, is how it's written- so roughly 79% of the air around us is nitrogen and it's in our ... inhaled air- we breathe it in. It's just not very soluble so ... we breathe it out, it doesn't go into our blood normally. O2 is around 21% is what we say of room air.
1:22
We have a little bit of water vapor, that depends on the humidity, and then room air is very very low and CO2 only .04%. So we need to look at something called partial ... pressures, and partial pressures, basically just what it sounds like, it's the pressure exerted by a gas in an area. so we were to look at room air if we had a lot more of a ... particular gas then we're going to have a higher partial pressure. And so the idea is if we use 760 as our atmospheric pressure.
1:58
If we know what percent the gas is so we know oxygen is 21 percent then we just multiply that by 21% and we get about a 159 and we're using mmhg and so ... what this is if we write P
2:17
O2 and what that means is that's my partial pressure of oxygen. So if we know the atmospheric pressure which ... at sea level is 760. Now remember that pressure falls with altitude.
2:32
So if we go up in altitude. That's going to decrease, let's say it drops to 700 Then notice that my PO2 will also decrease.
2:46
In this case it would fall to about 147. So when we go up in altitude since our pressure falls, our atmospheric pressure falls so does are P02 so ... that's why people will say that there's less oxygen. There is because the pressure has fallen, it's still 21%, so you know technically the same amount percentage of gas but because the pressure is ... lower it definitely affects our P02 and you'll see this is ... what is going to drive the diffusion in our lungs right we ...
3:19
need to bring it in. Now we know that CO2 and ... nitrogen each have different percentages so the ones we ... will focus on is 02. And then we will look at CO2- so same idea if we take 760 + ... x .04% which is .00 we get .3 so look ... at my PCO2, very very low in room air but ... my PO2 is much higher. So you're not again memorizing all of these but ... obviously nitrogen makes up a lot more so it has a higher ... partial pressure and notice in the alveolie,
3:53
so I told you we still do, that are does go into our ... alveolie with the nitrogen, but once we get to our alveoli, our pressure, our PO2 falls, it's around 159 what we inhale and then by the time it ... gets down in our lungs it's going to fall. Part of it mixes in those conducting zone, that dead space or some of it mixes with air then, it mixes with the humidity and so it falls to around a PO2
4:19
Have 104 inside the alveoli.
4:23
Notice the CO2 also changes it comes in .3
4:30
But it mixes with air in the dead space, which has more CO2 and so by the time that gets to my ... lungs to my alevolie, my PCO2 goes up because ... there's more CO2 in my airways, I'm trying to get it out and so that's going to rise to around 40.
4:48
Now if we wanted to measure the PO2 PCO2 in exhaled air, like what's leaving your lungs- you can see that you ... know room air is 21% but exhaled air is still around ... 16% and it also has you know ... some more carbon dioxide and the reason I mention this ... is when you - you look at mouth-to-mouth respiration, exhaled air it's still got oxygen in it so it's still ... valuable, it still can help deliver some ... oxygen to the patient. We have a lot of these ambu ...
5:19
bages, these basically bags that can ... either use room air or you can add oxygen to it but these are ... a little better because room air has more oxygen in it so ... you using those with room air is better than exhaled air, but exhaled air is better than nothing. The other gas law is called Henry's law and has two ... pieces to it and they're very intuitive. So one is gasses move from a higher partial pressure to a ... lower. Well that makes sense if I'm ...
5:50
giving someone a higher oxygen- 100% oxygen- the higher the partial pressure, the faster oxygen will move so you know if I have a PO2
6:00
In my alveoli of 04, but what if I increase that ... even higher? So it's just oxygen so we ... maybe I give him the PO2, I'm making this up now and ... it's like 200 right because we're going to increase the ... PO2 that will move faster. That's why we use pure oxygen and why use pure ... oxygen and why it's a tool. The other idea is that the ... amount of gas that dissolves and again, it's dissolving into fluid because it's dissolving into ... blood, depends on a solubility.
6:28
So the more soluble, the faster the diffusion. And CO2 is about 20 times more soluble than O2 and so ... it diffuses much faster iton our blood. And we mentioned, right, that we do have a lot of nitrogen and air around us ... and in what we inahle, but it doesn't go in our blood ... because it's not very soluble so normally nitrogen is not in the blood. When we have hyperbaric conditions this is based on ... Henry's law, this is pressurized gas.
6:56
So this is the hyperbaric chamber at the University of ... Maryland, one of my students had her ... husband and son spend a couple days in here because ... they had carbon monoxide poisoning. Now CO or carbon monoxide we've mentioned briefly. CO is dangerous right it can be fatal because what ... happens is when hemoglobin gets to your lungs. And we want hemoglobin to grab an oxygen right? Well carbon monoxide is 300 times more soluble than ...
7:26
oxygen so when hemoglobin gets up to your lungs it's ... going to bind to carbon monoxide so you going to ... come hypoxic which can be fatal. So these chambers are used if there's carbon monoxide ... poisoning because you use pressurized gas to force the ... oxygen o to the hemoglobin. A lot of times they are used for wounds or anaerobic ... bacteria because those anaerobic bacteria will not ... like all that oxygen coming in so they're used to quickly ...
7:54
oxygenate blood any time you're severely hypoxic. Or to also help with wound care. Now another application of Henry's law is for scuba ... diving. So you probably heard of ... decompression sickness aka the bens. So what happens is if you go deeper and deeper, we have nitrogen in our air, okay it's it's in the air, and it so it actually now it's pressurized so once it gets in ... our lungs its able to go into our blood because you're ... breathing and a mixture of air,
8:24
you trying to simulate air, you are not trying to breath ... just 100% oxygen. So the nitrogen because of the pressure goes in the ... lungs then blood. Well if you come up slowly these nitrogen, little black dots here, is going to slowly come out of ... the lungs at a nice slow level no problem. However if you come up too quickly. The nitrogen leaves the lung, excuse me, leaves the blood so Let me clarify as we move up. The nitrogen leaves the blood goes into the lungs and you get rid of it.
9:00
If we come up too quickly the nitrogen can't slowly leave ... the blood instead it kind of comes out quickly, they say it's almost like a ... boiling water, you see these these nitrogen ... bubbles start coming out of your blood. Well that's a problem for one thing they get in your joints ... you have excruciating pain that's why they call it the ... bends cause you're bent It can cause embolism it can be fatal so the issue again is ...
9:25
you need to come up slow to give the time for the nitrogen ... to leave the blood and be exhaled, too quickly is a problem and this is another example of Henry's law. All right external respiration now we are actually going to ... look at what's going on here we have the air in the aveoli ... and we have the blood in our pulmonary capillary. So what we're looking at our there's three things that ... effect this. We want to have rapid ... diffusion. So number one we come ...
9:53
back to Henry's law partial pressure gradients and gas ... solubilities number 2 we look at anatomy. The respiratory membrane, what is that membrane like ... that the gases must diffuse across? and number 3 is physiology we have to match the blood ... to the air. You only want to send your ... blood to the areas of the lung that are ventilating that have ... the best airflow. So when we look at our partial pressure gradients you ... just saw these numbers remember that when we're ...
10:22
looking out at atmospheric air, we will say 160 it's close enough, when it comes in the lungs it changes so that we know our PO2 our partial pressure of oxygen inside the alveoli is high ... because we're bringing it all in. Now when the blood is coming into the lung from the ... pulmonary capillaries- right remember the pulmonary ... arteries are going to bring blood up to the lung and ... they're bringing O2 poor blood in. So this is just showing you the right side of the heart and ...
10:52
the left side of the heart. We know that when we look ... at blood in the pulmonary arteries that we would say that it is. 02 poor
11:02
And CO2 rich.
11:05
So this blood is going to the lungs so that it can become oxygenated. And so when it becomes oxygenated we want it to ... leave and go back to the heart through pulmonary ... veins this time it'll be O2 rich and CO2 poor because of the gas exchange. So when it comes in with CO2 notice that the CO2 levels. and when we are ooking at the blood let me get my color.
11:33
Let me backup for 1 second- stick to oxygen here so I'm ... coming in low O2 around 40 I have an PO2 of 104. So where is it higher? It's higher in the lungs. So what that means is that ... oxygen will diffuse from an area of high pressure to low ... pressure until equilibrium is reached. So it's going to enter the blood until the blood leaves ... at a PO2 of 104. That's diffusion, so it comes in at 40, pickes up O2, picks up O2, once it's equal at 104, 10.4 no more movement of ...
12:11
that gas it leaves at a PO2 of 104.
12:15
Now if we look at the CO2, the CO2 moves in the ... opposite direction. So we said that blood coming ... from my pulmonary vessels is going to be CO2 rich
12:29
Because it's trying to get to the lungs to get rid of the ... CO2 so that comes in at a PCO2 of 45. Will remember the CO2 in alveoli is 40 So again we have a difference right -we have 45 ... to 40 so gases follow diffusion They will diffuse- CO2 will diffuse out of the blood into the alveoli. Because there's a pressure gradient of 5. That will happen until equilibrium is reached. So as it goes through and it gets rid of the CO2.
13:05
It's going to keep happening until it equilibrates with the alveoli. and so it's going to leave at a CO2 of 40 because that's ... what when its equal. Now a question I like to ask here is we're moving exact ... same amount of gas- oxygen and CO2, but remember that oxygen ... needed a steeper gradient- oxygen needed this gradient ... of 104 to 40, to force that oxygen in your ... blood but CO2 only needs a gradient of 5.
13:36
40 and 45 to move the exact same amount of air so why ... do you think that is?
13:42
Hopefully you said because it's more soluble. Because CO2 is more soluble it will move faster you don't ... need as steep of a partial gradient.
13:53
Now we mentioned the respiratory membrane as well. We looked at this previously remember it has three layers. So when you're looking at the membrane you have your ... simple squamous epithelial layer of your alveoli, your type one cells, you have your simple squamous epithelial layer, of your capillary, the endothelium, and then you had the basement membrane ... between. So we know it's very very ... thin, you don't have to memorize ... it's about one micrometer thick,
14:23
but remember a piece of tissue paper is 20 times ... thicker, it has a huge surface area. If you were to take your lungs, both lungs, and flatten out all the avleoli, it was fill half a tennis court that's the surface area inside ... your lungs, it's huge is over 300 million alveoli. So we know we need to have a large surface area and thin ... membrane and that brings us to something called Fick's ... law. And again this makes sense- ... diffusion is directly proportional to surface area ...
14:54
and inversely proportional to thickness. So what does that mean? If your surface area goes ... down, like maybe you have a tumor ... in a lung and you have part of your lung removed, or part of your lung isn't working so you decrease surface area.
15:11
S. A. surface area
15:14
It's directly proportional, you're going to decrease your ... diffusion rate it will take longer for gases to move. But it's inversely proportional to thickness. So if you increase the thickness of the membrane, maybe you have pneumonia. And this membrane and gets really thick and clogged with ... mucus will if you increase thickness, then you also decrease diffusion. And so we're pretty much, this doesn't change too much ... as far as it should be nice and thin wiht a large surface ...
15:45
area. What happens here is ... respiratory disease- pulmonary diseases typically ... are going to do what you see here they're going to do to ... have you lose surface area or make the membrane thicker ... and that's going to slow down diffusion. Which will be a problem because if you don't have ... enough time to move all those gases you become ... hypoxic and you have too much CO2 in your blood. And so the last thing is you got a match the air with the ... blood. So it's called ...
16:12
ventilation-perfusion coupling or they call it VQ. Sso a lot of times you'll see V Q V for ventilation and Q for ... profusion. So ventilation is how healthy ... are your lungs? Are your bronchioles open? Are you moving air? Are you fully ventilating? Where perfusion is how's the blood flow? Are you moving the blood to the area of the lung? And these two have to be in sync. So if you have an area of the lung, let's say we have an area where it's not healthy- maybe ...
16:42
you have bronchitis, or you have a tumor, or there's an area of your lobe that is damaged from ... smoking. We know that if we can't ... move we can't move the air, then we're going to basically ... have very low PO2 right? Because we can't get air to ... that area and we we can't get air out either so we're going ... to have low O2. Well what's going to happen is that your vessels to the ... area, the blood vessels will ... constrict, you're not going to send ...
17:11
blood to an area of your lung that it isn't working it doesn't ... make sense. So anytime we have what's ... called hypoventilation or an area that isn't healthy The ... PO2 falls which causes vasoconstriction of the blood ... vessels, the pulmonary vessels. What you're going to do is you're going to dilate the ... vessels to the area with the best 0the best ventilation. You're going to constrict the vessels will you have the worst.
17:38
Well anytime we have this hypoventilation we have an ... issue with CO2, we can't get O2 in we can't ... get CO2 out. Now for the CO2 we're going ... to change the bronchioles, because remember they're ... the tubes moving the air to and from the alveoli. So if we have poor ventilation and we have CO2 levels too ... high the bronchiole is going to open up to try to help you ... flush that CO2 out and try to move it If for some reason we had an area where we had like really ...
18:05
low CO2 then we would change the bronchioles and ... they would constrict. What you're most likely going ... to see is the situation with poor flow poor, ventilation is so you're going to want to open up. the bronchiole So when we look at this we would say that when we have ... what's called hypoventilation. Then inhypoventilation we're having low. PO2 right? Then and what's going to ... happen is we're going to vasoconstrict our pulmonary ...
18:34
vessels and because we're going to have high CO2 we're ... going to open up the bronchiole. So you're going to vasoconstrict the pulmonary ... vessels orarterioles and bronchodilate those ... bronchioles to try to move the air. And so what you might hear us when I called a V Q mismatch. And again ventilation- the airflow perfusion the blood flow. And when we look at things that can cause this mismatch, you know there are a lot of factors that can cause issues ... with the air: asthma,
19:10
bronchitis pneumonia emphysema, all of these are going to be ... associate with what we might say hypoventilation, you're not moving the air, and so in all of these ... situations we have this mismatch and so you know ... what's going to happen with the patient with emphysema ... is the pulmonary vessels will constrict and they'll try to ... open up those bronchioles to try to help move the air and ... get that fix that, mismatch, so you know there's things they can try to do to restore ...
19:38
an obviously treat the condition if possible. Okay so we talked about what happens, why the gasses move, how they move, some gas laws and we're going to wrap up with how ... are the gases transported? So we move them in the ... blood, how do they get from the ... blood, from your lungs to your tissue ... cells? Well oxygen has two ways ... that it is transported- a little bit of it just dissolves in ... plasma 1.5%, you already know most of it ...
20:06
binds to that heme on that hemoglobin and so 98.5% is going to travel that way. Remember that when we are ... looking at hemoglobin it actually had 4 heme groups ... and each heme has an iron, it's that iron that grabs that ... oxygen. So when we talk about ... oxygen being saturated it means that each hemoglobin ... has four molecules of oxygen. Sometimes we use the word association and ... disassociation. Association is when oxygen ... binds, when it binds to hemoglobin ...
20:37
and disassociation is when hemoglobin let's go of ... oxygen. So we're looking at external ... respiration right now so that would be the association and ... a lot of times I just call it loading. So we are going to be looking at oxygen loading onto that ... heme, that hemoglobin. And so there's one equation for this that we learn, and what you can see is remember this is reduced ... hemoglobin, so this is hemoglobin that ... might only have two molecules of oxygen. It's never empty by the way.
21:09
So it when it picks up oxygen in the lungs, so when we have O2 loading for external respiration- notice ... you have HHB + O2, remember your chemistry. The HHb grabs the oxygen and then there's that ... hydrogen so that's the equation. When we look at internal respiration, notice it's going to go the opposite direction. So it's one equation, you got to know which way ... it's going is oxygen loading or unloading? And so we have oxyhemoglobin which is when ... it's full with four, and we have ...
21:42
deoxyhemoglobin which is often just called reduced hemoglobin. Either term is fine probably easier to write reduced ... hemoglobin and that's when it's when it's not empty, we'll just a has around 2. And that's how oxyen moves, picks it up and drops it off.
21:59
Now CO2 we will talk a little more about for internal, because remember it's actually made by your cells. But, CO2 has three ways. Notice a little more of it just dissolves because it's more ... soluble so that's easy. Some hemoglobin, binds to hemoglobin, try that again, some CO2 binds to hemoglobin and notice ... roughly 20 to 25% and it should look the exact same of what you just saw. Here we had reduced hemoglobin and O2 forms. Oxyhemoglobin and H+. Well reduced hemoglobin ...
22:33
picks up the CO2 to form carbaminohemoglobin and ... hydrogen, same thing right it goes both ways. So we can have CO2 Loading or unloading so when we're looking at ... external respiration. We're looking at the exchange in the lungs So what's happening in the lungs with CO2? Well remember we're getting rid of it- we have CO2 ... unloading from our blood because it's going from the ... blood into the alveoli. so you can exhale it. so again we it's going to come in attached and then ...
23:11
we're going to have the equation go this way so that ... the CO2 can be exhaled. So again One equation the arrow tells you what you're forming and ... just think about are you trying to get rid of CO2 and exhale ... it? or you trying to attach it and transport it? But the main way that CO2 travels in the body is actually ... hidden in this bicarb, see that HCO3? That's bicarbonate ion- CO2 is right inside of that. So most of it travels this way and you've seen this equation ...
23:43
before it was an equation that we did for buffering.
23:51
Notice again the arrows go both directions right ... depending if you're if you're binding it or releasing it. So in the lungs remember we are trying, oops, In the lungs remember we're trying to- I'll ust move it down ... here -we're trying to get rid of it.
24:09
So what's going to happen is, it comes in as bicarb that's ... how it travels, so it's actually HCO3 In the plasma.
24:23
So we have the HCO3 that's how is traveling in your blood. And then when it gets up to your lungs.
24:35
It's HCO3, and then it's actually going to ... go into a red blood cell,. So red blood cells have an ... enzyme- this is an enzyme right here, CA - carbonic anhydrase is a really important enzyme. Remember that enzymes allow chemical reactions to ... happen faster? So this reaction happens best ... inside a red blood cell but because the HCO3, is out in the plasma, you got to get it inside the red ... blood cell. So this will just be a little red ...
25:01
blood cell and this is coming up on the next screen but I'll ... just do it here so what happens is the HCO3 comes ... inside the cell. So we can do this reaction. But you can't just throw negative charges inside a cell ... you have to replace the.m So inside the cell there's a lot of ... chloride, they each are -1, so the chloride has to leave. Its called a chloride shift: HCO3 comes in and chloride comes out- just to keep the ...
25:28
charge the same but once it gets in and notice it combines with hydrogen. And then you form is called H2CO3 which is known as carbonic acid.
25:40
Seen this equation I know you had it in 119 for sure and ... then carbonic acid is going to break down because of the enzyme ... carbonic anhydrase into CO2 and water.
25:53
So the CO2 is going to leave. So you can exhale it. So most of it travels this way and you might be wondering ... why does it through all that? Well the reason is bicarb is ... one of the best buffers in your body and so as it travels ... as bicarb from your big toe to your lungs it buffers, It's a really important buffer so basically it does double duty. So let's put this together you have this picture in your ... notes. This is what I want for ... external respiration to put it all together.
26:26
So if we're looking at this- the setup -we're looking at ... external respiration, we're looking at blood ... between the gas exchange between the alveoli in the ... lungs and the blood in the pulmonary capillary. This is just representing plasma. This is my capillary in the box and this is my red blood cell. So we know the blood is coming in that we know its ... O2 poor so it's O2 poor, it's going to have a PO2 of 40 ... now you would know the units are mmhg but I will never
27:00
I'm not going to keep writing them right now. We also know that if we have this 02 poor blood that it's CO2 rich. Has a lot of CO2 and so we memorize that it's 45. So we have some oxygen that's just dissolved in it. and we have a little bit of CO2 again it's dissolved, so I'm just writing it over here in the plasma because it's dissolved. We know that most of that oxygen now right is it when ... we're trying to like move this oxygen or the CO2.
27:29
Let's do the oxygen first -so we know that when we're ... looking at our O2 levels that our levels in our alveoli.
27:42
that it's O2 rich at 104, now it was 159, but as it goes all the way down to the conducting zone ... down to the respiratory zone we know that the 02 mixes ... with air, and a little bit of water vapor ... so it's 104 when it hits the lungs.
28:16
Now what's going on here? Sso we have this 02 poor ... blood coming in CO2 rich. We know that there's three ... ways that CO2 is coming in here - so we know that some ... of it is carbaminohemoglobin and we know that a lot of it is out here in the plasma and I ... wrote some here but it will just be, we have CO2 dissolved. Okay so I said I would do oxygen first. What's going to happen is we will move oxygen it will follow ... its partial pressure gradient so that it will move from the ...
28:50
higher PO2 of 104 Into the blood and it'll be on a red blood cell and it will also be dissolved And so we have this O2 loading
29:05
And that means were loading it, we are talking about the direction into the blood. Now as it passes by it comes in at 40 Oxygen enters Until the PO2 reaches 104.
29:19
Now the PO2 by the way is representing the amount dissolved. So the amount dissolved in your plasma- right- the higher ... the gas the higher the PO2 so a PO2 of 40 dissolved has ... less oxygen in it then when it leaves
29:38
At a PO2 of 104. But remember most of it, is going to be attached to ... hemoglobin. So here's my oxygen loading ... it's going to bind to reduced hemoglobin, notice my arrow and now I have oxyhemoglobin and ... that's how 98.5% of that is transported. Now I kick off a little hydrogen here right? we got to deal with that in a minute. So when oxygen, attached to hemoglobin- ... when hemoglobin picks it up, another way we measure our ... oxygen content is we say that hemoglobin is 98%
30:13
saturated with oxygen. It's never a hundred percent ... because of the shape. But it picks it up and it's going to be 98% saturated and there's one more way we measure the ... amount of oxygen in our blood we say for every 100 ml of blood.
30:32
There will be 20 mLs of oxygen.
30:38
So when we're talking about oxygen we have three ways ... of discussing it. We can mention the PO2 ... which reflects the amount dissolved in plasma. We can look specifically at the hemoglobin how ... saturated is it? And we can also look, at we can take a blood sample, and we can measure the amount of oxygen in it.
30:57
And FYI how do they get this 20/100? The way they get that is they know that each gram of ... hemoglobin, and you won't have to do this math But every gram of hemoglobin actually carries 1.34 mLS of oxygen. So the more hemoglobin you ... have, the more oxygen you carry, so they do this- the number I'm giving you is based on ... someone having 15 g of hemoglobin 15 * 1.34 is 20. So if your patient has less hemoglobin then these ... numbers will fall.
31:33
And if they have more they'll go up so you can see why ... you might want to know your hemoglobin level. Now, one thing I want you to ... understand though is this process in the lungs, if you're trying to time, you know how long does a ... red blood cell have to go by an alveolus, and need your blood flowing you have a blood pressure - ... is pushing the blood through and heart rate. So it's moving it's not like I can just hang out forever for ...
31:59
all that oxygen to load. And so what we know is that ... if you were going to time, let's say you're going from ... point A to point B, so this is in the lungs and I ... want to know how long it takes my little red blood cell. To pass through from A to B in the lungs. Well we know that it has about three-quarters of a ... second at normal heart rate and normal blood pressure. And if everythings, you know fine and dandy. So what happens is that it actually,
32:27
remember the PO2 is 104 and it comes in at 40, it actually oxygenates really fast and then the rest of the ... time, it's not doing anything, it's just passing through -so we know that it only takes. .25 seconds to fully oxygenate your blood to get it ... right up there to 104, it's pretty quick thing and so ... then it has an extra half a second. So that you have .5 seconds here that really nothing is ... going on. Well, you know,you might wonder again what's going on?
32:57
Well geeze, it makes sense right? like maybe your heart rate goes up and your blood ... pressure goes up like your exercising and now it's ... moving faster maybe it doesn't have .75 s becaues ... your heart rate and blood pressure higher, maybe only has half a second. You're good it only needs .25 or maybe have a problem ... with diffusion, maybe your respiratory ... membrane is too thick, because you have ... pneumonia or covid, or maybe you've lost surface ...
33:26
area. Well you have an extra half a ... second in there to give you more time for that diffusion to ... occur. So this is really good ... because again with pulmonary diseases if we ... didn't have any backup. you know we would probably ... die really fast from pneumonia and all these. So when you have a patient and their PO2 level is low ... they've exceeded that extra half a second- like there's ... something going on in their lungs. And again it leaves 98% saturated and every 100 ml is ...
33:55
a blood is going to have 20 mLs of oxygen. Well if you look at the CO2 part for a minute -remember ... that CO2 is going to be moving the opposite ... directions, I'm going to get rid of some of ... this really quick.
34:11
And we know that CO2 is going to come in and it's ... going to be unloaded so we're going to have CO2 unloading.
34:20
Because we need to get it into our alveoli so we can exhale it
34:25
So CO2 again some of it, had it here some of its just ... dissolved in plasma on it just leavesm some of it comes in as that carbaminohemoglobin and then it's released Now remember when we did 02 loading we always form ... this hydrogen and we really want to make sure that we ... don't have too many hydrogen's building up ... because that would be bad- that would change the pH. But what's kind of cool is that hydrogen that got kicked off ... by forming the oxyhemoglobin.
34:56
Is used to kick off the CO2- it's actually used in both of ... these equations. So we don't have any change ... in pH with breathing because all the hydrogen formed are ... actually used to get rid of CO2. Which is a really cool thing -it's actually called the ... Haldene Effect. So somebody named ... Haldene figured this out and he's he just basically showing ... how these equations drive each other. So when we unload CO2, let's look at this one here,
35:23
when we unload CO2 see that little reduced ... hemoglobin? well that's just used to pick up oxygen And then we pick up oxygen that hydrogen kicks it off and ... so we have this nice little feedback loop here where ... they're driving each other. Now which came first? I have no idea - and so as we unload CO2 we get reduced ... hemoglobin to increase O2 loadin, and that gives a hydrogen which increases CO2 unloading And that hydrogen again is used down for the bulk of it
35:53
So my bicarb remember is out in my plasma- that comes ... into my red blood cell my chloride leaves so I have my ... chloride shift. Now I run this equation in my cell I get carbonic acid which ... is very rapidly broken down into water and CO2 and ... that's how it leaves. So when my CO2 comes in at ... 45 remember that the CO2 inside my alveoli is going to ... be low because I'm always exhaling it. So now I have a diffusion gradient I have a pressure ... gradient we're going from 45 to 40.
36:30
Same thing CO2 drop it off, unload from my plasma, until equilibrium is reached and so when my PCO2 as it goes through By the lungs, it's going to drop from 45 to 40. Now it's equal and it leaves the lungs. And so when I look at my levels for my O2 rich blood. In my pulmonary veins going to the left side of the heart ... my PO2 is 104 and my PCO2 is going to be lower- ... remember my PCO2 is going to be.
37:07
40 and we would say that oxygen is in my blood- my ... hemoglobin is 98% saturated with oxygen and ... every 100 ml of blood would have 20 mLs of O2. And that's how we rest with external respiration and the ... next lecture will look at internal.
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