hello and welcome to the review of chapter 41 Gaiden and holes medical physiology textbook in this chapter we will be going over how oxygen and carbon dioxide is transported within the blood from the lungs to the tissues and then back again if you enjoy this video and you're feeling generous please don't forget to give the video a like and subscribe to the channel as it does help us out greatly and if you're in need of the textbook there is an affiliate link within the description otherwise feel free just to follow along as we discuss the
chapter so it starts off by talking about how the transport of oxygen and carbon dioxide within the blood is dramatically increased by having these components which help to increase the transport for instance hemoglobin increases the amount of oxygen that's able to be transported around the blood and hemoglobin and other chemical substances also contribute and being able to move carbon dioxide around the blood rather than just relying on them dissolving into the plasma and moving in that regard an order for oxygen and carbon dioxide to get in and out of the blood either within there from
the alveolar into the blood or from the tissues into the blood or vice versa it relies completely on diffusion so it's relying on the partial pressure difference between the tissues in the blood of all the blood in the lungs and in addition to that you also have to obviously worry about the distance that has to travel but in a normal situation the distance that it has to travel was pretty minimal because the blood and tissue area or the blood and alveolar area that wall is very very thin now the diffusion of oxygen that from the
alveoli into the blood vessels there is a pressure gradient of around 64 millimeters of mercury as the alveolus averages around 104 millimeters of mercury and then the arteriole end of the pulmonary capillary ravages around 40 millimeters of mercury now an important note here is there most of this diffusion of oxygen from the alveolus into the capillary occurs within the first third of the blood flow past the alveolus so as you can see here as the blood flows from this end over to this end we go from a po2 of 40 to a po2 of 104
within the blood vessel you can see that that jump occurs right in that first third of that pulmonary capillary so then by the time their the Bloods traveling from here all the way across there's very minimal movement and that's important because when we exercise we suddenly increase our blood flow so suddenly we have to head the movement of oxygen from the alveolus into the pulmonary capillary at a faster rate because the blood is coming through here at the faster rate and this provides a little bit of a buffer but of a safety factor to really
allow the blood flow to increase and times of exercise and still allow our oxygen to get fully oxygenated now our blood oxygen content doesn't stay at 104 millimeters of mercury because of our bronchial vessels remember bronchial vessels come off the a order o towards our lung and tissues and then also our trachea and supplies the oxygen needed for the lung to survive as an organ and has nothing to do with gaseous exchange that venous blood that supplied all of those tissues then comes back and actually goes back to the left side of the heart which
is usually the oxygenated blood coming from the lungs so since we have a a slight mix of a very small amount of venous deoxygenated blood without oxygenated blood coming from the lungs we end up with this little depth in our oxygen content so our po2 which gets up to 104 after coming from the lungs of being oxygenated once it mixes with the bronchial vessels all those venous vessels from the bronchial supply we get a slight dip and we end up sitting at around 95 millimeters of mercury by the time the blood actually reaches all the
tissues once it reaches the tissues at 95 millimeters of mercury there is a dramatic change in the pressure difference because our tissues are obviously using oxygen so our po2 reduces once it reaches our tissues all the way down to 40 millimeters of mercury now if we increase our blood flow through this region then we're going to actually increase our po2 within our tissues because we're giving the tissues more oxygen then they can use so we're over supplying what they need for metabolism and that's shown here in Figure 41 for with an increased blood flow and
normal interstitial fluid po2 level increases now on the flip side if we reduce our blood flow to our tissues then obviously we're going to start to use up more oxygen and our tissues than has being supplied so here to level within our interstitial fluid is going to reduce so as we reduce our blood flow our interstitial fluid po2 reduces so that's one influence on what our tissue po2 level is the other influences you can see on this graph is our oxygen consumption so if we increase our oxygen consumption we're obviously going to increase our usage
of oxygen over what our blood flow is supplying us so we in order for us to have a decision vo2 level of say a of 40 millimeters of mercury we're going to have to increase our blood flow up to 400 percent of normal 450 percent of normal because we are using more than is able to be supplied but then from the metabolism or the oxygen consumption of that tissue reduces so suddenly we're not using as much oxygen then the amount of blood supply that we need to supply those tissues reduces so then if our oxygen
consumption reduces as shown by this top line over here in order to keep it an interstitial fluid of a then we need about 25 percent of normal blood flow so those are our two factors affecting tissue po2 level our rate of oxygen transport our blood flow and then our second one is the rate of oxygen consumption so how about carbon dioxide carbon dioxide functions pretty similarly to how oxygen functions in terms of transport but is completely opposite to oxygen another main component is that the diffusion of carbon dioxide is a lot faster than oxygen so
20 times as rapid as oxygen so that means that we don't need as much of a pressure gradient in order to move the same amount or even more how the dioxide that's shown here with these examples how the intracellular P co2 levels 46 interstitial is 45 so in order to move carbon dioxide from the cell to the decision we only able one millimeter of mercury pressure differential when it comes to the lungs in order to move carbon dioxide into the lungs we have a pressure difference of five millimeters of mercury because we have a PCI
o2 level of 45 millimeters of mercury coming from the tissues which then ends up being 40 millimeters of mercury after it's left the lungs so we actually have a five millimeter of mercury pressure difference to move our co2 and get expelled by the lungs versus that sixty four millimeters of mercury is at the oxygen needed it does show the same characteristic as the oxygen that there the majority of carbon dioxide gets diffused into the alveolus within that first third of blood flow and that just really once again helps with exercise so we have that safety
factor that if we increase blood flow to our lungs we're still able to get rid of all the carbon dioxide that we need now if we think about the interstitial fluid P co2 as well talking about what the oxygen level the same effectors apply but in Reverse so if we've reduced our blood flow then we are not getting rid of the interstitial fluid carbon dioxide because that blood flow is too sluggish to get rid of all that carbon dioxide getting produced by the tissues so with a reduction in blood flow we have an increase in
P co2 level and with an increased blood flow we have a reduction and pco2 level with interstitial fluid and then if we have increased metabolism so we're producing more carbon dioxide and we will need an increased blood flow to get rid of that metabolism so the same factors that we are talking about with our oxygen content just in Reverse so next up is this oxygen hemoglobin and dissociation curve and this is extremely important this curve here really explains how our hemoglobin is such a good role in actually transporting oxygen around the body and the key
points here is how this curve is shaped so we have this steep increase and then of plateauing right at the top here and the key point about this is that what if the pressure of oxygen is corresponds to a certain amount of hemoglobin saturation so if we have a high pressure of oxygen for instance in the lungs where it's around 104 millimeters of mercury in the amount of hemoglobin that's saturated with blood is gonna be high at 97% now if we have a low pressure of oxygen so around 40 millimeters of mercury such as our
now tissues we have a reduced hemoglobin saturation at around 70% showing that if that hemoglobin came from the lungs it's now given up about the difference between 97 and 70% of oxygen so that is the key points here showing that whatever the partial pressure of oxygen is corresponds to hemoglobin saturation now the shape of this curve becomes important because one the hemoglobin is a bit of an oxygen buffer in this region and in this region when we start to really need the oxygen it's able to supply more oxygen to our tissues because of the steepness
of the curve so if we break those two components down let's talk about the oxygen buffers capacity of hemoglobin so the main point here is that if we are breathing in a partial pressure of oxygen and 104 millimeters of mercury and then go up higher altitude let's say and then we end up breathing a partial pressure of just under half of that so the example they give is 60 millimeters of mercury so that would seem like a dramatic reduction in our atmospheric partial pressure of oxygen but if we use this oxygen hemoglobin dissociation curve we
can see there even though we've gone down and by just under half of our breathed and oxygen our saturation of hemoglobin still remains at 89% which is still good enough to get oxygen around the body so you're still able to actually oxygenate and provide oxygen for metabolism around your body despite a pretty severe reduction and now atmospheric oxygen content and on the other side what if we breathe in a dramatically high pressure of oxygen the example they give is 500 millimeters of mercury of oxygen what's going to happen at that point well we plateau right
so we can only get a hundred percent so it doesn't matter if you're breathing more than 120 millimeters of mercury because your hemoglobin saturation is going to stay 100% and we do have to be careful there because chronically breathing in too much oxygen you actually start to carry more oxygen in your plasma and you can actually get oxygen toxicity which results in neurological conditions the key here is that if you suddenly start to breathe too much oxygen or oxygen than normal you plateau the out at a hundred percent and then if you breathe in a
dramatic reduction and atmospheric if you go to high altitude your hemoglobin still able to saturate to a certain degree so then the next component of this oxygen hemoglobin dissociation curve is this portion the steep portion and the importance of this region is really showing that FL tissues start to use more oxygen so when we're exercising and then our po2 about oxygen reduces and our tissues from 4d let's say down to 20 or 10 because this curve is so steep we start to dramatically release more and more oxygen from the hemoglobin because at 20 millimeters of
mercury beginning down to 30% saturation of hemoglobin with oxygen so it's starting to release more oxygen as it gets to the tissue which has a low partial pressure of oxygen because it's using so much so the greater the oxygen metabolism in a certain region the more likely the hemoglobin is going to let go of its oxygen content will be less saturated another combination with an increased cardiac output with the exercise is able to deliver a lot more oxygen to our tissues because in the lungs just still have your partial pressure of 104 so within your
lungs your hemoglobin still getting saturated at 97% but then by the time that hemoglobin gets down to your muscles which are working and using a lot of oxygen and they say they're sitting around 20 millimeters of mercury we're giving from 97% down to 30% of oxygen that was within their hemoglobin so that hemoglobin is releasing all of that oxygen now you are able to quantify how much that is and it talks about that talking about volumes bussines and the math here works out is there 15 that grams of hemoglobin is within 100 millimeters of blood
and in one gram of hemoglobin able to carry 1.3 4 millimeters of oxygen so if your times at one point three four times that 15 grams of hemoglobin you get that that hemoglobin within the blood in combined with 20 millimeters of oxygen for each 100 millimeter of blood so if that hemoglobin contains 20 millimeters of oxygen more than 20 millimeters of blood that means that it's 100% saturated so the term used to describe that is 20 volumes percent because 20 millimeters of oxygen is within that 100 millimeters of blood if you have a reduced oxygen
saturation of your hemoglobin in you're going to have less oxygen within that hundred millimeters of blood so then you're gonna have a reduced volumes percent so that's showing here a figure 41 9 where when we are at 100% hemoglobin saturation we're at 20 volumes percent as we reduce down so say we're at 40 millimeters of mercury or partial pressure of oxygen which corresponds usually to around 70 percent of oxygen saturation that means we're gonna have roughly 70% of oxygen within our blood which corresponds to around 14 volumes percent because that's at 70 percent of 20
millimeters oh the maths makes sense to you but if it doesn't just have a quick read through it again it's really just a way to quantify how much oxygen they're being carried in the blood correspondingly to hemoglobin saturation now the last concept here that we'll talk about before we move on is utilization coefficient and that's just saying how much oxygen is released by hemoglobin as it passes through a tissue capillary so normally it's about 25 percent of that oxygen is released and exercise when we start to reduce our interstitial partial pressure of oxygen in such
a release more hemoglobin the utilization coefficient increases to 75 to 85 percent so we do have some factors that fix this oxygen hemoglobin dissociation curve and keep shifted to the right or to the left the best way to think about this is that you are going to want to release more oxygen and states with higher metabolism in states with higher metabolism you're going to have high carbon dioxide I hydrogen ions a higher temperature because you say you're exercising and increase vpg BPG is two three by phosphoglycerate you can just think of that as a byproduct
of metabolism that's a easy way to think about that so all of these four components increase when we have higher metabolism let's say because of exercising when we exercising and we have an increased of these metabolic products we want to release more oxygen we want more oxygen to go towards that tissue because our metabolism is higher so in order to release more oxygen we have to shift the curve to the right because we need to lower our hemoglobin saturation her pressure of oxygen within the blood so for instance if we have a partial pressure of
oxygen of 40 within the blood by shifting the curve to the right we're able to reduce this level from let's say around 60 down to this curve here which is around about 50 so we now have reduced our hemoglobin saturation by 10% and we're releasing more oxygen so all of those conditions where we have increased metabolism or even hypoxic conditions or any reason for having higher carbon dioxide higher hydrogen high temperature or higher BP G we are going to be wanting to release more oxygen to those tissues so then we want to shift our curve
to the right so what is our limiting factors to chemical reactions taking place they obviously need oxygen to take the place so surely oxygen is the limiting factor if that is the main thing that's used for chemical reactions the cells have actually worked out that they only need a small amount of oxygen for chemical reactions to take place so they're not dependent on oxygen as the leg rate limiting step instead they have switched it to where they dependent on ADP which is you know a byproduct of using energy so if you are a cell that's
using a lot of energy you're going to create a lot more ADP which is going to then tell yourself to increase your rate of oxygen usage which is smart because just because you have a lot of oxygen doesn't mean you should produce a lot of ATP you should only produce a lot of ATP if you're using it and a way to tell with you using a lot of ATP seeing how much of the byproduct there is so a lot of ATP means that you're using a lot of energy you're using a lot of ATP so
let's start to use that oxygen to create more ATP and that's what's shown here in Figure 4111 where if we increase our ADP level we increase our rate of oxygen usage and you can see that our oxygen usage is only depended on intracellular oxygen content in at least in one millimeter of mercury which is a pretty small level so as long as we have greater than one millimeter of mercury in our cell we're going to have a normal usage of oxygen which is then dependent on how much ADP is present within the cell now sometimes
the quantity of oxygen does become a factor in how much is used because either the distance between the cell and the capillary where the oxygen is coming from is too great which can occur in pathological conditions and that's called diffusion limited or because the blood flow supplying the oxygen has now been impeded either because the quantity of oxygen with them the blood is too low or because the rate of Bloods flow is too low and that means we're blood flow limited so then that means we're starting to get too low oxygen content and we can't
have metabolism taking place or oxygen being used now we can't live in those states for very long and that starts to create a selfish so next up is talking about carbon dioxide we've talked about oxygen quite and depth so next up is how does carbon dioxide get from the tissues to the alveoli and it really does that in three ways number one is just by getting diffused into the plasma and moving in that direction and that is only used for around 7% of carbon dioxide transport the bulk of carbon dioxide transport actually occurs through the
carbonic anhydrase equation and because of an enzyme within the red blood cell we convert carbon dioxide and water into carbonic acid which quickly dissociates into bicarbonate and acid that acid then binds with our haemoglobin because it has a buffer component to it deep bicarbonate ion then leaves the cell and actually gets replaced by chloride ions so making the chloride shift in the venous blood as more chloride goes into the blood cell now 70% of carbon dioxide is transported in this method and this actually plays a major role in our acid-base balance if we remember back
to our acid base chapter and the renal chapter and this explains why not all of the carbon dioxide within the blood actually gets expired when the issue reaches the alveolar we only expire a small portion because we're using carbon dioxide as a buffer for acid-base balance we're using it and whenever there's a slight metabolic derangement and we're able to adjust and either capture more hydrogen ions or release more AG hydrogen ions if need be if there's an acid based disorder developing so this is a dual function of red blood cells being able to help with
acid-base providing a buffering component but then also with transporting carbon dioxide and lastly the third method carbon dioxide has moved as by to the carbon dioxide directly binding with hemoglobin forming carbon meno hemoglobin and when we take into account how fast this reaction occurs that accounts for around about 20% of total carbon dioxide transport so that's our three methods we have just diffused within the plasma table amino hemoglobin and there's bicarbonate now another effect that we should talk about which is the opposite of the Bohr effect which we didn't actually mention before the or effect
is just how when there's a lot of carbon dioxide you actually encourage oxygen to be dissociated from the hemoglobin Haldane effect is the opposite of the Bohr effect which means that when there's a lot of oxygen around you make a carbon dioxide leave the cell so remember that oxygen dissociation curve showing the shift to the right that's the Bohr effect but the Haldane effect is using the carbon dioxide Association curve showing how when there's a lot of oxygen within the blood we get a dissociation of carbon dioxide and quantitatively this is a greater effect than
the Bohr effect because as you can see here we have our two curves here so our curve when there's a po2 level of 100 millimeters of mercury meaning there and pco2 level so let's just say a PCO to level 40 we have a certain amount of carbon dioxide which is going to be bliss then if there's less partial pressure of oxygen at 40 millimeters of mercury so if we take into effect where we're going to see these two levels so within the interstitial fluid we're gonna have a po2 level of around 40 millimeters of mercury
so we're gonna be operating at this top curve and our pH co2 level is gonna be around 45 millimeters of mercury so the quantity of carbon dioxide within our blood sits there eh now when we get to our lungs where our P co2 level drops down to 40 if we weren't to take into effect the partial pressure of oxygen then we would only reduce down to here which you know is only just going from just above 50 to just below 50 however a partial pressure of oxygen is greater so then the Haldane effect shifts this
curve down and now we end up at point B showing that we get a dramatic change and how much carbon dioxide is actually within the blood so quantitatively we release a lot more carbon dioxide now the last thing we'll mention here before wrapping up the chapter is a respiratory exchange ratio and the respiratory exchange ratio is just the ratio between the carbon dioxide output and the rate of oxygen uptake so if we have more carbon dioxide being produced and less oxygen being absorbed in we're going to have a higher r-value or respiratory exchange coefficient and
this gets covered in a later chapter so just a brief introduction there and that summarizes our chapter for today I hope you enjoyed it feel free to drop a comment otherwise we'll see you in the next video
