 Oxygen is transported in blood in two forms one is a dissolved in our blood itself so that is dissolved form and next is combined with hemoglobin. Now you see dissolved form is responsible for only one percent of transport of oxygen and 99 percent of oxygen is transported in combination with hemoglobin. Well the amount of oxygen which is carried by dissolved form can be determined by Henry's law which states that the partial pressure of the gas which is dissolved in a liquid is directly proportional to the concentration of the gas in the liquid. So very important partial pressure of oxygen will be directly proportional to the concentration of that that is the amount of that gas which is there in the blood. It is calculated by this formula concentration is equal to absorption coefficient which is basically dependent on the solubility of the gas in the blood and the pressure of the gas there. So by this formula we can determine that how much amount of oxygen is dissolved in the blood at partial pressure of 100 millimeter mercury that is the arterial partial pressure of oxygen isn't it. So if we solve this equation we are not going into the detail of this equation what happens fundamentally that we find that for 1 millimeter mercury of the partial pressure of oxygen 0.003 ml of oxygen is dissolved in 100 ml of solution. Okay so this is simple to remember you can remember this that 0.003 ml of oxygen is dissolved for a pressure of 1 millimeter mercury in 100 ml of solution. So you can deduce that how much oxygen will be in dissolved form in arteries and in veins. So in arteries the partial pressure of oxygen is how much it is 100 millimeter mercury. So simply multiply this by 100 and you will get 0.3 ml of oxygen per 100 ml of blood. So this much oxygen is present in dissolved form in arteries and the same thing if we calculate for veins it will be we have to get for 40 millimeter mercury because that is the partial pressure of oxygen in veins so it will come to 0.12 ml per 100 ml of the blood. So this is the amount of oxygen which is carried in dissolved form it is very less isn't it 0.3 ml only. So that is why hemoglobin is important. So let us see that how oxygen is carried bound with hemoglobin. Well fundamentally first we should know that hemoglobin has four chains adult hemoglobin we are talking about adult hemoglobin there is alpha chains which are two in number and there are beta chains which again are two in number and each hemoglobin can bind with four molecules of oxygen. So each hemoglobin can bind with four molecules of oxygen and remember that this binding with hemoglobin is actually reversible. So when oxygen binds with hemoglobin it forms oxy hemoglobin. So when the concentration of oxygen or the partial pressure of oxygen and more it binds preferably with hemoglobin and forms oxy hemoglobin and as the partial pressure of oxygen decreases since this reaction is reversible the oxygen which is bound to hemoglobin will be released from the hemoglobin. So this is known as reversible binding of oxygen with hemoglobin. So we said that each hemoglobin can bind with four molecules of oxygen. So if we determine in terms of volume that maximum amount of oxygen which can be carried by hemoglobin is known as oxygen carrying capacity. So this is important oxygen carrying capacity total capacity which is there for carrying oxygen. So that will happen when the entire hemoglobin which is present all the sites are occupied by oxygen. So that is the total oxygen carrying capacity and with this we have another component that is the percentage hemoglobin saturation. Very important we will see this in the graph when we will talk about oxy hemoglobin dissociation curve. So there is percentage hemoglobin saturation which is given as oxygen combined with hemoglobin. So at a particular partial pressure of oxygen there will be some oxygen which is combined with hemoglobin right. So at that time not all the hemoglobin sites are occupied. So oxygen combined with hemoglobin divided by total oxygen capacity total binding capacity of hemoglobin. So that gives the percentage hemoglobin saturation. By the way one gram of hemoglobin can carry 1.34 ml of oxygen. Now remember that some books give it as 1.39 ml right. So some books say that this is the oxygen carrying capacity for one gram hemoglobin while some books say 1.39 ml. Well both are correct. Actually this is the actual form if all the hemoglobin which is present in blood is adult hemoglobin. So this is calculated experimentally. However physiologically we will find that it is 1.34 ml which is being carried because actually physiologically in blood we have to make correction for some forms of hemoglobin which cannot combine with oxygen like a met hemoglobin. So physiologically we consider this value 1.34 ml fine. So with this concept of oxygen carrying capacity and percentage hemoglobin saturation let's see how oxygen is transported by hemoglobin how it binds with hemoglobin. So this is given by oxy hemoglobin dissociation curve and this is the curve we are talking oxy hemoglobin dissociation curve. Now let's try to understand this curve. Here x axis is showing the partial pressure of oxygen in millimeter mercury and y axis is showing the percentage hemoglobin saturation what we have seen before that the percentage of hemoglobin binding sites where oxygen has combined so that is percentage hemoglobin saturation. And when we are talking about partial pressure of oxygen just note here that we are not talking about that where is this partial pressure is this in arteries it is in veins wherever it is depending on the partial pressure of oxygen there will be hemoglobin saturation. So let us note certain things in this curve first of all you see that here that curve is little flat compared to you see the center portion it is almost straight line here it is little flatter and in the end it is much flatter right so this is the flat portion this is the flat portion and in between it is much straight line and this is known as sigmoid shape so the curve is sigmoid shape and if we see the value wise then why it is becoming sigmoid shape you see that at the partial pressure of oxygen of 10 millimeter mercury we have 10 percent hemoglobin saturation then after this the saturation is increasing considerably with a small rise in partial pressure of oxygen. So here it is the 26 millimeter mercury these values are important for drawing of the graph okay so this at 26 millimeter mercury the hemoglobin is 50 percent saturation so at 10 only 10 percent saturated but at 26 millimeter mercury it is 50 percent saturated then at a partial pressure of 40 millimeter mercury hemoglobin is saturated 75 percent okay so here it is 75 percent saturated and by 60 millimeter mercury it is 90 percent saturated so you see now there is not much space left in hemoglobin only 10 percent is left and it is filled after 60 millimeter mercury partial pressure of oxygen so first of all drawing the curve then we will see the characteristics also that why it is so and how it is important physiologically so for drawing the curve properly so that this s-shaped curve comes you have to obviously mark properly x-axis and y-axis then you have to put a scale properly and at equal distances mark these 10 10 points so 10 20 30 40 they should come at equal distances and similarly on the y-axis they should come at equal distances then just remember these points that at 10 millimeter partial pressure of oxygen hemoglobin is 10 percent saturated at 26 millimeter mercury it is 50 percent saturated then at 40 millimeter mercury it is 75 percent saturated and then at 60 millimeter mercury hemoglobin is 90 percent saturated so if you remember these points and mark them first like I have drawn these lines and then just draw a graph joining these lines you will get the graph properly fine so now let's see the characteristics of this curve and why we have taken such points so as I told you before that this is the flat portion of the curve now you see partial pressure of oxygen in arteries is around 100 millimeter mercury ideally it is 97 millimeter mercury but for simplicity sake for understanding we are taking this number so partial pressure of arterial oxygen is 100 millimeter mercury now we are saying that at 60 millimeter mercury itself the hemoglobin is 90 percent saturated that means even if there is change in partial pressure from 60 to 100 millimeter mercury not much change in percentage hemoglobin saturation is occurring isn't it so not much change in content of oxygen is also occurring so this is kind of a reserve which is acting for example if somebody goes at high altitude and where this partial pressure of oxygen atmosphere starts falling then obviously the arterial partial pressure of oxygen will also start falling but you see that with the fall of partial pressure from 100 to 60 millimeter mercury not much change in transport of oxygen is taking place almost similar amount of oxygen is getting transported because hemoglobin is 90 percent saturated fine so that is the importance of the flat portion of the curve right so this is the flat portion second now you see the steep portion steep portion is starting after here 40 millimeter mercury to 20 millimeter mercury but before you see that this 40 millimeter mercury point we saw right 40 millimeter mercury hemoglobin is 75 percent saturated now where in circulation we have partial pressure of oxygen as 40 millimeter mercury it is in veins isn't it so in veins we say that okay hemoglobin is deoxygenated but here we are saying that it is 75 percent saturated so that 75 percent saturation only we are referring as deoxygenated so this 40 millimeter mercury or 75 percent saturation is based on all the blood which is coming from various tissues and going into the veins right but at the level of the tissues what happens that there is considerable fall in partial pressure of oxygen in tissues so especially in metabolizing tissues lot of metabolic activity is taking place lot of oxygen is being utilized and there is decrease in partial pressure of oxygen so in that case you see how the curve is going down there is a steep fall right so as the partial pressure of oxygen is decreasing there is a steep release of oxygen from hemoglobin what is known as unloading of oxygen from hemoglobin so this is a dissociation part we are talking here which is happening at the level of the tissues so this is the importance of steep portion of the curve so significance of the flat portion of the curve and significance of the steep portion of the curve fine but first of all why are we having such kind of thing why hemoglobin saturation is affected like this when partial pressure of oxygen is changing why here at 60 millimeter mercury doesn't become like this right and it ends it becomes 100 saturated at 70 millimeter mercury why it becomes flat here well this is because the binding of oxygen with hemoglobin follows something known as positive cooperativity positive cooperativity what is this actually when hemoglobin is not bound with oxygen we say that hemoglobin is in tensed state it is in tensed state so the oxygen finds it difficult to find the binding sites in hemoglobin because the binding sites are kept close together so that is tensed state now as oxygen starts binding right here some oxygen starts binding so because of the binding of the oxygen there is change in the configuration of the hemoglobin such that it opens up the binding sites which are present inside right initially which were present inside so then we say that the hemoglobin has changed its state to relax this state so from tensed state it is becoming relaxed state so that is why here there is a steep change in the affinity of hemoglobin to oxygen you see as pressure pressure of oxygen is increasing more and more hemoglobin is getting saturated very fast and finally here why it becomes flat here because not much of the binding sites on hemoglobin are available now very few are available so oxygen finds it difficult to actually discover that site where is it right and wherever it finds it goes and fits there so because not much binding sites are available so this phenomena is known as positive cooperativity where binding of oxygen to hemoglobin increases the affinity of hemoglobin to oxygen so that was about the oxy hemoglobin dissociation curve by the way we are calling it oxy hemoglobin dissociation curve but remember that the name is more about talking about dissociation but here basically it is a relationship between the pressure of oxygen and percentage hemoglobin saturation because you see here we were talking about the association of hemoglobin that how oxygen is binding with hemoglobin and in this portion we spoke about the dissociation of oxygen from hemoglobin so even though the name is dissociation curve it represents both binding of oxygen to hemoglobin and release of the oxygen from the hemoglobin now this curve can actually shift a little bit that is the affinity of hemoglobin to oxygen can change depending on certain conditions for example sometimes the curve can become like this and in others this curve can become like this so this is known as right shift of the curve okay and this is the left shift of the curve and this happens when certain baseline conditions are changed so right shift happens when there is increase in hydrogen ion concentration there is increase in partial pressure of carbon dioxide increase in temperature and increase in 2-3 PPG so these factors can cause right shift of the curve on the other hand left shift can occur in the opposite factors that is there is decrease in hydrogen ions decrease in partial pressure of carbon dioxide decrease in temperature and decrease in 2-3 PPG so these are the factors which can cause left and right shift of the curve so what is the importance simple see when we talk about right shift if we see certain points say suppose that 40 millimeter mercury let us see now you see the original curve at 40 millimeter mercury it is 75 saturated but in the right shift curve it is only 50 saturated okay so that means more release of oxygen is occurring so in right shift there is more release of oxygen that is the affinity of hemoglobin to oxygen has decreased causing more unloading of oxygen and on the other hand left shift left shift will cause more loading of oxygen so let us see here say suppose actually I have drawn too much left shift it is not like that it will it will be something like here okay so let us see a 26 millimeter mercury here it is 50 percent saturated in this curve it will see it is 60 percent saturated that means hemoglobin is not willing to release oxygen so this is increased affinity of hemoglobin to oxygen fine now where it happens actually if we see that all these conditions increase in hydrogen ion increase in partial pressure of carbon dioxide increase in temperature all these happen near the metabolizing tissues right because these are the end products and the heat is being released so there if the tissue is metabolizing obviously the requirement of oxygen will be more so oxygen should reach there more so all this will cause the right shift of the curve that means basically decrease the affinity of hemoglobin to oxygen causing the release of oxygen and this effect of partial pressure of carbon dioxide on the transport of oxygen is known as Bohr's effect okay nothing it is just the decrease in the affinity of hemoglobin to oxygen fine by the way one thing I forgot before we proceed there is a concept known as p50 p50 is the partial pressure of oxygen at which hemoglobin is 50 percent saturated so here in the first curve which we saw it is 26 millimeter mercury so that is the partial pressure of oxygen at which hemoglobin is 50 percent saturated if you see that in right shift curve it becomes 40 millimeter mercury and in left shift curve it is how much here it has shifted right so this p50 is an indicator of the affinity of hemoglobin to oxygen and indicates the right or left shift of the curve fine with this let us see how much oxygen is carried bound to hemoglobin so there are two graphs shown here if you see this is the normal graph where partial pressure of oxygen is 100 millimeter mercury and y axis is showing oxygen content in ml right so if hemoglobin adult hemoglobin is 100 percent saturated it is 20 ml of oxygen is being carried we saw that in dissolved form how much is there 0.3 ml is being carried in dissolved form that means rest 19.7 ml is being carried bound to hemoglobin right so total 20 ml of oxygen is being carried now in this case you see what has happened we are saying that hemoglobin is still 100 saturated with the oxygen then why oxygen content is less because amount of hemoglobin which is there is less so two things are important that is the amount of hemoglobin is important along with that saturation of hemoglobin is also important so both of them will determine the total oxygen which is being carried by hemoglobin let's see another one in which saturation of hemoglobin is affected despite everything else being normal that is partial pressure of oxygen is also normal and amount of hemoglobin is also normal so that happens in case of carbon monoxide poisoning so in carbon monoxide poisoning what happens that carbon monoxide goes and binds with hemoglobin because it has very high affinity with hemoglobin around 210 times more than that of oxygen so it preferably binds with hemoglobin and oxygen is not able to bind because its sites are being occupied by carbon monoxide so you see that despite partial pressure of oxygen being 100 ml the oxygen content has decreased right so this graph is about less hemoglobin but this blue graph is about normal amount of hemoglobin but not saturated with oxygen saturated with carbon monoxide so we see that the total oxygen content is less plus one thing more you note here that the graph is kind of left shifted right so what happens that it causes the shift of the curve this carbon monoxide causes the shift of the curve to the left side so if this is adult hemoglobin and if we see that how carbon monoxide will affect the graph it will be something like this that is with oxygen saturation is much less right and there is left shift of the curve that means first of all oxygen is not able to bind to hemoglobin and second that whatever is bound it is not being able to release right is because we said that left shift means increased definitive of hemoglobin to oxygen right so it also affects the release of oxygen it affects the binding of oxygen carbon monoxide also affects the release of oxygen that is why it is very very dangerous fine finally let's come to the other hemoglobin graphs that is fetal hemoglobin and myoglobin so this fetal hemoglobin graph I have drawn oxy hemoglobin dissociation curve you see it is somewhat left shifted why is it so well fetal hemoglobin has two chains like adult hemoglobin but the chains are different there is alpha chain and there is gamma chain so this gamma chain basically cannot bind with two three BPG so we said that two three BPG actually shifts the curve to the right and beta chains somewhat are always bound with this PPG so if gamma chains are not able to bind here obviously there will be some left shift of the curve and that's why fetal hemoglobin have more affinity for oxygen than that of the adult hemoglobin so that was about fetal hemoglobin next comes myoglobin myoglobin has a hyperbolic curve so you see what happens that much of the binding with oxygen is happening very soon you see here that around 15 millimeter mercury it is almost fully saturated right and this cheap slope if we see when it will release it is very very late when the partial pressure is around 5 millimeter mercury okay so what happens that as adult hemoglobin releases oxygen this myoglobin is present in muscle so as adult hemoglobin releases oxygen because the partial pressure of oxygen is more this myoglobin will bind with oxygen only when the partial pressure of oxygen falls less than 10 millimeter mercury then only there will be release of oxygen and where is this happening it is happening in metabolizing tissues right especially exercising muscles so we can say that myoglobin basically acts as a store for oxygen in the muscles so that's all about transport of oxygen we saw various aspects that how oxygen is carried in various form dissolved form bound with hemoglobin then we saw oxymoglobin dissociation curve it's shift to right and left then how carbon monoxide affects the curve how fetal hemoglobin and myoglobin curves are different well thanks for watching the video if you liked it do press the like button share the video with others and don't forget to subscribe to the channel physiology open thank you