in the previous video we talked about something known as the red blood cell and the structure and I did mention that the red blood cell contains something called hemoglobin now just a revision on hemoglobin hemoglobin is referred to as a globular protein the reason why it's globular is because it is ball shaped and water soluble it is also referred to as a quaternary protein because it is made out of four polypeptide chains and the four chains are named as follows the two alpha globin polypeptides and nd2 beta globin polypeptides and each polypeptide chain has a heme group okay now so I'm drawing it out over here where I'm labeled out the structure of the hemoglobin and you also see those red colored dots and the red color dots are just the Hem group and they contain a particular type of mineral called iron because the iron is the part of the hemoglobin that will bind to oxygen that is the important thing incidentally that is why red blood cells are red in color because when iron binds to the oxygen it forms iron oxide and the iron oxide has a particularly reddish brown color which is where the red blood cells get their colors from so for this video we are going to be focusing on the hemoglobin molecule the first thing we have to understand about the hemoglobin molecule is the fact that one hemoglobin can bind to four oxygen molecules the reason why that is so is because uh one hemoglobin has four hem group each hem group can attach to one oxygen molecules and therefore it becomes oxyhemoglobin or also known as hbo8 okay so it's four oxygen molecule or eight oxygen atoms just be wary of that the important thing to know is the chemical reaction where HB plus 402 becomes hbo8 incidentally what you have to know is this reaction is reversible all right so we are going to elaborate on that in a while so let's talk about hemoglobin the weird thing about hemoglobin is the fact that it has a duality now what does what do I mean by a duality is a duality is when it has two properties that are opposites of each other okay so let's talk about this Duality that hemoglobin has you see the first thing that hemoglobin has is hemoglobin has this characteristic where it readily wants to bind to oxygen which means to say hemoglobin loves oxygen or has a high Affinity to oxygen so when it binds to the oxygen it forms oxyhemoglobin so you would think that this hemoglobin is this molecule or this protein that just wants to hold on to oxygen and never wants to let go of this oxygen but that's where the second characteristic of hemoglobin comes in which is why it's a duality is that hemoglobin will readily release the oxygen when it's necessary so the hemoglobin here is attached to the oxygen it gives the oxygen a kick and it yields the oxygen away all right so this is the weird thing about hemoglobin hemoglobin loves oxygen and it wants to keep hold on to oxygen as much as possible but at the same time hemoglobin is this sort of generous uh protein or generous molecule that would just give oxygen or let go of the oxygen when it is necessary so hemoglobin is over the whole molecule that you want to have a relationship with it loves you but it's also willing to let you go right we are we are really steering into a different part okay back to biology back to biology now so let's get back to biology so this hemoglobin actually has a kind of weird love-hate relationship with oxygen where it loves oxygen it wants to keep on to the oxygen but it also Heats I guess you can say it hates oxygen and it also wants to kick the oxygen or let go of the oxygen when possible so that is what I'm that is what I meant when I said that hemoglobin has a duality now why is this Duality important so one of the problems with this topic when I teach my students is the oxygen dissociation curve okay so this curve is something that you might have seen in your textbook where on the y-axis it has the percentage saturation of oxygen and hemoglobin and on the x-axis is the partial pressure of oxygen measured in kilopascal and the general shape of the curve is like a sigmoid or an s-shaped curve okay so when students look at this graph they go well I what is going on here what is this okay what is this whole thing about percentage saturation what is partial pressure of oxygen I want to know all that in detail okay so let's break it down first before we go through the curve we have to understand a few things let's look at the partial pressure of oxygen what does it mean by a partial pressure of oxygen partial pressure of oxygen just basically means the concentration of oxygen gas in one area okay so we use the word concentration of gas or partial pressure of gas interchangeably for example you are in a room and the room over here has low amounts of oxygen and the room on the right has a higher amount of oxygen we can just say that the room on the left has a lower partial pressure of oxygen and the room on the right has a higher partial pressure of oxygen that's just basically what it means partial pressure of oxygen just means the concentration of oxygen in the air or in one particular area that's it okay so some students will go can I use the word concentration of oxygen instead of partial pressure you can but just be aware that in the exam they will use the word partial pressure when you're talking about gases it's always better to use the word partial pressure instead of concentration when you're talking about Solutions however then we use the word concentration that's the difference okay now then comes the other concept which is the percentage saturation of oxygen in hemoglobin okay this is a bit of a confusing one all right now to understand this you don't need to memorize now I don't need you to memorize this part of the explanation I just need you to understand it okay so one with blood cell can contain at least about 250 million hemoglobin molecules you don't have to memorize that I just want you to know that now instead of blowing out all 250 million hemoglobin I'm just going to draw out five hemoglobin molecule which I've represented in HB so you can see those five HBS over there each HB represents one hemoglobin now remember I told you earlier that one hemoglobin can bind to four oxygen molecules so my question to you is this if this red blood cell has five hemoglobin how many oxygen molecules can it carry in maximum capacity so the answer is well one hemoglobin can bind to four but since this red blood cell has five hemoglobin molecules it can carry a total of 20 antigen molecules in total now imagine this red blood cell I'm just drawing out some oxygen molecules attached to the hemoglobin now what I want you to do is I want you to count the number of oxygen inside the red blood cell so when you count it you can actually see so let's count the number of oxygen molecules as we can see here so we have one two three four five six seven eight nine ten it has only 10 oxygen molecules within the red blood cell so what is the percentage saturation the percentage saturation equals to 10 oxygen molecules that it's carrying divided by 20 because that's the maximum that it can carry multiplied by a hundred and we will get a 50 saturation of oxygen in hemoglobin which means to say that the hemoglobin molecules within the red blood cells are only 50 or half saturated and it is only having it's only carrying oxygen at 50 capacity which means to say it just has uh 50 more room to carry oxygen that's what it means let's try another one okay and in this case over here let's count it out let's count out the amount of oxygen okay so we're going to do it one at a time so one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen Seventeen eighteen nineteen twenty so this red blood cell is carrying 20 oxygen molecules divided by 20 oxygen molecules which is the capacity that it can carry multiplied by a hundred which means to say that the red blood cells are the percentage saturation of oxygen is 100 oxygen saturation it the way blood cell is fully saturated with uh oxygen and it cannot carry any more oxygen even if it wanted to so this is its Max Capacity that's what I just want you to understand you don't have to memorize this calculation all I just want you to know what percentage oxygen saturation means so 100 oxygen saturation is just the way blood cell is 100 filled with oxygen 75 just basically means it's three quarter full or 75 saturated and 15 just basically means that it only has the hemoglobin has bound to only 15 percent of oxygen and there is extra room within the red blood cells to carry more oxygen if it wanted to this is what is meant by percentage oxygen saturation in hemoglobin now coming back to the curve on the x-axis I put two values low partial pressure of oxygen and high partial pressure of oxygen remember what that means is you are just in a room or in an area where the air has a low concentration of oxygen and in on a high partial pressure this means you have you are in a room where it has a high partial pressure of oxygen okay now if I were to just basically put a line on the low partial pressure of oxygen it corresponds to about 20 oxygen saturation and a high partial pressure of oxygen corresponds to at least let's say for example a hundred percent oxygen saturation in hemoglobin so of course what does this actually mean okay what it means is in this case if you are in a room with a low partial pressure of oxygen and you took a deep breath in you took you just took a breath in the a concentration of oxygen that goes into your lung alveolus will be very low because you only breathe in very little oxygen right so when there is very little oxygen in your lung alveolus very little oxygen will then diffuse into the red blood cell and thus your red blood cells will only be 20 saturated with oxygen that's what that means it means when you breathe in a low concentration of oxygen your red blood cells are only going to be saturated at a very low percentage like 20 conversely if you're in a room where it has a lot of oxygen and you took a deep breath in you you took a deep breath in and a lot of oxygen entered the lung alveolus what happens then is more oxygen is able to diffuse into the red blood cells in the capillaries and thus your red blood cells will be a hundred percent saturated with oxygen which means the red blood cell is fully saturated Okay so that's just what it means if you breathe in a low concentration of oxygen your red blood cells will be less saturated with oxygen if you breathe in a high concentration of oxygen or a high partial pressure of oxygen it just means that your red blood cells are going to be fully saturated with oxygen simple all right so this is where the first characteristic of hemoglobin is important if the hemoglobin is exposed to a high partial pressure of oxygen the percentage saturation of oxygen in hemoglobin will also be high very straightforward quite simple okay so so students are like well yeah that's obvious however what we have to understand is there is also another way to interpret the graph I want you to see that word the name of this curve the name of this curve is known as the oxygen dissociation curve okay dissociation actually means split what split am I talking about the split that I'm talking about is when the hemoglobin kicks the oxygen away okay it splits itself from the oxygen right and this is what we want to talk about now I'm going to evolve the graph and I do need you to memorize these values now let's say two kilopascals partial pressure of two kilopascals will give 10 saturation a partial pressure of 4 kilopascals will give 40 percent oxygen saturation all right now let's imagine for the second that I have a red blood cell and look at the percentage oxygen saturation in there the red blood cells traveling in the blood vessel and how many percent oxygen is saturated it is a hundred percent oxygen saturation that means the red blood cell is filled to the brim with oxygen it cannot carry any more oxygen if it wanted to okay now let's say it's passing by a body cell now remember a body cell constantly needs oxygen because of aerobic respiration so the red blood cell over here it has a lot of oxygen and their function is to give the oxygen to the body cells okay so what happens is for example the red blood cell travels reaches the capillaries and then this is where the hemoglobin has to let go of some of the oxygen so that the body cell receives the oxygen right okay so the red blood cell on the left is still attached to the oxygen oxyhemoglobin but when it reaches the body cell the hemoglobin splits with the oxygen and releases the oxygen decision so that the oxygen is able to reach the body cells simple enough so this explains that hemoglobin must have a second characteristic where it must readily release the oxygen to the body cells not only must it keep the oxygen but it must also be willing to part with the oxygen so that the body cells can receive the oxygen so what does this have to do with the Curve okay let's explain this imagine two situations I have a situation where the weight blood cell there's a there's a one at the top and there's one at the bottom here okay so for example the body cell at the top has four kilopascals of oxygen and the body cell at the bottom has only two kilopascals of oxygen so which body cell has more oxygen within itself correct the body cell at the top still has a lot of oxygen but the body cell at the bottom has very little oxygen left so in this case where we simply put the body cell at the top well it needs oxygen but it doesn't need a lot of oxygen because it still has a reserve but the body cell at the bottom it only has two kilopascals of oxygen so it kind of needs extra oxygen from the red blood cells right so what happens is when the red blood cell at the top reaches the body cell based on the graph when it's exposed to a cell with four kilopascals of oxygen if you look at the graph the percentage saturation is 40 automatically the red blood cells oxygen saturation becomes 40 percent because that's what the graph says okay so from a hundred percent of oxygen saturation the red blood cell now only has 40 oxygen saturation then of course I will ask my questions to the student okay where did the 60 of oxygen vanish off to so where's the 60 okay the sixty percent of oxygen was basically released into the cells because the cell needed some oxygen okay if we look at the situation at the bottom so when the red blood cell reaches the body cell at the bottom the red blood cell is exposed to two kilopascals of oxygen only okay and based on the graph two kilopascals of oxygen corresponds to 10 so automatically the saturation in the red blood cell becomes 10 from a hundred percent it becomes ten percent so where did the 90 go off to the 90 in this case over here is released into the body cells isn't this spectacular you see the Cell at the top needed less oxygen so the red blood cell released only 60 percent but the Cell at the bottom needed more oxygen so the red blood cells released out 90 of its oxygen so that it is only left with 10 oxygen saturation within itself so what this means is hemoglobin radially releases more oxygen when the partial pressure of oxygen is very low okay this is a this is a weird thing about hemoglobin hemoglobin is this uh weird molecule where if the cell needs less oxygen the hemoglobin is like okay fine I'm going to give you some oxygen right especially at the top but in the situation at the bottom the cell needed a lot of oxygen so the hemoglobin is like okay fine I'm gonna give you more okay so of course students will ask how is the hemoglobin able to know this okay we will talk about that in the next video okay so this is a pretty spectacular characteristic of hemoglobin now to bring it together what I'm going to do is I'm just going to show you a simple diagram of a circulation just throwing out the curve and you have the curve like that you have a lung alveolus and because you're breathing in constantly the lung ovulus usually has a high partial pressure of oxygen body cells usually have a low partial pressure of oxygen because they are constantly using up oxygen for aerobic respiration now based on the curve I'm just drawing out this curve over here let's say that the lung alveolus has a partial pressure of 12 kilopascals so when the red blood cell reaches the lung alveolus it is exposed to 12 kilopascals of oxygen based on the curve okay when it's exposed to 12 kilopascals of oxygen based on that line as you can see there in yellow it will become a hundred percent oxygen saturation so the red blood cells are automatically filled up with oxygen because the oxygen diffused into the red blood cells from the lung alveolus okay so these red blood cells will then move towards the body cells and let's say the body cell has a three kilopascal worth of oxygen so in that case when the red blood cell reaches the body cell based on the graph three kilopascals correspond to 20 the saturation in the red blood cell will automatically become 20 so you're like hey wait a second why is it 20 where did the eighty percent go off to the 80 percent is released into the body cells that needed the oxygen this is how you interpret the graph so these are the two characteristics where on the left hemoglobin radially binds to oxygen when partial pressure of oxygen is high but hemoglobin readily releases oxygen when the partial pressure of oxygen is low