so in this video what we are looking at is how carbon dioxide is transported in the blood one of my questions that I like to ask my students is how do you think CO2 is transported inside the blood and in most cases my students will say well um oxygen binds to hemoglobin and they are transported inside the red blood cells so therefore I think CO2 carbon dioxide also goes through the same steps they will go into the red blood cell bind to the hemoglobin and they are transported inside the blood in most cases uh in when you think about the answer the answer is almost technically correct or rather that's not the full story carbon dioxide Transportation inside the blood is a little bit more complicated than that so let's talk about it we have our body cells and our body cells produce CO2 I'm drawing out the capillaries here and the CO2 will diffuse into the blood to the capillary walls and they diffuse because the body cell has a higher partial pressure or higher concentration of CO2 and the blood has a lower partial pressure or lower concentration of CO2 so diffusion works from a higher to lower concentration gradient or down the concentration gradient so once CO2 diffuses into the blood then what happens well the first thing is now when the CO2 is in the blood plasma see notice that I'm drawing out the red blood cell and outside the red blood cell is the plasma which is known as the liquid part of the blood if you remember the plasma is mostly made out of water and some dissolved substances so you see only about five percent of the CO2 can dissolve inside the plasma because carbon dioxide themselves are not actually very polar molecules in fact we call them nonpolar molecules and because they are nonpolar they have difficulty interacting with water therefore they cannot really dissolve in water that is why only five percent of them will actually dissolve inside the plasma so about 95 of the CO2 will then diffuse or enter the red blood cell and 10 of the carbon dioxide will bind together to the hemoglobin to form something called carb aminohemoglobin quite a mouthful of quite a mouthful isn't it carb Amino hemoglobin and a few students will go wait a second it's only 10 that binds to hemoglobin I thought all the CO2 binds to hemoglobin in fact no very little carbon dioxide directly points to hemoglobin to form carb Amino hemoglobin now let's break down that very long word carbamino hemoglobin can be broken down into three parts hemoglobin being you know the pigment or the protein inside the red blood cell carb which references or corresponds to the carbon dioxide and amino now the amino in this case means the protein part you see when CO2 binds to hemoglobin I'm drawing out the hemoglobin here you can see the four polypeptide chains and the heme group which have represented in the red dots the CO2 does not bind to the heme group Like Oxygen does oxygen binds to the heme group but carbon dioxide actually does not bind to the heme group in fact carbon dioxide only binds to something called the terminal amine groups of the polypeptide chain terminal amine groups being the uh the last amine group of each polypeptide chain so each hemoglobin has four polypeptide chains and therefore they have four terminal mine groups that's basically what it is but if you do not want to explain that in the exam it is sufficient for you to say that carbon dioxide binds to the polypeptide chain of hemoglobin that's good too the point is I don't want you to say that carbon dioxide binds to the heme group because that is wrong that is why it gets the name carb Amino hemoglobin because the carbon dioxide binds to the amine group of the hemoglobin that's where the nomenclature or the naming comes from so from 95 of it 10 binds to the hemoglobin directly so you are left with 85 percent of it so in this 85 of the carbon dioxide what they will do is they will then bind together with water and they are catalyzed by an enzyme known as Carbonic anhydrase and together they will form something known as carbonic acid now Carbonic acids chemical formula is h2co3 okay so what happens is the carbonic acid is the one that will then split to become hydrogen carbonate ions which are negative ions and hydrogen ions which are positive ions now those hydrogen ions will then bind directly to hemoglobin to form hemoglobinic acid hhp and the hydrogen carbonate ions will diffuse into the plasma and 85 percent of carbon dioxide is actually transported this way you see hydrogen carbonate ions are anions they are polar molecules okay and because they're polar they have charges it is very easy for them to dissolve in the plasma that is why most of the carbon dioxide is actually transported this way which is 85 percent of it so this is the complicated nature in the way of in which carbon dioxide is transported now we're still not done yet what I'm going to do is I'm going to you know remove a few of the clutters I want to remove the five percent and the carbon Amino hemoglobin so that we focus on the 85 percent of the carbon dioxide so in this 85 of the carbon dioxide they will bind with water from carbonic acid split to become hydrogen ion and hydrogen carbon in ions and hydrogen ions will bind to hemoglobin let's focus on that first part so there's an important point to note when hydrogen ion binds to hemoglobin you see they form they need to form hemoglobinic acid for two very important reasons the first important reason is if you leave hydrogen ion to float around inside the cytoplasm it is much too dangerous it is dangerous because if you study chemistry you know that hydrogen ion contributes to acidity so when you have too much hydrogen ion floating around it lowers the blood pH now I don't need you to memorize this next part but I just need you to understand that blood pH is about 7.35 to 7.45 okay anytime your blood pH goes any lower in fact it goes down to even like 7.05 or 7.15 in medicine we say that this is acidosis or the blood pH is too acidic in nature and this is dangerous because there's too much hydrogen ion floating around so to solve this problem or to to to evade this danger the hemoglobin will bind to the hydrogen ions and the acidic effect is then reduced so the hemoglobin acts as a buffer some students will notice that when hemoglobin binds to a hydrogen ion it forms hemoglobinic acid and they will ask me wait hemoglobinic acid is also an acid isn't that dangerous we don't have to worry because hemoglobinic acid is a weak acid so it does not acidify or lower the blood pH as much so that's a good thing so just to show you as an example here I have a red blood cell and the pH inside the red blood cell is 7.35 and CO2 diffuses into the red blood cell binds together with water forms carbonic acid and the carbonic acid splits to become many hydrogen ions and many hydrogen carbonate ions notice what happens to the blood pH the blood pH becomes 7.15 and I told you this is not a good thing we call this acidosis and it's quite dangerous the reason it can be quite dangerous is because it throws off the natural pH of the blood it may cause very important proteins such as enzymes in your blood to denature and you don't want that to happen because they may not be able to function at their Optimum level so to solve this problem what happens then the hydrogen ion binds directly to the hemoglobin to form something called hemoglobinic acid so the hemoglobin traps the hydrogen ion and look at the blood pH the blood pH goes back up to 7.35 and this is a good thing so the pH of the blood remains stable at that Optimum level do you have to memorize that blood pH is 7.35 you don't have to but it's good to know that when you have more CO2 it will make the blood more acidic that's a good that's a good point to take note of by the way um now the next spot that we must also understand is the formation of hemoglobinic acid is also important because when hydrogen ion binds binds to hemoglobin it causes the hemoglobin to readily release oxygen and you go hey wait a second that sounds familiar it is familiar you have studied it it's called The Ball effect or the ball shift so the ball effect of the ball shift states that when you have more CO2 it leads to more carbonic acid which leads to more hydrogen ions which leads to more formation of hemoglobining acid and it forces the hemoglobin to release its oxygen and if you look at the part where I just Bridge it in yellow it is just basically the part where I have set so when you have more carbon dioxide you it will cause the hemoglobin to release more oxygen readily so you are like oh that's where the ball shift happens so that is the summary so that is how the ball shift happens in a more comprehensive manner that's basically it so to draw it out again so as you can see here if I'm just showing it to you here I'm just going on an uh oxyhemoglobin and if you remember hemoglobin binds to four oxygen molecules due to four hem groups so when the CO2 enters into the red blood cell it binds together with water it forms carbonic acid splits to become hydrogen ion and hydrogen carbonate ion the hydrogen ion binds to the hemoglobin and it forces the hemoglobin to release oxygen if is this good this is actually a fantastic thing that needs to happen why because remember if you look back into your red blood cell in the capillary remember the body cell has a low partial pressure of oxygen because it's constantly using up oxygen so the body cell constantly needs oxygen for aerobic respiration so as you can see the CO2 diffuse uses into the blood it will form it will bind together with water I'm repeating myself again it forms carbonic acid the carbonic acid splits to become hydrogen carbon in ions and hydrogen ions and the hydrogen ion interacts with the hemoglobin and it forces the hemoglobin to release the oxygen this is good because when it forces the hemoglobin to release oxygen what does the oxygen do the oxygen will diffuse into the body cells where they are very much needed so this is good this is how ball effect happens in a more complex or comprehensive manner so the formation of hemoglobining acid is important for two reasons it is important for number one to make sure that the pH of the blood does not significantly significantly decrease and it also tells the hemoglobin or it forces the hemoglobin to radially release the oxygen for so that the body cells can uh so that the body cells can receive the oxygen that they very much need now another very important point to note is the hydrogen carbonate ion you see when the hydrogen carbonate ions are formed they will then diffuse out of the blood and dissolve in the plasma when hydrogen carbonate ions diffuse out of the cells chloride ions will move into the cells to rebalance the negative charges this significant process is known as the chloride shift now why does this chloride shift actually need to happen I told you if you see that I've told you that it rebalances the negative charge but what do I mean by that so let's consider it so you have you have some carbon dioxide okay I'm repeating myself again they diffuse into the red blood cells fine so and then the carbon dioxide interacts with water and they form carbonic acid and the carbonic acid will then split to become many hydrogen ions and many hydrogen carbonate ions so far so good now I want you to focus look there in my diagram I've drawn out five hydrogen ions which are five positive charges and five hydrogen carbonate ions which have five negative charges in this case we say that they there's charge within the wet blood cell is balanced because there is an equal amount of positive and negative charges this is good for the red blood cell but when the hydrogen carbonate ions diffuse out what happens is now you have an abundance or there are too much cations or positive ions within the red blood cell which throws off the balance of the charge and this may again affect important proteins within the red blood cells so we don't want the charges in the red blood cells to be either too positive or too negative this is a problem so to compensate for the lack of negative charges within the red blood cells chloride ions from the plasma diffuse in and the charges within the red blood cell is now rebalanced where you have an equal amount of positive and negative charges that's basically why the chloride shift needs to happen so there are very significant points that we need to note here with hydrogen ions and hydrogen carbonate ions they may ask a lot of questions on this part I would like you guys students to understand why hemoglobinic acid formation is important and why the chloride shift is also very important as well so to summarize the whole thing let's bring it all back together when you have carbon dioxide diffuse into the blood five percent of them will dissolve into the plasma and about most of them will diffuse into the red blood cells and out of that 10 of them will bind together with hemoglobin to form carb Amino hemoglobin as a reminder carbon dioxide does not directly bind to the heme group but they bind to the amine group or the polypeptide chain of the hemoglobin now the rest of the carbon dioxide will bind together with water catalyzed by Carbonic anhydrase to form carbonic acid carbonic acid will then split to become hydrogen carbonate ions and the hydrogen carbonate ions which are polar diffuse out of the red blood cells so that they can dissolve easily inside the plasma 85 percent of carbon dioxide is transported this way but to compensate for the lack of negative charges inside the red blood cells or to rebalance the charges inside the red blood cells the chloride shift happens where chloride ions move into the red blood cells now when the carbonic acid splits it did form the hydrogen carbonate ions and it also formed hydrogen ions the hydrogen ions will then bind to hemoglobin to form hemoglobinic acid this is good for two reasons because it prevents the blood pH from decreasing too much or making the blood too acidic and it also makes the hemoglobin readily release more oxygen that's basically it so questions that they may ask in the XMS they may say list out the three ways carbon dioxide is transported in our blood but we waste are number one dissolved in plasma number two transported as carb Amino hemoglobin on number three transported as hydrogen carbonate ions in the plasma those are the three ways other questions that they may ask is why is it important that hemoglobin binds to hydrogen ions the reason is because they need to do that so that it prevents a sharp decrease of pH or it's to make sure that the PH does not become too acidic and it also makes the hemoglobin release more oxygen why must the chloride shift happen it's to make sure that the electrical charges within the red blood cell or the ionic charge within the red blood cell is not imbalanced other questions that they may ask is they may say explain why more carbon dioxide leads to blood pH becoming more acidic the answer to that question is because CO2 binds with water to form carbonic acid and carbonic acid splits to become hydrogen ion and hydrogen carbonate ions and the hydrogen ion makes the blood pH lower or slightly more acidic these are some of the ways the questions can be asked in the exam