now one of the final functions of the gas exchange system is to maintain a concentration gradient or a pressure gradient between the air in the alvus and also the blood in the capillaries what I mean by that is oxygen must constantly be diffusing from the air into the blood as you can see the one where I'm circling there and carbon dioxide must constantly be diffusing from the blood into the air all right so the reason why this needs to happen is because obviously uh why does why must oxygen constantly be diffusing into the blood well obviously because our blood must always be oxygenated as much as possible so that most of the cells in our body would be able to receive oxygen to carry out respiration because if our cells are not able to receive oxygen uh the cells will die it's as simple as that and also very importantly our blood must have very little carbon dioxide so we must remove the carbon dioxide out of the blood by making it diffuse into the alvus this is because when there are too much carbon dioxide in the blood carbon dioxide can make the blood very acidic how can carbon dioxide make the blood very acidic uh that one you have to revise back the transport of carbon dioxide in the blood where carbon dioxide can bind to water with the help of Carbonic and hydr it becomes carbonic acid and the carbonic acid will split to become hydrogen ions and hydrogen carbonate ions and then the hydrogen ions are the ones that will lower the blood pH and we do not want our blood pH to be very low or very acidic therefore carbon dioxide must also be removed from the blood so in this case over here for gas exchange to happen our body must always maintain a concentration gradient between the two places the alvus and the blood so what I'm drawing here is I'm just throwing out a single alvus where it's filled with air and also a blood capillary and the blood is coming one arrow is coming from the heart and the other arrow is the blood is going back to the heart now let's just focus on oxygen which I've represented in orange color dots right now as you can see what actually happens is there is a high partial pressure or concentration of oxygen in the alvus and a low partial pressure of oxygen or concentration of oxygen in the blood therefore in this case there is a concentration gradient or a pressure gradient is this a good or bad thing this is a good thing because in this case over here the oxygen will diffuse from the alvus into the blood down the concentration gradient or down the pressure gradient that's what it means now once oxygen diffuses into the blood I want you to compare the concentration of oxygen in the blood and in in the air what do you notice in this case over here the concentration of oxygen or partial pressure of oxygen in the blood and the concentration of oxygen in the air are exactly the same so will diffusion continue to happen will oxygen continue to diffuse from the air into the blood no it won't because there is no more concentration gradient so what we have to do here is we have to reestablish the concentration gradient what do I mean by reestablishing the concentration gradient if you look at that particular diagram I need to increase the concentration or partial pressure of oxygen in the lungs that's the first thing I have to do so which means to say I have to add more oxygen into the Alvi or the alveolus so the question here is how do I actually increase more oxygen into the alvas very simple you just have to breathe in and when you breathe in what will actually happen is you will add more oxygen into the alvas as you can see over there but how do I get rid of that extra oxygen inside the blood because I need I need the blood to have a lower concentration or partial pressure of oxygen remember as I've highlighted over here blue color just means deoxygenated pink color means oxygenated so once the blood once the oxygen diffuses into the alvas the blood becomes oxygenated correct so how do I make more deoxygenated blood move towards the alvas very simple what the heart has to do is the heart has to contct and when the heart contacts it pushes the blood and look the new blood that is coming towards the alvus is deoxygenated which means to say the blood has less oxygen in this case you have reestablish the concentration gradient you have made the concentration of oxygen in the alvas to be higher and the concentration of oxygen in the blood to be lower and therefore this is called the maintaining of the concentration gradient to allow oxygen to constantly diffuse into the blood so if a question were to ask you how does the gas exchange system maintain a concentration gradient between the alvs and the blood number one it's by breathing in and breathing out and number two it's by the confection of the heart to constantly deliver the oxygenated blood to the lungs if you're still quite confused about this let's try it again let's now compare carbon dioxide and oxygen okay now as you can see over here the orange color dot represents the oxygen and the blue color dots represent the carbon dioxide and the part where I'm circling right now that is called deoxygenated blood why is it deoxygenated blood because the blood has less oxygen now what I want you to do is I want you to compare the concentration or par IAL pressure of oxygen between the alvus and blood you notice that the alvus has a higher partial pressure or concentration of oxygen the blood is lower and for carbon dioxide let's compare alvers and blood in the blood carbon dioxide is higher in the alvus carbon dioxide is lower so do we have a concentration gradient yes we do because we have a concentration gradient can diffusion happen yes diffusion can happen where oxygen will diffuse from the alvus into the blood from a high concentration to low concentration and carbon dioxide will diffuse from the blood into the alvas from a high concentration to a low concentration so once this has actually happened look at the blood the blood is now oxygenated as you can see over here but look at the concentration of oxygen and carbon dioxide in the two areas they have equalized once they have equalized this means that there is no more concentration gradient right so there's no more concentration gradient which means to say no more diffusion I need to make the alvus have a low concentration of carbon dioxide and a high concentration of oxygen and how do I do that by the way okay very simple all we just have to do is we first have to breathe out that air you just breathe it out and when you inhale new air a into the alvus the new Air that comes in will always have a higher concentration of oxygen and lower concentration of carbon dioxide so now you have basically corrected the problem in the alvus but how do we correct the problem in the blood capillary look at the heart the heart will contract and when the heart contracts it will push more deoxygenated blood towards the capillary so when there's more deoxygenated blood reaching the capillary look at what happens to the concent ation gradient it reestablishes the concentration gradient or creates a new concentration gradient so that oxygen can constantly diffuse into the blood and carbon dioxide can constantly diffuse from the blood into the air this is what we have to understand about the process so to maintain the concentration gradient for exam purposes you just have to mention two things lung ventilation which is breathing in this ensures that the alv will always have a high concentration or partial pressure of oxygen and a low concentration or partial pressure of carbon dioxide and the contraction of the heart constantly pushes deoxygenated blood to the lungs and this ensures that the blood near the alvus will always have a low partial pressure or concentration of oxygen any High partial pressure or concentration of carbon dioxide the word partial pressure and concentration for gases can be used interchangeably so you don't have to worry about that