 So, we are into animal physiology course of the NPTEL. So, today we will be starting the aspect of respiration where basically the gaseous exchange taking place. We take the air from there the oxygen is being absorbed by the blood vessels and deoxygenated blood which is rich in carbon dioxide is being thrown out of the body. So, this whole process takes place in the lungs and this whole mechanism by which this gaseous exchange is taking place falls under the process of respiration. And one of the driving force of respiration is the partial pressure of the different gases which are present in the air. So, let us start it. So, this is our section 7, section 7 respiration. So, before we get into respiration, let us see what are the different gases present in the air, gases in the air. One of the major percentages of nitrogen then you have oxygen, you have carbon dioxide and you have water vapor and few other gases there. And our major concern are with two gases one of them is carbon dioxide which is the byproduct of all the metabolism byproduct of metabolism which needs to be got rid of this has to be rejected from the body. And since we live in oxygenated environment in oxygen world. So, oxygen is the driving force for metabolism. So, these are the two gases which is our major concern along with significant presence of water vapor because this is the medium where these gases absorb or kind of mix with each other. So, essentially what is happening in this whole process? Essentially what is happening in this process? Let us divide the process into two different parts. Part one the hot is receiving all the impure blood which is completely laden with carbon dioxide. And these carbon dioxide rich blood is being sent to the lungs where those blood vessels throw away the carbon dioxide and picks up the oxygenated blood. And through pulmonary vein the only vein which brings pure blood comes back to the heart that is being pumped. So, there is a small circuit which is called pulmonary circulation. And then there is a phase two which is responsible for this process to take place is we are inhaling the air and from the air the process by which carbon dioxide is being thrown out and oxygen is being taken in. So, if I had to put it in diagrammatic manner then this is how it will look like. So, this is the heart out here the four chambers with the connection I have done right. So, here all the impure bloods are coming in it moves to the lower chamber. So, this is our heart and from here this impure blood which is rich in carbon dioxide plus CO 2 blood goes to the lungs these are the two lungs. In the lungs it get rid of the carbon dioxide. In the meantime it picks up oxygen and this oxygen rich blood. Now comes back here from here it is being sent all over the body and these are the arterial vessels. This is just a recap of what you have done in the heart and the circulation and these are the venous vessels here you have the area of huge network of capillary exchange. This is the zone of capillary exchange and this one is called this vessel is called pulmonary vein which is carrying oxygen rich blood all over the place and this one is called pulmonary artery. So, this is pretty much is the layout of the system and this part this part of the circuit is called pulmonary circulation. So, the important part here is the zone where this exchange is taking place and this is exceptionally important to understand where this exchange is taking place and how it is taking place. So, moving on to this basically it has been observed at the exchange zone is also called pulmonary membrane. If I go back to this zone where this exchange is taking place this is called pulmonary membrane. Now at the pulmonary membrane pulmonary membrane can be as such defined as the boundary between the alveolar gas and pulmonary capillary pulmonary membrane boundary between alveolar gas and pulmonary blood capillaries and the exchange is taking place by passive diffusion. This is the simple diffusion process which is taking place. So, what exactly happened essentially is at the pulmonary vein at the sorry at the pulmonary membrane oxygen diffuse from alveoli into the blood step one whereas CO2 from the blood moves on to the alveolus. Though I have not defined what is an alveolus and what is the structure. So, now next what I will do I will define the structure. So, other word if you diagrammatically or graphically show it this is how it looks like graphical representation will be something like this. If this is the pulmonary membrane here is the membrane with the this is the pulmonary membrane from this side the oxygen. So, this is basically the alveolus these are the RBCs red blood cells. So, the red blood cell picks up the oxygen from the alveolus whereas through away their carbon dioxide along the pulmonary membrane. So, if you see there are two membranes here one is the membrane of the red blood cell out here which I am darkening up and then you have the pulmonary membrane. So, essentially what is happening the RBCs which are reaching this is basically the RBC which is exchanging the gas it is not the other blood component there are WBCs and platelets and they are not involved in any kind of oxygen exchange. And specifically in the RBCs what will be covering is that there is a molecule called hemoglobin which is essentially is the molecule which binds to the oxygen and distributed all over the body and vice versa it binds to the carbon dioxide and brings it back and throw the carbon dioxide from its body and picks up the oxygen. So, what essentially we will do we will study this at two level the level out here why this exchange is taking place at the alveolar membrane and the level two is out here how this I am just putting the short form of hemoglobin HB how the hemoglobin is actually binding to CO2 or O2 and how it is getting rid of O2 and how it is getting rid of CO2. This whole dynamics by which this hemoglobin molecule works will be studying in part two of this particular chapter. So, now what I will do I will give you the gross anatomy that will help you to understand how we are so how this whole structure works to in order to understand the gross anatomy it is very easy if you look at yourself. So, we inhale the air through our nose like this that here that air which we inhale passes through the trachea there is a vessel called trachea the trachea takes it to the two lungs which are present here which are basically the one which is involved in all the exchange of gases. So, at some point or other you must have at least seen this picture. So, this is the nose. So, here is the trachea moving through and this trachea eventually essentially split up. So, if I show the frontal view now if this trachea in the front this is the side view I am showing. So, the frontal view is like this the trachea split up into two and then there are multiple splitting will come to that and here is the organ called lungs and we have two lungs left and the right lungs. So, here is moving like this or here is moving along this and getting split up. So, now what we will do we will look in depth how this structure really looks like save it. So, if you look at the cross section of this. So, say for example, this tube what I just now drawn for you if you cut this over it or somewhere out here you cut it take a cross section of it. So, the cross section looks something like this. So, this is the cross section I am now drawing. So, I will just draw one side of this vessel that is good enough for once. So, this is the split thing here you have like this some membrane like structure and inside this you have another membrane a sac which is surrounded by this is the blood vessel which is coming in close proximity to it. So, the red color what you see you will see is the blood vessel double membrane. So, I am not drawing the this side I am I am just showing you one magnified view of it. So, this is where the alveolar ventilation is taking place which is this nothing but exchange of oxygen and carbon dioxide alveolar ventilation is taking place ventilation and now what is happening here you have the venous blood coming or you can call it like you know the arterial blood which is coming which is plus CO 2 blood which is reaching out here in the proximity of the alveolar. So, alveolar is basically. So, this is structure what you see is the is called alveolar sac or containing alveolar gas and here you have the capillaries here have the blood flowing through. So, here the blood comes and exchange is taking place which I am highlighting now this is the zone where the exchange is taking place. Now, we will talk about how this exchange is taking place and this is essentially this membrane a structure what you see what I am going to highlight now is this is the pulmonary membrane venous structure which is actually responsible this is pulmonary membrane this is the one which will be talking about why and how this structure is involved in any kind of exchange of gases couple of things which I expect you people to go back to your very basics of class 8 or 9 Dalton's law partial pressure this is very I will be covering, but you can just can go through it that will help you to understand. So, the whole idea before even I go to the nitty gritty details of it is the very basic idea of the gaseous exchange is very straight forward always remember this logic if the partial pressure of say gas x is higher at one point and lower at another point say gas x. So, what will happen is that where this gas is in higher partial pressure will move to the zone of lower partial pressure by the simple potential drop this is the most simplest logic by which you can understand the whole gaseous exchange phenomena. So, in other word if I see this now recollect what I was trying to tell you this is a situation where the impure blood or carbon dioxide rich blood which is coming to the lungs has to throw away the carbon dioxide from the blood to outside the body and that thing will take place through the alveolar ventilation passage. So, essentially that means the partial pressure of carbon dioxide inside the impure blood vessel should be higher than the partial pressure of the alveolas where the exchange is taking place then only it is possible the carbon dioxide will move from a higher partial pressure to a lower partial pressure and vice versa in the case of oxygen because these RBCs will have to pick up the oxygen that is only possible when the partial pressure of oxygen inside the alveoli is much higher as compared to the partial pressure of the RBCs of oxygen and from the higher partial pressure they will move towards the lower partial pressure. This is the basic basic fundamental thumb rule which you have to remember as long as this fundamental one because this whole thing revolves around partial pressure as long as this simple concept of partial pressure is clear to you rest is all cake walk rest is all kind of you know technical details which you are feeling it to understand, but soul the governing dynamics of this whole gaseous exchange revolves around this partial pressure and solubility and I will be enumerating this just to give you an flare so that so let us summarize what we have done we talked about the nose from the nose you inhale then there is a trachea trachea bifurcates into two parts like this and one for the left lungs another for the right lungs inside the lungs they have much more further distribution eventually they form they end up with forming a big sac like structure which is called alveolus which are in closest proximity with the blood capillaries or the blood vessels which are entering the lungs to oxygenate the blood. So, this is the overall I should say the anatomy and the visual picture which people need to get in your mind that and as I told you and this whole thing is governed the governing part of this if this is the structural part of it the functionality is been determined by the simple thumb rule of partial pressure these two concepts just have a picture in your mind we are inhaling it through the trachea trachea bifurcates into several distribute trees and at the end it form a almost around one micron thick membrane which is the alveolar pulmonary membrane or alveolar membrane what is it we call which is what we call that it is a very huge surface for gaseous exchange and they are in close proximity with the blood vessels and from the blood vessels within the blood vessels you have these RBC's which throws away the carbon dioxide and picks up the oxygen and that is all taking place in the alveoli so and that is because of the partial pressure. Now, let us get back to some of those technical details what we need to know with this basic understanding let us move on to news light and let us talk about the factors determining the rate of so what we are going to discuss now I partially discuss this but now I am just formalize the whole factors determining the rate by which gas is exchange across the pulmonary membrane the rate at which gas diffuse across pulmonary membrane across pulmonary membranes. So, there are two factors which governs that first factor is the diffusion coefficient of the gas factor one diffusion coefficient what we meant by diffusion coefficient of the gas that means the measure of how easily the gas passes through membrane basically diffusion coefficient could be termed as a measure of how easily a gas passes through membrane. So, that is called diffusion coefficient the second factor which is involved in it factor two is the area and thickness of the membrane where the exchange is taking place area and thickness of the membrane where gaseous exchange is taking place exchange is taking place and the third most important factor one of the most important factor is the partial pressure which I was explaining just few minutes back of the gases on either side of the membrane. These are the three factors which essentially determines that how the gases are going to diffuse across the membrane always remember that partial pressure gradient rather than concentration gradient this is another way important rather than concentration gradient provides the driving force provides the driving force for diffusion across air liquid interface. This is important for you people to understand what is air liquid interface basically when the gaseous exchange is taking place it is essentially taking place the lungs the alveolus what I have explained and the blood vessel is in the liquid phase all the blood are in they are in a liquid phase where the RBCs are flowing through whereas air phase is the alveolus. So, at that zone that unique zone of air liquid interface it is completely driven by the partial pressure as compared to the concentration gradient it is the partial pressure gradient which dictates term at that zone. So, coming back to some of the other basics what need to do we will talk about now we will talk about the structure which I did not complete at that time. So, this is basically how the structure of the airways look like. So, this is the trachea start off with starting off with trachea structure is something like this if you look at any anatomical book it is like you know which are expandable these are arranged in such a way these they can move back and forth and then they split up into two and from here they entered each of the lungs which I drew then sorry the further bifurcate keeps on bifurcating mirror and then eventually what happens as they and they become thinner and thinner as they keep on bifurcating then eventually they have this kind of structure which are called alveolar duct or alveoli alveoli sorry for the interruption in between also slight error glitch. So, coming back to the structure of the trachea I did not really go in depth I told you I will just I will show you how it looks like. So, let us look at it how it looks like. So, this is basically the trachea how it is and you know it looks like if you go through any text book it will be looking like this it is basically those of you have seen like you know one slide slide over another cylinder another cylinder another cylinder their slides over each other. So, that they are flexible because they had to with this time I mean handling fast. So, the the the airways have to you know move back and forth. So, it is kind of a sliding kind of structure it is like cartilaginous kind of a structure. So, it looks like this. So, then this trachea bifurcating into two and then these are called bronchus and you must have heard this bronchitis somebody is saying bronchitis basically it is the blockage on those airways. Then you have something called and they keep on you know splitting splitting and splitting and splitting and as they keep on splitting into smaller narrower and narrower narrower diameter. The thickness also keeps on reducing and by the time if they become the alveolar duct the thickness is almost around 1 micron it is that level, but simultaneous surface area goes like I mean crazily huge surface area where it takes place. So, here you have the alveolar duct and these are the alveolus where and essentially what is happening the blood vessels are coming through like this they are moving through like this. So, this is the zone where I was telling this is the zone of pulmonary membrane where all the exchange of gases is taking place the CO2 and oxygen and everything is taking place. This is the critical zone where this whole process is taking place. So, coming back to some of the thing what about the. So, if you look at it the this something which will strike you if you look at this whole thing this whole process there is no exchange taking place is hardly any exchange there is no exchange of any gases here it is only out here, but yet this passage is always filled with gas. So, this that is why this passage where the gas which is stored it is called anatomical dead space or anatomical dead volume basically it is represent by V d anatomically dead volume this is not really important and this is the zone where it is taking place this is called alveolar volume this is the amount of gas what is being exchange approximately there are even more than 300 million alveoli or even way more than that actually I am just giving an approximate number and if you look at the geometry of the alveoli there is it has a thickness of thickness of alveoli is 0.1 to 1 micron thick depending on which location it is this is the thickness of alveolar membrane and it has a huge surface area almost 80 meter square it is a kind of thing. And there are two more things where I wish to highlight here some of the pathological situation which you may hear sometime they call it when we will be covering this anyway just to give you a flare you hear about pulmonary edema. Pulmonary edema is basically anything edema means swelling or something. So, pulmonary edema is a common disorder which takes place in high altitude especially in region where the oxygen tension is very low especially along the northern frontiers of India along lay, Ladakh, Sikkim and the north eastern areas of India along the high altitudes of Himalayas oxygen is fairly low and this is the place where because of low oxygen it leads to hypoxia and the pressure is also low. So, which leads to a hypobaric condition bar means the pressure hypo means low. So, these are the zones which has hypobaric hypoxia low pressure and low oxygen and low pressure and low oxygen on top of that a low temperature fairly low to below freezing temperature at times leads to something called pulmonary edema. I will come to the pathology while we will be talking about high altitude disorders and aviation and everything, but during pulmonary edema one of the thing which happens is that what I told you I told you that point 1 micron to 1 micron the thickness of alveolar that thickness increases. So, once the thickness of that alveolus increases the exchange of gases takes place slowly. So, these person suffers this kind of situation happens with these people they cannot breathe properly and as a matter of fact most of the soldiers who are stationed in those high altitude suffers from pulmonary edema. So, they have to be you know habituated before or they could be condition they have to be condition before they could be stationed in those high terrains of Himalayas for a longer period of time. Otherwise you have a shortness of breath and all those kind of complex situation there is another side of it there is another disorder called pulmonary. So, if this is pulmonary edema and I request you people please go through online and check these are some very common disorder in high altitude and there is another called pulmonary emphysema emphysema. So, pulmonary emphysema is basically the rate of diffusion in the lungs for x y's it reasons may be pathology may be some other reason may be some physiological reason. The diffusion across the pulmonary membrane goes down very sharply. So, these are the situation when essentially what is happening think of it from a very global perspective whenever this gaseous exchange is going down. In other word your body is not receiving sufficient oxygen and it is unable to throw away the excess carbon dioxide and that leads to suffocation and under extreme situation that may even lead to death of an individual. So, these are some of the things which you people need to understand by just by think over it. I mean these are the small pieces of information which will help you to think over it and let us move on to with this overall idea about you know we are inhaling the air passing through the trachea moving to the bronchioles from the bronchioles it moves through the alveolar duct to the alveolus where alveolus is in contact is in close proximity. If this is the alveolar membrane if this hand is my alveolar membrane and this is the capillary membrane of the blood there is in close proximity and this is where all the exchange of gaseous is taking place along these two membrane. On this side on the capillary side you have this RBCs which are present there which are carrying carbon dioxide rich blood through the carbon dioxide and picks up the oxygen. Now let us come back to the diffusion aspect of diffusion constants of oxygen and CO2. So, there are two aspects which determine there are two factors which determine the diffusion. One is the solubility of the gas obviously solubility in the air in the in the water obviously solubility in the air in the in the water and the second thing which is determined is the molecular weight. So, these are the two factors which governs the diffusion constant of the different gases, but let me tell let me give you a very interesting fact on that if we talk about oxygen and carbon dioxide think of it and I told you I gave you two situation, but if you look at it if you look at the literature you will find carbon dioxide diffuses 20 times faster than oxygen. Now look at carbon dioxide and look at I told you I gave you two situation solubility of the gas and molecular weight let us look at the molecular weight. So, molecular weight wise let me go back molecular weight wise the one which is having higher molecular weight will diffuse slowly because it is heavy fine something which is heavy moves slowly whereas, something which is light moves fast. So, theoretically carbon dioxide should move slowly as compared to oxygen, but there is another aspect called solubility of the gas in water in any kind of moist water medium. So, which is more solubility. So, coming back here so this it has been observed in terms of the diffusion this is almost 20 times more easily diffusible than oxygen. Though the molecular wise this has an additional weight molecular weight of carbon as compared to oxygen is there, but then the advantage of CO 2 is that it solubility is phenomenally high and it solubility is so high that it out smarts the higher molecular weight as compared to oxygen and diffuses much more faster as compared to oxygen. So, always remember these things there are different factors and they are intricate and you have to understand it and you might ask another question that in the year we talk about nitrogen. So, nitrogen is not really taking part in any kind of gaseous exchange in our body. So, we are not taking nitrogen into consideration. So, what I will do is this with this brief background of overall idea about how this whole respiration process is taking place. I will close in here and in the next class we will talk about two aspect of it. One aspect will be the partial pressure of oxygen, carbon dioxide and water vapor. With respect to the total partial pressure as I told in the beginning of the class I expected people to read this Dalton partial pressure Dalton's law of partial pressure because that will help you to appreciate it and then what we will do that will be the part one. So, we will see what are the partial. So, the way we will be dealing in the next classes we will have the values will calculate the values of the partial pressure of oxygen carbon dioxide or water vapor of the air which we are inhaling. Then what we will do we will measure the partial pressure of the oxygen and carbon dioxide with the blood vessels are carrying and I told you in the beginning the wherever for x y z except for gas oxygen. If the partial pressure of oxygen is higher in the inhaling air as compared to the partial pressure of oxygen in the blood vessel then oxygen will diffuse from high partial pressure to low partial pressure. So, for that we needed all these values. So, we will calculate all the values that is the first thing we will do and we will compare in a chart that this is what we are inhaling and this is what we are throwing out and this is the partial pressure of the oxygen and carbon dioxide in the blood vessel and then what we will do we will try to understand the mechanism. So, first of all we will understand this dynamics we have done with the anatomy now and little bit of the gas introduction of the different gases and the partial pressure and the factors which are determining it. Next we will talk about the gaseous exchange and along with it we will talk about how exactly carbon dioxide sorry carbon dioxide and oxygen are being carried by hemoglobin. What is that chemical association or dissociation which regulates this oxygen binding to hemoglobin and under what condition hemoglobin rejects the carbon dioxide which are present which is present there. So, and then we will talk about some of the pathological situation when this situation is being compromised. Thanks a lot.