 So, welcome back to NPTEL lecture series on animal physiology. So, we are in section of the respiratory physiology. So, we are done with the first two part of this section. So, today it will be exactly dealing with the exchange of the gases in the alveoli. What is the partial pressure of the gas inside the alveoli? So, what is the partial pressure of the gas outside and then we will be talking about some of the centers in the higher in the brain stem which controls the respiration. So, before I get into the lecture. So, let us talk about the basic mechanism or basic outline what is governing the process. So, what is essentially happening is that when the blood is saturated with oxygen which is being pumped from the heart to the rest of the body it travels and download the oxygen in the various respiration various cells and tissues. And while it is downloading the oxygen the blood cell picks up the carbon dioxide. So, while this blood is traveling which is loaded with oxygen to all the different tissues it downloads the oxygen which is consumed by mitochondria for production of ATP and cellular respiration. And during that process it picks up the carbon dioxide and this carbon dioxide is then brought back to the heart through the venous vessels and then it is being sent to the lungs for downloading that carbon dioxide and again end ranges of blood with oxygen. So, what essentially happens if you look at the concentration if you see the first lecture where I started the concentration of carbon dioxide in the air is fairly low it is very low. Whereas, the blood which comes back to the heart from all over the body through the venous vessel and which is sent to the lungs is fairly rich in carbon dioxide. And the partial pressure of carbon dioxide inside the blood vessel is very high as compared to the environment. So, automatically by the simple logic of partial pressure one which is at high partial pressure will flow down the gradient. So, if it is outside it is less than the carbon dioxide will be ejected out from the system that is what exactly happens carbon dioxide is being ejected out from the system. Whereas, in the case of oxygen what happens since this blood which is coming is devoid of oxygen. So, level of oxygen in the blood vessel at that point of time while it is going to the lungs is fairly low and oxygen partial pressure in the environment is high. So, automatically down the gradient what will happen the oxygen which is outside will be pulled inside the system and that is how it works the oxygen comes in and then again this blood becomes laden with oxygen filled with oxygen or oxygenated blood comes to the heart and from there it is being pumped all over the body. This is essentially what is happening in the whole process of a respiration and this is how the whole respiration system works. It is a simple partial pressure shift and the other gases which are in an environment does not really matter because they do not do any important physiological function. So, so they are binding on non binding does not really affect our whole process. So, what I will do now I will what I have explained now I will just diagrammatically put it. So, that that kind of gets engraved into your understanding and it will help you to analyze this case much more better. So, let us coming back. So, we are in section 7 lecture 3 respiratory physiology. So, the blood which is coming in the pulmonary capillaries. So, this is what I am representing as the pulmonary capillaries and I will use another different color to show you the alveolus which is in closed conjunction with the pulmonary capillaries. So, what is happening here is the venous blood which is coming whole special oxygen pressure p o 2 is around 40 whereas, p c o 2 is around 45 p is the partial pressure. These are the pulmonary capillaries now within the pulmonary capillaries here. So, here you have the alveolus this part which I am highlighting in green is called the respiratory membrane. It is essentially happening on this side your p o 2 is 100 partial pressure of oxygen is 100 and partial pressure of c o 2 is 40. So, if you now compare these values now here I am comparing p c o 2 out here and p c o 2 here. So, by the gradient carbon dioxide will move to this side because there partial pressure of carbon dioxide in alveolus is 40 and partial pressure here is 45. And by the same token the other side what will happen here you see partial pressure of oxygen is 40 inside the capillaries and partial pressure of oxygen in the alveolus is 100. So, automatically this oxygen will move into the capillaries. So, this is how the external respiration is taking place. So, there are two levels of respiration this is the external respiration. So, this is one part I have not introduced. So, just let me come back. So, whenever we use the word called respiration it immediately comes in mind that this is the exchange of gases which is taking place, but there are two level of respiration. This is an external respiration where you are taking the gross gas into your body and you are throwing out the gas which is undesirable for the metabolism or functioning of the body. But there is another level of respiration that is called cellular respiration or internal respiration that is the zone where this very gas which you are picking up from outside is being picked up by the different cells. So, at that zone. So, this is basically what is happening this first phase of external respiration is through the pulmonary circuit from in that situation it is the venous blood which reaches the heart and from there it is being sent to the lungs for purification and this is what I just now drew for you people that is basically essentially the external respiration. But now what I will draw with respect to the partial oxygen pressure and partial pressure of carbon dioxide will be the cellular respiration. So, just for your little bit more so basically what we are talking about now is we are dividing respiration into two parts respiration this is the external respiration in the pulmonary circuit external and this involves pulmonary circuit then there is an internal which is in the systemic circuit these are the two classifications of respiration. So, we have already done with the this part we have talked about this aspect now what I will do I will talk about the internal systemic circulation what is exactly happening in the next slide let us move on to the next slide. So, the blood which formed in the capillaries in the sorry in the in the pulmonary capillaries that blood has a partial oxygen pressure p o 2 which is equal to 100 and p c o 2 is equal to 40. Now, from here this is moving into the systemic capillaries now this is the zone from where so it came to heart and from there it was pumped now it is travelling in the systemic capillaries. So, these are the systemic in the systemic capillaries partial pressure of oxygen is around 95 and partial pressure of c o 2 is 40. Now, here is the equation where this blood which is travelling in the systemic capillaries has to be downloaded into the different tissues which are different cells and tissues which are present these are the different cells and tissues in the surrounding vicinity we are talking about these cells and tissues will be needing oxygen the partial pressure of oxygen in the interstitial fluid. So, this is we are in interstitial fluid. So, partial pressure of oxygen here is 40 and partial pressure of c o 2 is 45 this is just the reverse situation. So, what will essentially happen? So, c o 2 here if you compare these two values. So, c o 2 from here will start moving into the systemic capillaries whereas, if you look the other side of it which is partial pressure of oxygen and partial pressure of oxygen in the interstitial fluid. So, oxygen will be downloaded out here. So, the movement of oxygen will be from the systemic capillaries to the tissues and the movement of carbon dioxide will be from the interstitial fluid and to the systemic capillaries and this eventually this is the venous blood which is rich in c o 2 comes back to the heart again from here it is being pumped to the lungs and there it is getting purified and this is what you see is now trickling down. So, this is how the whole circulation continues and this is the part of the pulmonary circuit. So, this what you can say at the overview of the respiratory process and partial pressure during respiration so this is one of the key things which I wish to discuss with you people and from here what I will do I will move on to the control of respiration. So, we are done with the partial pressures and everything there are certain areas which if you are interested you may cover the respiratory mechanics when we are inhaling, excelling what are the different diaphragm movement which are taking place which I am not covering out here, but you are most welcome to go through a C guidance book or some other standard text book physiology which will give much in depth on this, but this is the basic fundamental understanding of respiratory physiology what I expect you people to understand. So, from here what we will do we will move on to the different control centers of respiration. So, most of these processes are very tightly controlled by the brain system and the higher centers of the brain otherwise it becomes really challenging because we have to adapt to different kind of situation sometime we are in a situation it is a fairly you know is sufficient oxygen and we can do a lot of you know gas exchange is fairly smooth yet there are situations when we reached a place where oxygen is deficient carbon dioxide is right or in a very damp place. So, we have to continuously regulate our respiration process and the body has to continuously adjust to this because if it fails to adjust then what will happen is this the buffering of the body will be compromised oxygen carrying capacity will be compromised and cellular metabolism will be compromised and essentially what will happen there will be a shift of homeostasis in that whole process. So, that is why these things are extremely essential to you know kind of has to be controlled in a very tightly regulated fashion. So, what we will do now is that I will talk about some of these control mechanism which will help to you know understand how exactly this local regulation are taking place in the respiration. So, let control respiration control of respiration. So, respiration control so on on the major thing what involves is that. So, the peripheral cells are continuously absorbing oxygen that we have already discussed from the interstitial fluid and generate carbon dioxide under normal conditions the cellular rate of absorption and generation are matched by capillary rates of delivery and removal. So, these rates are identical to those of oxygen absorption and carbon dioxide excretion at the lungs fine. So, what essentially is happening is the change in the blood flow and oxygen delivery that are regulated at the local level. So, essentially what is happening is that change in just presenting it is a change in blood flow oxygen delivery that are regulated at the local level local level and second is change in the depth and rate in respiration control of another control of the respiratory brain's respiratory centers. So, talking about the local factors which are involved in it one of them includes the local factors includes lung perfusion or in other word this is also be called as blood flow to the alveoli. One of the factor the second factor which is involved in that is alveolar ventilation which is basically the air flow over wide range of conditions and activities what does this essentially mean. So, this essentially means is the suppose we are in a situation when there is lack of oxygen in the environment and we need to take more oxygen. So, the first thing what is needed here we should have more and more blood flows to the lungs. So, that is what I meant by lung perfusion the more blood goes what is our oxygen is there in environment you can pick it up because you are exposing your system to more and more oxygen exposure. The second thing what is alveolar ventilation I told. So, if there is less oxygen we all always say take a deep breath. So, essentially what you are doing you are taking a lot of air into the system. So, what is our oxygen is available you should be able to pick it up why is our in the reverse situation there is you know excess say in like you do not have to bother. So, you are kind of you know you are slow you do not have to bother like I am in a room where which is proper oxygenated and everything. So, I do not have to bother, but if I am in a situation say high altitude. So, one of the classic situation is in high altitude situation why in high altitude let us talk about what is happening in a high altitude situation. So, as you go up. So, you meet a situation something like hypobaric hypoxia. So, essentially that means these are less in oxygen and the pressure is low air pressure is low because anyway as you are going up into a into a mountain or something places like Machu Picchu in Peru or Mexico city or places Ladakh and Leh. So, this is the situation when you are exposed to a low oxygen tension. So, the oxygen as you are going up then atmosphere is becoming rarer and rarer as it is the gas thing is reducing and you are exposed to a low oxygen automatically the carbon dioxide is also getting reduced. So, you are in a low oxygen situation. So, what you will do essentially the best thing you have to do is have to inhale slowly first in that process you are increasing the ventilation and in the meantime what brain will do the higher centers of the brain they will ensure that there is more and more circulation of the blood into the lungs. So, you are picking in picking in as much oxygen as possible. So, these falls under the local control now what we will do after talking about the local control I will move on to the respiratory centers of the brain. So, moving back to the respiratory centers of the brain. So, among the respiratory centers of the brain. So, what is essentially happening is this. So, think of a situation where say for example, this is a quiet breathing situation. Let us take two studies and two cases that will help you. So, here there is a quiet breathing. So, during quiet breathing this is start from somewhere inspiration you are in you are taking in air inspiration occurs. This is followed by dorsal respiratory groups inhibited. Inspiratory muscles relaxed relax then next thing which is happening is the passive expiration occurs followed by dorsal group dorsal respiratory groups. So, it is activated active inspiratory muscle contracts inspiratory muscle contracts and the inspiration takes place. So, this is what is happening in a inhalation which last for around two seconds and exhalation which last for around three seconds. So, this is the pattern of during quiet breathing. Now, what is happening during force breathing now when I am doing like this. So, this is a situation I am taking in lot of air. So, during force breathing the whole mechanism takes a slightly different route. Let us talk about what is happening during force breathing. So, during force breathing basically your d r g dorsal respiratory group and inspiratory centers of v r g v r g stand for ventral respiratory groups are inhibited essentially happen this is there. Inspiratory centers of ventral respiratory groups are active. So, you see ventral respiratory group now comes into play. Now, inspiratory muscle relax inspiratory muscle relax and expiratory muscle this is ex is expiratory INS is inspiratory muscle contract. So, and this leads to active expiration. So, there is an active expiration followed by again the reverse events now will take place as I was drawing the other side. So, d r g and inspiratory centers of v r g are active whereas, expiratory centers of v r g are active. Inhibited followed by your inspiratory muscle contracts inspiratory muscle contract and expiratory muscle relax this is where inspiration takes place again followed by the sequence. So, this is the situation of inhalation and here you have the situation of exhalation. So, this is a case of force breathing and regular breathing and this whole process is regulated both at the local and at the higher centers of the brain. Now, we will go and I will give you the out light or the diagrammatic representation of the brain stem the centers respiratory centers which are controlling or coordinating this whole process. So, that you know our homeostasis is being maintained let us talk about the brain stem centers. So, this is what essentially it looks like this is the brain stem we are talking about this is the pituitary the chemoreceptors coming in these are the stretch receptors coming in. So, these are the chemoreceptors and baroreceptors or carotid arteries chemoreceptor and baroreceptor of carotid arteries and iotic sinuses. So, these are the stretch receptors of lungs stretch receptors of lungs which helps the lungs to you know expands out and the this is your spinal cord here you have the different centers which includes pneumotaxic center these are the centers which are regulating under the influence of the higher centers of the brain pneumotaxic center. So, this is the brain stem with where I am putting this pneumotaxic center here you have the pons apneostic center what I drew just now to show that inhibitory and supporting circuit apneostic center these signals which are coming in either inhibiting the pons or regulating the pons regulating the apneostic centers and here you have something called CSF chemoreceptors and there are 2 nuclei here 1 nuclei is called dorsal root of ganglion or sensory neurons which you have talked about the other group is called ventral ventral respiratory group or VRG's ventral. So, these are the ones which I just now talked in the previous slide and these are also called under the heading respiratory rhythmic center respiratory rhythmicity center. And what you saw this sign I am putting that is basically for inhibition and whenever I am putting an arrow this is mean stimulation. So, these are the motor neuron which are coming through the ventral root which are motor neuron, motor neuron controlling diaphragm one of the things the motor neuron controlling respiratory muscle there are multiple job these motor neurons have and apart from it there are motor neuron. So, there are higher centers. So, this is what is basically the brain stem where we are talking about and behind the brain stem out here. So, out here what you see is the medulla oblongata highlighted part what I just now and from the higher centers of the brain are being controlled. So, these are the cerebrum and these are the higher centers of cerebral cortex limbic system which includes the hippocampus limbic system and hypothalamus. So, these are the different centers which are regulating this whole process out there. So, this is a complex circuits which brings up you should call it like something like pacemaker kind of thing is setting up the pace of the system and this all when I was drawing this respiratory respiratory rhythmic city centers is basically what that means you are setting the pace of the system whenever the lungs have to stretch those can control whenever the lung has to be in a normal condition they can control. So, it is totally under the control of the very higher centers of the brain including the limbic system which includes your hippocampus and the surrounding part of the brain they are controlling the hypothalamus and from hypothalamus it is the signals are being sent to the brain stem along the just behind it the medulla oblongata. So, essentially that is why it is being said on the back part of the brain you can actually make somebody unconscious or you know you can hit somebody badly here a person may die they may die because if I hit something like if you think of it say for example, a situation like this say for example, a person is getting a hit out here somewhere a hit like this. So, essentially what you are happening this hit is influencing this whole region and that is why what I was telling you that a hit like that could lead to a death of a person or somebody become unconscious because of that hit. So, it is just out here in the backside of the brain when the brain stem is sitting which is controlling by the controlled by the higher centers of the same. So, this is pretty much what I expect that you guys go through. So, Geiten has given a fairly good AC Geiten book has given a fairly good description of it and that will be a big help to go through it, but this is the overall outline of the different centers of the brain which are controlling the pons and pneumotastic centers and apnoistic centers in the brain stem controlled by the higher centers. So, that pretty much wind up our respiratory physiology section. Thanks a lot.