 Welcome back to the course in animal physiology in NPTEL. So, we are into the section 4 and this will be the third and the final lecture of the section 4. So, in this section we are talking about the circulation process. So, we have already discussed about the different vessels, their cross sectional area and how the pressure changes, how it is flowing once the blood is being pumped from the heart. So, if you remember when we drew the first overall outline of this section, we talked about the blood is flowing from the arteries to the arterioles, then through the capillaries to the venules and to the veins. And we talked about the cardiac output and the pressure differences and in the section of the can we talked about that we will be discussing the hormonal and neural control of this whole dynamics at some other point, while we will be talking about once we are finished with the neural and the hormonal part of it. So, today we are going to deal with this part the capillary and the capillary exchange. So, before I move on to the capillary and capillary exchange, while talking about all the different pressures what we have talked about, I just wish to ensure that you people are aware of anometer. This is the one which is used with doctors to measure the pressures and the pulse, just to update you on that once some of you are not aware of it. It is a simple device you have seen the doctor kind of put it there and kind of check your pulse and everything. So, this is the device which is being used, it has a valve which can see the undulation of the blood vessels and it can measure and it can hear to the noises and can give a whole bunch of informations. And you talked about that what we have talked about all the four sounds and everything is being done with this finger manometer. So, along with the stethoscope attached to it. So, now we will move on to the capillary exchange. So, let me give you before I get into any technical detail, let us see a practical situation. So, that will help you to appreciate this problem much better. So, whenever you have say for example, you know honey bee bites you or some kind of you know was bites you, you see there is a swelling at some point or other wherever it bites you see a swelling. Why there is a swelling? Did you ever ask this question and invariably people or the doctors or some learned person also there is an inflammation. So, that is why there is a swelling. What really is that swelling and if you go to the doctor, doctor will use a technical terminology called edema. It is a edema likewise and if you go through the dictionary it is the accumulation of fluid is called edema. So, why that edema occurs or why that accumulation of fluid occurs whenever there is some kind of you know insect bite or was bite or honey bee bite or x y z situation. You know there could be many other pathological situation, physiological disturbances during which it happens, but overall in a normal condition like I am standing here. I do not have any edema or any kind of inflammation at any point or any kind of you know fluid accumulation at any point. So, then what is this fluid accumulation? Why there is a fluid accumulation? Because if you realize while talking about. So, this is something people have to realize first before I get into the technical details of these definitions formulae and all those things those comes later. What is the first thing you have to realize that there is a philosophical understanding of the problem and that is very critical for you people to appreciate. So, if you look at the blood vessels and if you look at the way our network of blood transport is being designed. So, what is happening from the heart the blood is pumped out through the vessels it moves along the arteries and at the capillaries there is a exchange phenomena taking place. So, all the oxygenated blood is downloading the oxygen to the different tissues and from those tissues or cells it upload the carbon dioxide into the vessels and from there it comes back through the venules and the veins and the vena cava back to the heart. So, it is kind of a closed loop system which is continuously flushing every component. So, for example, this is me. So, from here like you know the blood is moving all over all over the hands all over the legs all over the body across the brain and everywhere and it is continuously flushing it out. So, there is no room that any. So, whenever this flushing will stop it is just like in your say for example, in your community or in your colony or wherever you are staying there is continuously there is a sewage or sewage line which is continuously flushing out all the things which are being dumped from your house or x y z houses. So, whenever there is a accumulation of fluid taking place it means there is some kind of a leakage in some kind of a vessel and this is very critical. There could be two three possibilities either there could be a leakage or there could be an abnormal situation by which the flow is cannot be cannot ensure that everything is being flushed out. This simple understanding is very essential to understand the capillary exchange process. So, as of now nice if I go back when I am repeatedly telling you that you know at the capillaries like if this is a capillary network imagine this is my cap this is the capillary network where I was drawing that if imagine that this thumb one of this thumb is the artery and this thumb the other thumb on the other side is your vein. So, from the arteries it is coming and the capillary the exchange is taking place. So, what ensures that carbon dioxide will be taken up by this capillaries and oxygen will be given out by this capillaries. What ensures that some of the solutes which are present there will be given out and some of the toxins which are present there will be taken in. What are those forces or what are those physical phenomena which dictates all that thing? So, in order to discuss this I will take you back to my lectures in memory and physiology section. There we talked about some of the forces if you remember we talked about osmosis one of the forces we talked about diffusion than other forces. So, if you remember in the diffusion I told you that basically from higher concentration to lower concentration. Say for example, you have lot of sugar out here and lesser sugar here in solution. So, from the higher sugar the sugar will try to diffuse to the lower concentration of sugar. Then we talked about filtration about filtration we talked about there should be a pressure difference by which the filtration will take place. We talked about osmosis and even in the last class also I told you the how to measure the osmotic pressure. So, if you remember I showed you that U tube on a U tube I told you that you know not the U tube U tube what you talked about in the net. This was the U shaped tube I showed you that from one side there is a semi permeable membrane in between and you are filling water on both sides and water can pass through the semi permeable membrane without any problem. But the condition is that the solute cannot pass through. So, if you have a higher concentration of solute on one side one arm of the tube as compared to the other arm of the tube. So, the solute concentration the side or the arm where the solute concentration is higher water molecules will try to move more towards that. And if you want to create a potential difference if you want to balance the potential difference somewhere or other then you have to give an equal and opposite force which is in the form of hydrostatic force. So, these are some of the forces. So, let me enumerate diffusion 1 filtration 2 osmosis 3 these are some of the forces which dictates and we will come to the different values which will help you to appreciate why oxygen is being downloaded carbon dioxide is being uploaded and all these features. So, these are the simple basic forces which ensures that the exchange takes place. Now, coming back where I started this I ask you like think of a situation when there is a fluid accumulation during fluid accumulation. What happens is that the permeability or because this is happening ensuring that the vessel permeability remains constant you are not you cannot change all the parameters you can change one parameter and you can read study the other parameters. So, because of x y z conditions the vessel permeability changes it mostly happens and I will again reiterate that at the end of the discussion when I will talk about all the forces. So, what happens whenever a toxin whenever a wasp or a honey bee or an insect bites it secretes certain toxins into your blood vessel and the toxin from the arteries travel all the way to the capillaries or from the veins it may go to the heart and comes back to the capillaries where the actual exchange taking place. And at the capillary what it does if you again recollect the structure of the capillaries it has fenestrated capillaries we have you know continuous capillaries and all. So, at the capillaries what it does it binds to the wall of capillaries and change the permeability or the exchange phenomena. And by virtue of which the body loses or not the body the vessel loses some of the more water which cannot take up. And if you if I take you further back in my lectures in memory and physiology if you remember I was telling you this there are toxins which can make channels. If you go back in the memory and physiology lecture you will see I talked about some of the valeno mycene gramacydene. And in that section while I was showing you then you know there are circular peptides which can form channels through which the water molecules can pass in and out. And I talked to you about the gramacydene and I specifically remember I drew the structure of valeno mycene gramacydene. And I talked to you that there may be a series of toxins, toxins, antibiotics which has the ability to form a pore along any kind of a membrane. And that is exactly what a toxin does when the toxin travels at the capillaries where the wall is much more I should say much more thinner because you know it is almost a single red blood cell it is around 8 micron. If you see your the dimensions which I have already taught you people. So, at 8 micron diameter basically it is almost one cell thick membrane like this. So, it creates holes along it. So, now what we will do we will come back to this you will be able to appreciate it much better once I tell all the forces which are involved. And the generic calculation based on that what I expect from by the end I in x 15 20 minutes once I am done with all the forces what I expect is that whenever you see a edema whenever you see a accumulation of fluid immediately these forces should come into your mind. What are the filtration forces what are the osmotic forces what are the diffusion forces what are the reabsorption and everything this should come straight without even a second thought it should be your second nature it should be able to immediately pick it up. So, it is basically these forces which are playing a role and based on that you should be able to you know at least have some form of Lehmann diagnosis into the situation. Now, let us enumerate the forces which are involved in the capillary exchange capillary exchange. So, the forces what we will be talking in this capillary exchange will be your diffusion filtration second force you have the reabsorption and it is basically the inter play between filtration and reabsorption is the inter play of this which regulates the exchange of the fluid across the capillary membrane. So, just to give you some of the some of the numbers and so one more thing which I actually did not mention. So, I thought I better discuss that first. So, whenever I showed you I have shown you this diagram. So, this is the one side is the capillaries sorry the arteries artery holes and on side is the venules and here is the exchange zone taking place at this exchange zone along the blood vessel there is a parallel vessel which runs that vessel is called lymphatic vessels will come to this lymphatic vessels while we will be talking about the white blood cells and the immunity. So, how it looks like physically is let me draw this will help you. So, if this is the artery side of it and this is where. So, this is the network of the capillaries. So, this is the capillary network the red is from here the venule network is picking up. So, the blood is coming like this and. So, these are the artery holes and these are the venules. So, the blood is coming from the artery hole side and here is the exchange taking place. So, let us represent the exchange by different arrows here is the exchange zone. So, at this zone there is a parallel vessel which is running and I will represent the parallel vessel in black. So, that you can distinguish it something like this this vessel equally has a very very fine mesh network. This whole network is a parallel system along with the blood vessel which is called the lymphatic system this run parallel. So, whenever there is a fluid which is being given out and this space which is in magenta this space is called interstitial space interstitial space and this black one is your lymphatic vessels. So, whenever there is a fluid which is coming out from the capillaries it is being reabsorbed by the lymphatic vessels and this is how the blood it is being insured by the body the fluid does not get accumulated. So, as a matter of fact almost about approximately about 3.6 liter of fluid flows out of capillaries to the lymphatics to the lymphatics lymphatic system which is further further this lymphatic system what it does it brings the blood black to the blood vessels. This is very very important for to understand that there is a continuous interplay of lymphatic system and the capillary system interplay of lymphatic system capillary system. And what it leads to this interplay of lymphatic and capillary system ensures that there should be a continuous flushing flushing action which will continuously flush all the tissues. It assist in transport of very large molecules which otherwise cannot be really transported which otherwise cannot be really transported this is the process which accelerates the rapid exchange of nutrient. Moreover it is the exact interplay between lymphatic this is the balancing of the lymphatic and the capillary vessels which ensures that we do not suffer from any kind of fluid accumulation or any other kind of situation. So, this is very very important for us to appreciate. So, these are some of the major functions is a part of the interplay of lymphatic system and the capillary system. From here we move on to all the forces what we have already discussed now we will come to the exact value. So, I am not again describing all the forces because I have already done that. So, now what I will do I will redraw the vessel and I will highlight the different forces which are involved there. So, this is the blood vessel let me draw it in a way so that it makes. So, this is the venial side so this is the arterial side it is taken and this is the venial side. So, here you have the arterial so blood is coming from this direction entry of the blood into the capillary network and this is the venial and imagine this zone is the capillary network zone. This zone is the both arrows I am showing is the capillary network zone. Now, there are two three terminologies which I am going to come and let me the first terminology is NFP net filtration pressure. So, we will be measuring the net filtration pressure at three different zone at the beginning of the capillaries the middle of the capillaries at the other end of the capillaries where. So, if you look at at the three zones if you look at it. So, this is the zone where capillaries involved in giving away oxygen because this is oxygen rich blood which is coming and this is the zone where capillaries are taking in carbon dioxide from the surrounding tissue these are the two zones. So, how it does so? So, before we understand this we have to realize the capillary hydrostatic pressure. So, I have already talked to you about this hydrostatic pressure. So, remember that when you put an equal and opposite pressure in that you know you you tube kind of things where I showed you that you put an you give an equal and opposite pressure against the osmotic pressure that is the hydrostatic pressure. So, what are the hydrostatic pressure capillary hydrostatic pressure or the hydrostatic pressure of the capillaries is called capillary hydrostatic pressure it varies from 35 millimeter mercury to 18 millimeter mercury in the capillary zone. So, at the beginning. So, the capillary hydrostatic pressure at this zone is. So, let us represented by C H P capillary hydrostatic pressure at this zone is 35 millimeter mercury capillary hydrostatic pressure in between out here is approximately 25 millimeter mercury C H P capillary hydrostatic pressure and at this fog end where it is meeting the renewals capillary hydrostatic pressure is equal to 18 millimeter mercury. These three values are exceptionally important and all along this point. So, there is see if I talk about the capillary hydrostatic pressure there is another pressure which is coming into play which is called colloidal osmotic pressure. So, colloidal osmotic pressure which is out here is remains constant and all throughout that is almost out here look at it colloidal osmotic pressure is 25 millimeter of mercury. And if I had to now. So, this is basically bulk colloidal osmotic pressure B C O P. So, now your net filtration pressure if I if you have to calculate these values these values I have not put all these green values I have not put. So, your net filtration pressure is equal to N F P is equal to capillary hydrostatic pressure minus interstitial hydrostatic pressure minus bulk capillary osmotic pressure minus interstitial capillary osmotic pressure. So, now the values what you know people know is this value is known to you which I am circling this value is known to you you do not know these values I H P I C O P these values are extremely difficult to calculate. So, this value interstitial hydrostatic pressure it varies from different part of the body in the brain it is approximately 5 millimeter mercury. And in other tissues it is around minus 5 it is a negative hydrostatic pressure. So, let us assume this as around 5 5 to minus 5 and whereas interstitial capillary osmotic pressure where it is it is approximately around 5 millimeter mercury. So, if you ensure that these two terms you are ignoring these two terms and boils down to capillary hydrostatic pressure minus capillary osmotic pressure. So, now if you do the calculation here it is capillary hydrostatic pressure is 35 millimeter mercury and your capillary osmotic pressure is 25 millimeter mercury this makes it 10 millimeter mercury. Whereas, if you do it here this is 25 this is 25 25 minus 25 it becomes 0. And if you do it here this becomes capillary hydrostatic pressure is 18 minus 25 that makes it minus 7. So, if you look at these 3 values that will give you a very simple idea is exactly what is happening. So, this is the zone where net filtration pressure favors NFP favors that nutrients goes out of the vessel. So, in that process the oxygen is getting downloaded because NFP or net filtration pressure is 10 millimeter positive 10 millimeter mercury whereas at this zone if you concentrate at this zone out here it is good I put this line you could demarcate all the three zone. There is hardly any exchange taking place because it is here the pressure difference between inside and outside is 0. So, if you remember in the membrane physiology talked about it is the pressure difference which ensures the filtration is taking place if there is no pressure difference there would not be any filtration taking place. So, at this zone where it is 25 minus 25 you cannot expect any filtration to taking place this value and this value ensures. So, the colloidal osmotic pressure and capillary hydrostatic pressure are equal whereas if you move to this zone where it is in the close proximity of the venules. It is in this zone where colloidal hydrostatic pressure is smaller it is approximately 18 whereas colloidal osmotic pressure is 25 and that gives you a total of minus 7 millimeter of mercury. This is the zone where ensure which ensures that different stuff which are present which has to be thrown out by the body is being picked up by the capillaries in close proximity of the venules. This is where carbon dioxide is being uploaded into the blood vessels and which eventually reaches along the venules to the veins to the vena kaiwe to the heart to the right atrium and to the right ventricle and then sent to the lungs where it is being downloaded and we again will come back in this all these forces will come into play while we will be talking about the lungs how the exchange is taking place in the lungs. How the how in the lungs the carbon dioxide is being downloaded and oxygen is uploaded from outside that is the reverse process which takes place in the lungs and again all these forces will come into play there we will talk about it. So, this is an overall simplified summary of the exchange process in the capillaries for downloading oxygen and uploading carbon dioxide and ensuring any kind of around any kind of other exchange processes. Here if you look at if you come back to the diagram again and if you look at the diagram what is very important to ensure is that if say for example, some x y z toxin is coming into play. Say if this is the toxin if this toxin reaches at some point and kind of you know change the permeability all along these places and this is the zone where all these forces all these capillary hydrostatic pressure capillary osmotic pressure all these are getting disturbed and whenever there is a disturbance in all these things the possibilities are there there will be some fluid accumulation or some kind of a fluid accumulation at some point. And this fluid accumulation is what you call edema. So, now on whenever you will see a edema or some form of accumulation of fluid always refer to this diagram and try to request the doctor or ask yourself what is the capillary hydrostatic pressure? What is the colloidal osmotic pressure or capillary osmotic pressure? What is the interstitial hydrostatic pressure? What is the interstitial osmotic pressure? As long as you follow this simple equation of understanding where net filtration pressure is equal to capillary hydrostatic pressure minus interstitial hydrostatic pressure or in other word this is the net hydrostatic pressure. If this holds some term I have to put it in terms of simple hydrostatic pressure and this once again sorry for the interruption and if this whole term has to be put together then this is called the osmotic pressure. So, if you look at it this very very simple terms hydrostatic pressure osmotic pressure and all other details these are very very simple terms and they ensure that your body is in perfect homeostasis. So, in other word if I had to put it in terms of so basically filtration is equal to hydrostatic pressure minus osmotic pressure. This is the broad term which describes this whole process. So, with this I will move on to the last tail piece of this which is basically the venous pressure and sorry venous pressure venous pumps. So, again I will take you to a practical situation which will help you to appreciate this. So, you must have seen that at times in the schools where or you are standing in an assembly you are standing in a like kind of you know very attention position some of the students faint down why that happens have you wondered is it some problem in the brain or something it is a very simple problems. So, what is happening think of it you stand up and look at yourself your blood from the rear part of the body from almost from your from the legs or something has to come back to the heart. So, it is doing so and especially along the vessels especially along the vessels of the veins because for the arteries it is easy already there is a huge amount of pressure or force with which it is being pumped and it goes all the way down and down and up of course, but there is a huge amount of pressure involved in it and it flows through, but in the veins the only assistive mechanism is your the valves which does not allow the black flow, but the blood has to flow against the gravity at times how that is being taken care there are two distinct forces which takes care of it one is called muscular compression. Muscular compression is all this muscle compression and all this taking place that generate sufficient pressure for the veins to ensure that the blood comes back to the heart, but say for example, you are standing in an attention position and none of your muscles are really activated at that time and you are in a standing position there is a possibility that because of lack of muscular compression the sufficient force which is needed by the veins to ensure that the blood flows fully to the heart is being reduced. So, that simultaneously ensure leads to a reduction in the cardiac output and that reduction in the cardiac output causes your fainting. Next time whenever you see a friend of yours fainting standing in an assembly or you know some prayer meeting or something has them to just relax and kind of you know much more easy position because it may because of the lack of muscular compression they may fain down and especially in a bright sunny afternoon of anywhere in the tropics or subtropics this is fairly prevalent. So, there is another pump which helps us to ensure that the blood flows through the veins that is called the respiratory pump that basically generate because of this you see the whole chest is moving that respiratory pump ensures that the venous blood comes back to the right atrium without much delay. So, these are some of the basic forces some of the very basic mechanisms by which our whole complete network of the cardiovascular system works. I did not go into the anatomical details, but that you can go through that is much of academic interest to understand what are the different names of the different arteries. What is more important than that is to understand the mechanism by which it does. So, with this I will close on this part of this section of cardiovascular physiology, but while we will be doing the nervous physiology and of course, I will take out scoop out certain time to talk about the hormonal control of the blood flow and the nervous control which ensures blood flow and another situation which we will be talking about how those are helpful in ensuring that we do not suffer from some kind of edema or something and how the anti-inflammatory drug works as we will proceed through the course probably by the once we will read the tail piece of the course we will be able to understand all this by ourselves as I will kind of regurgitate these things and kind of try to analyze all the situations. So, what is most important as we are proceeding through the course is that if people please think try to realize day to day life situation what exactly is happening because that is the best way to learn physiology. I can tell you a whole bunch of formulae and situations or you know diagrams or anything, but in your visual plane or in your mental plane you have to have visualization of the situation what possible is happening and that is how the most of the bigger discoveries are being made when people is see something try to rationalize in terms of simple physics, chemistry and mathematics and then come back to biology and explore it and make some very fundamental discoveries I will close in here. So, in the next section we will be taking up the partly the muscular system and the nervous system. Thank you.