 Welcome back to the lectures in animal physiology, named NPTEL. So, we have finished first three sections. We started with the introduction to physiology, where we covered two lectures. Then we moved on to membrane physiology, where we talked about the structure and dynamics of the membranes. We covered three lectures and then we moved on to the heart, the pumping station of blood in our body. So in that we finished three lectures, where we talked about the structure of the heart and the dynamics including the conduction and contractile system. Now we will move on to the fourth section of this course, that is the blood vessels and circulation. So now we have fairly good idea about how the heart is pumping the fluid. So what we will study is the vessels or the tubes, which forms a huge network all throughout our body. In order to supply the oxygenated blood, carry back the deoxygenated or carbon dioxide rich blood back to the heart and which is being transmitted to the lungs for further purification. And what are the features of these different vessels, which are carrying the oxygenated blood and the features of the vessels, which are carrying the deoxygenated blood. What are their specific characteristics and what are the conditions, which lead to some kind of pathological situation, that is what we are going to discuss now. In order to start it let us, so we are into one second, just give me a second let me just get that. We are in section 4 and in section 4 we are in section of blood vessels, blood vessels and circulation and at this we are in the total number of lectures will be 3, number of lectures will be 3 in this section and we are into the lecture 1 of this section. So in this section of section 4 and lecture 1, in this section what we are going to cover is the basic introduction of the circulatory system, introduction then we will be talking about, especially in this class we will be talking about the introduction and the anatomy of blood vessels. These are the 2 interesting aspects we are going to deal in this lecture. Third we will be moving on to cardio vascular physiology, where we will be talking about the different pressure regimen, which are needed. In the fourth we will be talking about cardio vascular regulation and then in very brief we will be talking about the different cardio vascular circuits, once again cardio vascular circuits and in those circuits we will be talking about 3 different circuits, one will be the fetal circulation, which is slightly different from the adult circulation and we will talk about the systemic and pulmonary. Part of it we have already done, so we just kind of a bit of a reputation of it. Coming back to the introduction, let us start with the introduction. So as we have already talked about the heart and which consists of 4 chambers, we know that right atrium, left atrium, right ventricle, left ventricle. So what is happening from the left ventricle, blood is coming out through the aorta, reaches the aortic trunk and the pulmonary and aortic trunk. From here this blood moves to the arteries, arteries are the ones which are carrying the oxygenated blood, from the arteries it moves to arterioles, which we will talk about all the dimensions of these arterioles. From arterioles it moves to the capillaries, capillaries are having the smallest diameter will come to that. And capillaries is the zone where there is a maximum exchange of nutrients, gases takes place exchange of gases, nutrients or takes place at the capillary bed. This is the major exchange zone, from there the deoxygenated blood as of now this is all oxygenated blood which is coming. And this is where most of the oxygen is being given off and all the carbon dioxide is being taken in by these vessels. And this carbon dioxide rich blood, now through the venules, reach to the veins, from the veins comes back to the right atrium and from there it moves to the right ventricle. From here it bypasses everything and moves to the lungs where it gets purified and then again the oxygenated blood plus oxygen blood come to the left atrium, move to the ventricle. So, this is how it goes, so if you look at the major zone where the maximum exchange of gases and fluid is taking place that is taking place in the capillary layer. And those are very specialized structure as a matter of fact, in this whole vessel that those are the perforated or fenestrated and will come to those in depth in detail. Those are very very special zones and this capillary beds are all around our cells. All the cells are kind of bathed continuously by the capillaries all around them which allows the maximum exchange of the excretory materials to be reabsorbed, the gases which has to be reabsorbed like carbon dioxide and those gases which has to be given to these cells to take care of all the metabolic activities. From here we move on to the bigger classification of the vessels, so before we move on to the vessel classification, let us see how the vessels look like very basic idea about the vessel. So, most of the vessels are like a cylindrical vessels which are continuous. So, if you take a cross section of this vessel something like a cross section view, so the cross section view of a vessel is like this. There are different layers on it, there is outer layer, there is a medium layer, middle layer and there is an internal layer likewise. So, this is the outer most layer which is called, this is the outer most layer and all the vessels have this, this is the common feature. They have tunica externa, tunica externa, this is the outer most layer, tunica externa. Then there is a middle layer that is called tunica media, this is this layer in the green color, this is called tunica media and then there is a third layer which is I am putting in magenta, this layer is called tunica interna. So, these are the three fundamental layer. Then within this layer you have this one is called this layer what you see here is called external elastic membrane and it varies from arteries and veins, external elastic membrane this is one. Then you have the internal elastic membrane which one is this one, this particular layer let me just mark it, this layer is called this one is called internal elastic membrane, internal elastic membrane and then you have this particular thing is called this green what you see is basically elastic fiber, this is the elastic fiber and the inner layer out here, this is called endothelium. So, this is the broad architecture of all the vessels and the size of these different layers varies. So, if I had to redraw this as a cross section it will look like this, this is the endothelial layer, the inner most layer this is tunica interna, tunica externa, tunica externa tunica media and here tunica externa and if I had to give the color code what I just followed black, green, magenta. So, this is the one which should be black completely black and this is in green and this one the inner layer will be in magenta and this one the inner this is the hollow cavity and this hollow cavity is called this hollow cavity is called lumen and this is the cross sectional view of the vessel that is how it looks like. So, based on that we will be talking about the classification of arteries and the veins, arteries are the ones of arteries and veins. So, arteries are the one which are carrying the oxygenated blood and these are the one which are carrying deoxygenated blood and rich in CO2. This is the very basic fundamental functional difference between the two apart from it there are some structural variations. Structural variation wise if you see the cross section of the veins it will be more like this look at the cross section. The cross section the lumen out here and if you look at the lumen of the arteries they are much more smaller. So, here is the lumen the cross sectional area here is the lumen look at the let me color it. So, that will make more sense. So, these are the walls what we talked about tunica inbica tunica interna tunica interna tunica media tunica external sorry let me redraw it again for you this is the lumen and this is and here if you look at the vessel wall that is much more thinner, but lumen is much more bigger and there are reasons and reasons for it. So, before we get into that let us talk about the further classifications which are there. So, I am just indicating arteries with A and veins with V. So, these are usually round with thick wall as you could see in the previous diagram I was showing they have a very thick wall this is very important and where is in the case of veins it is usually flattened or collapsed with a relatively thin wall. This is very very important relatively thin wall and it is much more collapsed structure. In terms of arteries in the vein the tunica interna I will talk about the tunica interna tunica interna is usually rippled due to vessel constriction. Whereas in this case tunica interna is often smooth arteries and veins the next classification is in terms of internal elastic membrane is internal elastic membrane is arteries is present. Whereas the internal elastic membrane is absent in the veins. So, if you go back what is what I am talking about is this structure you see there is an internal elastic membrane out here. So, this one is missing in the veins and this one is present in the arteries remember this please. Let me come back to the current slide often smooth. So, this is absent in it in terms of tunica media arteries and veins and here you have the tunica media dominated by this is structure is dominated by smooth muscle. This is another the third type of muscle I was telling you that I am going to discuss while I will be talking about the muscle. Muscle and have lot of elastic fibers the reason for these elastic fibers in this because they had to withstand a lot of pressure. In terms of tunica media in veins it is thin dominated by smooth muscle, but having collagen fibers. Now, in terms of external elastic membrane this is the arteries and this is the vein external elastic membrane is present in this whereas, elastic external elastic membrane is absent in it. In terms of arteries and veins in terms of tunica external it is present lot of collagen plus elastic fibers are there whereas, in terms of external elastic membrane this is absent in collagen smooth muscle fibers are present in the tunica external. So, that is pretty much the overall classification or overall differences between the arteries and the veins what we are talking about. So, now from here we will move about the different classification of the arteries. Arteries have different classifications arteries could be elastic as well as muscular. So, one thing I wish to highlight here as we were talking about the pressure with which the blood is pumped. So, if you recollect very correctly the pressure with which the left ventricle pumps the blood through the aorta is exceptionally high. So, in order to withstand that high pressure all the different structural features about this elasticity external elastic membrane internal elastic membrane the presence of lot of smooth muscle and much more wrinkled endothelium in the arteries are the features which help it to withstand that exceptionally high pressure because as the blood travels away from the heart as it moves through the arteries and eventually with the capillaries and with the vein the pressure falls down. So, those vessels which are in the vein which are much more flaccid you must have seen much more wider in a cross sectional area they do not need to withstand that high pressure what an artery has to withstand continuously and this continues till the last moment of your life. There is a continuous flow of blood and these arteries has to withstand that enormous pressure of pumping from the heart and that is why these structures have been designed in such a way. So, that they on an average life span is 70 to 75 years in a developed world or in a developing countries nowadays than for 75 long years these vessels should be able to withstand that enormous pressure and that is why these structural features what I just now highlighted in terms of tunica external tunica media tunica internal and all the elastic external elastic membrane internal elastic membrane is. So, very critical So, now we will talk about the classification of two classes of arteries which are present in our body. So, what are those? So, as I have mentioned one is called elastic elastic artery the other one is called muscular artery. So, what are the difference between elastic artery and muscular artery? So, these elastic arteries are also called conducting arteries whereas, muscular arteries are called medium sized arteries and there are certain dimensions which I am going to highlight. Now, this medium sized arteries are have an internal diameter mind it these are all internal diameter what I am drawing here diameter or 0.15 inches this is wherever I am mentioning in this chapter these are all internal diameter be careful these are all internal diameter. And in terms of conducting vessels these are large vessels and they have a diameter of 2.5 centimeter or approximately 1 inch these are much larger cross sectional vessels these are the first two features. The next features some of the examples are pulmonary and aortic trunk and in case of that includes your pulmonary artery, carotid artery, subclavian artery, subclavian artery subclavian artery and you have iliac artery and likewise. In terms of the muscular arteries they have a thick tunic media containing more smooth muscles as compared to elastic arteries and some of the other features of elastic or conducting arteries is that elastic or conducting arteries is these are much more resilient and I do not need to again highlight this point and withstand enormous pressure. They can withstand enormous pressure because these are the ones from where the from the just from the heart this is the heart just immediately from there these are the ones which constitute the elastic arteries and the muscular ones include some of the examples of the muscular ones are as follows external carotid artery, brachial artery, femoral artery, femoral artery. So, these are some of the broad classification of arteries there is one disease or one pathological condition which I wish to bring to your notice you may hear this or see this somewhere written like this is the word aneurysm aneurysm what exactly is aneurysm going by the definition of aneurysm aneurysm is basically the bulge in the weakened wall of an artery bulge in the weakened wall of an artery weakened wall of an artery. It is something like this see for example this is the normal artery because of some kind of unusual pressure at a specific point what it lead to is you will see at this spot it takes a bulge like this. This can happen for multiple reasons and some of the reasons in which includes are arteriosclerosis which makes the vessel less elastic and during arteriosclerosis what happens is that if this is the vessel there are deposition taking place like this. So, the elasticity of this zone is reduced there is a decrease in elasticity and eventually what happen the decrease in elasticity leads to some kind of a situation like this at some other point it bulges out like this and this layer this particular layer is extremely prone to hemorrhage and this becomes extremely challenging if such hemorrhage takes place in the brain. If aneurysm in the brain is one of the very fatal situation and there are other situation genetic situation which you will come back it is called morphine syndrome. Marphine syndrome is an genetic disorder of connective tissue genetic disorder of connective tissues which leads to your aneurysm. So, this is something there are several causes of aneurysm, but all the aneurysm are most of the aneurysms or aneurysms takes place in the arteries and because of the weakening of a specific part or because of clocking or choking of the arteries at different points. So, now from the broad a of arteries we move on to the next level which is our further. So, for example, if these are the arteries this is how the dimensions are changing from there we move on to something called the bigger arteries then smaller arteries and then we move on to something called artery holes which are much more thinner. So, this is the cross section of the first arteries we talked about I am representing it by a and these are the medium arteries which are we have already talked about if these are the elastic ones and these are the muscular ones we talked about these muscular arteries and then these are the artery holes. Artery holes are have a diameter of 30 internal diameter of 30 micrometer or less 30 this is micrometer be careful as of now I was talking about inches and centimeter. So, artery holes have a very less diameter and they are also sometime referred to as resistance vessels because they pose a lot of resistance in the blood flow resistance vessel and blood needs a lot of pressure the pressure is the needs pressure to more pressure is needed to make the blood flow through that for flow this is very essential for you people to understand. So, the next level of A is for example, we started like this with the bigger arteries then we move on to the artery holes the next thing what we know is the vessels where maximum exchange taking place those are the capillary vessels and you see in some of the places I am putting a dotted lines there is a reason for it and I will come to that why I am putting dotted lines likewise. So, likewise likewise so this is the part which we are talking about the major arteries this is the chip these are the muscular arteries. So, here are the artery holes and here you are entering the zone of capillaries here you have the capillaries going by the dimension of the capillaries capillaries are extremely narrow cross section and they are approximately 8 micrometer of internal diameter internal diameter internal diameter of 8 micrometer means they are almost of the same size of RBC the diameter of RBC red blood cells which will be coming next actually in the next section their diameter is almost equivalent to a diameter of a single red blood cells. So, this is the zone where all this oxygenated blood which is coming all along which is coming all along. So, this is all oxygen rich blood which is travelling through here basically what happens all the oxygen is being delivered to all the different cells and tissues which are there. So, and we will talk in depth about this structure and this is where from these cells the blood picks up the CO 2 carbon dioxide this is where this is where the CO 2 is getting inside the capillaries and oxygen is taken up by the cells at this point here the CO 2 is getting in which I am putting in blue for your understanding. So, now after this what happens is this. So, before I get into how the circuit continues is this let us talk about the classification of the capillaries capillaries are classified into two broad headings one is called continuous capillaries the other one is called fenestrated capillaries. There is a classification with there is a there are some certain basic differences between the two and that is what we are going to highlight what are the basic difference between the two. So, the continuous capillaries have a continuous endothelial lining whereas in the case of fenestrated capillaries there are gaps or pores in between the endothelial lining and if I draw both of them the continuous capillaries and fenestrated capillaries. They will look like this if this is the endothelial the outer layer. So, these are the endothelial cells these are the endothelial cells. Let me take pick up another color for your understanding these are the endothelial cells they are much more closely packed out here and within them you have these penocytic vehicles penocyte you remember in the membrane we talked about these are the penocytic vehicle penocytic vesicles and these are the basal membrane and you see very very narrow gaps here. Whereas in the case of fenestrated capillaries what you see is something like this much much bigger gaps likewise and these are almost like you know windows through which the exchange could take place much more easily especially for the bigger molecules windows or fenestration that is what it meant when you talk about fenestrated capillaries once again. And this is where we are talking about the continuous capillaries here you have the different penocytic vesicles. So, this is how the fenestrated capillaries and the continuous capillaries look like the continuous capillaries indeed promote exchange by the fenestrated capillaries with the window like structure promote more and more exchange of the nutrient gases and everything. So, this is the feature which ensures that all ourselves are supplied all ourselves receive sufficient oxygen and CO 2 is removed and all other nutrients are supplied. Now, coming back to the previous slide where I told you that let me the previous to previous slide. So, now what happens if I put a color code here. So, now the blood is much more blue. In other word what I wanted to indicate is now the blood has more carbon dioxide content in them. As of now the blood was all kind of you know red which is kind of a sign of all the. So, from here what happens is this these are picked up by the next series of vessels I am putting in slightly darker green which are called venules. These are the venules I am drawing now these are the venules which are now coming into play. These venules eventually led to the bigger vessels which are like this with the bigger vessels of wings. So, these are where your CO 2 rich blood is now traveling through all the CO 2 rich blood is traveling through this all CO 2 rich blood. Now, so this is all being take into the vena covers and this is what is coming from the Iota. So, after this exchange has taken place all these venus blood moves along these veins. But in order to do so let me go to the next set of classifications out there. So, the veins could be divided into now we have classified the arteries now the veins needed to be divided. They falls under medium size and large size veins medium size are around 2 to 9 millimeter internal diameter and then you have larger than that which falls under the large size veins and smaller than veins are the venules. Now, there is one interesting aspect of these veins since by this time it is clear to you that with respect to the arteries and if these are the arteries sorry if these are the arteries and these are the veins visually if you look at it they have a much much higher cross sectional area as I was showing in pretty much in the first slide. This is the diameter is diameter is much smaller as compared to the diameter of the veins. So, in this situation and by the time the blood reaches the veins the pressure of the blood has gone down because the maximum pressure of the blood is in the arteries. So, whenever we actually measure we measure from the arteries. So, when the blood reaches the veins that is the time when the pressure is very low. So, there is always a risk instead of blood flowing in one direction it may start doing a back flow risk of a back flow. So, how nature prevents the back flow of blood in the veins that is very important. So, that there comes a series of valves which are present only in the veins these are called venous valves. These are nothing but are folds of the tunica interna this is another. So, venous valves these are basically nothing but are the folds of the tunica interna. So, what they do the way they fold like that something like this way they are folding pattern is like that say for example, the blood has to flow like this. So, as soon as the blood moves they bend like this they close. So, that the blood cannot really go back in the from the direction from where it is coming. So, basically they are the folds of the tunica interna that projects from the vessel from the vessel wall and point in the direction of the flow. In other word what does that mean in the direction of the flow. So, if this is the vessel and the blood is flowing in this direction. So, initially they all look like this these are the valves and blood is flowing. As soon as the blood flows they close in like this sorry this is wrong once again as soon as the blood flows this is how it works they close in. So, these valves are exceptionally important and they are only present in the veins they are not present in the arteries. Now, what we will be talking about a distribution of the blood at one point of time all across this whole vessel. So, in the heart you have out of the total blood you have 7 percent of the blood in the heart in the pulmonary circuit you have 9 percent of the blood in the systemic arteries systemic arterial system. You have 15 percent of the blood in the systemic capillaries you have 7 percent of the blood and in systemic vein venous system you have 64 percent of the blood. So, this is how the blood is getting distributed you have 64 percent in the systemic venous system in the heart you have 7 percent in the systemic capillaries you have 7 percent in the systemic arterial system you have 13 percent and the pulmonary circuits you have 9 percent. This is the overall distribution of the blood in the body at one point of time at any given instance of time and from here we will close in this lecture which dealt with the anatomy of the arteries and the veins and the capillaries and we talked about the zone where the exchanges are taking place exchange of gases and exchange of nutrients and other energy rich molecules and how the cells are continuously bathed in the capillaries and we talked about the distribution of the blood in the different compartments of the body. From here we will move on to the cardiovascular physiology which will part 2 which will be our next lecture. Thank you.