 lectures on NPTEL on animal physiology. So, today we will be initiating the section 5, which is essentially the renal system or you can call it kidneys and the regulation of body fluids or excretory system. So, we have talked about the way the blood from the heart is being pumped and it goes the impure blood goes to the lungs where it gets the essential oxygen which it lacks after supplying the whole body. So, deoxygenated blood from the heart goes to the lungs gets oxygenated comes back and then it is being pumped all over the body. This is one mode of clearing of the blood there is another mode where basically you have to get rid of the other salts which are present in it which body does not need like urea and many other salts are there which has to be got rid of and you have to maintain the exact osmolarity osmolarity pH in all these things of the blood and that is taken care the biggest chunk of this purification takes place in the kidneys. Essentially what exactly happens here is that all the blood they go into the kidney and there is a kind of a very well developed filtration assembly where the blood gets filtered out of all the unwanted things and the filtered blood moves back to the body whereas, all the unfiltered agents which are being rejected by the blood while it passes through that mesh or the sieves it is just like in a filter it passes through and whatsoever is has to be rejected and it is selectively rejected. So, whenever you see a sieve so say for example, here you have a pot of tea. So, when you pass through it so all the tea leaves kind of get trapped so that is these are kind of sieves which are not like non selective things you cannot decide the whether the smaller leaves based on the size of the filter every things which are bigger than that will stay there things which are smaller than that will pass through it, but here when the nature has designed the sieving mechanism it is much more I should say a very smart material or much more like a very programmed thing based on there are different transporters which pulls it out through the sieves and it is much more I should say much more versatile as compared to a physical sieve whenever you think of. So, it passes through the sieve and unwanted things are being thrown out and then the blood goes back and those unwanted things along with certain amount of water is being excreted out from your body in the form of urine. So, here there are few things which has to be kept in mind this whole process has to be very tightly regulated because you cannot afford to lose a lot of water in that whole process because when you are pulling out some of the electrolytes which body does not need or some of the smaller molecules like urea and all these things you have to ensure that in that process of clearing up we should not lose sufficient water that we start suffering from dehydration or other physiological problem or the homeostasis goes on the wrong direction or the pH changes significantly. So, all these things are very tightly regulated. So, in order to understand this in this section what we will essentially do we will first in this class we will talk about the anatomy of the sieve or anatomy of the kidney is the first thing we will do today. And individual elements of the kidney which are responsible for this function and then we will move on to the part 2 where we will be talking about the exact mechanism osmosis reverse osmosis and all those mechanisms which are regulate this clearing up process and then the third part of this segment we will be talking about the different control mechanisms which regulates this process and simultaneously we will be talking about if there is a misregulation what is really meant by kidney failure what is meant by you know dehydrating condition when the water is being lost how the renaissance angiotensin system comes into plane. So, that will be the third part of this particular segment what we will be dealing with. So, today let us start with to give you an overall topology and morphology and anatomy of the kidney because that will go all along in your understanding how really the blood is getting into the kidney and how it is getting you know cleared up filtered and everything. So, let us start with the anatomy of kidney. So, we are into section 5, 5 kidneys and the body fluid and the regulation of blood fluid most of you have seen kind of at some point or other the structure of the kidney here I will just draw it it looks something like this. So, bean shaped organ to measure the abdominal lower than the abdominal part of your body and there are blood vessels coming in sorry. So, there are two kind of blood vessels which comes in the venous and the arterial blood likewise and then there is another organ which is called ureter. So, these bloods are towards the lungs towards the heart. So, and this is called ureter these are the blood vessels which are entering or exiting arteries and the veins. So, you have two kidneys and the veins now inside this is interesting how the blood vessels. So, this part is divided into like two segments one is called medulla the other one is called cortex. So, the cortical region is from here to here this is called the cortical region of the kidney or cortex of the kidney whereas, the inner part is called the medulla. So, now when the blood vessels enters this is very interesting the way. So, they distribute like this this geometry is very essential for people to understand because this geometry really helps in the whole clearing up process this glitches which are coming in between. It is almost like a tree like a structure by which it is completely getting you know spreading out all over the place likewise. So, now what is happening is that. So, blood is travelling. So, I just missed upon on the other blood vessels like this something like this just forget about it. So, now here is it the blood is entering and then the blood is moving all along these channels all over the place likewise and it all spread out there and all the finer branching us are all taking place at the far end of the cortical regions likewise and so on and so forth. So, at this cortical region what you essentially have something say if I had to kind of blew up this image this part one of the next slide where I am going to blow up this image in the cortical region. So, it is something like this. So, this is at the cortical region how this is all getting spread they are the branching of the blood vessels like this at the cortical region. There is a lot of finer branching and along this finer branching lies here very adjacent to them lies a set of tubular structure like this. These are the individual tubular structures something like this and this tubular structure what I am drawing in green what you are seeing now. These tubular structures are the structures which are essentially responsible these are the sieve elements or these are the filter elements and those are called nephrons. So, all along you will see a thousands and thousands of such a nephron structure. So, essentially what is happening if this is a blood vessel. So, there is a zone where the blood vessel is kind of under is kind of covered by like those of you have seen a distillation assembly you might remember there is a coiling. So, there are certain zones where the blood fine capillaries are being coiled around by this nephrons. So, what is happening to the blood is that there are two tubes likewise if this is the blood vessel if this hand what I am showing you now is my blood vessel is the blood is bringing. So, very close to it in close alignment this is the other hand it is in close alignment sitting like this and it is at these zones where they are in physical contact. So, mind it they are not connected tube they are two separate tubes like this there are two tubes it is something like this let me do it that will make more sense it is something like if I had to cross section it is like this. So, if this is the blood vessel then it is in close proximity you have these vessels going, but they are two separate entities. So, if I have to if I blow up this part it will be something like this there you will be able to physically see two independent walls and it is this zone this critical zone where all the different kind of exchange processes are taking place. So, this is the zone of filtering zone and this is very interesting to understand what is the architecture of the other tube which I was drawing in green the reason why I am highlighting on this part is this because unless this particular aspect is clear that how this whole topography is being maintained it is really really tough to understand how the kidney really functions. So, if you if now if I go back to this particular drawing. So, I can further so you will see in a text book whenever you will see you will see something like this. So, the structure of the kidney in a text book will be shown like this and on this you will find structures like this you all might have come across in class 7 or 8 or somewhere this kind of structure and here the blood vessels are entering into the kidney another series of blood vessels which are entering into the kidney and here the heater coming. So, essentially and and I told you that this is the the cortical region and the medullary region. So, all those what is being collected from here during this whole filtration process they showed you they are all eventually dumped on to this from all over the place by those vessels of what I called you the nephron. So, those filtration assemblies are called nephron which are in which are in close proximity with the with the blood vessels. So, essentially the physical difference between whenever we talk about sieving or filtering is that whenever we talk about filter we kind of from a tube we pour the whole fluid and it passes through a filter and goes through, but here no such thing is happening still the blood is not kind of venting out into any cavity or anything it is remaining in a tube and is surrounded by another tube in close proximity and there are some osmotic phenomena which is taking place reverse osmosis osmosis diffusion likewise there are two or three phenomena by which the solutes are getting moved from one side of the tube to the other side of the tube and that is what constitute the whole filtration with this overall understanding of it what I will do I will move on to the structure of those smallest component or those sieving elements which is the key for this particular class. Let us talk about the anatomy of those. So, essentially what we are talking about now we are dealing with the anatomy of this individual elements. So, the anatomy of the individual element is something like this. So, this whenever you go through any textbook it is a very complex structure, but I will try to simplify the structure as much as possible because that is this is the very key to our understanding. Now, these we are considering this as cortical nephrons. So, there are couple of terms you will get cortical nephron medullary nephron. So, basically what does that mean is that those nephrons which are lying in the cortical region there are nephrons which lies in the medullary region also. So, if they are lying in the cortical region they are called cortical nephrons, but if they lie in the medullary region they are called medullary nephron, but yet there are nephrons which was part part of their body lies in the cortical region, part of it lies in the medullary region. So, coming back and so this is what I will be drawing is essentially a cortical nephron. So, the structure is something like this, take time because this structure is very critical and one has to understand this structure nicely before one understands what is happening in the kidney. So, you see this is a very convoluted tube, it is kind of changing shape and size and all other things. So, now what I will do, let me just reason for this line is that the part of it which is… So, this is the part I was showing in the drawing if you go back to this slide. So, this one so if this is the if I told you that this is the medullary region. So, this part is the medullary region and these nephrons are lying all over it likewise. So, part of their body lies in the medullary region and part of it lies in the cortical region, this is very interesting. So, when the major filtration assembly is lying in the cortical region it is called cortical nephron and when their major filtration body is lying in the medullary region it is called medullary region. So, what we will do in this picture we will… So, this part is the cortical region cortex and this part where it gets extended is called medulla or the tube is kind of descending down. So, this region is called the distal t-vue, this is called the Baumann's capsule, this part is called the proximal t-vue and this one is called the thick segment, this one is called the thin segment and there are significance for this different thin segment and thick segments and this loop what you see the looping thing taking place this is called loop of Henle see this and this one is called the collecting duct I showed you. So, if you look at this structure it has it is kind of a very tubular structure like this it move like this move like this it is a very convoluted tubular structure and this is what all along the blood vessel it runs very parallel to the blood vessel. So, if I have to introduce the blood vessel so, this already is a complex structure with the loop of Henle and the collecting duct. So, these collecting ducts essentially what is happening I told you that all these the way the urine formation is taking place is yeah. So, all the collecting ducts what I just now drew all these collecting ducts are draining out onto the urator and which is nothing but your urine. So, in other word whenever we talk about that there is a kidney failure that essentially means is your nephronal structure is getting damage for some reason or other. So, this is and if you look at the nephron structure very carefully you will see that there are zones where the segments is thick there are zone where segment is thin and as we will move further you will see what are the functional significance of these different kind of thick segment thin segment and there are specific zones where specific. So, if I go back come back to that structure. So, if you look at this is so the blood vessels are now I am just introducing the blood vessels for your understanding like me. So, the blood vessels are two tubes the major chunk of it is here likewise we will come back in detail with all these things how the blood vessels really is kind of you know as I was showing you in one of the previous slide there are two parallel tubes side by side moving and this is how the complex it looks. So, that is why I kind of told you that I will draw a very simple diagram which will make you understand that how they are they are in side by side and there are specific zones. So, the way it is like there are specific and there are specific zones where a specific kind of functions are being taking place and there is something called counter current mechanism there are all the possible diffusion and movement of solute is taking place diffusion osmosis counter current mechanism everything. And as long as this basic structure is clear it is fairly essential it is fairly easy to understand the rest if there is a problem in this basic structure then you will have problem in understanding how this whole filtration assembly is functioning. So, now after that let us summarize what all we have done of now is that you have this arterial blood coming in into the kidney through the afferent arterial the one which is bringing the blood. An afferent arterial moves in to the glomerulus structure which is basically the nephrodontal structure glomerulus structure and then from there it moves on to the afferent arterials this exchange is essentially is taking place this is the part this is the zone where I was showing you inside the Baumann capsule where this is all entering this is that zone where this exchange is taking place and from here it moves on to the peritubular capillaries peritubular capillaries and from there it moves on to the venous blood. So, this is the whole schematics of the way the blood is getting purified. So, this is the zone from here whenever whatsoever the urine is being formed out here is being eventually in out is being essentially drained out in the form of urine this is how it works and this is the whole urine formation mechanism. So, again to summarize it so you have arterial blood coming in through the afferent arterials moving into the glomerulus or the nephrodontal network and in the nephrodontal network the whole filtration is taking place was a filtration takes place along with some of the water molecules it has to be conserved in mind it all the other like urea and all those things and few other which are not needed some of the electrolytes and it moves down along with some of the pus cells and everything in the form of urine. Whereas, the pure blood from here so here you have the pure blood here you have the impure ones this pure blood through the peritubular capillaries moves to the venous blood and then it moves on and then it goes to the heart and there basically the oxygen is taken from the lungs and then again it circulates all over the body. So, this is the overall geometry by which this whole thing works. So, what we will be doing next is after this we will come back and we will talk about how the exact filtration assembly is taking place. So, I will close in here so in the next class we will talk about the exact mechanism by which filtration is taking place and what are the different control mechanisms.