 Welcome back to the animal physiology course in NPTEL. So, today we will be starting a new section which is digestion. So, before I really give an overview of the digestion, let us talk little bit about how this whole thing works. So, body needs energy and for energy it has to process the food what we eat. So, in order to process the food there is a complex channel through with the food is the food moves through. It is just like a processing plant where you take the raw food raw or cooked whatsoever you take the net food and this food is broken down into small particles that is basically in other order what you are doing the way you process minerals you take it bring down the size of it. So, that the reaction takes place better after that this passes through different stages and different channels where different component of the food. So, food basically consists of four components if you look at food carbohydrate which is the major source of energy which includes your glucose, galactose, mannose, lactose this we all have discussed in the first section. Then the food contains the lipids which you have talked about the major constituent of the memory in the lipids fatty acids, color stroll and all other things. Then food contains a huge chunk of proteins the building block which includes which consists of the 21 different amino acids the permutation of combination of amino acids and apart from it food contains a lot of minerals which are essential as you could see the whole communication in the body is because of mineral sodium chloride and ionic state potassium magnesium calcium and apart from it there are few other small components which includes your vitamins at some hormones which are derived from outside the system vitamin like molecules and all those. So, overall if you have to classify you have the food could be classified as carbohydrate lipids or fats proteins minerals vitamins and few other accessory compounds similar to hormones of those kind of growth booster or thing. So, all these different components have to be absorbed in a different fashion they cannot be absorbed and they have to be regulated in a different fashion. So, this whole process by which the food initially what we intake so in the mouth basically using our teeth we grind it. So, this is the first thing is to grind the food in other word you are increasing its surface to volume ratio because as you are going down with the particle size you will increase it. So, basically what is happening what is over chemical within the body is going to act upon it to break it down further will get more surface area what we basically doing nanotechnology where you where you reduce the size of surface to volume ratio of a particle. Then a part of it then there are whole range of secretion of different hormones and different chemicals all along the pathway and at times this food is exposed to these particles are exposed to very acidic condition. Then they are exposed to basic conditions and there are action of different kind of molecules which dissolves the lipids for that you need lipid dissolving solutions. Then you need the absorption protein and then you need special absorption of other minerals and this whole thing takes place along the G I tract or gastrointestinal tract. So, all of you must have seen some picture of gastrointestinal tract here and there or insul bit batism or in a doctor's clinic or at least at one time in all these years you must have seen one picture. So, at times it may sounds to you very complex picture you know how this whole thing works. So, what I will try to do in this class I will give you a overall topology that how in a very simple in a block diagram which will clarify all your confusion and I am not going to exactly draw the way anatomies. I will just follow that I will break up the anatomical features into block diagram that will help you to appreciate how this whole structure looks like. Then what I will do the first thing is that I will give you the complete topological idea. The second thing what I will do is that because if you remember while we were talking about the nervous system I told you most of the digestive system is under the control of the sympathetic and the parasympathetic system. So, what I will do I will draw the connectivity of the sympathetic and parasympathetic system where all these are connected and that will help you to appreciate that how this different opposing nervous signal help the food to travel all along the GI tract from the mouth all the way down and the processed and the rest of the food which cannot be used is defecated out from our body as a fecal matter. So, that is the next aspect of the anatomy which I am going to share and the third thing what we will do we will talk I will draw the cross section of the GI tract to give you an idea how this whole tract is designed by nature over millions of years of evolution which helps it to absorb with extreme efficiency all the different things and on how that structure is being harmed when we take like you know we take excessive liquor or some other kind of agents which are not really very healthy for our body at a certain higher concentration. So, with this what I will do I will just summarize what I have just now told you and then we will move on to the block diagram of the digestive system. So, this is our digestive system that is what we are dealing with this is our lecture one. So, going back to next slide. So, we talked about the components of foods which includes your carbohydrate fats and lipids proteins and peptides and you have minerals then you have vitamins these are the components. Now, what I will do we will talk about the whole geometry of the or the topology of the digestive system. Let us start drawing it. So, I am drawing it horizontally instead of drawing it vertically because that way I will get more space to draw the whole thing. So, I will just put the label as soon as I am done with the drawing. So, this is the teeth. So, where the food intake is taking place. So, food is entering here and this is the zone where the food is broken down into small pieces. Now, you reach canal which is called esophagus come to that it looks like and there is a small and then we enter into stomach like this and this is stomach is exceptionally acidic come to that and this is the part where food experiences extreme acidic environment and it is because of this environment what is over drug which has to be administered in our body through the digestive system have to be insured that this could withstand that extreme acidic environment. Now, start labeling all of them one by one. So, the first one is the teeth where basically the food is getting this is the bulk amount of food of the smaller component breaking down into pieces step one this is the function of the teeth. Now, comes the second which is called the salivary gland. So, all of you are well versed with this one definitely because salivary gland is in your mouth and if you see some really good food you start salivating you know you start feeling with you know if I could get that food. So, this is completely driven by your brain when the saliva started to come or you are about to eat and you get a saliva. So, it is that salivary gland which regulates it and it is regulated by the higher centers of the brain through a series of sympathetic and parasympathetic module. Now, from here comes this canal which is your this whole part and mind it one thing I have done these are all double walled structure and will come in depth on this thing. So, this is your esophagus some people write it with O some light with E esophagus from esophagus the food enters into a completely acidic environment of stomach which has a p h in a around one. This is the next stage next stoppage for the food here the food gets kind of you know through and now it is reaching stomach. Now, here there are two organs which comes into play the biggest organ of the body which is here which is the liver. So, this is your liver inside that you see this structure this is the one which is present almost embedded into the structure this is gallbladder there was a reason because many a times whenever you see the picture of the digestive system anatomically it is being drawn it becomes really challenging for those who have not seen the physical digestive system another like the who have not done the dissection at times become really difficult for them to understand exactly what is connected to what that was the whole reason why I decided that I will give you a flow chart diagram. So, that will clarify all your like you know exactly what is the anatomical location. So, now from now on whenever you will look into a real anatomical image you will be able to figure out the connectivity between the different organs which constitute this whole G I tract coming back to this. So, this is the gallbladder and this is where there is another organ you could see out on the other side I have not drawn the organ full it looks more like this is your pancreas you might hear people suffer for pancreatitis and all those things. So, this is where lies your pancreas and we will be talking a lot about this because this is a seat of hormone secretion in the body here food enters into the small intestine the huge area where there is lot of absorption taking place and which is very well inner very nicely supplied with the blood vessels. So, that they can absorb as much food particle or the inner different component of the food particle as possible. So, this is very well vascularized structure in the body. So, then comes the small intestine and then comes the structure where you can see which is called cologne or large intestine. So, out here basically the major job of this is to absorbs a lot of the residual matter large intestine. So, this is the G I tract intestine and in terms of anatomical perspective if I draw it if I look it. So, if you are using this picture horizontally if I draw it anatomically then this is how it will look like if this is the head and this is the rest of the body it is something like this. This is how it will look like this is where you are taking your food. So, this is the same structure which I just if I go back slide in the previous slide. So, this is what is happening. So, food is entering from the mouth. So, this is the mouth then there is a series of secretion which are taking place here from the salivary gland after that the food moves through the isophagus then it moves into the stomach in the stomach it is exposed to a lot of it is a total acidic environment. So, the reason what I was trying to highlight is that say for example. So, this is something to a very application oriented situation say for example, you have to take a drug through the oral route. So, the first thing what happens is that once you take the drug this drug experiences are extreme acidic environment in the stomach. So, if this drug has to be absorbed somewhere because as I told you it is in the small intestine where the maximum absorption is taking place because it is a very well vascularized supplied with lot of blood vessels it is if that has to happen and one has to ensure that that drug in the intestine sorry in the stomach survives the heavy acidic environment. And this is a big challenge whenever you have to take a drug directly through the oral route because the drug goes through a whole range of modification pH changing environment has to be stable it has to be stable at different pH. So, that it is finally being absorbed in the right place which is the small intestine that is why I just put that acidic environment. From this acidic environment of the stomach it moves to the large intestine which I told you is the zone where there is a lot of absorption taking place which I am showing by the arrow enormous amount of absorption is taking place absorption of by the blood vessels. So, after this what is over so it is that it is in this particular zone where you have secretions from the liver gallbladder and pancreas. So, all the secretions which are there are taking place at this zone and all the different absorption are taking place it is here where glucose is being regulated it is here where the islet cells of Langerhans are regulating your glucose level and all other things it is here where any defect in this zone leads to a person being diabetic or some kind of you know liver problem or something it is at this critical zone of the pathway which is essentially this is the zone where major problem arises it can be in the form of liver cancer it could be in the form of pancreatitis it could be a form of some kind of problem in the gallbladder blast where the gallbladder burst out. So, these are the this is a very critical zone of the anatomy where lot of absorption takes place and lot of very critical functions are being regulated here. So, most of the gastrointestinal pathologies in terms of liver or bilory problems liver problem pancreatic problem they all are concentrated in this very critical part of the anatomical structure a chunk of it as a matter of fact if you if you look at some of the institutes of NIH or even an in India we have a specific institutes for this national institute or for you know liver likewise I mean this is so very important it is a very interesting zone especially we are passing for very interesting time when people are trying to you know the tissue engineering liver they are trying to if there is a problem in the liver they could you know replace a part of it or they are trying to tissue engineer pancreas some part of it if they could put it back. So, these are some of the very critical zones where there is enormous amount of studies going on across the world where people are trying to ensure that you know how we could you know reduce the pain and the problems of the people who suffer from liver disorders you hear these things very commonly fatty livers or liver cancer or liver damage or you know because of excessive taking excessive wine or some form of liquor there is a liver has a problem or same way in the pancreas you hear this pancreatitis many celebrities die of this particular problem. So, this is a very very critical zone of the whole GI tract and then after that whatsoever absorption taking place in the small intestine then rest of the food which is not absorbed now moves to the large intestine large intestine is another zone it is fairly huge zone and it is not that this whole zone is very very functional. So, the major idea of the large intestine is to absorb the residual minerals and all other things which could which has not been absorbed in the small intestine. So, this is the last frontier and after that through the anus. So, here you have the anus you defecate whenever the concentration of the material to be thrown out of the body goes beyond a concentration you feel you have to you know defecate out you throw away the food. So, this is an open channel. So, if you look at it from the mount through the anus this is an open channel which is running through the body along the cross section of the body. So, if I had to give you another analogy of it is something like this. So, if this is a cartoon of a human being look at it like this. So, basically what is happening. So, here is a channel which is moving like this if this is the mouth and this is the anus. So, here are the anus here you have the mouth and along this conduit tube you take any amount of food out here. This is getting the important material of the food is getting absorbed all along this track after processing of course, it is getting process inside and. So, this is the food material. So, it is getting absorbed and rest of it is being defecated out. So, this is a both side open ended channel it opens one at the mouth one at the anus and along that track all this phenomenal events are taking place and this is what I wish you people to appreciate that it is. So, it looks so simple, but it is it is really a marvel of nature how the food enters and goes through all these different structures and in those the structure it goes through a different process and different components of the food carbohydrate your fat proteins vitamins minerals water in water water needs a specific absorption process. There are specific water channels which helps the water to be absorbed slowly. So, how this all these wonderful things are happening along that channel this is exceptionally important for people to appreciate and understand with this what I will do I will highlight one very interesting thing which is called peristaltic movement. So, basically the word is this peristaltic or it is also called peristalsis peristaltic movement what really is peristaltic movement. So, excuse me so whenever we take food. So, what happens how the food really moves through this channel I draw the channel for you now the food moves in the form of a bolus. So, when you take a food it is just like we chew the food like this once we chew the food it forms a bolus or a ball like structure that ball moves imagine you have a flexible tube like this and you drop a ball how the ball will move. So, the ball moves like this if you if you look at it. So, if this is a flexible tube you have likewise and here I have a ball something like let me redraw this this is so that and I have a ball like this now this ball has to get through and this is a very flexible this is fairly flexible. So, what will happen when the ball will be here stage one when the ball will be here this all this wall will get inflated like this to accommodate this then once this ball will move here then this part will get inflated then as the ball moves here then this part will get inflated to accommodate that big ball and eventually once it comes out and this is a flexible membrane. So, this whole motion of the ball this whole motion of the ball as it is moving through the digestive tract like that is called peristalsis and this whole motion is called peristaltic movement. So, this is how the food moves through this narrow tube in the form of a bolus it goes through like this and this whole peristalsis is governed not only by the nature of this muscle the smooth muscle along with it there are nerve signals which regulates this process and this is very very important. This is one of the areas of research which is currently a lot of attention has been put that how the nerve signals are regulating this motion of food like this something like this if you follow my hand likewise it is moving like this and this is very very important this whole motion of the food along the pathway. So, what I will do now as I told you now I will draw the connectivity because this is a complex tube. So, every point of it people have to understand that you know there are lot of connectivity issues here who is connected to what and how these these connections are taking place. So, what I will do now I will add on that the component of parasympathetic and sympathetic where they are regulating the whole process. So, let me see if I could do it in this diagram bit tricky. So, I will redraw it that is easier. So, I will again redraw the whole structure so that on a fresh a you can. So, here you have this library gland and then you have the stomach coming through and then you have the small intestine then you have the large intestine and then you have the anus here you have the salivary gland salivary gland leading to the stomach from the stomach it moves through here the pancreatic and liver connection and this is large intestine and here you have the anus and here on this side you have the gall bladder and here you have the liver on this side you have the pancreas. So, you just put the nomenclature so here you have the teeth then you have the salivary gland salivary gland esophagus you have stomach the liver gall bladder small intestine pancreas the seat of endocrine system large intestine. Now, I will introduce in the red and the blue the sympathetic and parasympathetic connectivity. So, it works like this so this is the parasympathetic I am drawing this is the parasympathetic route moving through when you have this parasympathetic connectivity of this whole structure out here then you have parasympathetic connectivity of the whole large intestine. So, this is your parasympathetic connection. So, if you look at the parasympathetic connection carefully you will see the salivary gland stomach your small intestine and large intestine is under the parasympathetic control. So, this is parasympathetic control now where is the sympathetic control which I told you I will show in green. So, the sympathetic control exactly moves in the same way here is the sympathetic control moving through on the stomach then you have the sympathetic control exactly at the same point where you have the parasympathetic control and here you have the ok. So, this is basically the parasympathetic control. So, I told you that there is the way the food moves I will show it in your green the way the food moves is something like this along this path and this is what is what we call as peristalsis. So, this whole peristalsis process along with this along with this along with this here also the same thing happens it moves like this. This peristalsis process along with the motion of the bolus along the muscle like you know changing the elasticity of the muscle as it moves through is also governed by this sympathetic and parasympathetic. So, if I say this one gets a positive signal here. So, for example, it is a positive signal it gets simultaneously a negative signal from here or vice versa which is over we want to call it if it gets a positive here it will get a negative here same way if it gets a negative signal here then it will get a positive. So, there are always reverse signal which helps. So, for example, I say on off on off on off on. So, this whole tube is being regulated by this on off switches on off on off on off on off and this is whole completely inner weighted with this sympathetic and parasympathetic neurons and apart from it it is very very well vascularized best because if you go back to the previous slide if you look at this. So, this is under the complete. So, if I draw the vascular like this in with the pink color. So, it is completely vascularized is a huge amount of blood vessel vascularizing it because it is here the body has to you know absorb all it nutrients. If you look at the cross section of it since I have drawn this what I will do I will draw the after the sympathetic and parasympathetic control thing I will draw the cross section. So, the cross section is very interesting. So, it has multiple layers. So, basically what I am trying to show you is this. So, what I am essentially is drawing is the cross section of this. So, if you cut it like this. So, if I have the tube like this and I cut it like this. So, this is the tube say for example, this is the top part of the tube from where the food is traveling down all the and this is the anus. So, I am cutting the tube in a cross section like this and this is what I am going to show you the cross section. So, the cross section shows this is how the cross section looks like there are multiple layers and this is the outermost layer what I am drawing now the double layer looks like. Then inside this layer you have the next layer which is something like this just for your understanding sake I am doing it like that because if you see an anatomy book it is far more complex than way I am just trying to draw a block diagram. So, that you people understand it in a simple way that how that looks like and I appreciate the beauty of this channel which is pretty much our life line. So, this next layer so, the space between this and this is called Seroza S-E-R-O-S-A Seroza and this is called this you see this this layer this is called Longichirinal smooth muscle. There are two different kind of smooth muscle and I have already talked to you about the muscle physiology and between the Longichirinal smooth muscle you see these structures these important structure these are called Gat junctions. This is how the electrical impulse from one muscle is being shifted to the or transferred to the next muscle. Then comes the next layer I am going to draw now something like this draw this then I will tell you exactly what is the role. So, this layer what I have drawn now is called circular smooth muscle layer circular smooth muscle layer. Then within the circular smooth muscle layer you have another layer which is this layer which is called mucosal layer. This is of course, a double I am once again let me just change that. So, this is a double double layer structure all of them are pretty much double layer structures thick double layer structure and this is called your mucosal layer and the central cavity which you see out here is called lumen. So, we talked about and in between there is a layer in between these two this is called sub mucosal layer sub mucosal. So, if you look at it so you have the outermost covering then you have the surrosal layer which is here. Then you have then you have longitudinal smooth muscle layer which is the next layer it has gap junctions in it. Then you have the next layer which is the circular smooth muscle layer and then you have the mucosal layer and of course, in the center which is the lumen through which the bolus passes. So, this is the kind of cross sectional view of the g i tract what we have just now discussed along these lines. So, these are the cross sectional view with little bit of here and there some of them will have you know kind of you know brush border like this for enhancing the absorption and all those things these are further modification, but overall geometry of the g i tract is like this. So, let us summarize what we have covered just now. So, we talked about the components of the food including carbohydrate, fats and lipids, proteins, minerals and vitamins. Then we talked about the overall topology this is the topology of the g i tract gastrointestinal. Tract with mouth salivary gland, isophagus, stomach, liver, pancreas, small intestine and the large intestine and the anus. Then we talked about give you a feel how the vasculature is functioning these are the vasculature for the blood vessel which are all along and it is open in the tube. So, this is open here and it opens at the end at the anus and the phagin at the anus. So, it is open tube through with the food passes and it is getting absorbed. Then we talked about the peristaltic moment how the food is moving through and we talked about the parasympathetic and the sympathetic control and then we talked about the cross sectional view of the g i tract itself. With this overview I will move also I will close in this lecture and I will move on to the next lecture we will be talking little bit more about the real process where every where which aspect or which part of the food is getting absorbed in which part of the body. Thank you.