 to the NPTEL lecture series on animal physiology. So, I have given you so today we will be discussing the digestive system. So, I have given you a complete outline of the digestive system starts in the mouth. The food travels through the esophagus goes to the acid rich compartment of stomach from there it moves to small intestine and then via where the maximum absorption taking place and then moving into unabsorbed to move to large intestine. There also some degree of absorption taking place and then whatsoever is not absorbed or to be rejected by the body is excreted in the form of feces. And in that whole tract I have shown you that there are different organ liver, pancreas as well as well the very moment you swallow the food there are salivary gland which secreting a whole bunch of fluids which leads to which essentially helps in the once again which essentially helps in the digestion of the food. So, the way we will go I have given you the complete outline and we have already talked about the sympathetic and parasympathetic control and the peristaltic movement of the food along this whole tract. And I have highlighted the cross section of the GI tract or digestive tract. So, what we will do today we will divide this into 2 or 3 parts. The part 1 we will be talking what we will be discussing now is the first set of chemical reactions which are taking place in the form of saliva from there we what we will do. So, see we have to realize one thing this whole thing is basically a chemical reactor you can kind of comprehend it as a chemical reactor where you have the input coming in the form of a food. And the output going as which cannot be utilized by the body and in that whole process there are channels where the major component of the food in the form of amino acids, carbohydrates, fats, lipids these are being absorbed. And these are absorbed by the blood vessels which are surrounding this whole tube. So, what we will do first so we will start with the saliva we will talk about essentially the composition of saliva what saliva does. So, again we will talk about the formation of the saliva what how it is being controlled regulated. Third what leads to the secretion of the saliva these are the 3 things what we will be discussing in this class. And I will try to make it as diagrammatic as possible so that kind of get a feel exactly what is happening instead of you know getting into technicalities of it. So, that will enhance your imagination. So, let us start with it we are into the section 12 of the lecture 2 in the digestion. So, we will be talking about the saliva. So, we will be talking about composition of saliva that is the first thing we will be dealing with then we will be dealing with formation of saliva and then the secretion. So, why the secretion is very important is this. So, all of you must be aware that whenever we see something some good food you know we started salivating. So, we do start doing like that I should get this food how that happens there is a whole range of neuronal control which regulates that thing or we do not like some food we say I do not want to eat that. All these things are regulated by the higher centers of the brain and. So, in other words essentially what does that mean is that all your salivary glands which are present are all innervated by neurons by the different parasympathetic and sympathetic neurons which are eventually regulated by the higher centers of the brain. And it is a very well coordinated kind of a very well coordinated signal response by virtue of which we respond to different kind of foods in a different way. So, now let us first of all talk about the composition essentially the composition going to the composition let us put the second slide the composition of saliva there are different composition of the saliva different component of the saliva some of the important component of course includes. So, I will be highlighting some of the important component the alpha amylase does. So, alpha amylase essentially takes care of the carbohydrates that is a major. So, basically in other word what it does it breaks it down into smaller component and that is the major function. So, whenever you take something say for example, you take a chunk of sugar or a sweet this is the alpha amylase which goes started binding all over the place and start to you know cut the long polypeptide chains of these different carbohydrates into small small small pieces into small component. Because the more smaller you go chances of that it is being absorbed by the body is more bulk it is lesser of the chances that it will be it will be absorbed. So, fast apart from it always remember one thing saliva has certain role to play in the oral hygiene it has some very interesting role to play we will come to that. So, from here we will move on to the next component of that then you have certain immunoglobulins which are present which are immunoglobulins are IgA IgA are present there then you have something called lysosine second component and this is the third component then you have peroxidase this is very important you almost have seen that you know there are different peroxidase which are used for say for example, you take a food which is slightly contaminated with some pathogen or bacteria or something it is not that every time you fell ill because body at every level has a difference mechanism it can take care of these different pathogen till it fails you will not fell ill. So, this peroxidase what it does if the food has some of these microbes or contaminant the peroxidase tries to go and shop it off that is the function of the peroxidase. So, that is why I told you that it has a role in the oral hygiene if your mouth has a lot of bacteria something you will be spelling foul in your breath or when you do like this, but if your peroxidase concentration is right and peroxidase could manage to take care of these bacteria and everything there are some which are helpful there are some which are not helpful. So, peroxidase plays that plays that role apart from peroxidase what we have is peroxidase then we have very high concentration of HCO3 minus and this is involved in the pH regulation in the major role and peroxidase is in the defense mechanism. So, do lysosine. So, these are major component and the pH of this whole thing is approximately 7.8 this is around where the pH of it 7 to 8 this is generally the pH of the saliva and if you kind of look at the anatomy how this looks like once again the anatomy is something like this. So, if this is the mouth and this is the G I tract which is moving. So, out here you will see put that in the red out here you will see some of those organs which are sitting there these are group of three group of organs which form the and this is your mouth in the back of the mouth you have this salivary glands. There are different salivary glands which are presented and they have different functions come to that there are three major salivary glands which are present parotid gland then you have sub mandibular gland parotid gland sub mandibular gland and then you have sublingual gland. Some total of this is they have different role to play this parotid just put it in blue this leads to more of a watery saliva a different kind of secretion profile which is sub mandibular gland is more like a green mucin like saliva is a polymer and sublingual gland is basically the mucous more like mucous kind of secretion which takes place and if you look at the output of salivary gland I am just putting it as g salivary gland is around 0.5 to 1.5 theta per day this is pretty much is the and the flow rate of it saliva flow rate varies from 0.1 to 4 ml per minute this is the pretty much is this is how the saliva kind of is kind of regulated or this is the kind of the amount of saliva which is produced by the body by the mouth actually at any point of time. Now, these structures what I just now drew for you some mandibular sublingual parotid they have a very specific structure and what we are going to deal now. So, now we have so I told you there are three aspects what I am going to cover we will be talking about the composition of the saliva and the organs which are producing saliva and then we will be talking about exact formation of the saliva. So, these three what I mentioned the parotid sublingual as a mandibular they have a specific cellular structure of called asinine they form this asinine structures are the one which are involved in the synthesis of the saliva. So, what we will do I will just draw one of the generic asinine structure and I will show you I will kind of highlight the fact that how the formation takes place and what are the signals which comes. So, it is what is this asinine kind of structure it is something like this say for example, there are secretes cell all around this cover it like this and then there is a duct where all of them secret and along the duct that fluid is formed and that duct eventually opens up in the mouth that once again through the duct the fluid is being secreted out and that fluid is in the form of saliva and that secretion is controlled by the nervous system. So, that will be the third part of this class where we will be talking about what are the nervous impulse we send signal ask that duct to open and secreted. So, now what we will be doing we have done with the composition we have done with the anatomy now we will be talking about how the formation takes place in those ducts it is getting back to the slides. So, the duct as I was trying to show you the duct look like more like this and of the structure of the duct like this. So, these are called this is where the primary saliva is formed and these cells what you see out here this kind of you know pyramidal kind of shape kind of cell body these are called asinine cells. From these asinine cells there is lining second set of cells which are present underneath are the lining out here. So, this is something like this these are called the connecting segments what I am doing now is that individual lining it is the cell individual cells which are forming the lining of this. Now, this part I will just put it in blue kind of you know just to give you an idea this part is called connecting segment. Those are the asinine cells which are involved in the synthesis of the saliva and this is where the primary saliva is formed as the saliva gets modified become like that. So, this is where this is where the primary saliva is forming and this saliva actually flows down this. So, this is where all the secretions are taking place as I was trying to tell you this asinine cells are involved in this and these asinine cells are essentially involved in the they are involved in the secretion and will come to that what kind of secretion they do and the walls you see there are lot of exchange which are taking place and I will come to that. So, this is the these are the connecting cells and underneath the connecting cells you have called strip segment something called strict segment which lies somewhere here and underneath the strict segment is set of cells which are present out here which are called interlobular duct before I go into that DOCT interlobular. So, the way it works is something like this. So, there are these asinine structures like this and all over. So, imagine these are the individual I have shown you one individual structure and these are you know dumping like a drain then it forms a major drain like this. So, what happens? So, if you go back to the previous structure. So, this is one unit and when these kind of duct like structures are formed there are multiple such unit and I have just drawn six for you and these multiple units actually. So, here is a secretion secretion formation here. So, this is the zone where the formation is taking place all this blue what you see I am rounding them off these are the where the formation is taking place and then they have the duct system through which all this fluid is moving like this. This is the duct system which I was drawing in the previous slide and from here all this is being secreted under the control under a very tightly regulated nervous control. So, this is the overall geometry. So, it is like this you have this asinine structure what I just now draw where this synthesis another one another one another one another one likewise and then there is a huge duct and again another set which has a huge duct coming that another set which has a there are multiple such units along these different parotid sublingual and the there are some annular parotid and sublingual blend that whole structure is called asinine structure where all this kind of secretion and as a matter of fact all across geology or anatomy if you look at it these kind of duct structures fairly similar to this there are lot of cells around and they form a duct kind of thing and where it all secreted and it moves through. So, coming back to next slide. So, what we will do now this is one thing I just slipped out from my mind I will do this will help you I told you the composition I did not tell you the electrolyte in the saliva I will come to that and then again I will come back to the synthesis structure because this will help you to realize something electrolyte of the saliva and then will come to the formation again because there is a very tightly regulated electrolyte concentration. So, the way it is x axis will be the concentration there is millimole per liter let us put it like this 20 40 60 80 100 100 20 100 40 this is 20 this is 40 this is 60 80 100 120. Now I will pick up four different colors for four different ions. So, I am picking up for sodium I am picking up red for potassium I am picking up blue for chloride I am picking up green and for HCO 3 I am picking up light green HCO 3 minus. So, if you look at it when you talk about the sodium concentration is something like this sodium by the way and the x axis is you are showing your salivary flow salivary flow will be will be in ml per minute 1 2 3 4. So, 1 ml per minute likewise and if you look at the profile of sodium sodium profile is something like this it goes up with this as the secretion proceeds and if you look at the HCO 3 profile that also follows a very similar trend like sodium but slightly lower concentration like this. Whereas, if you look at the potassium concentration which is the green. So, potassium will be something like that it increases and then it sorry something like this it remains far lower and if you look at the calcium concentration this is very interesting which is shown by 1 second I did the potassium wrong sorry I picked up the wrong color. So, let me redraw it actually. So, potassium is something like this and if you look at the chloride concentration. So, chloride concentration which is in dark green chloride concentration is very interesting chloride moves of slowly and then it becomes like this. So, this is how the chloride moves this is your potassium and you have the sodium out here and this is the HCO 3. So, this is HCO 3 minus and here you have the sodium. So, this electrolyte profile is very important because now again I will be coming back to my the asinary structure where I was coming back to the asinary structure. I will redraw that structure for you people so that we can talk about how this ionic balance is being maintained here. So, this is the duct which is getting formed and along the duct is that this is where all the saliva is getting saliva is moving and those are the asinary cells fine. So, now along this there are whole range bunch of sodium and potassium and chloride channels and their movement is something like this. So, what you see essentially here. So, sodium moves out and there is a potassium which is moving in and there are channels I will come in depth on those channels and you have H plus ions moving out then you have HCO 3 moving in mostly the potassium which is moving in and this whole process is being one of the major component in the saliva is the chloride and chloride is being regulated here by a transporter called sodium potassium to Cl minus co-transporter. This is the major transporter which are present. So, if you look at it see you are taking care of cations, cations and anions negatively charged positively charged positively charged and this is all co-transported along and they all enter inside the lumen inside the duct and there is a huge chloride channel population of chloride channels which are present there and this chloride channels are further regulated. Now, I will come on to the regulation part. So, what we will do in the regulation essentially is that I showed you this structure. Now, at this stage what exactly is happening how the movement are being regulated. So, we will be discussing that. So, if I highlight this part first picture I showed you that now I am highlighting the aciners cells the whole formation of the saliva. So, in these cells there are different kind of things. So, these are the let me just mark it aciners cells. These cells needs a lot of sodium to enter through population of sodium is essential as I have shown you that that is the highest concentration of electrolyte in the saliva and you need lot of chloride to get in. So, what regulates chloride this is very interesting to highlight here what is regulating the chloride concentration chloride is being regulated by calcium. And what essentially calcium does it stimulates the chloride channels and calcium is regulated by another series of events which I will be coming. But, before that there are other events which are stimulating the entry of calcium into this game and those are different receptors like you know substance p this is one kind of receptor. Then you have acetylcholine which we have talked about in neuromuscular junction. Then you have norepinephrine alpha and beta sub sub types these all stimulates the entry of calcium. They play a significant role in the entry of calcium and once the calcium enters into the game calcium along with in calmodulin dependent manner stimulates the chloride channels to be opened. And this calcium further gets activated by the cyclic m p the presence of cyclic m p. So, from ATP I have talked about the cyclic m p with you guys the cyclic m p along with calcium leads to the secretion of certain proteins. These proteins are also entering here. So, now you have proteins which are entering here and you have the chloride which is entering here you have the calcium which is a which is entering here and all these eventually form that whole saliva which is form out here. This what makes your saliva. Now, if you look at that previous graph which I showed you out here not this one not this one this one. If you look at this graph saliva has a huge concentration of sodium huge concentration of chloride and HCO 3. Now, if you look back out here that will help you to now if you look at it. So, this is where sodium is getting through. So, there are gated sodium channels chloride is being regulated by multiple routes through calcium specially and calcium is being regulated further by this different substance P acetylcholine norepinephrine. And then that calcium not only regulates chloride entry calcium regulated chloride entry. So, this is very highlighting feature here calcium regulated chloride entry that calcium further plays a role in secretion exocytosis of. So, here exocytosis of proteins. So, and this whole complex eventually leads to the formation of the saliva. So, this is what I wish to highlight that this is a very tightly regulated event where the nervous system plays a critical role in the formation of saliva. So, you see it is not a role of norepinephrine activating the alpha and beta adrenergic receptors. Then acetylcholine activating the cholinergic receptors you see substance P all these three regulates the calcium concentration and calcium higher calcium concentration regulates the chloride entry. The entry of chloride is further controlled by other other mechanisms which are present in the form of transporters. Whereas, the sodium enters directly and then the whole composition the fluid in the presence of HCO 3 which is HCO 3 minus which is maintaining the buffering it the presence of and then sodium you have this chloride. Then you have a bunch of proteins which makes. So, it forms a very complex mixture of different electrolytes and proteins and enzymes and even peroxide I told you told you the opposition and peroxidase which makes it is very essential that is the first set of chemicals to which a food is exposed to where it kind of started kind of making the food mushy kind of thing mushy kind of bolus which eventually goes through your isophagus and then it reaches the your stomach where it is exposed to a very high acetic environment from 7 to 8 pH it goes all the way to 1 that is the shift the food experiences. Now, what we will do? So, we have talked about let us summarize what we have talked we have talked about the composition of the saliva we have talked about the electrolyte composition we talked about the organs which are involved in making of the saliva and the rate at which they make. Then we talked about the exact formation along the assender cells how that how along this duct all these things are formed and then we talked about the role of calcium role of calcium calmotidine role of cyclic AMP in exocytosis along with calcium. Then we talked about what regulates the calcium entry and how calcium regulates the chloride concentration entry. So, now what we will do the third part the last part of this class is we will talk about all the neuronal control which regulates salivary secretion in our body coming back to the slides. So, next slide is where we will be talking about we will be drawing the. So, what we will do the easier way to draw it is something like this because there are multiple receptors which are involved here. So, this is essentially is your nose because that also plays a critical role just draw it then it everything will make sense to you guys. So, this is where you have the smell receptors coming because you know by smelling of food your saliva start secreting. So, and this are controlled. So, these are the smell of a food and this is controlled by hypothalamus and which is further controlled by the higher centers of the brain this is the first level. Then that same hypothalamus is controlling the salivary centers from here to here you have let me put some dark color that will help you to understand. Here you have a parotid gland parotid and here you have just underneath your teeth out here you have the sublingual and very close to it sublingual and very very close to it some out here just out here this is all connected with each other by the way is submandibular gland. So, these all are connected from the salivary centers these all are connected by this all are connected by this sympathetic and parasympathetic further this also connect to the parotid. So, these are the sympathetic and parasympathetic control. So, this is where all these controls are taking place and apart from it there are another set of controllers which are present here which includes your whose receptors are all over the place this is those are the taste and touch they are all connected with the higher centers of the brain. So, essentially what is happening is that this whole thing has been controlled at multiple level it is controlled by the higher centers of the brain which are telling hypothalamus to act then or hypothalamus receives a signal based on that it acts vice versa it is a two way traffic and then underneath you have the salivary centers which are controlling of all these secretions by employing the sympathetic and the parasympathetic route and whereas, apart from it you have this smell centers you have the touch when the food comes in contact and apart from it you have these taste buds which are also sending signal to the brain. So, it is a very complex process and a very complex computational process by which saliva formation is being regulated by the nervous system. So, to summarize we talked about the composition we talked about the electrolyte composition talked about where saliva is being formed and it is being formed what are the different sodium channels which are there there are sodium potassium and chloride co-transporters which are involved in it and then we talked about the exact anatomical features of the as in ourselves which are involved in the synthesis of the or the formation of the saliva along its duct system and we I tried to give you a visualization of how the duct system really looks like and here we we are closing on the lecture by the different nervous system routes which are controlling the secretion process of the saliva. Thank you the next we will move on to after this to the stomach where we will be talking about exactly in the same fashion we will see how the food what are the different secretion which takes place and what kind of changes which take place in the food once the food from 7 to 8 p h gets into a chamber which has a p h close to 1. Thank you.