 So, welcome back to the NPTEL series of animal physiology lectures. Today, we will be starting a new unit endocrinology and reproduction. So, this unit, so just to give you an overview, body is controlled by three sets of systems. One is the nervous system, which we have completely covered and you must have appreciated it at different level of our body control system, how the nervous system plays a very important role. The second line of command, which dictates a lot of our physiological activity, especially the way the autonomic nervous system controls. So, many functions is regulated by the endocrine system and the third system in that line, which we have not touched it will be coming as the immune system. So, now we will be talking about the endocrine. So, what really is endocrine? So, technically speaking there are different modes of information transfer within the body. One of the mode, which we have studied very extensively is the synaptic mode, where you have a presynaptic neuron and then there is a postsynaptic neuron. So, when the presynaptic neuron secretes a neurotransmitter, postsynaptic neuron accepts it and then conveys the message or transmit the message to the next, like if you consider them as node from one node to another node to the third node to the fourth node, likewise along the nodes that information travels. This is one mode of transport or one mode of control route. The second mode of transport is the endocrine mode, where you have to do a very long term transmission. So, let us formally start it. So, we are in this section. So, this section is basically endocrinology and reproduction. So, this is our first lecture in that series, endocrinology reproduction in this section once again. So, there are different modes of information transport. Let us enumerate all the different modes of information transport. So, one of them which just now I discussed with you is called synaptic mode, where you have a presynaptic neuron. This is presynaptic and here you have a postsynaptic neuron and you have the neurotransmitters which are sending the signal from pre to post. So, then there is another mode which is called autocrine mode. Autocrine mode means here you have a cell. This cell secretes certain chemicals which act on the cell itself or two. It means on itself. So, this is the second mode of transport. The third mode of transport in that line is something called a paracrine mode. So, this is cell 1 and this is cell 2. Just for simplicity sake, it could be here a cell 3, you know there could be nth number of cell n in a close proximity, but always remember they are in a close proximity. So, if this cell secretes some information say for example, from this cell there is a secretion of some kind of compounds secreted by this. These compounds are being received by these cells likewise from 1 to be from 1 to 2, 1 to 3, 1 to 4. So, this mode of transport is called paracrine mode of transport. Now, there is a third mode of transport which is called endocrine mode of transport which is also called in other word it is also called a long distance transport. Something like say for example, imagine say for example, let me just once again from the brain and this is the spinal cord and say for example, from somewhere out here. So, this location from here some signal has to reach all the way to say somewhere in your hand or somewhere in your say your kidney and which is not following the neural route which is not following a neural. So, long distance transport these kind of long distance transport is exclusively carried by the blood vessel and that is fall under endocrine mode. Endocrine and if I had to given outline of the endocrine mode it pretty much looks like this there is a endocrine system which consists of and we enumerating them. So, endocrine system the major function of the endocrine system is to regulate the metabolic function. Now, wide range of metabolic functions are being regulated by the endocrine mode metabolic functions. So, how it does so? So, the way it does is they secrete hormones these are series they are different kind of hormones and will come to that into the blood and these hormones have specific receptors. So, for example something say for example, let us give you a simple example that will help you to understand say for example, in your kidney something is secreted kidney has one of the endocrine blood which is called adrenal. So, this is the adrenal just on top of kidney say for example, adrenal secrete some specific say some specific hormone. So, this hormone what this will do is essentially this hormone let me put this in green will be easy to show the blood vessel. So, this particular hormone from here along the blood vessel will travel to say for example, it has to go to the go to see your heart say for example, it has to do something in the in your heart this is your heart. So, what will happen is that along the blood vessel this compound will travel, but while it is travelling along the along the blood vessel. So, along this blood vessel this is crossing through several other systems it is not that that this is exclusively that you know from this compound will there is a separate channel from the adrenal along the kidney it will reach to the heart it is travelling all along the body because the blood is circulating, but then how it identify that it has to reach to the heart it is just like say for example, you have a how the postman identifies think of it how a postman identifies that this is your address this is where I have to deliver house number say 23 and say gully number this or street number this and the city x y z and then the state and then the country and then there is a something called you see the pin code or a zip code a six digit number by which you identify. So, there are several level of identification same way in the biological system there are another same way there are kind of a zip code or a pin code in the form of these heart has specific receptors for this particular molecule all along wherever it has the target. So, whenever this receptor identifies the molecule out here it binds on them and then it shows its action. So, this kind of transport which is completely dependent on the blood vessel except one region I will come to that where it is not blood vessel dependent it is neural dependent other than that it is all blood vessel dependent. So, this mode of transport is this mode of information transfer falls under endocrine system. So, this is the broad overview of the endocrine system. So, and to summarize up till now. So, I told you about synaptic mode paracrine mode auto-crime mode and here you have the endocrine mode. So, next what we will do we will enumerate all the different endocrine systems which are present in our body save it. So, broadly speaking now I am just showing you a cartoon and give you an idea of where each one of this different endocrine systems are located. So, up in the brain out here there is an organ called it is not very well developed in human though and I will come to that it is called pineal gland. This has this is very well developed in birds and other avian systems and some of the migratory animals where they have to kind of understand the biological clobbery right they have to understand the seasonal variation very correctly based on that they are migratory roots are being kind of dictated. So, pineal is very well developed in those kind of systems where there is a lot of interplay of circadian rhythm or the biological clock and all these things. So, this is up in the brain somewhere is located it is called a pineal gland. So, this is one of the endocrine system and the next one in the line is just if I have to draw the brain like this or let me draw it side wise then it will be easy for me. So, if this is the side wise view somewhere out here somewhere out here there is a I am just trying a cartoon out here called hypothalamus hypothalamus just never confused with hippocampus because many a times I used to do that mistake the two words are fairly close and underneath the hypothalamus just attached to it just underneath that if you anyone of you or those of you have the dissection facilities we used to do this dissection they are just underneath it is a small gland it is pretty much just underneath out here is called pituitary. Pituitary these are all very close proximity of the brain almost within the brain underneath along the trachea you have a very major organ sitting like this which is called thyroid and parathyroid. So, this one is the thyroid and R o I t and the one which you see like this is called parathyroid. Like this the bottom two also it is called parathyroid parathyroid and underneath is you have got here and I will once I will independently talk about this and I will talk about where exactly these are located thymus. This has immense role in your immune mechanics mechanism which is the third control which you are going to deal with not have a confusion arrows right. So, these are these two are adrenal which is in top of the so adrenal is mostly located if this is the kidney. So, on top of the kidney is your adrenal gland adrenal and underneath along the it is just behind it actually is the pancreas which is also an endocrine gland as well as the digestive system a major part of the digestive system pancreas and then you have the gonads or the sex organs which are involved in all the endocrine regulation of puberty and reproduction all these things. So, these are the major endocrine systems in your body starting from hypothalamus, pituitary, parathyroid, thyroid, thymus, adrenal, pancreas and gonads and they are all linked with rich blood vessels. So, what is over the secretion takes place under the influence of different control you come to those different controls they travel through this conduit tubes of blood vessels to the different organs and wherever they have their receptors they act accordingly. So, in other word what I was trying to make you understand. So, say for example, something is secreted out here and it has to so it is travelling all over the body. So, it will only reach to the place where it has the receptors it would not bind. So, it will reach everywhere, but it would not bind at any place till it finds its own receptor. So, this is very very important for you to understand because it is travelling all over the body because it is in a blood vessel, but then it will only find its wherever it will find its receptor it will bind there only other than that it is not going to bind anywhere else and this is very very important of fundamental understanding is very essential for the for this kind this system. Now, coming back to who are the systems who are controlling these different units. So, who are the control partner in this game. So, this is being controlled by one of the one which you have already studied is autonomic nervous system. This is one of the major controller then there is another controller it is the level of the hormone itself this is very important. So, if the level of the hormone exceeds certain limits which body does not need then it has a feedback loop or a negative feedback loop to say hey do not secret mode it is just like if say for example, I say I need 20 molecules the body needs 20 molecules, but if it exceeds 20 molecules then what will happen there will be an auto inhibitory effect. In other word there will be a negative feedback loop which will say please do not secret mode I have sufficient I have 20 with me and I do not need anymore. So, anything exceeding 20 I will say no shut down. So, that is another way there is a third way third way is it is being controlled like is by different metabolites say for example, glucose if there is a decrease in the glucose level in the body. So, you are kind of running out of energy molecule the glucose is our major energy molecule. So, if you tie it then this endocrine system comes into play and the then it will say hey you know I need more energy. So, I need to break down the reserve it is just like you know you are running out of money you go to the bank and tell you you know withdraw money or you go to an ATM machine you withdraw money exactly the same way hey I am running out of energy. So, there are storage molecules which breaks down and release energy. So, those kind of regulations are taken care by endocrine. So, basically what is happening if the metabolite level goes down then they get triggered and vice versa if the metabolite level goes up. So, for example, sodium goes up in the body and you have to ensure that there is not excess sodium. So, there are system which comes into play and which will be talking about it or say for example, the glucose level goes up then there are system which triggers to ensure that the glucose is being pulled out from the blood vessels because otherwise the viscosity and everything will get affected same way if the blood glucose level goes down body is kind of you know running out of energy we have to ensure that the body gets sufficient amount of energy molecule there should be a mechanism by which you can you know regulate this process. So, the metabolites is the third level of control here the metabolites. So, these are the three level of control which may be sodium it could be glucose and there with thousand other things which control. So, these are the different control units which regulates all these different seven or eight which I have enumerated for you people pituitary hypothalamus adrenal and all these things. So, from here we will move on to the next one what is the mechanism of action this is very important this is something before I draw I will give you an overall idea how they function. The endocrine function in the time window could be classified into two groups some actions may be very immediate. So, for example, the body needs energy there is shortage of glucose immediately I have to ensure within your liver you have glycogen molecules which are kind of in a thick polymer I mean like thick big polymer molecules which could be broken down to glucose. So, this is an instantaneous process it has to be done now because body cannot wait say for example, I am you are feeling thirsty now you have to drink water now you cannot wait till the evening to drink water or body is running out of energy now the body immediately needs energy this is one which is short term effect and it has to be done very fast very quick yet there are certain changes say for example, what of the changes is that while I was young I was not having this moustache. So, the moustache develop over a period of time as I was kind of in my adolescent. So, these are long term effect they take time it does not happen in a day slowly I see you know my moustache started coming and you know I become young and you know I become a youthful person or vice versa my some of these hair colors or some of these changes which are taking place they are changing they are becoming white I am getting old these are long processes these are not something instantaneous I need energy and I will get it. So, these are the two broad classification in our in the endocrine system one is a short term instantaneous effect the other one is a long term and prolonged persistent effect. So, for this kind of two pathways the body follows two different molecular routes and depending on the in result what has to be achieved by the body it decides what kind of route it is going to follow and based on that the identity of the molecules are being determined by nature where it is going to act how it is going to act. So, broadly speaking in terms of time frame if I had to classify. So, I will classify them as the if under the heading of. So, this falls under mechanism of hormone action and within the mechanism I have a rapid onset and short duration rapid onset and short duration this is one route the other one is slow onset and long duration slow onset and long duration based on that you have the two classification. So, the short one falls under second messenger pathway. So, this is the biochemical route which will be talking about second messenger pathway and the long lasting effect the other one right hand side is falls under steroid hormone action what exactly that means. So, this discuss this and then I will draw the flow chart for your better understanding graphical understanding of the situation. So, what is the second messenger system really how that word all came together. So, for example, let us go back to the diagram where I was drawing that the along the blood vessel the hormones are travelling. So, this hormone has two options. So, first of all the first first and major thing is that it should have a receptor on the surface of the target cell. So, imagine like if this is the one which is secreting hormone and this is the one which is the target this pen is the target. So, the molecule which are travelling here they should have a receptor on them first of all they have to bind to the receptors once they bind to the receptors it has two options it either gets inside the cell or it acts from outside it acts from outside. If it acts from outside then in that situation the hormone itself is the first messenger. So, it is just like a postman comes to your door and put the letter in your letter box postman is the messenger. So, just like the hormone is the messenger here and it binds to the surface of the cell the target cell. So, now within the target cell there are series of actions which takes place which are carried out by another set of messenger and that messenger if the first messenger was the hormone itself and the second messenger as those downstream which are inside the cell who are taking care of the other action and the final result resultant thing is being seen falls under the second messenger. So, with this background I will draw it that will make you to appreciate it better. So, if imagine this is the cell and this is the membrane I am drawing. So, this is the cell membrane and here you have a receptor for a specific hormone. So, and then here is the here is the hormone. So, this is the receptor in the cell surface receptor for this thing this hormone and here you have the hormone molecule. So, hormone comes along the blood vessels and it binds to the receptor once it binds to the receptor what happens inside the cell. So, this is outside the cell this is inside the cell once it binds there then it leads to a cascade of reaction inside thereby one of the major reaction which takes place which is I talked about adenosine triphosphate this under the action of an enzyme called adenylate cyclase adenylate cyclase what it does is basically it removes the two phosphate group from ATP. So, it becomes A M P. So, what is happening essentially is that adenosine triphosphate. So, there are three three phosphate moieties attached to it this becomes A M P and in that process the two phosphates are being thrown out and that phosphate which is out here it cyclized it forms something called a molecule called cyclic A M P. It is a cyclic reaction which takes place within this molecule and this is done by this enzyme called cyclase adenylate cyclase where the ATP binding site is there and it remove the two phosphates and what it does it make a cyclic molecule of A M P either it could be A M P adenosine monophosphate with a single phosphate moiety or it is a cyclic molecule called cyclic A M P. The cyclic A M P is the if this is your hormone is your first messenger and this cyclic A M P is your second messenger and this is the second messenger system and then this particular second messenger goes to the target tissue and shows its action. And one such very classic example which is being followed by the body using a second messenger system is by glucagon. Glucagon is secreted by pancreas and this glucagon goes to the liver. So, this goes to the liver and there it converts the glycogen to you and that is exactly it is the glucagon. Now, think of it if this glucagon is your this thing this moiety and let me go back to the previous slide. So, here is glucagon binding glucagon binds follows a cascade of reaction cyclic A M P and everything this cyclic A M P then involved in breaking line of the glycogen to glucose. So, this is one of the classic example other than that you have the adrenal other hormone which follows this is the adrenal gland secreting the epinephrine. This also follows the same routine as followed by the glucagon. So, this is one mode where the first messenger or the hormone is not entering inside the cell it just binds and the rest is all cascade of reactions which is taking inside the cell. Now, we will move on to the second one which is the hormone is entering. So, this is this is once again this is all about your short term always this second messenger is a short term effect short term and instantaneous effect. Now, we will move on to the long term effect what are the long term effects and how they work. So, the long term effects are dictated by the steroid hormone and how they work and most of this long term if you look at them they are mostly in the adrenal cortex. This is the example of long term effect and adrenal cortex of the gonads follow the long term rule. So, coming back so again we will draw the cell to explain this. So, this is the cell membrane here you have the hormone molecule it binds and to its receptor and directly enters inside the cell. Once it enter inside the cell most of them act directly inside the nucleus inside. So, this is the nucleus inside the cell. So, this is inside the cell and this is this whole area is the cytoplasm this is outside the cell this is the area of the nucleus. Now, once it enter inside the inside the cell inside the nucleus it binds to the receptor protein in the nucleus. So, this is the red color is the receptor protein inside the nucleus and this complex of steroid hormone and receptor protein then binds to the DNA out here and then leading to the transcription and generation of mRNA and this mRNA comes and from the ribosome the proteins are being secret proteins are being formed and this proteins then show their long term effect and this whole process is also the translation process. So, this is essentially a how a steroid hormone functions. So, a long term effect a short term effect a short term effect where you have the second messenger a long term effect where the steroid molecule directly enters inside the nucleus inside the cell and to the nucleus and there it has specific receptor protein molecules it binds to them binds to the DNA and leads to specific expression of the genes and which leads to the specific expression of the certain kind of specific proteins which are needed by the body for a long term action as I showed you development of the moustache development of the sexual behavior all these kind of things are a very long term changes they do not happen in a day they take over a period of time it happens. So, this these are the two broader ways by which the classification of the action of the endocrine system is being regulated. So, from here what we will do we will move on to the first system which will be talking about the basic architecture of the pituitary first if you remember pituitary. So, I showed you the location of the pituitary in one of the beginning slides. So, it is somewhere if this is the spinal cord and it is sitting somewhere out here small piece of small red color almond shape organ is called pituitary. So, pituitary if you have to kind of draw it it is something like this and it has two parts one part is called posterior pituitary and posterior pituitary the other part is called anterior pituitary and both have different functions and different circuits anterior pituitary and there are other terminologies for them this is also called adenohypophysis this is called neurohypophysis there is a reason for that and this is one of those I was telling rest of the places it is all controlled by blood vessel this and posterior pituitary is not controlled by blood vessels. So, pituitary is controlled by another higher center within the brain somewhere here which is called hypothalamus here is hypothalamus hypothalamus has two modes of control there are two ways by which hypothalamus can control pituitary hypothalamus is one of the master organ and it is deeply embedded within the brain. So, one mode is that hypothalamus has secret certain things and which along a small local blood vessel reaches the pituitary that hypothalamus does for anterior pituitary but for posterior pituitary I told you that there is only one place within the endocrine system which is directly under the nervous control in the posterior pituitary what happens is that posterior pituitary is in direct neural connection of the hypothalamus and that is why sometime in the literature it is also considered as an extension of the hypothalamus and that is why it is called neurohypophysis. So, after giving this idea I will show you how it works. So, if these are the neurons of hypothalamus they directly innervate within the posterior pituitary whereas, in the hypothalamus there is another set of neurons which are controlling anterior pituitary they stimulate a local blood vessel out here whenever the secretion takes place these are the blood vessels which comes and dump the signal which are sent by the hypothalamus. So, this is the basic anatopical architecture what you have to appreciate about and if these are the hormones they are travelling like this and if I had to like put this in whole perspective of the nervous system and it is like this there are higher centers of the brains which are higher centers of the brain crosstalking with the hypothalamus the double arrow showing the crosstalk hypothalamus and hypothalamus then tells the pituitary to act which is one of the master master endocrine system we will appreciate that then pituitary tells me other endocrine systems to act accordingly and there are different control mechanism in at every root how they are being controlled and there is a crosstalk. So, if you look at this these are the higher centers of the brain which are which are part of the nervous system and this is where the different system started converging and the area which falls under this whole interaction is called neuro endocrinology. This is the whole field which is developed over the years is the area of neuro endocrinology and now there is even more one addition into this which is where the immune system is crosstalking with it. So, this falls under neuro end neuro immuno endocrinology these are some of the future areas where because if you look at it initially we used to treat every system separately. This is digestive this is endocrine this is nervous this is heart or this is lungs or this is respiration but now only things are converging because we are realizing there are multiple level of controls and there are there is a integrate control of nervous system endocrine system immune system continuously at interplay it is a very dynamic system. So, the things are now the way we look at things are slowly changing and we are realizing there are common molecules look at norepinephrine. I told you norepinephrine is a neurotransmitter yet norepinephrine also functions as an as a hormone. So, see I mean the same molecule functioning as a hormone as well as the neurotransmitter. So, there is nothing called like you know very hard and fast water tight compartment no this is this and this is biology is all you know mixed up out there like chemical or the molecules changes their duty based on the context it is a very context dependent the same molecule may behave in a totally different way or follow the totally different route of action as compared to when it functions as a as a part of the nervous system as well when it is part acting as a part of the endocrine system they may convert they may diverge. So, this is these are some of the small things which you people need to appreciate. So, coming back where I was in the previous slide I wanted to I just forgot to tell you something. So, this is small local blood vessel which is present which is sending which is sending the sending the from the hypothalamus to the pituitary is also called hypothalamic pituitary hypophyceal portal system portal system. This is the direct name of the blood vessels which are local blood vessels and one more thing. So, from here one more thing I am going to show you. So, along. So, these are the blood vessels which are carrying the hormones which are secreted by. So, this is something very for you people to understand appreciate is that most of the hormones are carried by the venous bloods which is the veins which are basically receiving the hormones and they are the ones which carry it all over the body. So, this is something that is why I specifically wrote that it is the venous blood vessels which are carrying these signals. So, I will end here and then we will resume from the pituitary the next class and then we will go to pituitary and the all the hormones secreted by the pituitary and then how the hypothalamus is controlling and then we will go one by one and we will finish this section thanks a lot.