Free Biology NEET Video Lectures for Chemical Coordination And Integration

00:00:01 [Music] la welcome everyone to today's lecture on the chemical coordination and integration systems of our body this is the part one of the lecture and in the next part you will hear uh the series will be completed so in the previous part of the lectures you have learned about the neural system and how it coordinates the various organs and the entire function of the human body today we are going to learn about the other part of the coordinating and integrating system that is present in our body which

00:01:09 is the chemical coordinating system so what do we mean by this so This actually refers to what is known as the endocrine glands and the products of these endocrine glands are called hormones so let me tell you a little bit more about this why do we need to have such a endocrine gland and hormone system as as chemical coordinators in the human body the reason is because as you have heard about the nervous system before although it is a very good and quick method of regulating and coordinating the multiple

00:01:44 actions that take place throughout the human body however nerve fibers do not innervate all cells of the body and because of this the cellular functions need to be continuously regulated and many of the cells in the body in many different organs do not have a direct inovation from the nervous system so their cellular functions are not regulated by the nervous system so in order to regulate these cellular functions in different organs that are situated all over the body you need another special kind of system so the

00:02:16 special kind of system for coordination and integration is the hormonal system and the product of the endocrine glands which are the hormones so classically hormones have been defined as the product of the endocrine glands and we will come to know about more details in today's lecture so as I've have said before the neural system and the endocrine system are the two arms of the coordinating system within our body and they jointly coordinate and regulate all the physiological functions that are

00:02:48 present in our body so endocrine glands what are these so endocrine glands are typically known as ductless glands what do we mean by ductless glands so normally many glands that you've heard of in your body have du ducts for example the pancreas is a gland the pancreatic duct is what is like a tube that connects the um pancreatic gland to the digestive system so this tube is the duct through which the product of this gland can travel and enter the digestive uh the digestive tube so similarly the endocrine glands

00:03:25 however also produce hormones but they do not secrete them through the ducts rather they secrete them directly into the bloodstream hence endocrine glands are known as ductless glands and their secretions as I already referred to before are called hormones so I was telling you that classically hormones were defined as the product of an endocrine gland which is released into the blood and very importantly transported to distantly located Target organs this concept of something that is far away from the site of the gland

00:04:02 where the hormone is produced being regulated by the hormone is what was used classically to define hormones however this classical definition has now been updated and it is a little bit different it has become more broader to include many more substances that can also be called as hormones so the current definition of hormones are that hormones are non-nutrient chemicals which act as intercellular Messengers that is Messengers between cells that communicate from one cell to the next and are produced in Trace Amounts

00:04:37 they're not produced in huge quantities unlike certain things like digestive enzymes okay so this current definition of the hormones is much much broader hence it covers a large number of new molecules in addition to the hormones that we already knew from the classical definition of hormones which are secreted by organized endo glands now invertebrate systems have very few substances that function as hormones and whereas in vertebrates including us humans there are large number of chemicals which have been

00:05:13 classified as hormones so let us learn then about more about these hormones in more details since we're going to study the human endocrine system there are uh several endocrine glands that produce hormones and some of these are not GL PL but they are tissues or cells located in different parts of the body which together constitute the endocrine system and this is depicted in this diagram uh that I'm showing you here so there are many different uh tissues and organs which come under this uh endocrine

00:05:47 system and we'll discuss all of them uh one by one so you may have heard of many of these so the pituitary which is situated in the brain then um the pineal gland which is also very closly situated to the pitutary in the brain and then you come down lower there is in the throat there is the thymus gland in the chest and the thyroid and the parathyroid glands in the uh throat at the beginning of the throat and then if you go down further below we have this huge gland called the pancreatic gland

00:06:21 which performs uh several uh functions that are important for digestion of food and then on top of the two kidneys we have this triangle shaped gland which is called the adrenal gland and then further down below when as part of the reproductive system which is different in the males and the females you have the ovary in the females and the testes in the males which perform regulatory functions for the reproductive system so in addition to this classical uh endocrine glands that many of you might be familiar with today's

00:06:57 definition also includes some other organ orans under the um endocrine system so what are these organs there is the gastrointestinal tract the liver the kidney the heart they are also known to produce certain substances that communicate between cells and are produced in Trace Amounts hence they fit into the non-classical OR current definition of hormones and we will learn about all the products of the classical endocrine system as well as the newer definition of the endocrine system uh in this lecture and the part two of the the

00:07:30 lecture which is to follow after this so first we will talk about certain general characteristics of hormones and how they function so the types of hormones uh that are there they can be classified into few different groups based on what kind of chemical composition these hormones are made up of so they can be divided into one class which is composed of peptides or Pro polypeptides or longer chains which are made up of many many amino acids and are called as proteins and the examples of these are insulin which is produced from

00:08:10 the pancreas and glucagon also produced from the pancreas many of the pituitary hormones and also the hypothalamic hormones now I have not mentioned the hypothalamus explicitly in the previous slide but actually the hypothalamus is a part of the brain but it also performs uh endocrine functions because it secretes many hormones which you will see in the coming slides so other than peptide and polypeptide and protein hormones we also have a second type of hormones which are known as steroids so these steroids are different from

00:08:44 proteins and peptides because they belong to the lipid class of macromolecules and the examples of these are cortisol testosterone which is secreted from the testes estd oil and progesterone which are secreted from the ovaries in females so these are reproductive hormones as well as certain other hormones produced from the adrenal gland are called together as steroid hormones now the second uh class was steroid hormones the Third Kind is actually divided into two groups one of these is called iodothyronines they are derived from

00:09:20 amino acid tyrosine but they are distinct from the other class in that these tyrosines are modified by the addition of the um iodine on them so these iodothyronines are what is comprises the thyroid hormones and amino acid derivatives uh other than these um Ido thyronine are known as epinephrine and norepinephrine these two are secreted by the adrenal medula in the adrenal gland so we will learn about all of these various classes of hormones in much greater detail in the rest of this lecture now that you know that there are

00:09:58 different types of hormones let us learn about how these hormones are produced and how they are secreted from the endocrine glands so the polypeptide and protein hormones we will talk about first so these are actually produced in the endocrine glands and stored inside the cells in secretory vesicles ready to be released when needed right so how does this process actually take place so this is a diagram of a typical eukaryotic cell and you familiar with this so here is the nucleus and here is the um endoplasmic

00:10:38 reticulum with these dots which are the ribosomes for protein synthesis and then we have the g g which is located here right and there are many many smaller circles here which are called the secretary vesicles Okay so so most of the hormones that are polypeptide or protein in nature are uh the major class of hormones that are present in our body the protein and peptide hormones are produced by transcription of genes in the nucleus and the MRNA when it comes out of the nucleus it goes to what is

00:11:18 known as the endoplasmic reticulum and there the ribosomes which try to translate this mRNA sit on the endoplasmic reticulum and because this is a secretory protein it is translated meaning it protein is made from the MRNA and this protein goes into the Lumen of the endoplasmic reticulum and there it is released however they are synthesized as larger proteins than actual the actual hormone that is secreted out of the cells these are not biologically active and they are called as the prepr hormones now I'll explain to you

00:12:01 what the prepro term means and what it actually means is say this is actually the full length of the prepro hormone and this is the full length of the polypeptide or protein chain that is produced now there is a small part which will be cleaved about cleaved out and then this will become the pro hormone now this part will be further processed and some more segments will be removed and then this will be become the final version of the hormone which is biologically active and ready to be secreted out so this processing of the

00:12:37 hormone from the prepr version takes place partly in the endoplasmic reticulum so the smaller pro hormone is actually produced in the endoplasmic reticulum and then it is secreted out of the endoplasmic reticulum in vesicles so these vesicles contain the pro hormone inside now where do they go after after this so after they are secreted out of the sorry not secreted out released from the endoplasmic reticulum in these vesicles these vesicles carrying the pro hormone will fuse with the GGI you know

00:13:14 that GGI has three different uh Parts the Cy trans and the median GGI and the different parts are specialized to perform different functions so these vesicle will fuse with the CIS part of the GGI compartment and there it will undergo go step-wise modifications and further processing so what will happen it will cleave the pro hormone into smaller biologically active version of the hormone so the actual final processing of the hormone is taking place in the GGI complex and as it goes through the uh various stacks of the GGI

00:13:50 from the Cy to the trans at the trans fate what is released out is this vesicle containing the final processed biologically active version of the hormone now this hormone is stored in the cytoplasm ready to be released when needed from the cell this is the plasma membrane of the cell which is a lipid B layer and this cytoplasmic vesicle with the hormone sometimes remains in the some cases in the cytoplasm itself or sometimes it is closely associated with the membrane waiting for the trigger to release it so this trigger occurs when

00:14:29 then these secretory vesicles will then fuse with the membrane and release this so the trigger comes from some kind of a uh signal which comes from outside the cell and this signal conveys a message into the cell which usually leads to the increase in the levels of intracellular levels of calcium this high level of calcium is what triggers the fusion of these vesicles with the plasma membrane so the vesicles are also Bound By A lipid Bayer and as they fuse with the membrane they will release their

00:15:06 contents out into the extracellular space into the interstitial space and sometimes directly into the bloodstream so this process is called as exocytosis and through this secretion of uh protein or peptide hormones takes place now let's look at steroid hormones the other kind of hormones that we know about so these steroid hormones are usually synthesized from a molecule called cholesterol which you have probably heard a lot about this cholesterol is the normal constituent of animal cell plasma membranes right and

00:15:44 these steroid hormones are not stored so they are synthesized as and when they are required from the precursor which is called cholesterol and they're released as in when required so this is the structure of cholesterol and the structure of these steroid hormones because they are derived from cholesterol they resemble cholesterol to a large extent and what do they look like they are lipid soluble because obviously cholesterol is a lipid molecule and it consists of three six carbon Rings cyclohexane rings and one

00:16:22 five carbon cyclopentane ring besides this there is an additional group attached here and there is a hydroxy group attached here now when this cholesterol molecule under goes a series of modifications so different groups are attached or removed from this molecule it results in the formation of the different kinds of steroid hormones that we will talk about later anyway the large stores of cholesterol Esters are present in the cytoplasm in ready to be mobilized into steroid synthesis when necessary so when

00:16:59 the cell that makes these hormones these steroid hormones receives a signal from outside that yes you need to release these hormones into the blood what it does it rapidly mobilizes the stored cholesterol and synthesizes the steroid hormones that are necessary through the action of several enzymes that are involved in this pathway and then finally because the steroids are highly lipid soluble they don't need to be packaged into vesicles as they are synthesized they can simply diffuse AC Ross the cell membrane and enter the

00:17:31 interstitial fluid and then the blood where they have to bind to certain proteins in order to be transported to the Target organ their destination right so with this we'll now move on to the third type of hormones which are called as Amino hormones so these Amin hormones are derived from this amino acid tyrosine and there are two kinds one group of hormones are derived from tyrosine the thyroid gland secretes these and these are called the pyronin and the other group of hormones are secreted from the adrenal medula and

00:18:06 these are called as um adrenal medary hormones which are epinephrine and norepinephrine so first I will talk about the tyrosine which is turned into thyroid hormone in the thyroid gland so these both these kinds of hormones however are produced from tyrosine through the action of a series of enzymes which are present in the ooplasmic compartments of these cells in case of thyroid hormone it is synthesized and stored in the thyroid gland so if this is a cell typical cell in the thyroid gland it incorporates the

00:18:46 tyrosine into it transports it inside and then on the other surface in the Lumen facing the Lumen of the gland you have addition of iodines to this thyrosine so this gives rise to two kinds of molecules triiodothyronine or thyroxin which has four iodines so this T3 and T4 are then again taken up back into this cell and they are Incorporated because they tyrosines they're amino acids so they are incorporated into the synthesis of this protein which is called as thyroglobulin and once it is incorporated into this thyroglobulin it

00:19:30 is stored in that form until there is a trigger which tells the Cell release the thyroid hormone so this then activates a peptidase which Cleaves off the tyrosine residues it Cleaves off the T3 and the T4 which are then released into the bloodstream so in this way the thyroid hormone is released from the thyroid gland the other class of amine hormones are also derived from the amino acid tyrosine but they are produced by the adrenal medula and they are called the epinephrine molecule and the nor

00:20:07 epinephrine which are together known as camines okay these camines are taken up into pre-formed vesicles and stored until secreted but how are they generated so the first step starts with tyrosine or L tyrosine which is an amino acid so a hydroxy group is added by an enzyme which leads to formation of dihydroxy phenyalanine which is in short known as elopa so this lopa then loses a carboxy group and it becomes dopamine now this dopamine then again loses a hydroxy group and becomes norepinephrine then another enzyme will

00:20:50 add a methy group to this and then this becomes epinephrine so as you can see nor epinephrine and epinephrine are both very closely related to each other they are synthesized in the same pathway and they only differ by the addition of one methy group so these are camines and they are similar to protein hormones they are stored in secretory granules these are also released from the adrenal medary cells by exocytosis just like I described for the polypeptide or protein hormones with this we have learned about

00:21:26 how hormones are produced in the cells in the uh that form the endocrine glands and how they're released on triggering uh how their release is triggered by certain stimuli which these cells receive then let us talk about the next part which is the mechanism of action of these hormones fine these cells are produced by the endocrine glands and they're released into the blood then they bind to certain proteins in the blood and they're transported to all different parts of the body then what do

00:21:55 they do they have to act on what is known as their target organs and produce certain physiological functions so how does this happen hormones produce their effects on target tissues by binding to what is known as specific proteins which are hormone receptors now you I will introduce you to the concept of a receptor so a receptor is a molecule which is present on a particular cell which is able to recognize to and specifically bind to another molecule which is known as the liend so the liend in this case is the hormone so the

00:22:35 target tissue in other words must contain a hormone receptor in order to become a target for that particular hormone Now The Binding of the hormone to its receptor leads to the formation of what is known as a hormone receptor complex so if this is the receptor molecule which is present on the plasma membrane of the cell well the hormone comes along and it binds to the receptor specifically doesn't bind to any other protein that is present on the cell or any other cell and together this is known as the hormone receptor

00:23:12 complex this receptor as I said specifically binds to one hormone only and hence receptors are very very specific hormone receptor complex formation leads to certain biochemical changes that will occur inside the cell in in the Target tissue which will be manifested as the physiological function of this hormone so we look into that in a little bit more detail in the next few slides so how are hormone receptors then communicating this process of binding of the hormone to the surface the first step of the hormone's action is to bind

00:23:52 to specific receptors at the Target cell now I told you that cells that are Target targets must have receptors any cell that lacks receptors for for this particular hormone will not be able to respond to the hormone even if the hormone is present right outside the cell so the locations of different hormone receptors are different depending on what kind of hormone we are talking about and so we are going to classify them according to where the receptor is located in the cell so the first kind which I already

00:24:29 described is the receptor which is located in or on the surface of the cell membrane usually it is a protein which is embedded into the Bayer or the plasma membrane the membrane receptors are specific mostly for protein peptide and camine hormones so those hormones which are protein or peptide in nature or the camine hormones have membrane bound receptors and and you have to think about why it is so and towards the end of the lecture I will try to answer that question for you now in the cell cytoplasm so there are another class of

00:25:11 receptors for a different type of hormone which are present in the Target cell cytoplasm not on the membrane so the primary receptors for different steroid hormones are found mainly in the cytoplasm why because steroid hormones can easily enter into the cell so so once they enter into the cell they can have the receptor in the cytoplasm they don't need to have it on the surface of the cell in the membrane in order to detect the presence of the hormone so since they can enter into the cell these

00:25:42 receptors are found in the cytoplasm now another type of intracellular receptors are also there which are found in the cell nucleus within the nucleus so this is the thyroid hormone receptor which is found in the nucleus and is believed to be located in direct association with one or more chromosomes meaning it is bound on the DNA and ready to go so in the next few slides we'll learn about what it exactly does why is it bound to the DNA so let's first talk about the membrane bound receptors so these

00:26:18 molecules which are proteins mostly they cannot enter into the cell because they're too big and they are too hydrophilic to pass through the h hydrophobic Bayer which is the membrane so therefore their receptors have to be located on the celf surface and they can recognize the hormone which doesn't have to enter into the cell so one example of such a hormone is follicle stimulating hormone I will talk about uh this in the latest slides and these usually bind to the membrane receptors The Binding of

00:26:50 the hormone triggers a change in the shape of the receptor which activates what is known as a second messenger system system so what is the first messenger here the first messenger is the hormone the hormone is bringing a message to the cell that yes there is uh uh something to be done okay because of which the hormone has been produced so now that something has to be done has to be conveyed inside the cell so since the hormone cannot get in it binds to the receptor and it conveys this message by

00:27:23 changing the shape of the receptor which activates a second messenger the second Messengers are usually very small molecules such as adenosin monophosphate or amp or calcium and we'll talk a bit about these second messengers in the next slide this second messenger activates other molecules which will convey the message further and this leads to activation of certain proteins either the messages conveyed to the nucleus or within the cytoplasm itself so these are leading to several biochemical responses within the

00:28:02 cytoplasm or sometimes this leads to entry of certain proteins into the nucleus resulting in transcription and synthesis of proteins which will then mediate the physiological response of this hormone so the message from the outside of the cell has now been communicated all the way to the genes that are present within the nucleus so two major types of second messenger systems exist so I'll there are others but I will focus on just two most important ones so these are called the Adin Cycles cyclic amp second

00:28:42 messenger system or the cell membrane phospholipid second messenger system so it describe each one of these one by one so The Binding of the hormone with the receptor in this case actually activates what is known as a g protein so if this is the the membrane bound receptor usually the liant comes the hormone comes and binds to this receptor this membrane bound receptor is associated with what is known as a g protein so this G protein will then activate another membrane bound enzyme which is known as Adin cyclas so this

00:29:21 Adin Cycles will catalyze the formation of a molecule called cyclic amp so ATP which you are all familiar with is converted to cyclic amp by this Adin cyclas enzyme so then this activates the cyclic a is a small molecule which can go and bind to another protein which is known as protein kyese which is an enzyme that can add phosphate groups to other proteins so this protein kyese is normally in an inactive form only when there is cyclicamp does it become activated and now it can add phosphates to various other proteins and

00:30:08 activate them in turn ultimately this often results in activation of several cytoplasmic proteins or even the activation of certain nuclear proteins which leads to Gene transcription the other second messenger system is actually uh involving the phospholipids which are present in the membrane so some hormones will activate receptors that binding of the hormone leads to activation of an enzyme called phospholipase C this phospholipase C enzyme will act on the phospholipid that is present in the membrane itself so

00:30:50 this phospholipid which is present in the membrane itself has a polar head group and it has two hydrocarbon chains which are hydrop iic in nature so this phospholes C enzyme actually splits this phospholes molecule which is p I2 into two components ip3 and Dy glycerol or D A what this ip3 does is it goes to the endoplasmic reticulum and this endoplasmic reticulum stores a lot of calcium inside so ip3 binding to its receptor on the ER leads to release of this calcium from the stor that is in the ER right now calcium is

00:31:35 released in the cell and D is also there so this calcium has certain effects it activates certain proteins and D also activates another protein cyas which is known as protein kyese C so this protein kyes C then again catalyzes the phosphorilation of many other enzymes or proteins in the cell and leads to the cellular response of this particular hormone system so now we have learned about those hormones which interact with membrane bound receptors how they convey the message into the cell by binding to

00:32:14 the receptor activating second messenger systems which can be of various types ultimately leading to modifications of several proteins by enzymes which lead to their activity and the response of the cell now what about about those hormones which have intracellular receptors as I told you before there are two kinds steroid and thyroid hormones which both have intracellular receptors and they're usually present binding of these receptors to the proteins uh to these sorry steroid hormones they lead to binding to

00:32:49 specific DNA sequences which cause gene transcription so The Binding of the hormone to the receptor can lead to either entry of the hor steroid hormone as I said before its receptor is present in the cytoplasm not in the nucleus this binding to the hormone actually allows the hormone receptor complex to enter the nucleus so before this the receptor was not able to get into the nucleus so only on binding to the uh complex uh to the hormone can it get into the nucleus and then it is free to bind to certain specific points

00:34:25 on the DNA which are Upstream of certain and genes that are Target genes of this receptor and they lead to the transcription of these into mRNA which will then mediate the response of these cells so what happens here you have the plasma membrane this is the steroid hormone it comes in here is the receptor which is then binds to this without the uh hormone it was not able to get into the nucleus but now on binding to the steroid hormone it can get into the nucleus and on getting into the nucleus

00:35:00 this whole complex will bind on specific sequences of DNA and then recruit the machinery for Activation of Gene transcription so an mRNA will be made which will be translated into proteins and then mediate the response of the cell on the other hand thyroid hormone acts very similarly but there are a little bit of difference so here the recept ctors are present already in the nucleus so what do you have you have the cell you have the nucleus you have the DNA and the thyroid response genes are already bound

00:35:40 to a receptor which is poised and ready to transcribe these genes but it's not transcribing yet so what happens is as soon as the hormone enters into the cell it can also get into the nucleus and it binds to the receptor once it binds to the receptor the receptor under go a change in its shape so this change in this confirmation of the receptor allows it to Now activate transcription it becomes a transcriptional activator and it transcribes the MRNA for this Gene and this is then translated into the protein and again

00:36:16 mediates the response of the cell the main difference is in the location of the receptor between these two the steroid hormone and the thyroid hormone now let us start start with the endocrine system per se so the first one that we going to talk about is the hypothalamus so the hypothalamus is located in the brain as you have learned about in the previous lectures we talked about the neural system so there the hypothalamus was described to be in the diyon part of the brain which is in the forbrain so this is a magnified image of

00:36:54 this region so this is the thalamus and this is the hyp hypothalamus which is below it right so this Thalamus and the hypothalamus have also a stalk attached to them through which the pitutary gland hangs there so the hypothalamus is in close assoc association with the pitutary gland so this hypothalamus regulates a wide spectrum of body functions through the hormones which it secretes so it contains several groups of neuro secretory cells so these are different from all the other kinds of cells that I was talking about before

00:37:34 which are usually not neuronal in nature they are Endocrine cells present in endocrine glands the exception The Only Exception is the hypothalamus which has neurons that are capable of secreting hormones now these hormones regulate the synthesis and secretion of pitutary hormones as we will see in the subsequent slides so let us see what is the relationship between the hypothalamus and the pitutary Not only are they physically placed very close to each other they also have a hierarchical relationship for example the

00:38:10 hypothalamic hormones are required to uh release the hormones from the pituitary only when the pituitary cells receive the signal from the hypothalamus do they release their own hormones so what are the these kinds of hormones that are produced by the hypothalamus there two kind kinds they are known as releasing hormones and inhibiting hormones the name itself tells you what they mean so the releasing hormones will stimulate the secretion of pituary hormones and the inhibiting hormones will inhibit the

00:38:42 secretion of certain pitutary hormones so this is a diagrammatic representation of the hypothalamus and the closely associated pitutary gland which is there in the brain the hypothalamic hormone an example of this releasing hormone is the gonadotropin releasing hormone which is in short known as G&R this stimulates the pitutary gland to synthesize and release a class of hormones known as gonadotropins while somatostatin is an example from which is secreted from the hypothalamus but belongs to the

00:39:19 inhibitory kind of hormone which inhibits the release of the growth hormone from the pitutary gland so these are two examples one one of a releasing hormone and the other of a inhibiting hormone these hormone how are they conveyed from the hypothalamus to the pitutary so these hormones originate in the hypothalamic neurons so these are the hypothalamic neurons which produce them and they travel in membrane vesicles through the axon come to the synapse or the end of the axon and are released here in by the fusion of the

00:39:56 vesicles to the membrane brain on this surface and this is very close to certain blood vessels which are called as the portal circulatory system so this portal circulatory system picks up these hormones and conveys them directly to the anterior pitutary and most of these hormones are required for releasing the hormones in the anterior anterior pitutary the posterior pit on the other hand is a different story here there are no cellss celles which release hormones but the hypothalamic neurons of a different class have their

00:40:35 axons terminating directly within the posterior pitutary and they release the hormones directly within the posterior pitutary and these then become as though they are being released from the posterior pitutary cells themselves but they are not they are being released from the hypothalamic neurons and then these posterior pitutary um hormones are then further taken up by the Circ system and taken throughout the body from the posterior pitutary okay let's talk about these various releasing and inhibitory

00:41:08 hormones that control the function of the anterior pitutary gland primarily because as I told you the posterior gland doesn't have any direct secreting hormones that are produced by the posterior pitutary so in the anterior pituary there are several releasing hormones which will act on the anterior pituary what are these they're known as thyrotropin releasing hormone so all these names themselves will tell you what they do so this is abbreviated as trh which causes the release of thyroid

00:41:39 stimulating hormone or TSH from the anterior pitutary then corticotropin releasing hormone of CR causes the release of AC from the pitutary gland so here we are talking about this region of the brain and all the local activity that is taking place here then growth hormone releasing hormone ghrh the name says it also causes the release of growth hormone from the anti- repit and now comes one inhibitory hormone which is called as somatostatin which inhibits the release of growth hormone so growth hormone has

00:42:22 two Regulators a releasing hormone and an inhibitory hormone both from the hypothalamus the SEC the fourth one is gonadotropin releasing hormone or G&R which I just mentioned before this causes the release of gonadotropic hormones such as LH lutenizing hormone and FSH which is also known as follicle stimulating hormone from the anterior pitutary and last is Prolactin inhibitory hormone so this is another example of an inhibitory hormone which causes the inhibition of prolactin secretion from the anterior pituitary so

00:42:58 these are all the various SEC releasing and inhibitory hormones that are secreted from the hypothalamus and act mostly on the anterior pitutary gland okay let's now move on to the pitutary gland so the pitutary gland as I said is located just below the hypothalamus and is connected by a stock to the hypothalamus this is located in a bony cavity within the skull which is called called as cellat and it is attached to the hypothalamus as I just said by a stock now it is divided into two parts so the part colored in Darker orange

00:43:39 here is called as the adino hypothesis and the part colored in lighter orange here is called as the neuro hypothesis so I have kind of explained to you what this means uh so I will not say that again so the adino hypophysis is the anterior pitutary and it consist of two portions one is called as the parse distalis or the distal portion and the other is called as the parse intermedia which is the intermediate portion in the human pitutary most of these uh cells are actually merged together so there it is hard to

00:44:13 distinguish between the pars distalis and the pars intermedia okay so what are the hormones that are produced by the par distalis you have already kind of heard them in the context of the releasing hormones that are produced from the hypothalamus so the first of these is the growth hormone which is abbreviated as GH second is Prolactin which is called PRL thyroid stimulating hormone which is called TSH adrenocorticotrophic hormone called AC leutinizing hormone called LH and folicle stimulating hormone abbreviated

00:44:53 as FSH so these are all of the hormones that are secreted from the anterior part of the pitutary the pars distalis part now another hormone is also secreted from the anterior pitutary the parts intermediate part and this is called as melanite stimulating hormone or it is abbreviated as msh now let's move on to the posterior part of the pitutary and although this does not secrete hormones by itself it has the hypothalamic axons uh neurons that have their axons within the posterior pituary and they release two hormones which are

00:45:32 stored in the posterior pitutary this is oxytocin and vasopressin which as I said are actually synthesized by the hypothalamus and transported axonally to the neuro hypothesis now let us talk about the functions of each of these pitutary hormones one by one so first we will talk about the hormones of the anterior pitutary and the first among these is known as growth hormone as the name itself suggests growth hormone is promoting the growth of many many body tissues so growth hormone is also called

00:46:10 as somatotropic hormone Soma means cell so somatotropic means something that causes the growth of cells or somatotropin it is a small protein molecules contains only 191 amino acids and all in a single chain and has a molecular weight of about 22,000 Daltons it causes the growth of all tissues in the body that are capable of growing at a particular time so if you provide with growth hormone not all tissues are capable of growing only those that are capable of responding to this growth hormone will respond by

00:46:46 growing so what does it do to promote growth it increases the sizes of the cells so the cells become bigger it increases mitosis which is cell division or cell proliferation so one cell becomes two with the development of Greater number of cells and specific differentiation of certain types of cells so these cells will not only divide and increase in number they will also undergo this process of differenciation which is known as specialization so that they become uh specialized to perform the function that

00:47:20 they are supposed to perform in that tissue or organ and for example bone growth and early muscle cells are known to respond very much to growth hormone now what if you have an imbalance in these hormones so there are certain conditions under which you can get excessive secretion of growth hormone and this promotes naturally abnormal growth of the body leading to what is known as gigantism so you might have heard of certain people who are abnormally tall for example 8 ft or I don't know what the Guinness Book of

00:47:56 World Record is right now so such people are usually uh that tall because of excessive secretion of growth hormones and the opposite end of the spectrum on the other hand is decreased secretion of growth hormones so this as you may have guessed leads to dhism a particular type of dwarfism which is called pitutary dwarfism because it is due to the growth hormone deficiency which is produced by the pitutary gland so now you know what the function of growth hormone is so the next hormone that we will talk about

00:48:28 also from the anterior pitutary is Prolactin so prolactin as the name suggests Pro and lactin lacto refers to milk so it is regulating the secretion of or production of milk in the memory glands and it also regulates the growth of the memory glands themselves so it is to deal with reproductive functions when the um memory glands are required to produce milk prolactin will stimulate this process then we come to the next one which is TSH so now we are moving down into the sight of action of these hormones so we

00:49:07 have already talked about prolactin which acts on the memory glands now we are going to talk about thyroid stimulating hormone which is produced by the anterior pitutary and acts on the thyroid gland so this stimulates the synthesis and secretion of thyroid hormones from the thyroid gland and the name explains why it is called as the thyroid stimulating hormone the next one is called act or adreno corticotrophic hormone which is again released from the pitutary gland but acts on the cortex of the adrenal gland which is

00:49:43 situated on top of the kidneys and this leads to the secretion of hormones called as glucocorticoids from the cortex of the adrenal gland so the adrenal gland has two regions the outer region is called the cortex and the inner region is called the medula so we have already heard of certain hormones that come from the medula remember epinephrine and norepinephrine and now we are talking about certain steroid hormones which are produced by the cortex now the last hormone in this series is gonadotropins

00:50:19 which are LH and FSH they're two hormones so together they are called as gonadotropins and the name itself tells you they work work on the gonads which are the reproductive organs the ovaries and the testes and they function to cause several uh effects on the ovaries and the testes which I'm going to enumerate now so they have different activities in males and females in males the lutenizing hormone or LH stimulates the synthesis of hormones called androgens which one of which is you might be familiar with

00:50:54 testosterone from the testes in males FSH on the other hand stimulates the process of spermatogenesis or production of sperm in the testes in the females however they have other functions in females the same LH induces ovulation or production of OV or egg from the ovary and release of this egg from the ovary and then after the egg is actually released from the ovary there is a structure that REM remains in the ovary which is called the Corpus litium CL I will abbreviate it as CL this Corpus litium has many functions in the human

00:51:36 reproduction so this Corpus litium is maintained for some time by the action of the LH hormone now FSH on the other hand Works before this process it works to stimulate the production of the follicles maturation of the follicles in the ovary which lead to the release of the egg okay so together LH and FSH function in the reproductive U maintenance of the reproductive functions of the ovary and the testes in the females and the males respectively now uh we are still missing some more hormones which are secreted by

00:52:15 the actually the intermediate part of the um anterior pitutary this is called as melany stimulating hormone which acts on melanocytes what are melanocytes these are skin cells that produce the pigment so the color of your skin is determined by how many melanin containing cells and how much melanin they have in them so this is stimulated by msh and this regulates the pigmentation of the Skin So when you need to uh get more pigmentation for example you've been exposed to the Sun the melany stimulating hormone will

00:52:50 increase the production of melanin and it will lead to a darkening of your skin color then let us talk about the hormones of the posterior pitutary so the posterior pitutary has two hormones the first one was oxytocin so oxytocin is known to act on the smooth muscles of our body so if you are aware there are two kinds of muscles rather three kinds of muscles in our body the skeletal muscles which are present in the limbs and which are required for movement then we have smooth muscles which are lining

00:53:24 the internal organs in our body including cluding the blood vessels and the gut which are required for the contraction or movement or motility of these um of whatever passes through the gut or in the in case of blood vessels it regulates the constriction and relaxation of blood vessels and the broni which are there in the Airways all of these have smooth muscles the Third Kind of muscle is the cardiac muscle which we have referred to when we talked about the circulatory system so anyway oxytocin acts on the smooth muscles of

00:53:55 the body and stimulates the contraction and this is particularly of importance in certain cases in females it stimulates the vigorous contraction of the uterus at the time of child birth and it is required for ejection of milk from the mamory gland so there also it requires um certain muscles to be contracted for ejection of milk from the memory gland when the baby is suckling so this is the function of oxytocin and then we go to the next one or the last one which is vasopressin this as the name tells you itself

00:54:34 vasopressin regulates the constriction of blood vessels it is actually acting mainly in the kidney and stimulates the resorption of water and electrolytes by the distal tubules and thereby reduces the loss of water through the urine this process of loss of water in the urine is known as diuresis so therefore the other name of vasopressin is anti diuretic hormone or ADH it prevents the loss of fluid in the urine so when you've had a lot of loss of fluid because of other reasons you have evaporated as you have sweed a lot

00:55:13 or you have lost a lot of water because you had diarrhea and and the gut was not able to absorb enough water then your body needs to conserve water so then this vasopressin will come into action and it will cause it will concentrate your urine so that you don't lose any additional amount of water in your urine and you're able to conserve the water in the body so this is why it is called as antidiuretic hormone so with this I'm going to finish today's lecture but before I go it's time for

00:55:44 questions so what are the questions that I will discuss with you today so the first question is what are the differences between the steroid hormones and the thyroid hormone in terms of the mechanism of action so this I have already described to you before the steroid hormones and the thyroid hormones both are able to enter into the cell but the receptor is located for the steroid hormone in the cytoplasm whereas in case of the thyroid hormone it is located inside the nucleus already bound to the DNA but in either cases the gene

00:56:25 transcription is not active without the presence of the hormone when the hormone enters if it's a steroid hormone it will somehow allow this whole complex to enter into the nucleus and when it is a thyroid hormone it straight goes and binds to the nuclear receptor and this initiates the process of transcriptional Activation so this receptor hormone complex is now able to transcribe genes that are targets of this hormone system so this is the primary difference between the two now the second question

00:57:00 is which part of the endocrine system has neurons that secrete hormones and this is very easy which I've already discussed with you this is the hypothalamus so remember the hypothalamus is made up of specialized kind of neurons which are neuros secretory in nature meaning they don't just produce neurotransmitters they also produce certain hormones and their axons either communicate these hormones and release them into the blood vessel system or in case of the posterior pitutary they secrete them directly into

00:57:37 the posterior part of the pitutary gland so these are the neurons that actually can secrete hormones the third question is how do hormones that bind to the membrane receptors regulate the function of the cell so these hormones are out outside the cell how are they going to communicate that that they're there to the cell inside so how do they do this is through the following process they have certain membrane bound receptors when the hormone comes along it can bind specifically to these membrane bound

00:58:14 receptors by the way only in those cells which have the receptors so these cells will then be able to receive the signal in terms of the hormone binding to the receptor but this re a signal has to be conveyed to the inside of the cell how is this done this binding causes a change in the shape of this receptor once this receptor is changed it activates certain other proteins which are associated with it which will result in the production of certain second messengers so the second messenger system is used to communicate The

00:58:50 Binding of the hormone to the receptor and finally activate more cellular protein which are actually kinases which can phosphorate other proteins and activate them further ultimately mediating the activity or response of the cell to this hormone now what is the hierarchy of action within the endocrine system I don't know if you notice this because I didn't explicitly talk about it but there is a hierarchy and this hierarchy begins top down both anatomically and with respect to function so the brain

00:59:27 which is the master regulator of everything has the top boss of this whole system so this is the hypothalamus which releases what is known as releasing hormones or inhibitory hormones so these releasing hormones and inhibitory hormones will act on the pitutary which will cause or regulate the release of pitutary hormones which are usually called as stimulatory hormones so the stimulatory hormones then will act on different endocrine glands ranging from the thyroid gland to the adrenal gland to the testes and ovaries to the pancreas 01:

00:06 and so on and regulate the release of various hormones from there so this is the hierarchy that exists in the endocrine system now the last question is how do you determine if a particular organ or tissue is the is that Target of a particular hormone so the way you determine this this is by detecting the presence of the receptor first on that organ or tissue only if that organ or tissue has the receptor either displayed on the membrane or present within the cytoplasm or nucleus depending on the 01:

00:44 kind of hormone will it be able to be a target for that hormone not only this it also has to respond to the presence of the hormone by activating the signaling Cascade Downstream which will ultimately lead to the response or the physiological response that is expected so with this we end today's lecture and thank you all for [Music] listening