hello bio3 this will be our first lesson on the endocrine system so in this lesson I'll just introduce you to an overview of the endocrine system we'll talk about the two different broad categories of hormones which are the protein and the steroid hormones and we'll talk a little bit about some interactions in the brain between the hypothalamus and the pituitary gland so this first picture that I have here what I'm trying to show is that the endocrine system as with the nervous system it has to do with a couple of things first of all homeostasis maintain the ideal internal conditions and also communication in the case of the nervous system that communication is really shortterm in the sense that the chemical biochemical message only has to diffuse across the synaptic Clift whereas with the Endo system these chemical Messengers they're going to travel throughout the body so much much longer distance in terms of the message being sent so uh the endocrine system is sometimes called the hormonal system because it does involve the release of hormones into the blood and for biology 30 there are in fact plant hormones as well but here we are going to focus on the animal hormones and in particular melan and even more specifically the human hormones so they are yeah secreted directly into the blood the circulatory system they are for Communication in terms of maintaining homeostasis throughout the body so just like with the nervous system they're going to have to be able to detect any changes that are taking place whether it is in the internal or the external environment and then they're going to have to using these biochemical Messengers enable a response to take place in order to maintain homeostasis we will come across a number of different hormones that are referred to as trop hormones so for example gonadotropic hormone and these are hormones that in themselves don't have any specific physiological function in the body other than to trigger another gland to release a hormone as well so hormones they're released in response to yeah all kinds of different stimuli many many different functions throughout the body I just list three of them here growth development and reproduction and again in terms of the long-term communication they can reach all parts of the body but it's not all parts of the body it's not all cells tissues and organs that are going to respond to a given hormone it's only ones that are going to be what we refer to as the target cells and those are the ones that are going to have receptors that are going to be specific for that particular hormone of which there are dozens of produced by the human body so yes they are chemical signals they need to B to receptor proteins so these receptor proteins as we will see sometimes they are on the cell sticking out of the cell membrane kind of like those receptor channels for neurotransmitters but in other cases they might actually be inside of the target cell so the hormone has to travel through the plasma membrane and into the cell first of all so once again it's only going to be the target cells that are going to respond and what we are talking about here are end endine glands Endo means in so this is going to be the biochemical Messengers that are released inside of the body so this picture that we have here so on the left hand side this cell would represent a cell or a gland that is producing a hormone the red dots those are representing the chemical messenger the hormone and it is a hormone because it goes into the blood because it is transported in the blood that's why it is referred to to now as a hormone eventually it will leave the blood and it will find its specific target cells tissues and organs and those are the only ones that are going to have the corresponding receptor that the hormone can bind to and that's going to lead to eventually a response by those cells tissues or organs so I just distinguish that initially between the endocrine and the exocrine glands so exocrine glands you also have these in your body but they release their contents onto the surface of your body rather than into the blood so the surface might be your skin in the case of your sweat glands it might be your mouth in the case of the salivary glands it might be the lining of the small intestine in the case of the pancreas which also happens to act both as an endocrine and an exocrine gland so the two different um categories or classes of hormones the first one I'm just going to call it the protein hormones but they do go by some different names they're protein hormones because they are comprised of amino acids all proteins are comprised of amino acids virtually all of the hormones that we are going to talk about they are going to be protein hormones there are just a few exceptions that are the other categories and they are only produced really by four different regions in your body these ones here they are water but not lipid soluble which means they do not diffuse across the cell membrane they do not actually enter the cell they're transported fairly easily in the blood because blood is mostly water and they are water soluble so the picture that we're taking a look at at the left hand side here at the top this would be our gland and it looks very similar to what we saw with neurotransmitters we have this vesicle that contains in this case the biochemical messenger which is the hormone so why is it a hormone when it is released by exocytosis it goes into the blood so this is the blood that we're taking a look at here that's how it's trans ported around and that is why this is now going to be a hormone rather than a neurotransmitter Target cell that we have here it does have the very very specific receptor that is for this and only this hormone so that hormone when it does make its way out of the blood will bind to that receptor and without actually entering the cell it's going to lead to a response in that cell so how is it then that we can actually get a response in the cell when it doesn't actually enter the cell I'm just going to go back here and turn off my audio because this animation that I'm going to play for you here I'm just going to narrate it myself narrate it myself because the audio doesn't come out great so we'll play it and I'll kind of uh talk through here what is going on with this animation so to orient ourselves first of all um this is showing here our Target cell and in purple this is going to be our receptor for a hormone that we don't see in the picture yet so the hormone we refer to as the first messenger but in order to get a response in the cell we're going to have well the title of this is a second messenger and although you don't need to know all of the details of what goes on inside of the cell the second messenger in this case it's going to be something that is referred to as cyclical amp so so taking a look at this animation we see the hormone coming in here that is our signaling molecule and they say that in this case it is the epinephrine binds to a receptor and here again don't be concerned about all these details that we're seeing here we have a Cascade of reactions enzymes that are involved intermediates that are involved but ultimately what what is going to happen is inside of the cell it's going to me to a change and that change is going to be the activation of a protein that is already present within the cytoplasm and this is just going to turn on this protein and lead to a cell change and lead to a response so again the actual hormone does not enter the cell it needs to bind to a receptor that is embedded in the cell membrane but that still does lead to a change inside of the cell so that's what we see with the protein hormones and we'll see it's going to be a little bit different with the other kind of hormon this one here again um is actually showing the same hormone the epinephrine same thing just in a picture here it does give us a couple of the different responses though so this orangish band going across that's phospholipid bilayer and this hormone here epinephrine is a protein hormone and it simply cannot cross that phospholipid binder this is the receptor again a Cascade of a whole bunch of changes that you don't need to know anything about but then it does say that we're going to activate this protein right here and these are some of the responses that we're going to see inside of the cell when we do have the epinephrine that is binding to the receptor so that is the way that these protein hormones are going to function the other category or class of hormone they are referred to as the steroid hormones again there are some different names but that's the one I will use these ones are not made up of amino acids but they're made up of a complex ring likee structure of carbon hydrogen and oxygen these hormones try and remember this they're only produced by four different glands in your body so one of them is the outer region of the adrenal gland which is called the adrenal cortex cortex is on the outside and these are a couple of the hormones that you will need to know about that are steroid hormones produced by the adrenal cortex the only other places have to do with reproduction so in the male the testes they produce testosterone that is a steroid hormone in females in the ovaries estrogen and progesterone those are steroid hormones and if a female is pregnant the placenta which is the connection between the embryo the fetus and the mother that will also produce these sex hormones estrogen and progesterone which are also steroid Hearts okay so try and keep that in mind it's only these four different lcos the patients anywhere else in the body if it's producing a hormone and then they're going to be the protein hormones so the key with these ones that leads to the difference in terms of the mechanism is these ones are lipid soluble so that means they aren't transported quite as well in the blood taking a look at this picture here but they can pass through the cell membran okay this is the cell membrane right here so the hormone produced by a gland makes its way into the blood leaves the blood there's no receptor in the cell membrane there might be a receptor in the cytoplasm but it can pass directly through the phospholipid bilayer not only of the cell membrane but also of the nucleus so this is the nucleus that we see at the lower right hand side it can go directly into the nucleus so what can happen when it goes into the nucleus is it can have a direct impact on not just on the activation of proteins that are already there but it can lead to the what we call Sy is or the production of new proteins so similar animation here to show these events with the steroid hormone so we have S for our steroid hormone here we're starting with the blood not with the gland that produced it a carrier because it doesn't dissolve that readily in the blood eventually though that hormone is going to leave the blood and take a look at this passes directly through the phospholipid bilay sometimes there's a carrier inside of the cytoplasm but not always at any rate it's going to go into the nucleus this is the DNA that's the genetic information and that's where the instructions are for the synthesis of proteins so what it's going to show here and again you don't need to be concerned about all of the details at this point is it's going to trigger the reading of information in the nucleus the instructions from the DNA on how to make a protein and then that's going to allow for the making the synthesis of a new protein inside of the cell and that actually happens inside of the cytoplasm where we have the production of the synthesis of a new protein that they're showing you all right so key differences again um really it's that it does now pass through the phospholipid Byer it enters the nucleus not only does it lead to an activation of proteins but it leads to the synthesis of entirely new proteins by that cell so the example here uh estrad is estrogen the female sex hormone and it's just showing that it passes through again the cell membrane here it does bind to a receptor in the cytoplasm into the nucleus and the point is that it leads to the production of this here which in fact is a protein so this protein wasn't already there inside of the cytoplasm it was synthesized it was made new because of the instructions coming from or the stimulus coming from this hormone so each hormone can in fact have different effects on target cells and that's because of various different things uh there might be different receptors on different cells inside of the cell what's going on with these changes that signaling pathway it's called the signal transduction pathway that might be different in different cells and there might be different proteins that are turned on in different cells as well leading to different responses also kind of interesting quite often other species not just mammals but other species um also have the same hormone but they might have different effects than what we do see in humans so really nice picture here that just kind of shows how one single hormone and again it's the same one that we're taking a look at here the protein hormone epinephrine this is the stress hormone it is a stress hormone you might know it by another name which is adrenaline and this is a hormone that is produced by the adrenal medula which is the inner gland of the adrenal gland outer one is the cortex inner one is the medula so what does epinephrine do when it circulates around well it helps your body to deal with the stress so a good example of stress an excellent example of stress is just exercise so what goes on during this stress while your body needs some fuel your muscles need some fuel and that is glucose so one of the things that epinephrine does is it binds to a receptor on your liver cells and your livers are or your liver is one of the major storage places for glycogen which is stored energy and what epinephrine tells the liver cells to do is to break down that glycogen release the glucose which goes into the blood and now you can circulate it around your muscle cells that need that glucose for cellular respiration in order to contract the muscles at the same time you also need well blood going to those muscles so epinephrine is also going to bind to receptors on different kinds of cells liver but now it's the blood vessels in sceletal muscles and what it's going to do is it's going to tell them to dilate what does that accomplish more blood being delivered to those muscles that need the oxygen that need the glucose again for C respiration in order to make the ATP if it's a stress situation like exercise this isn't really the time to be digesting food so epinephrine actually has the opposite effect on blood vessels that are going through your gut area so there are receptors on these blood vessels as well only now as we can see it doesn't lead to dilation but it leads to constriction you don't need as much blood going to your intestines to digest food if you're exercising or you're dealing with some sort of a stressed situation regulation in biology hugely important so we'll talk about a different a couple of different ways that the endocrine system is regulated um huge one here negative feedback we're going to come across many many many examples of negative feedback and the other one just a couple of examples of these are antagonistic hormones one hormone does one thing the other hormone is going to do exactly the opposite so very shortly here we'll take a look at a bunch of different examples of negative feedback loops and in the end what it leads to is the inhibition of the response that you do get by reducing the initial stimuli so reg negative feedback is going to regulate U many in fact most of the hormone Pathways that we're going to be discussing and the whole point again is to keep the body in homeostasis and not move it further away from homeostasis antagonistic hormon hormones will come across a couple of these so um two of them are insulin and glucagon both of them are produced by the liver but they have have exactly opposite effects whereas insulin is going to decrease the blood glucose glucagon is going to increase blood glucose so a few examples that we'll just kind of run through here taking a look at negative feedback this in fact isn't a bio3 example but we do have here as food is going through the gut the low PH coming from the stomach the acid in the stomach goes into the first section of the small intestine that's going to lead to the production of this hormone secren by the duodenum and what it's going to do is tell the pancreas to release bicarbonate bicarbonate is a base it's going to neutralize the acid that has now gone into the small intestine so that's going to be the response is the neutralization once you have neutralized it well now you want to go back and kind of say well we no longer have that stimulus so you don't need to make the secreton anymore you don't need to make the bicarbonate anymore more so a negative feedback is going to ensure that yes there is bicarbonate that is produced but there's not too much that is produced and you're not wasting energy and resources making more of the bicarbonate when it's no longer necessary so negative feedback is going to inhibit any further response when that response is no longer required we're going to see a pattern like this um where we're going to see three different glands a sequence of three different glands that I have labeled here as glands a b and c and three different hormones as well and the pattern is going to be gland a is going to produce a hormone and this is going to be a Tropic hormone because its sole function is going to be telling gland D to produce another hormone which is also going to be a Tropic hormone because it as well is only going to tell the third gland gland C to produce this last hormone so it's this last hormone that's really going to be carrying out the response and leading to a response so why not just have one gland and one hormone well this allows for a couple of things very very fine control and regulation of the production of the hormones and it also allows for amplification so hormones they do work in incredibly low concentrations we might be talking about parts per million parts per billion or even parts per trillion very very low concentrations of these hormones circulating around in your blood and this sequence does allow for the amplification going from hormone one hormone two and eventually to hormone number three but the point right here is that we also have this negative feedback and the key is that it's this third hormone that's going to be regulating its own production for this last hormone this is the hormone right here so on the receptor cells there will be a receptor for that hormone to lead to a response but they're also going to be receptors on gland a and gland B and maybe even gland C and when there are enough of those hormones circulating around we get a response but this is also a mechanism to say to gland see there's enough of that hormone so let's not make any more to gland B there's enough of that hormone let's not make any more and to gland a there's enough let's not make any more so there may be all three of these Loops involved there may only be one or there may be two out of the three but in this case the negative here it does mean that these are in fact negative feedbacks so yes sometimes there are long loops and sometimes there are the short Loops that are involved this is a specific example the point here is not to memorize all the details even though this is one that you will need to know all the details on the point right now though again is just to take a look at the negative feedback that it is showing in this picture here so what we do have is the sequence of three different glands so this would be our gland a this would be our gland oops this one down here gland B and this would be our peripheral endocrine gland or gland C this would be our hormone number one it's a Tropic hormone hormone number two it's a Tropic hormone and hormone number three that actually binds to the target cells and carries out a response once you do have that last hormone though not only does it trigger the target cells and cause a response but it also goes back to previous endocrine glands to regulate its own production the final hormone is going to regulate its own production when the concentration is high enough and you don't don't need any more of it to be produced so it's not a good thing when you have an inappropriate response a low response but it's also inappropriate to have too much of a response so this allows for that very very fine control so it was so it is an appropriate finely tuned respon resp that you do get um there are also some examples of positive feedback and there are a couple of them in biology 30 that we won't actually see until we talk about the reproductive system so instead of turning it off this is actually going to lead to an even more enhanced response so one of the examples that again we will eventually get to does deal with this hormone here oxytocin it's produced by the hypothalamus released by the pituitary gland and what it does lead to is the release of milk when an infant is feeding so this response doesn't turn off any further production of the oxytocin in fact it turns on more production of the oxytocin so more milk is released and there's more food that is available for that feeding infant these are the major glands in the human body and what I'm going to talk about for the rest of this lesson is what is going on in this region right here with the hypothalamus and the pituitary gland so those two there's a very very fine relationship and control that does take place between the hypothalamus and the pituitary gland so we'll talk a little bit about those interactions so if we take a look at this uh cross-section through the brain you can only see this when you're taking a look at the interior and what we're going to focus on is the hypothalamus they do have neurons or there are neurons in the hypothalamus but these neurons they are secreting chemicals into the blood in other words they're producing hormones and for that reason because it is neurons that are producing these hormones they are referred to as neuro hormones that are produced by the hypothalamus so yes it is a little bit blurred when we're talking about this part of the brain is it neurons that we're talking about is it glands producing hormones that we're talking about well it's actually both when we are dealing with the hypothalamus so the hypothalamus is going to have an influence on the pituitary gland which hangs down below the hypothalamus and we divide it into two different categories the anterior that's the front posterior is the back and what we'll see is that the hypothalamus it's going to influence the back of the pituitary a little bit different than the front of the pituitary and by the way um this is also referred to as the master gland pituitary gland the master gland because it has a influence on a whole bunch of other peripheral glands in your body like gats testes and ovaries like the adrenal gland the adrenal cortex like the thyroid gland but in reality this master gland truly takes its instructions from the hypothalamus and from the central nervous system so let's zoom in and take a look at that portion of the brain so hypothalamus at the top here in yellow pituitary at the bottom so the first couple slides here are taking a look at the posterior pituitary this one's a little bit simpler because there are only two hormones that eventually you will need to know about and they are ADH or anti-diuretic hormone and the other one that we actually just saw is oxytocin at this point you don't need to know any of the details about these two hormones that's not the point of talking about them right now the point of mentioning them right now is that it involves the posterior pituitary and the influence coming from the hypothalamus so if we take a look at all of these cells here you might recognize these they are neurons but they're a special kind of neuron because they are neurons that have at the axon Terminal A chemical that's released that goes into the blood in other words they're not neur trans transmitters they are now called hormones even though they're released in exactly the same mechanism as neurotransmitters so the hormones that are released from the axon terminal they were actually made up here in the cell body so that is why we say that these two hormones ADH and oxytocin even though they are released into the blood from the posterior pituitary that's not where they're produced they are actually produced in the hypothalamus they travel down along the length of the axon and when they get the stimulus they are released into the blood so for the ADH the stimulus would be dehydration for oxytocin the stimulus would be uh well birth itself it causes uterine contractions and the delivering of milk the contraction of the muscles in the glands the mamory BLS so those are the only two hormones that do involve the posterior pituitary and those two hormones are not produced there they're produced in the hypothalamus little more complicated with the anterior pter again we still see that we have these neurons but notice that the neurons they don't go all the way down to the pituitary hormones are still produced in the cell body they travel down the Oxon they are released but where they're released is still in the hypothalamus they go into blood vessels and I just like to call this the local circulation it's the blood vessels that are going between hypothalamus and the pituitary so those hormones once they travel this short distance they go out of the blood and they bind your receptors on the cells in the anterior pituitary and they then lead to the release of a second hormone so all of these hormones here released by The axon terminals they would then be Tropic hormones because they only go down to the anterior pituitary and cause the release of a second hormone but it just turns out that all of these or most of them end up being Tropic hormones as well so there are are a whole bunch of these hormones but this is the pattern that we see now the hypothalamus is actually that in general terms hormone or gland a that I was referring to the pituitary and this is specifically the anterior pituitary would be gland B and some sort of peripheral endocrine gland the thyroid the adrenal cortex the testes the ovaries those would be the third peripheral endocrine gland and this is where we have the sequence where hormone number one what they are going to be is into one of two categories they will either be releasing hormones abbreviated RH or inhibiting hormones abbreviated IH if it's a releasing hormone it just tells the anterior po AR to release another hormone if it's an inhibiting hormone it tells the anti pituitary not to release it so whenever you see releasing or inhibiting hormone these are hormones that are released by the hypothalamus that have an influence on the anterior pituitary in particular so one example in fact that we already saw is thyroid releasing hormone is produced by the hypothalamus and it causes the anterior pituitary to produce and release what is called thyroid stimulating hormone which then tells the thyroid gland to produce thyroid hormones various different thyroid hormones that would then have various different functions throughout the bot so this picture here and I'll show you an animation in a second it shows eventually yeah there are a lot of them for ones that you do need to know that are produced by the anterior pituitary so these ones here they would get a stimulus from the hypothalamus and that stimulus is what is referred to as gonadotropin releasing hormone that's why these two hormones are released this one here would get a stimulus from the hypothalamus and that stimulus is from thyroid releasing hormone act gets a stimulus from the hypothalamus and it's called crh corticotropic releasing hormone this one here there is both a releasing and an inhibiting hormone p and Pi this one you don't need to know about and this one here as well this is growth hormone so there will also be a growth hormone releasing okay so all of the releasing hormones and inhibiting hormones they are all produced by and released by the hypothalamus into the local circulation they are all Tropic hormones of these ones here they are all released by the anterior pituitary and they are all Tropic hormones except for this one which can actually be both a Tropic hormone and have effects on its own so let's take a look at a one more animation here which is going to very very nicely show us the anterior and the posterior pituitary and how they're a little different so uh yeah we're taking a look at a brain here of course cross-section through the B brain we're taking a look at the interior so all of these structures of course you should already know the folded portion here on the outside that is the cerebrum the cerebral cortex the four different loes of the brain we can see the cerebellum which is at the back and then uh we can see the interior structures so this light color here that is the Corpus colossum the connection between the two hemispheres down below is the thalamus and then down below there is the hypothalamus and down below the hypothalamus is the pituitary GL this is the pawns this is medulla Lata and the spinal cord so let's zoom in on now the hypothalamus at the top and the two different loes of the pituitary gland the anterior and the posterior pituitary so they're showing that the anterior pituitary is glandular tissue and that just means it produces hormones and the posterior pituitary is not it doesn't produce any hormones so we're starting with h the posterior pituitary then and we have these long long axons of the neurons which are neuros secr neuros secretory cells the cell bodies are in the hypothalamus that is where the hormones are produced but the extensions go all the way down into the end or posterior pituitary and that is where they are going to be released they're nicely showing two different colors here and the idea behind that is that there are different sets of neurons that are producing the ADH the cells that are producing the oxytocin in both cases though they travel down the length of the axon to the axon terminal and then they stay there until they get the stimulus for their release when they are released they go into the general circulation where they can reach potentially any cell in your body so in the case of the ADH the target tissues are going to be the kidneys uh the stimulus is dehydration so the response is actually going to be to pull back to reabsorb the water to conserve the water and that also plays a role in maintaining the blood pressure again we're not really concerned with the stimuli and the functions the mechanism for each of these hormones we're really just concerned at this point about how the hypothalamus is going to have an influence on the posterior pituitary and in this in this case so we have no Tropic hormones here hormones are produced by the hypothalamus they're stored in the axon terminal which is in the posterior pituitary and that's where they are released from for the anterior pituitary again it's many more hor hormones that are involved here and they do produce or there are hormones that are produced directly by the cells of the anterior pituitary again very nice with the coloration what they're trying to show is each one of these different colors are different cells responsible for the production of different hormones and again the same sort of color cating with these neuron that they're showing up in the hypothalamus so the green will produce one kind of hormone which targets the green cells in the hypo in the Anor pituitary and leads to the production of a third hormone so very very specific receptors this is a hormone which only binds to this receptor and will only tell those cells to reduce or to produce and release the second hormone in this sequence again in this case it's going to be releasing hormones and inhibiting hormones that are produced by the hypothalamus it's going to be the second hormones that are produced and released by the anterior pituary in fact both of them are Tropic hormones but they have it labeled here as the releasing hormones by the hypothalamus and the Tropic hormon by the anterior and again all of these eventually you do need to know except for the last one you don't need to know about that one and the final slide here is just a reminder that there is a a lot of information um again we haven't really been getting into any of the details yet but for each one of the different hormones it's a lot that you do need to know so for each hormone you need to know the gland that's actually producing that hormone you need to know the Target or sometimes it's more than one target for that specific hormone you need to know what was the stimulus in the first place that caused the gland to release that hormone you need to know what is the response that you're going to get from that Target cell tissue or organ and then ALS Al the feedback typically the negative feedback sometimes the positive feedback you need to know this for many many different hormones so as I say here about 11 of them with the current unit and seven of them when we go on to the reproductive system and this isn't really even taking into account those releasing hormones the inhibiting hormones and uh the Tropic hormones that are produced by the enture pituitary