Endocrine System

Hi. In this lesson, we'll be talking about the endocrine system, which is a chemical signaling system used throughout the body. Now, before we get into the specifics of the endocrine system, I want to review some other types of chemical signaling. Now. Pheromones are chemical signals that air released to the environment and allow organisms to communicate with each other. They're commonly used by insects and mammals, but they are used by other organisms as well. Oughta. Quran signaling is a type of self signaling where a cell actually will secrete a chemical signal that stimulates receptors on its own membrane. And you can see oughta Quran signaling happening right here where this cell is releasing these signaling molecules and they're gonna bind to the receptors on that sells surface. An example of this are the site a kinds that are released by T cells. Thes will actually acts an autocrat signal for those T cells. Now just a Quran. Signaling is also a close range type of signaling, but this is where cells will actually signal their neighbors that they have physical contact with eso. Frequently, this will be signaling through something like gap junctions or in the case of plants. Plasma does model, and you can see unexamined of these neighboring cells communicating with each other through this physical contact. Signaling through those physical connections, Peregrine signaling is when cells release chemicals that will communicate with nearby and neighboring cells. Eso broader range than just a Quran, signaling they don't necessarily have to be in physical contact with one another. And you can see peregrine signaling happening right here, where this cell that's close by to the cell is going to release these chemicals and those air going to stimulate receptor on the other cells membrane. Now these signaling molecules known as local regulators, can actually act as both oughta Quran and peregrine signals, as both of those uh, types of cell signaling will result in, cells secrete ing signaling molecules to their environments. Now nitric oxide is an example of local regulator, and it actually can act as a hormone causing vaso dilation or dilation of blood vessels. And it also acts in the brain as a neurotransmitter, though its effects there are, uh, a little too complicated for us to get into right now. But the point is that thes molecules can have many effects in different parts of the body. Now, another example of peregrine signaling is prostaglandins, which are going to promote inflammatory responses and additionally, the famous hormones insulin glue, Kagen and Samata statin, which are secreted by the pancreas. And we'll be talking about in, uh, this lesson. They actually will also have peregrine effects on the pancreas. So really, I'm just trying to give you these examples to show that these molecules, these signaling molecules, have a really broad array of effects. Now, we're really only going to be talking about, you know, some of the effects, like the main important ones for our purposes and understanding physiology of certain systems. But they you know, they have many, many different effects and, you know, spread all throughout the body. And also, as you can see with these peregrine signals that will act locally, Aziz Well, and finally, we have endocrine signaling. This is gonna be what we focus on. And this is when cells will secrete hormones that actually will travel through the bloodstream to reach distant targets. So, you know these cells, they're gonna be, um, you know, community trying to communicate with cells that are far away from them. That's one of the defining features about endocrine signaling is it allows for long distance chemical communication in the body, and it uses the blood stream sort of a highway for those hormones to get around. Let's flip the page.

the endocrine system is tightly linked with the other major signaling system of the body, the nervous system. Synaptic signaling. The signaling of the nervous system involves these cells, called neurons, which you can see an example of here, and these neurons will actually transmit electrical signals through their body. And when they reach the target, essentially, what happens is that electric signal gets translated into a chemical signal and released to the other cell as a chemical signal. And we call this connection between the two cells, the synapse and the cell that has the electric signal going through it. That's my little lightning bolt for electric Signal is going to translate that signal into neurotransmitters thes chemicals it will release that will cross this very small gap known as the synapse, and they'll bind to receptors on the cell it's trying to communicate with. So in this way, Thesiger Nell's are both electrical and chemical in nature. Now, the parts of, uh, the endocrine and nervous system that are linked together are known as, you know, nure omd, Quran elements. And so no Euro endocrine signaling is going to be when, uh, neuronal signals cause hormone secretion right So instead of just simply releasing some neuro transmitters to be picked up by another cell, this is going to involve, uh, hormone secretion, as is part of the endocrine system. So this is going to be the type of signaling that links those two communication systems in the body and the signaling molecules. It's going thio release. We call nure Oh, hormones. So these air hormones that are produced by neuroendocrine cells or cells that are involved in, you know, nervous signaling and endocrine signaling or synaptic signaling and endocrine signaling however you wanna think of it. Uh, now, the nervous system, uh, and the endocrine system are are really going thio be linked together in these two organs or brain, brain, region and a gland. Really, I should say, the hypothalamus and the pituitary gland this is going to be these guys are gonna be the major players of the endocrine system. And Thehyperfix Lemus is going to be a major player in the nervous system is well, so over here you can see the major endocrine glands on, and here you can see behind me. You can see the nervous system and here is kind of ah zoomed in image of a person's brain. And so the hypothalamus sits right above the pituitary gland. And again, the hypothalamus is going to be, uh, that major connection between the nervous system and the endocrine system. And it's, ah, a very special brain region. It will actually have a hand in a lot of other functions, too. But, uh, one of its maiden jobs is connecting the nervous system in the endocrine system, and that's because, in part, it is a super involved in Homo Stasis. So with that, let's flip the page and get into the nitty gritty details.

the endocrine system is made up of glands, and these glands secrete hormones into the bloodstream. We call them endocrine glands because they're also glands that will secrete substances into ducts that will be delivered to various other sites in the body. And these air called X a cream glands now in terms of the digestive system, uh, the liver, for example, has a duct that connects to the small intestine as well as this structure here, the gall bladder. And it's going to secrete bile into that duct, and the bile will eventually be delivered into the small intestine. So in that sense, the liver functions as an exa Quran gland in that way, and it's not mutually. The two types of glands are not mutually exclusive. For example, the pancreas here, this particular gland acts as both an endocrine and extra Quran gland. It's going to act as an extra Quran gland in digestion, secreting digestive hormones into small intestine. But it also is a super important endocrine gland and helps maintain blood sugar homeostasis. So what is a hormone? Technically, it's just a signaling molecule produced in a gland that gets secreted into the blood stream and in the bloodstream. It's going to be able to travel great distances and the body to communicate with cells very far away from the source that secreted it. Now the endocrine system has a hand in a ton of different functions in the body. It's gonna play a super important role in development, growth and reproduction. I mean, for example, think about puberty. That's when your hormones start going crazy, right? Well, that's gonna be a lot of endocrine signaling happening now. The endocrine system will also help you respond to the environment in certain ways. A great example of this is the fight or flight response, which will trigger, you know, a surge of hormones in your body from the undercurrent system that help mediate your essentially your defenses In a tense moment, we'll talk more about that later. Uh, in. In addition, the endocrine system is going to be very important for home of static mechanisms. For example, we mentioned the pancreas and its role in blood sugar homeostasis. But pretty soon we're going to talk about, for example, how the thyroid and parathyroid help with calcium homey a Stasis. Now they're actually three types of hormone structures that hormones kind of get grouped into. And you know, these, uh, these labels are can be a little flexible. Maybe I should say so. Uh, if you encounter a different labeling system for them, that's totally fine. So, for example, we have poly peptide hormones. Sometimes people separate this into, uh, you know, peptide hormones and protein hormones. Because of the very different sizes of the two molecules, I'm just gonna keep them all together to make it simple. So these they're gonna be generally larger hormones and polar because they're made of amino acids. And that's gonna actually mean that they can't cross the cell membrane, but they're going to be water soluble now. This is important because whether or not a hormone can cross the cell membrane as we're going to see shortly will affect how that hormone eyes going to bind to receptors and act on a cell. And additionally, the fact that it's water soluble means that it can diffuse into the bloodstream and move through the bloodstream unassisted. Now a mean hormones Ah, sometimes called amino acid derived hormones are gonna be synthesized from the amino acids tyrosine, and these tend to be fairly polar, you can see an example of an amine hormone right here. Here we have on a mean hormone and behind me, much larger. We have a poly peptide now in the middle here. What we have is a steroid hormone, and these, hopefully you'll recognize this structure of cholesterol in this hormone. These are lipid soluble hormones, meaning that they'll be able to cross that cell membrane unassisted. They'll just diffuse through. But it also means they won't be soluble in water, which is why they have to be transported by proteins in the blood. And here again, this is a steroid hormone now, in addition to these classifications on structure hormones or sometimes also classified based on whether they act directly on tissues or whether they stimulate some other gland to secrete hormones. And we call thes two classes direct hormones, those that act directly on tissues to produce some result, and tropic hormones that stimulate other glands to secrete hormones. Because, as you'll see in the endocrine system, it's quite common for one thing. To chemically signal another thing. To have that chemically signal another thing and basically develop these signaling cascades of different glands with different hormones. So with that, let's go ahead and turn the page

As I said previously, steroid hormones can readily cross the membrane because their lipid soluble in fact, cholesterol, is a major, important component of the cell membrane. And because steroid hormones will readily move through the membrane, they actually tend to have interest cellular receptors or just receptors that air found inside the cell. And they tend to act in ways that modify gene expression. And they'll do this either by binding to a receptor and having that receptor hormone complex act as some type of transcription factor. Or they will trigger some signal in the cell that will activate other transcription factors. Now the elements that ah hormone receptor complex will bind you. Thio help initiate transcription is known as a hormone response element, and you can see that whole process kind of playing out in this image behind me, where we have a steroid hormone that would have had to been transported through the blood assisted by proteins because it's not water soluble, but it's gonna easily diffuse through the cell membrane bind to this interest cellular receptor, and that's gonna actually move into the nucleus where this is going to find its hormone response element, and it's going Thio, Modify transcription. And here you can see in this case it's going to lead to the translation of some new protein. Now it's worth noting that although thyroid hormones are actually a mean hormones, they behave like steroid hormones because they're non polar. And this is due to the iodine atoms, uh, that air found in thyroid hormones. Uh, we'll talk more about thyroid hormones and just a bit. I do just want to point out this exception because thyroid hormones are again going to behave similar to what we see happening in this image as opposed thio how water soluble hormones will behave Now Water soluble hormones are gonna bind to cell surface receptors because they can't cross the membrane. And what they'll end up doing is activating some type of signal transaction pathway that's going to communicate that hormone signal within the cell. Often, they're gonna be using G couple G protein coupled receptors as well as second messengers to transmit these signals, and you can see a little model of that happening here with this hormone is gonna go ahead and bind to this G protein coupled receptor. Here, you can see the GTP being exchanged for the GDP, and this is going to go ahead and let me jump out of the way. Activate this protein here, which is a dental liel cyclists and dental cyclist is going to take at P and turn it into cyclic ATP and sick. I'm sorry. Cyclic a m p not ATP Cyclic A M P is a very common second messenger used and will frequently be part of these signal transaction pathways. Now, a second messenger to be clear is just any non protein intracellular signaling molecule. And often these signature instruction cascades will involve ah, Siris of activations or in activations, where both of various molecules, you know frequently you will have, you know, protein kindnesses and phosphor laces and defrost for laces. Uh, you know, phosphor awaiting and defrost for relating each other in a Siris of steps that, um, you know, will transmit the signal. What's cool about that, though, is along the way, the signal can get amplified. And you know, this is due to the fact that you know to just sort of model it really quickly, Let's say, like one signaling molecule can actually activate two other downstream signaling molecules and If those guys come both activate to, then you can see how over time or rather, over the course of transmission of the signal, it gets amplified mawr and more molecules air communicating that signal. So these were just common features of these water soluble hormones. With that, let's flip the page.

Hello, everyone. In this lesson, we're going to be talking about how the different types of hormones actually get into the cell and do the jobs that they need to dio. Okay, so let's go into our lesson. And we're gonna be talking about the two major classes of hormones. They're gonna be steroid hormones or lipid soluble hormones, and they're gonna be water soluble hormones. So basically, there's a set of hormones that air hydrophobic and a set that air hydro Filic, and this is going to determine how they're going to get into the cell and how they're going to bind with their receptor. Okay, everyone. So we know that hormones are going to be long distance signals. They travel through the bloodstream and they're going to be made by very specific glands, and they're gonna be taken up by very specific cells. So we're talking about steroid hormones and water soluble hormones and steroid hormones and water soluble hormones are different because of their composition, but they're also going to be different based on how they affect the cell. Steroid hormones generally have very long term effects, and it's going to be a very slow cellular response is going to take a long time for that cell to respond to a steroid hormone. Now, water soluble hormones actually have very quick effects, but they don't last terribly long. So there's two different types of hormones that are gonna have two different types of effects. So whenever you're talking about a steroid hormone, this is going to be one that's derived from lipids. It's gonna be something that's hydrophobic. And if you guys were wondering examples of steroid hormones are gonna be the sex hormones and the thyroid hormones. They are all made out of lipid, so estrogen, testosterone, thigh rocks and these are all going to be lipid soluble hormones or steroid hormones. Now water soluble hormones are going to be a little bit different. You guys may recognize one of these, and that is epinephrine. Epinephrine and other water soluble hormones are going to be composed of hydro filic components like proteins or amino acids and things like that. Okay, all right, so let's have a look at our diagram here because it's going to be depicting how these two different types of hormones are going to get into the cell. So this is a steroid hormone right here, meaning that it's lipid soluble. It is hydrophobic, and then we're going to have a water soluble hormone right here. So it's hydro filic. It is not lipid soluble. It's water soluble. So first off, let's start with our steroid hormone. We can see that it has this line where the steroid hormone just simply goes through the plasma membrane. And that's exactly what happens with steroid hormones. Because they're hydrophobic and their lipid soluble, they can easily travel through the hydrophobic plasma membrane so they just go right through the plasma membrane. They don't need any membrane bound protein receptor. They do bind to a receptor, but it's gonna be in the cytoplasm, as you guys can see. Uh, sorry. As you guys can see right here, this is going to be it's cytoplasmic receptor. And then, once the steroid hormone, maybe it's estrogen. Maybe it's testosterone binds with its receptor in the cytoplasm. It is then going to travel into the nucleus, and this is really interesting steroid hormones. Their main job is to alter genetic expression off that particular cell, so the complex of the steroid hormone and its receptor are actually going to determine which genes are gonna be transcribed. Which ones are not so which genes are going to be expressed in which sells. And that is going to create these newly created Marianas, which will become these new proteins, or new gene products. So, for example, a hormone that does this would be estradiol, which is a form of estrogen, and it is going to enter liver cells and it's going toe. Alter the genetic expression of liver cells. And this genetic expression is going to be making these products that the female will use to build eggs so you guys can think about this. Building eggs and forming eggs is a very long term process. It takes a lot of energy and a lot of effort and takes a long time. And steroid hormones are going to trigger that beginning of that long process off the liver, creating these different components off the egg cells. Specifically, the liver is going to be important for creating the yolk of the egg cell. But I told you, steroid hormones take a little while to have their effects, and that one does as well. So now let's move over to this one right here. I'm going to go out of the picture so you guys can actually see the rest of this image. Okay, so we have this particular hormone called a C th You guys can look it up if you want to. You don't particularly have to know that at this moment you'll learn more about that. I believe in Osma regulation and excretion. But you don't have to know that exactly at this moment. So a C T. H is very interesting because it is water soluble water soluble. So what does that tell us? That tells us that it is a hydra filic molecule, meaning that it can't simply diffuse through the hydrophobic cellular membrane like our steroid hormone did. So it's going to have these receptors. You guys can see them here in the cell membrane, and a C T H has actually bound to one of them. This is going to trigger a response. This is going to trigger a trans duck shin cascade or a cascade of the secondary messengers. So you guys see it cyclic A. M P is here sick, like A and P is a very common secondary messenger. So basically what's going on here is the A. C T H cannot get into the cell itself because it cannot get past the plasma membrane, so it's gonna bind to the receptor, and then the receptor is going to send off all of these interest cellular signals or secondary messenger signals, and the secondary messengers are then going to cause this cascade to happen. So as you guys can see, we have these cyclic amp molecules here. They're gonna be activating whatever these particular molecules are here. And then those molecules they're going to activate thes. And then you guys can see that cortisol, which is a different type of signal, was actually made. That is going to be the cellular response. So this this process here of creating or activating all of these different messengers and these different proteins is going to be called a signal cascade or a transaction cascade. It's something happening where it's triggering all of these different signals, and then they're going to make the gene product, which is gonna be cortisol, and this is actually a relatively short process, and it's not going to involve the changing of the genetic expression, so it's gonna happen very quickly and it's not gonna last a very long time. Cortisol is involved in stress, so it will only stay around as long as you are stressed. So it's a short term period kind of thing. Okay, guys. So now we're going to scroll down, and we're going to look it a little bit more stuff. We're gonna look at how these different hormones can actually trigger different responses in the cell. Okay. All right. So we're told that a hormone binds to the cell receptor, and then it's going to cause a particular cellular response. Well, it's interesting to know that depending on which cell that hormone is triggering, it's going to depend the type of response that cell is going to have. So the effect of a hormone depends on the presence of specific receptors. So unique receptors for the same hormone will cause different cellular responses. So, for example, one hormone can have many receptors, So epinephrine, which is also called adrenaline, is going to have many different types of receptors. Epinephrine is gonna be a water soluble hormone, so you're gonna have many different cell membrane receptors, and depending on which receptor the cell has, is going to depend how it's going to react. So in some cells it can increase blood flow to the muscles, so in particular muscle cells, it will increase the blood flow in the digestive system. It will decrease the blood flow in the liver. It will tell the liver to start breaking down glycogen so it can put glucose into the blood. So your body has fuel. So epinephrine has many different jobs, depending on which particular cellular receptor that self has. So these are some examples of the ones. For epinephrine. You have Alfa one Alfa to a beta receptors. These air very common receptors for epinephrine, and they're going to cause different things to happen. So you guys can see down here that the first Alfa one is going to lead to a cellular response, that it's smooth muscle contraction. And whenever you're talking about epinephrine, smooth muscle contraction is generally going to be dealing with the blood vessels constricting the blood blood vessels, raising the blood pressure in diverting blood to the areas of the body that need it like your muscles in your brain. Okay. And you guys can see that it also does smooth muscle contraction here. It's going to inhibit certain other molecules from transmitting because of the stress response. And very interestingly, it will cause the heart muscles to contract because they're pumping harder, pumping the blood. Because epinephrine, if you guys don't know epinephrine is used in your fight or flight response, which is gonna be your emergency response. So if you're being chased by a bear, you're being attacked or you forgot something in your panicking epinephrine is going to kick in, and it's going to cause your muscles to actually get more blood so you can run away from the dangerous thing. It's going to cause your heart muscles to contract. So you pump all that blood to your muscles that need it, and it's going to cause the glycogen Allah. I can never say that glycogen analysis, which is the breaking down of glycogen in your liver toe. Fill your blood with glucose so your muscles have energy to actually run or do whatever you need. So everyone in this lesson it was very important to realize there's two different types of hormones hydrophobic or steroid hormones and hydro filic or water soluble hormones, and they're gonna have different receptors on in different areas of the cell, and one hormone can have many different receptors, which will lead to many different outcomes or cellular responses. Okay, everyone, let's go into our next topic.

the hypothalamus is that brain structure that bridges the nervous and the endocrine system, and this is going to interact directly with a gland called the pituitary gland. And the pituitary gland actually has two lobes, and the hypothalamus is going to have two different interactions with these two lobes. Now it's worth noting that the hypothalamus is the home use static center for many regulatory systems, including body temperature and blood pressure, and the way in which it's going to interact with these two lobes of the pituitary gland are through linked blood vessels, which you can see over on this side. These were supposed to be blood vessels that are directly linked to blood vessels on the anterior pituitary gland, as it's called, and on the posterior side or the posterior pituitary gland, the hypothalamus is actually gonna have these nerves. So neuron XYZ that are from the hypothalamus up here and actually extend what's called their axons down to the posterior pituitary, and then they synapse or connect to the posterior pituitary. And they'll actually release, uh, nure oh, hormones there to the posterior pituitary. And remember, Nure oh, hormones are gonna be hormones that get released by, uh, neuron. So these two different interactions are going to be significant in terms of, uh, you know what hormones are being delivered to which part of the pituitary and we'll get into that in just a little bit now. The other structure I want to mention is the pineal gland that's a small endocrine gland in the brain. And it produces this hormone called melatonin that is involved in circadian rhythms, and that stuff makes you sleepy. Now the thing I want you to take note of is that the hypothalamus sits right on top of the pituitary gland, and in terms of the anterior pituitary, we'll get to the posterior pituitary and just a little bit. But in terms of the anterior pituitary ah, lot of the basically what the hypothalamus is going to be doing is releasing hormones that are tropic hormones that caused the pituitary to release some other hormone. Now we're not gonna focus too much on the hormones the hypothalamus releases, because they're really just there to stimulate the pituitary to release its hormones. So I'm mainly gonna look at the hormones of the anterior pituitary, but I just want to give you a quick example of how the hypothalamus will actually release something called thyroid trope in releasing hormone and thats going thio go to the anterior pituitary and cause the release of thyroid stimulating hormone. Likewise, you have Kordic a trope in releasing hormone that's going to stimulate the release of adrenal cortical tropic hormone. So these the hypothalamus. A lot of what it releases are just these releasing hormones that are just going to stimulate something in the anterior pituitary to be released. With that, let's flip the page.

Okay, everyone, in this lesson, we're going to be learning about specific glands in the endocrine system, and specifically, we're gonna be talking about the pituitary gland. Okay, so let's get into the lesson, and we're going to talk about the pituitary gland. But it's hard to talk about the pituitary gland without talking about the hypothalamus gland because they are very, very strongly linked. So we have the pituitary gland, and it's going to be composed of two sections. Thean, teary er, pituitary gland and the posterior pituitary gland. Now the hypothalamus, which we learned about in our last lesson, is also going to be part of the indifferent system. But remember, the hypothalamus main job is to connect the nervous system with the endocrine system. The nervous system is going to send the hypothalamus signals about the exterior world, or what the brain is feeling or what the body is feeling, and then the endocrine system. We are sorry the hypothalamus will process those signals and tell the rest of the endocrine system what it needs to dio. So, for example, if the nervous system detects seasonal changes like drops in temperature or less sunlight, then it will tell the hypothalamus that information and perhaps the hypothalamus will tell the rest of the body that it needs to start making sex hormones because perhaps it's breeding season for that particular animal. That's gonna be one way that the hypothalamus is going to work. But the hypothalamus doesn't really send out these hormones on its own. What it does is it tells the pituitary gland to send out these hormones. And there are two parts right, the anterior and the posterior pituitary, and they're going to do different things. So first, let's talk about the anterior pituitary. Now the anterior pituitary is going to secrete Tropic and direct hormones. Trophic hormones are gonna be hormones that affect other indifferent glands. Direct hormones are going to affect other body parts that are not endocrine glands. Maybe it has something to do with hormone signaling thio the muscles or the liver. But if it's a hormone that signals another endocrine gland like perhaps the test ease or the ovaries that do make these different hormones, then it's a tropic hormone. Okay, so tropic hormones signal Thio, other India Quran glands, and the anterior pituitary is going to make these tropic and direct signals and it is going to be linked to the hypothalamus via blood vessels. And that is because the hypothalamus is going to direct what the anterior pituitary is going to do. Theater pituitary is its own gland. It makes its own hormones, but it can't release them or stop releasing them until the hypothalamus tells it that it can. And the way that the hypothalamus does This is the hypothalamus is in the brain, and so is the pituitary gland. And they're very close together, and in fact, they're going to have these blood vessels that connect them. And these air generally called the portal vessels or the portal system. And these were gonna be very short blood vessels that transfer the signals from the hypothalamus to the pituitary gland. And the anterior pituitary is going to get it signals from the portal system. Now, the hypothalamus secretes hormones into this portal system, and they're going to tell the anterior pituitary what to do. Now, This list of hormones F s, H, L H, a, C, T, h, TSH, prolactin and GH are all gonna be the different types of hormones that the interior pituitary makes and can secrete so follicle stimulating hormone and lutin izing hormone are gonna be dealing with sexual reproduction and the producing of GAM. It's You guys will learn more about these hormones whenever we learn about animal reproduction. But I just wanted to put them in here because they are made by the anterior pituitary gland. So the follicle stimulating hormone, or FSH, stimulates follicles and maturation and spur Mata Genesis follicles are going to be things that actually make the gametes. For example, follicles in ovaries make the eggs so follicle stimulating hormone is very important for the production of gametes lutin izing hormone stimulates ovulation and testosterone synthesis. Ovulation is going to be the releasing of the egg from the ovaries into the fallopian tubes and testosterone synthesis is simply the creation of the male sex hormone. So these were going to be mostly important for sexual habits. Okay, now we have these different hormones. We're gonna have the adrenal cortical, a tropic hormone or simply a C T H. And it is going to stimulate the adrenal cortex to secrete other hormones, or glucocorticoids, which is hard to say like cortisol. So this one right here is going to be a tropic hormone because it is going to signal to another indifferent gland to create more hormones, kind of like a stepwise process. And then you're gonna have the thyroid stimulating hormone, which is another tropic hormone, because your thyroid is going to be another endocrine gland. Very important, one which will learn in our next lesson. And the thyroid stimulating hormone does exactly what it sounds like. It's going to stimulate the thyroid to create those thyroid hormones, and then you're gonna have prolactin. Prolactin is very important for the secretion of milk in the mammary glands of mammals, and it is going to be secreted in the production of milk after the baby is born. But I also want you guys to know it is also very important for your immune system, your metabolism and your pancreas actions. Okay, so it does more than just produce milk, but that's its main function. Then you have the human growth hormone or simply growth hormone, and it's going to stimulate the regeneration and the creation off new cells. Now down here is going to be a diagram of how the anterior pituitary and the hypothalamus are going to interact with one another. So these are gonna be the hypothalamic hormones that it creates by the hypothalamus. Okay, and these are going to be delivered via the portal system or the portal vessels to the anterior pituitary. And then these particular hormones or hypothalamic hormones, are going to be telling the anterior pituitary what to make. So G N r. H is the gonadotropin releasing hormone, and it's going to tell the anterior pituitary to release the gonad hormones or the FSH and LH hormones, which go to the gonads. So you'll find that the naming of the hormones that come from the hypothalamus are pretty self explanatory because they are the releasing hormone or the inhibiting hormone. Because the I found this comptel, the interior pituitary, to release something or inhibit something. So the gonadotropin releasing hormone tells it to release the gonad hormones. C. R H is gonna be the cortical trope in releasing hormone, telling it to release the cortical trope in hormones and T R H is the dire a trope in releasing hormones, which you're gonna be the thyroid hormones. It's gonna tell the interior pituitary to release those thyroid stimulating hormones. Now the only one that's a little different is gonna be D A d A is gonna be dopamine. So it doesn't really fit its name All that well. Um, but dopamine is actually going to tell Prolactin to stop being released at a particular time. Okay, While the thyroid trope in releasing Hormone is going to tell prolactin to be made now, the G h r h is simply the growth hormone releasing hormone. Pretty self explanatory. It's going to tell the anterior pituitary to release the growth hormone, which you guys can see as the plus. Just you guys know the plus science here are telling the anterior pituitary to secrete that hormone. Now, the minuses are telling the anterior pituitary to stop releasing that hormone. So G h r h is telling the interior pituitary to make growth hormone, but s T is telling it to not make growth hormone. Do you guys know what s T actually is? S t is gonna be somatic toe statin. Do you guys know what this is? Samat, A statin is actually another word for growth hormone. So the growth hormone is actually going to be a negative feedback system whenever there's too much growth hormone or too much so mad a statin it is going to go back to the hypothalamus, and the hypothalamus is going to tell the anterior pituitary to stop making growth hormone. So growth hormone basically tells itself to turn off, which is kind of interesting. So I hope this makes sense. This is going to be how the anterior pituitary interacts with the hypothalamus. The hypothalamus doesn't make any of the anterior pituitary hormones, but it does tell the anterior pituitary to either release or inhibit those hormones that it makes on its own. Put the post eerie pituitary is quite different. The posterior pituitary does not make its own hormones. It is going to release the hormones that the hypothalamus makes. So the hypothalamus is basically going to make these two hormones and those they're going to be the oxytocin hormone and the anti diuretic hormone, and it's going to store them in the posterior pituitary gland. And then it will tell the posterior pituitary gland when it is allowed to actually release these particular hormones. So the posterior pituitary secretes direct hormones, thes air, not going to be hormones that interact with other indifferent glands. they're going to affect tissues directly, and it is linked to the hypothalamus by these neuron ax ons. And these neuron axons are going to be the pathway that oxytocin and a D. H actually travel to get to the posterior pituitary. So the hypothalamus produces these neuron hormones neuro hormones, and it stores them in the neurons that connect the two the posterior pituitary. So simply the posterior pituitary is the storage location. And then the hypothalamic axons synapse on these capillaries and tell the post Terry Pituitary when it is allowed to release oxytocin or a D. H. Okay, guys, you can actually see these structures here. This is gonna be appear in blue. This whole thing right here is the hypothalamus, and it is actually connected to the posterior pituitary via these Exxon's, which you guys can see here. So let me highlight that a little bit better for you guys. These were going to be the ax ons, and they're gonna have or the, um neurons, and they're gonna have their axons. They go all the way down into the posterior pituitary. And then whenever the hypothalamus tells the axons, the axons tell the posterior pituitary to release oxytocin or a D. H. Now, oxytocin and a D. H are very important hormones. Whenever you're talking about the survival of your body, a. D. H. You guys will learn more about whenever we learn about Osma regulation and excretion. But just know that it's used greatly whenever you are dehydrated or you have blood loss. Because A D. H, also called vasopressin, increases your water re absorption in your kidneys, and you don't lose as much water in your urine, so build water back up in your blood. Now oxytocin has a huge range of these different functions that it can dio. It is used in females to signal lactation after the baby's born. It will cause milk to be lactate ID. It also stimulates contractions and labor and really cool this one right here. It plays an important role in social bonding. They have done studies that show that oxytocin is greatly linked to maternal behavior. So whenever a mother has a baby and then she holds the baby, her oxytocin levels go up, her oxytocin levels go up, and she feels more maternal, has more maternal instincts. Also, oxytocin is used when partners interact or loved ones interact your oxytocin levels go up, so it's correlated with bonding. They've even done studies on pets and seeing that animals such as dogs, whenever they interact with you like you pet them, they're oxytocin levels go up, so that's really neat. It's basically the bonding hormone, and it's used for reproduction as well, in the form of labor contractions and lactation. But that's all the information I have for you guys on the pituitary gland. Remember, it has two components. The anterior pituitary gland, which makes a whole bunch of hormones on its own and is told by the hypothalamus, went to release those hormones and the posterior pituitary gland, which is given hormones by the hypothalamus and then secretes those hormones when the hypothalamus tells it to. But in our next lesson, we're going to learn about the thyroid and how it plays a part in the endocrine system.

The thyroid gland is an endocrine gland that's involved in the regulation of metabolic rate and calcium homeostasis. Now thyroid hormones, of which there are two commonly referred to as T three and T four are synthesized from tyrosine, making them mean hormones. However, they act like steroid hormones because of the iodine attached to their structures, which essentially shield the molecule. And these two different thyroid hormones are. Our purpose is going to be treated the same. I mean, they largely have the same effects. However, there are two different types, and you should be aware there are two different structures, and their structures differ in that. T three has three iodine atoms and t four has four. I Dine Adams so pretty easy to remember there now, the thyroid hormones T three and T four have a wide range of effects, but generally they're going to affect metabolic rates, heart rate and heat production in the body, which is actually pretty pretty intricately linked to these other rates. Now thyroid hormones are going thio act in a negative feedback loop, and they're going to block the release of thyroid trope in releasing hormone from the hypothalamus and thyroid stimulating hormone from the anterior pituitary. So really nice negative feedback loop here, where the downstream product, so to speak of this chain of events will feedback and shut off the release of the hormones that stimulate its release. Very clean negative feedback loop there. Now the parathyroid gland is going to be involved in calcium homeostasis along with the thyroid. They each kind of secrete a hormone that eyes counterbalance to the other. So the parathyroid glands actually kind of sit on the thyroid more or less. They're not as distinct as the thyroid, so they're kind of hard to picture. But they're going to release parathyroid hormone, which is gonna act in opposition Thio calcitonin. So first, let me talk about parathyroid hormone, and then I'll get back to calcitonin. So parathyroid hormone is going to essentially try to increase calcium levels in the blood when it did, when it detects low, or when the body detects low calcium levels, it's going to secrete this hormone, and that's going to cause the bones to get re absorbed, which is going thio, extract calcium from the bone and put it in the bloodstream. It's also going to decrease calcium excretion in the kidneys, meaning that the body is going to retain mawr calcium. Additionally, it increases calcium absorption in the gut, so your body is going to get more efficient at, uh, taking in the calcium from the food you eat. So this all serves to raise blood calcium levels. However, Calcitonin works in opposition to that. This is, ah, peptide hormone that's secreted by the thyroid, and it's going to be secreted in response to high levels of calcium in the blood. And what it's gonna do is essentially increased calcium storage in the bone. So opposite effect. From that right, it's. Instead of pulling calcium out of the bone, it's gonna start depositing calcium into the bone. And it's also going to increase, uh, calcium excretion in the kidneys. So again, opposite of that, it's going to make sure that the body gets rid of more calcium because it has too much. Lastly, it's going to decrease calcium absorption in the gut, so opposite effect of that these two hormones work to balance each other out Calcitonin. The way to remember what it does is it tones down calcium, so tones down calcium and remember that calcitonin is secreted by the thyroid on parathyroid hormone is secreted by the parathyroid. With that, let's flip the page

before getting to the adrenal glands that sit on top of the kidneys. I want to mention the kidneys. Own hormone erythropoetin. This hormone is secreted by the kidneys to stimulate red blood cell production in bone marrow. Now the adrenal glands sit on top of the kidneys, and like the kidneys, they have this to layer structure where they have an outer cortex and an inner medulla. Now this outer cortex is an endocrine gland, and the inner medulla is actually a neuro endocrine gland. The adrenal cortex is it called, as it's called secretes, mineral core dacoits and glucocorticoids. Now the hypothalamus is going to secrete C. R. H. And that stimulates the pituitary to secrete a C T. H. And that's going to stimulate the release of these glucocorticoids thes glucocorticoids are named because they're involved in glucose metabolism. But don't let that fool you. They do lots of other stuff, too. Now the one to know is cortisol. Cortisol is definitely the most important glucocorticoids. It's a steroid hormone involved in long term stress responses and fight or flight responses. Now the mineral core dacoits are steroid hormones that they're going to cause the kidney. Thio or they're going to help the kidney regulate water balance and electrolyte balance. And this is gonna be, you know, the main hormone to know is Aldo Austrian. And if you want to know more about that, check out our lesson on Osma regulation and the kidneys. Now, the adrenal medulla is the inner gland that's gonna secrete epinephrine and norepinephrine in response to synaptic signals. Because this is a neuro endocrine gland. Now, epinephrine, you may have heard called adrenaline, but it's the same hormone and same thing with norepinephrine, which is sometimes referred to as nor adrenaline. Now, epinephrine is in a mean hormone, and it's gonna be involved in stress response. Uh, and we're gonna talk about this special stress response right now. The fight or flight responses of short term stress response. It's gonna be triggered by a division of the peripheral nervous system called the Sympathetic Nervous System. Now, the hypothalamus is essentially going to send synaptic and endocrine signals to the adrenal gland in response to some type of perceived threat. Like you see happening here, where this dog and this cat kind of wigging out when they see each other right there. Either about Thio throw down and scrap right now or probably run away in either direction. That's, you know, typical fight or flight response. Now the synaptic signals they're gonna cause the adrenal medulla to secrete epinephrine and norepinephrine. And these were gonna lead Teoh a variety of physiological changes. And the, um, the endocrine signals are going thio cause the adrenal cortex to secrete cortisol. Now, these, uh, these were gonna affect the body in in many different ways. But the main ideas that they're going thio lead the body, uh, to basically prepare toe. Either you fight for your life or run like heck And you know, the effects are gonna involve things like increased breathing rate, you know, to get more oxygen in your blood to get more oxygen to your muscles so that you can either, you know, uh, fight for your life literally or, you know, Runas fast. You can. It's also going to do things like increase blood pressure. It's gonna dilate your pupils, and it's going thio, increase your blood glucose levels, and that is going to help provide mawr glucose for your brain and provide more glucose, especially to your muscles, which are gonna need it. Now. The stress response is controlled by this famous negative feedback loop known as the H P a axis or hypothalamic pituitary adrenal axis. And this is a negative feedback loop that's going to control stress levels, particularly with cord is all you know, think cord is all when you're thinking about these levels. So we know the hypothalamus of secretes CRH and that causes the anterior pituitary to secrete a C T. H, which causes the adrenal cortex to secrete that stress hormone. Cortisol is gonna jump out of the way here so you can see this image better and the when cortisol is secreted by the adrenal cortex, it's actually gonna feedback negatively to both the hypothalamus and the pituitary gland and shut off the release of CRH and a C T. H. Now this is important because over doing it on the stress response can lead to some negative consequences for the body. For example, it can lead thio suppression of the immune system, which is obviously very bad. Now, if you're a C T h secretion really gets out of control, you can have this persistent stress response knows Cushing's disease, and this is bad news has a bunch of different negative effects on the body. Um, for example, high blood pressure, you know, just all around. Not what you want. You stress response is something that's good in the short term, but needs Thio, you know, be controlled very tightly so it doesn't run amok in the body. With that, let's go ahead and flip the page.

gonads are endocrine glands that produce gametes like sperm and egg. And they're also going to be responsible for secrete ing sex hormones. They're gonna be regulated by lutin izing hormone and follicle stimulating hormone from the pituitary. Now, the test is there gonna be male gonads and these air gonna produce steroid hormones called androgens, which are male sex hormones. The most famous and the main one is testosterone. This is going to regulate the development and maintenance of male sexual characteristics. For example, the deepening of the voice now malaria, inhibitory substances also gonna be secreted by the test ease. And this is going to prevent female reproductive anatomy development. There's this saying that nature's default is a female. So essentially, without the test is producing this hormone. The body would default and sort of, you know, develop female reproductive anatomy. Now the ovaries are female gonads, and these air gonna produce estrogen's, which are female sex hormones. The main estrogen is extra dial, and this regulates the development and maintenance of female sexual characteristics like breast development. Progesterone is another estrogen, and this is a steroid hormone that's gonna be involved in the menstrual cycle and pregnancy now. These days we have a lot of what are known as xeno estrogens in the environment, these air foreign substances that combined estrogen receptors and disrupt endocrine function. It's especially frightening because we're seeing a huge rise in the development of secondary sexual characteristics in very young girls, due to all these xeno estrogens that are out in the environment now, normally, these secondary sexual characteristics aren't initiated until puberty, which is this, uh, Siris of physical changes their initiated by hormonal signals and prepare a child's body your sexual reproduction. So it's going to develop the sexual characteristics necessary. You can see a nice outline of the connection between the Patou it Terry gland and the go nads here, and notice that testosterone and estrogen will have a negative feedback. The fact on G N r H release, which is going to come from the hypothalamus to you stimulate the pituitary gland. So these sex hormones are gonna cause, uh, you know, cause negative negative feedback at that point. All right with that, let's go ahead and flip the page

just a few more hormones to cover here. First up growth hormone, which is a peptide hormones secreted by the anterior pituitary that generally leads to increased growth. Behind me, you can see one of the tallest people in history, Robert Wad Low, who had an excess of human growth hormone that led to his massive size. Now the pancreas is both an endocrine gland and an exa Greenland. It's gonna have execute functions in the digestive system and endocrine functions that include the secretion of some at a Staten, which is a peptide hormone that inhibits the effects of growth hormone. Now the pancreas is better known for its endocrine involvement in blood sugar. Homeostasis by secreted the hormones, insulin and glucose gone. The pancreas is going to produce its hormones in these special clusters of cells called islets of longer Hans. Now, if we look at the human body here, you can see the pancreas sort of nestled on top of the intestines there and right next to the gall bladder. And if we zoom in on part of the pancreas, we can see that it has these cell clusters like you see here. Those are islets of longer Hans, and they're going to contain Alfa cells, beta cells and delta cells. Now Alfa cells produce glue. Coogan beta cells produce insulin and delta cells produce Samat of Staten. The pancreas is actually going to receive hormonal signals from the duodenum during digestion in the form of secret. In this hormone released by the duodenum to the pancreas is going to stimulate bicarbonate secretion from the pancreas, which is important when the kym during digestion hits the duodenum it needs. All that acid needs to be neutralized. Now. Hunger and satiation, or sort of the feelings of being hungry and being full, are controlled by a pair of hormones that have antagonistic effects. Hopefully, you're noticing that pattern thus far that there's lots of hormones that act in pairs and have effects that counter each other. Now, lepton is gonna be the hormone produced by atavus sites or fat cells, and it has receptors in the hypothalamus that inhibit appetite. So, you know, if you think about it in terms of, um, you know, eating a big meal, taking in lots of nutrients, including some fats, those atavus sites air going thio stimulate satiation. Grell in is a hormone that works opposite tau lepton and actually stimulates appetite. And here you can see a pair of mice. And what's interesting is this giant mouse over here has actually been manipulated so that it does not respond Tau lepton. And because it doesn't respond, toe left in it doesn't get that appetite inhibition and well, over eat. All right, that's all I have for this one. I'll see you guys next time.