so this lecture is going to focus on the endocrine system uh it's a it's an interesting system it is not the most exciting system to lecture about it's largely a focus on the hormones that are produced by specific organs and in turn what organ or organ systems those hormones actually Target okay so the there there is some overlap here in the function between the endocrine system and the nervous system and it's important to make sure that we understand exactly the the roles that each of these systems play now we just got done talking about the nervous system not that long ago and the nervous system is ultimately focused on shortterm immediate responses and communication to the body and it is it is focused on homeostasis just as the endocrine system is the difference is is that the endocrine system is going to bring about long-term changes and longer term messages to the body whereas the the nervous system is much more about that short-term communication now both systems do use specific communication methods and both do also affect specific Target organs they just do it in a very different way nervous system will do it by by sending nerve impulses to very specific locations in the body however the endocrine system is going to release hormones into the bloodstream broadly so they will go throughout the body however those hormones only affect certain cells in certain organs by Design so so they function specifically to only bind to certain cells we're going to get into that a little bit later now there are two types of glands uh that we've talked about and we need to make sure that we have the distinction between these uh right off the bat an exocrine gland is a is a gland in which the secretions it produces are released into ducts that open onto an epithelial surface now this is not the type of uh gland that we're interested in talking about during this chapter instead an endocrine gland these are ductless organs so these things actually have no ducts and they secrete their secretions their products the hormones directly into the blood instead and so unlike exocrine glands which use the actual epithelium to be their delivery system the endocrine system is going to use the blood as the delivery system now all Endocrine cells are located within highly vascularized regions regions uh and that's again intentional because you want to make sure that they have good access to the bloodstream so they can get their product out now what is a hormone a hormone is a uh a very specifically shaped molecule it that is that functions to have a very specific effect again on a very specific organ so only target cells that have specific receptors that this hormone can actually bind to will in turn respond to that hormone so that's why the endocrine system can actually broadcast it can send out these hormones throughout the body and not be concerned that the the wrong organ is going to respond to its message because only certain cells in the body have those receptors that are shaped and compatible with that actual hormone so the rest of them rest of the hor the organs in the body just interact with these hormones and have absolutely no response to them they just they run into each other but there's no there's no effect it's like trying to use the wrong key on a lock it wasn't designed for you can put a key in whatever lock you want to but you're not going to open anything you're not going to turn anything it's that key only works with a specific lock and same thing here now organs tissues and cells that lack that specific receptor obviously are not going to respond at all to its stimulating effects so again just like what I've been saying now there are three types of hormones that we'll talk about uh peptide hormones steroid hormones and what are called bio enic hormones now peptide hormones are the vast majority of the body's hormones these are formed from chains of amino acids and we call them protein hormones because that's what they're composed of an amino acid right formed into you know multiple amino acids link together is considered to be a protein and by Essence this is a protein hormone so if you remember uh the the bond that actually connects two amino acids together is called a peptide bond now these combined with receptors On Target cell membranes and function like a second messenger system so you've got this the receptor on the cell is going to bind with that hormone and that in turn will actually trigger a response within the cell to have that cell do something and that is the secondary messenger system good example of this one I mean there's a lot of examples of peptide hormones but a good example of this one is growth hormone okay now steroid hormones on the other hand are derived from steroid-based lipids and a good example of this one uh is testosterone now steroid hormones are derived from cholesterol molecules they these molecules these hormones easily diffuse through the cell membranes so they pass right through the cell membranes without issue they're going to form hormone receptor complexes in the nucleus that is the organel within the actual cell and that in turn can activate specific genes to begin functioning and doing their job by transcribing mRNA and making proteins so in essence what happen here is that these steroid hormones pass through the actual cell membrane bind to that receptor complex on the nucleus and then they're going to turn on a gene and the Gene's going to start doing its job it's going to start uh TR being transcribed into messenger RNA messenger RNA is the mechanism by which the cell uses to take the Gene's message and make it into an actual product and in this case the product is the the pro lastly there are biogenic hormone biogenic amines or biogenic hormones these are small molecules uh produced by altering the structure of a specific amino acid so they're amino acid based but they're single amino acids they're not chains and these can either bind to receptors on the cell membrane or they can bind within the cytoplasm good example of these are thyroid hormones or sorry thyroid hormone all right now let's talk about feedback loops right because when we talk about hormones we have to talk about the feedback loops that they in turn control now in a negative feedback loop a stimulus is going to start the process and eventually either the hormone that is secreted or a product of its effects so that is a product that's that's produced by the hormone being secreted and being targeting cells is going to cause the process to slow down or turn off this is the most common control system used in the body and a good example of this is the regulation of blood glucose levels in the body obviously a very important pathway and so let's break this down a little bit let's look at it so apparently here's me eating a burger and as you do that as you know as you're you're eating in this case uh largely the the fruits and vegetables as well as the bread around this burger are actually going to have a lot of sugars in them and so those are going to be break down breaking down into the body and absorbed and so that blood gluc your blood glucose level is naturally going to rise as a result of feeding eating on the eating these and so that in turn causes the pancreas to actually respond because the pancreas is going to attack this high blood GL glucose level um by insulin secreting cells in the pancreas and so the pancreas is in turn is going to secrete the hormone insulin and that's going to cause liver cells to actually take up glucose so the liver itself is actually going to be induced to begin absorbing in essence um glucose from the blood and forming them as like glycogens so it's going to be or yeah glycogen so it's going to take them those individual glucose monomers monosaccharides and it's going to now bind them together into this large complex carbohydrate we call glycogen so it's a storage form of glucose now most body cells in this case will also take up more glucose in the process and as the body takes up more glucose that glucose level is going to decline it's going to go down it's going to decrease and once that blood glucose level drops to a particular level the insulin secretion stops and thus the negative feedback loop so now that you've returned back back to a homeostatic level all is right with the world in essence we have brought that glucose level back down to normal we have stored glucose appropriately and now there's no need to continue to scret insulin or to bring that level down that is a negative feedback loop now a positive feedback loop is is different this accelerates the original process either to ensure that whatever pathway that's occurring continues to run or it speeds up its activities in order to continue to doing the job just more effectively there's only a few positive feedback loops that occur the best one that we can show is process of milk from the mammory glands right so so a newborn child right is going to feed right and it's going to uh uh feed on breast milk from the mother and so in this case it's the suckling that actually uh begins this whole process right so this suckling actually sends impulses to the hypothalamus and the hypothalamus in turn signals the posterior pituitary gland to release oxytocin and oxytocin then is released and stimulates milk injection from the mamory gland in the breast now milk is then released the baby feeds and as the baby continues to feed the suckling sends more impulses to the typo alamis which in turn signals the posterior pituitary to release oxytocin and more milk is ejected from the mamine glands and more milk is then fed upon by the child and so on and so forth notice the positive feedback as long as the suckling continues in a regular in a in a regular manner this feedback loop will continue to grow because the stimulus is constantly there now we have to look at the the overarching control system that delegates down so so to speak orders to the endocrine system so we have to look to the hypothalamus because the hypothalamus ultimately controls the endocrine system now um it's going to oversee most endocrine activity now special cells here are going to secrete hormones that influence the activity the secretory activity of the anterior pituitary so that's what that ant pit stands for right these are regulatory hormones we have two releasing hormones RH and inhibiting hormones IH and this directly oversees the stimulation and hormone secretion of the adrenal gland Adrenal medulla now specifically the hypothalamus is going to produce two hormones that are transported and stored in the posterior pituitary that's what post pit stands for oxytocin is one an antidiuretic hormone is the other an anti-diuretic hormone by the way is abbreviated ADH now some Endocrine cells are not under Direct Control from the hypothalamus a good example of that one is the parathyroid hormone we'll come back to talking about that here in a bit now the PO the pituitary gland is connected to the hypothalamus via a structure we call the infundibulum right so here is the hypothalamus and here is that infundibulum and then here is the posterior pituitary now the I'm sorry not the posterior pituitary just the pituitary gland and the pituitary gland is sometimes referred to as the hypothesis now I find that to be horribly confusing because it sounds a lot like hypothesis um and so you find that I often I always refer to it as the pituitary gland it's it's more readily identifiable most students have heard of the pituitary gland uh rarely have students actually heard of the term hypothesis so I give you that second name but it does not mean that I will actually use it right pituitary gland is what I will use lies immediately inferior to the hypothalamus and this is a small slightly oval-shaped gland that's housed within the cellura of the sphenoid bone so that the Cela forms that cup that bony cup that actually protects the actual pituitary and as I said the hypothalamus itself is actually attached to the pituitary gland via the infundibulum So This Is How They communicate with one another and we have two portions of the pituitary the anterior pituitary and the posterior pituitary and the pituitary gland is controlled by regulatory hormones from the hypothalamus so hormones are going to reach the anterior pituitary via what we call the and this is the best ever hypothal hypo fisal portal system so there in fact is a portal system of blood vessels through here called the hypothal hypohyal portal system let's look at some of those anterior pituitary secreet ctions we've got growth hormone that's secreted here abbreviated GH the function of or the effect of growth hormone is to stimulate growth to stimulate protein synthes synthesis and lipid mobilization and it targets all cells if we're going to grow we're looking to grow systemically or systemwide not just specific portions of the body thyroid stimulating hormone on the other hand is a bre TC TSH TCH TSH this stimulates thyroid gland secretions and the target here is going to be the thyroid gland and then we have the adreno corticotropic hormone always fun to really try to spell by the way don't worry you won't have to actually spell these in an exam that'll already be spelled for you uh the abbreviation for adreno corticotropic hormone is act and act stimulates glucocorticoid secretions and its Target is going to be the adrenal cortex lutenizing hormone is also produced by the anterior pituitary luteinizing hormone is uh abbreviated LH luteinizing hormone affects ovulation it affects uterine lining production and it affects progesterone secretion Target here is going to be the ovary cells as well as the uterus ovary for progesterone uterine lining and ovulation well and uterine lining for the uterus follicle stimulating hormone or FSH is going to affect estrogen secretion and it's going to affect follicle development the target here is specifically going to be just the ovary prolactin abbreviated PRL affects milk production and the target here as you would expect would be the mammory glands now the p uh posterior pituitary um the secretions here are actually produced by the hypothalamus but they're released by the posterior pituitary and we call them neuros secretions these are the those two that we talked about antidiuretic hormone or ADH ADH is responsible for the reabsorption of water and the increase blood increase of blood volume within the kidney so its Target is going to be the kidney oxytocin abbreviated OT uh in the male is going [Music] to affect the ejection of secretions from particular targets right the target here is going to be ductus deferens and the PO on the prostate so we're talking about essentially ejaculation here um in the female it's evolved in or it's is involved in labor cont uh contractions as well as milk ejection so the targets here are going to be the uterus and the mamory gland the thyroid gland is located immediately inferior to the thy thid cartilage so we talked about this a bit when we talked about the thyroid cartilage that big anterior sort of Shield or plow like structure right on the front of the larynx and anterior to the trachea overall so it's you're going to you're going to actually see it basically right on front right in front of the actual trachea and thyroid or not thyroid uh larynx it is palpated very easily size is going to vary depending on the individual and its shape is very distinctive it shape shaped very much like a butterfly again I'm not sure why this butterfly theme continues to occur in by in anatomy but nonetheless it does and it's due to its left and right loes which are connected in the middle via structure we call the ismos and regulation of the thyroid hormone secretion depends upon this thyroid gland pituitary gland negative feedback process it starts with the hypothalamus release in TR thyroid regulating hormone and then the anterior pituitary releases TSH which is thyroid s stimulating hormone then the thyroid gland releases T4 to the bones we're going to talk more about T4 here in a second T4 or TX not Texas uh these are the two abbreviations for the horm hormone thyroxin thyroxin affects the follicle epithelium and regulates metabolism and O2 consumption its Target is most cells calcitonin is probably the one we'll spend much more time talking about because it has larger kind of effect and it has this antagonistic effect uh with other hormones calcitonin is abbreviated CT and it's released by the C cells uh and it decreases calcium ion concentration in body fluids it inhibits Osteo class Osteo class if you recall actually breakdown um bone so its job is to inhibit the process of breaking down bone and by doing that it's going to decrease calcium concentration in body fluids and it's at the same time going to stimulate calcium excr by the kidneys so notice that it's kind of attempting to reduce calcium overall in the body fluids via inhibiting breaking down bone and at the same time also increasing the excretion of calcium by the kidneys now its Target is going to be dual it's going to Target both the bone and the kidneys for obvious reasons here yeah we're not doing that the parathyroid glands are these small brownish red glands are basically like nodules that are located on the posterior surface of the thyroid gland now usually there are four small nodules however this can range between any anywhere between two and six in terms of numbers and there are two different types of cells in the par par parathyroid glands they are the chief cells and they're the oxfile cells and the interesting thing about the oxop cells is that the function of these cells are actually not known so even though we've been we've been looking at anatomy and physiology for about as long as we've had science we still don't know the function of these cells so here are the parathyroid glands and they're not big obviously these are just nodules right and so here are the the typical four that we often see uh the parathyroid hormone or pth is produced by the chief cells within the par parathyroid glands now these are going to stimulate at Osteo class so uh in this case we have we just talked about calcitonin and how it inhibits osteoclast now we've got this antagonistic effect with the parathyroid hormone that's going to stimulate osteoclast to reabsorb Bone so they're going to break down bone reabsorb bone and that calcium from that bone matrix is going to be released into the bloodstream so we're going to be increasing the calcium concentration within the blood very antagonistic to calcitonin now this also stimulates Cal calcitriol hormone synthesis in the kidney and it promotes calcium absorption in the small intestine this also prevents loss of calcium during formation of urination so formation of urine so right prior to urination the again this is meant to be an antagonistic hormone to Cal calcitonin and the targets here again bone and kidney the adrenal gland sits at top the kidneys and it's yellow it's very fatty very lipid and it's in a pyramidal shape surrounded by a capsule now the adrenal glands produce a lot of different types of steroid hormones uh we collectively call them cortical steroids uh we're not going to cover all 25 of those because that's just a lot uh so we're going to focus in on a a few but uh but the corticosteroid synthesis is stimulated by act uh that's produced by the anterior pituitary so you remember we talked about act already cortical steroids are vital to survival right uh trauma to the adrenal glands or removal of the adrenal glands requires cortical steroid supplementation or supplementation throughout life so you damage your adrenal glands or you lose them due to some necessity uh then you require to you're you need to supplement your body with cortical steroids throughout the rest of your life now the adrenal glands uh there's two different portions of these we've got the medulla which is that inner core think of medulla or middle as being the same kind of thing it's that inner core uh we've got a lot of blood vessels in here and it works very strongly with the autonomic IC nervous system and so the medulla is going to produce epinephrine and norepinephrine and these in turn increase heart rate cardiac muscle contraction blood pressure gly glycogen breakdown and these Target most cells cortex the cortex is the outer sections of the adrenal gland and these are associated with the cortical steroids uh the two big ones that we're going to talk about here are going to be aldosterone aldosterone is going to increase the kidneys absorption renal absorption of sodium and water uh it's going to increase urinary loss of potassium and the targets here by function right are going to be targeting the kidneys because these are all roles of the kidney glucocorticoid or abbreviated GC releases amino acids from skeletal muscle lipids from atap POS and has an anti-in inflammatory effect this is the cortisol effect right and it's Target here are most cells you'll see me flipping past figures and slides and it's not because they're not important but those really just rein they're they're visuals that reinforce the topics I've already been discussing so I leave it to you to to look at those and go over those if you'd like and be able to trace back what it is that I was talking about the pancreas is look it's a it's a the pancreas is kind of a weird looking organ essentially it's a a weird chewed up looking gland that's finger shaped and it's pointing just a bit to the left so it's pointing to the left and you see this who whoa that was a really really not useful okay there we go sorry about that you see right here it's this finger-shaped organ and notice the the the the point of that finger so to speak is pointing to the left so that's the reason I call it finger shaped organ pointing to the left now this is located between the stomach and small intestine it's very slender it's pinkish and it's very nodular so it looks like it's been chewed it's a that's really kind of a bad way of looking at it but it it does so now it has two different roles here we're going to focus on the endocrine role but we can't ignore the exocrine Ro as well we've already talked about that a bit its exin role is in the secretion of digestive enzymes right that that are received by the small intestine so we've talked about that a bit in the digestive uh system we can't ignore it because it's a huge part of the pancreas but we do want to turn our attention to the endocrine function here in the pancreas and this is produced by the pancreatic elets uh that is the more recent term for these structures uh historically these have been called the eyelets of longer Hans so again I will use pancreatic eyelets but just be aware that that other term exists now there's a lot of endocrine uh there's a lot of uh hormone production that occurs in the pancreas so we this is a bit of a domino like effect so we want to make sure we we go through this a bit glucagon is produced by alpha cells there's a lots of different Alpha Beta Gamma Delta cells that we see in the pancreas right there all named by these Greek letters glucagon produced by the alpha cells within the pancreas uh increases blood glucose levels so this is a case where it say your blood glucose is decreasing right maybe because you haven't eaten or you haven't snacked in a while and your blood glucose has been used uh to a large extent by activity uh and so it's IDE the the function here is to increase blood glucose levels by encouraging both glycogen and lipid breakdown and so the targets here are going to be the liver where glycogen is stored and uh adapost tissue where lipids are stored now insulin has a very different effect obviously has an antagonistic effect effect this is produced by the beta cells insulin decreases blood glucose levels uh and encourages uptake of glucose by target cells so it's going to basically promote the decrease of blood glucose level by encouraging cells to uptake that glucose inside those cells specifically we see here uh in places like the liver uh it does promote glycogen and lipid formation so we want to take that glucose and store it in forms such as glycogen in the liver or lipid in the ose tissue and the target here are most cells because we're trying to get cells of the body involved in decreasing overall blood glucose levels before they come dangerous become dangerous now this is kind of fun because glucagon and Insulin are antagonistic to one another and so anast Statin controls both so samast Statin is is produced by the Delta cells and this is going to inhibit production and secretion of both glucagon and insulin and it slows rate of food absorption overall and the target here is going to be the alpha and beta cells both of which produce either glucagon or insulin and somatostatin is affected by pancreatic polypeptide this is produced by the F cells and pancreatic polypeptide suppresses somat Statin secretion so basically pancreatic polypeptide is going to suppress the the for uh the the secretion of sast Statin and this it's the seus it's the secretion of sast Statin that in turn controls the activity of both of these two glucagon and Insulin so if we're releasing pancreatic polypeptide somatostatin is not produced and glucagon and Insulin can do their jobs however pancreatic poly polypeptide is not being secreted then somatostatin is not being ressed and it's being released and thus both glucagon and Insulin are being inhibited notice the domino effect there the pineal gland is sometimes referred to as the pineal body we see inside the dianon of the brain this is a small cone-shaped structure that it's attached to the posterior region of the epithalamus and this secretes melatonin melatonin is responsible for regulating that circadian rhythm this is that 24-hour body clock it affects the synthesis of the hypothalamic regulatory hormones uh that in turn encourages FSH and LH synthesis its role in sexual maturation is not well understood it's known to have some role but just not how much of one it's isn't best understood yet and it's derived from the neurotransmitter serotonin the thymus we talked about the thymus already a bit in the immune system the thymus is a biobed structure within the med uh medyum it's superior to the heart and posterior to the sternum this decreases a great deal in size as we age and the functions it functions in association with the lymphatic system to regulate and maintain body immunity and it produces complimentary hormones thop potin and thymosins these two hormones act by stimulating and promoting differentiation growth and maturation of those lymphocytes what we would think of as t t lymphocytes or te- cells and thymus derived lymphocytes so again it's going it's going to produce hormones that in turn act upon its own functions the endocrine functions of the heart and GI tract these are kind of unique because we don't often associate these um organs of the urinary system cardiovascular system Digestive and resp and reproductive systems all contain their own Endocrine cells which secrete their own hormones and these have a variety of Regulation functions they regulate red blood cell production they regulate blood volume they regulate blood pressure they regulate electrolyte uh concentration in the blood they uh regulate digestive system activities as well as sexual maturation so there's a lot of wide ranging effects that we need to see from these sort of bundles of Endocrine cells within each of these individual organs that we don't associate with the endocrine system the kidneys are going to produce uh several hormones that we're going to talk about renin converts into Ang tensin 2 and this stimulates the secretion of aldosterone by the adrenal cortex this one is specifically going to stimulate um aldosterone secretion erthal poetin now erthal means red and as I told you before poetin always means produce or generate so they call this EPO and we'll come back to the significance of EO here in a second but arthop potin stimulates red blood cell production by bone marrow it's released when uh blood pressure and blood O2 so blood O2 saturation drops in the kidney so it's monitored by blood pressure and blood O2 saturation are monitored by the kidney and that in turn uh encourages the release of epo now EPO has some cultural significance um a lot of the blood doping or blood drugging that they talk about in certain Sports is attributed to EPO so um individuals like say Lance Armstrong for example who have been accused of um doping to increase their abilities in these very um long-term very athletic very um it's the term I'm looking for uh Marathon like events without the actual running but they're they're long-term athletic events um increased numbers of red blood cells are greatly going to increase their their abilities because it's going to make them incredibly more efficient at um regenerating O2 uh concentration within their body and then getting CO2 out so it's going to make them going to increase their endurance a great deal and so EO is one of those those uh um hormones that is is illegal in those Sports you cannot use them within those Sports it's considered a violation um calat trial is released in response to pth so parathyroid hormone and stimulates both calcium and phosphate absorption by the intestine the heart is going to secrete atrial peptin uh this is uh also otherwise ter termed atrial ntic peptide or& this is released by the right atrium in response to excessive stretch caused by increased blood volume or blood pressure now& atriopeptin we just talked about here is going to reduce blood volume by causing water loss and sodium excretion from blood and urine and thereby decreasing blood volume and blood pressure so it essentially acts to decrease the excessive stretch that occurs within the right atrium by decreasing in overall blood volume and blood pressure reproductive glands we've got the ovaries the ovaries produce estrogen estrogen is produced by the follicle cells and it affects maturation of oyes not oyes by by the way we're going to talk about that maturation of O sites uh the uterine lining and secondary sexual character uh characteristics or traits its Target is most cells because secondary sex traits really are most cells that are going to be affected by that progesterone is produced by the Corpus the Corpus lutetium this prepares the uterus for implantation by a fertilized egg and it also prepares the mamory glands so its targets are going to be both the uterus and the mammary glands inhibin is produced by the follicle cells and this decreet FSH or follicle stimulating hormone its Target is the anterior pituitary now this is a a view obviously of the reproductive glands for females so the testes are the male equivalent there testosterone is produced by the testes these are produced by the interstitial cells within the testies and affect the formation of gametes as well as secondary sexual characteristics and so the targets here are going to be the testes as well as all cells within the body inhibin is secreted by the susten susten cells and this decreases follicle stimulating hormone keeps sperm production at normal levels its Target is going to be the anterior pituitary as well