and welcome to the live lesson I'm just gonna leave this open for a little while while some more members join and they click the link in our community page um as per many of your requests and looking at your comments the most popular suggestions were for us to do some endocrine and homeostasis revision which is what I want to do for you today don't forget there is a comment section at the bottom of the page where you can leave questions for me so that I can answer you and give you a little bit more guidance as to what you want to know this lesson is going to be a little bit different in that I'm going to actually teach the topics um we're not going to go into any past paper questions or anything like that as the name suggests it's going to be a revision lesson of things that you would have done in class so I'm just going to give it a couple more seconds for everyone to enjoy to join us um if you like you should get a piece of paper perhaps make the same note that I am making on the topics that we're doing and they are going to simplify your studying and also don't forget if you are a member you should have access to the study guide the study guide makes this particular section really simple and easy because I've summarized everything you need to know literally in a couple of diagrams and a table which makes studying so simple um I'm gonna wait for a couple more seconds before we begin Hi singita how are you once again don't forget that there is a comment section at the bottom of your page where you'll be able to ask me questions on what we're doing today all right I'm going to then skip into the work so that there is no more waiting I'm going to go straight in to learning about the endocrine system and the homeostatic system okay so first things first I need everybody to know that these two systems actually work very very well together in other words they are sister systems your endocrine system is linked to your homeostatic system and so often I'm just going to put that here now your endocrine system and homeostasis now they work together because ultimately one produces substances for the other so the endocrine system is linked to hormones right and those hormones are linked to a stimulus that you've received right you need to digest food your carbon dioxide levels are not good so we need to change the the amount of carbon dioxide there's something inside of you that is disrupted right that's where hormones come in hormones are remember chemical messages and these chemical messages are actually slow released and what I mean by that is they are slowly released over a long period of time and the change they have is slow as well it's not rapid unlike the nervous system which is fast and immediate this is a lot more slow now how does this link into homeostasis well hormones are linked to homeostasis because they are the ones triggering homeostasis to be stable so just let's recap what homeostasis is homeostasis is when the internal environment is stable right so internal environment is stable and what does that mean that is linked to things like your pH um your water balance um your glucose level and the list actually goes on and you actually need to know quite a number of these and we'll go over them today and so these two things are synced with one another endocrine and homeostasis because of their jobs now in order to keep the body uh the internal environment stable you need hormones okay because these chemical messages are going to control these substances the hormones are going to control your pH they're going to control your water levels they're going to control your glucose your salts and so many more things and that is why these two often work together and we need to understand how they work together now one thing I just want to remind everybody because um I think we also forget what the word also endocrine means and I was actually reading um a report uh yesterday about mistakes grade 12s make most often and that is they don't know the difference between a exocrine um and an endocrine gland just as a recap um the exocrine glands versus the endocrine glands you may have remembered these um when we did the pancreas the pancreas is both EXO and endo um and it's important to know the difference because we actually swap um the the functions of these two very very often and so the difference between the two is your exocrine gland uses a duct versus your endocrine is straight into the bloodstream now as I said to you the pancreas can do both but the pancreas is unique in that it can do both um whereas something like your let's say adrenal gland is only an endocrine gland your pituitary gland is only an endocrine gland your salivary glands exocrine glands so I'll make a little list underneath here so like this would be a salivary gland because we're going to a duct and that duct would go into your mouth where saliva is but then endocrine on this side would be um what did I say your adrenal gland so the main difference is where the destination of the substance is going so again a lot of us don't know the difference between these two I suggest that you make a little note to yourself of what the difference is between EXO and endocrine because we get that wrong very very often in exams of or our endocrine glands which is what we want to revise today and I know that was a popular choice I am I'm going to be honest with all of you I actually think if you learn your other sections really well you are learning your endocrine system and let me explain right so let's quickly just list off all the endocrine glands we need to know so according to our guidelines and remember you must use your guidelines when you are preparing for exams we need to know the high per thalamus we need to know the pituitary gland always forget how to spell pituitary it's Sneaky second eye pituitary we need to know the thyroid we need to know the pancreas uh what else to say the adrenal gland uh then the ovaries and the testes I think that's it yeah okay so that is the list of our endocrine oops sorry I've changed my pledge now that is the list of our endocrine glands that we need to know if you look at the list a lot of these you would have actually done in other topics or other years for that matter right so for example if we go to the pancreas we would have done the pancreas in grade 11. so you actually should have hopefully everyone some background knowledge on that if you look at ovaries and testes this is what we did in grade 12 but this is from the reproduction section so we should know the hormones that come out of the ovaries and testes likewise with the pituitary gland we learned about the pituitary gland also in the reproductive system because that is where FSH and LH come from um what else uh the hypothalamus this one we would have learned in grade 11 and some of you like I don't remember learning that in grade 11 it is linked to ADH but I'm going to link all the hormones down now so you can see how we are going to learn them the only two newer ones are the thyroid and the adrenal gland so in other words if you have actually learned this work pretty well and you have a good memory of grade 11's work you've actually done a lot of the foundational knowledge already especially if you know the pituitary ovaries and testes from the reproductive system you're actually going to have a very easy time now in terms of the hormones that we need to know when we study the hypothalamus the hypothalamus is linked to ADH foreign and if we have forgotten what ADH does that is for water the pituitary gland has a lot of hormones linked to it remember it's the master gland it's the gland that is responsible for telling everybody what to do and this one has so many it's got thyroid stimulating hormone it's got luteinizing hormone it's got follicle stimulating hormone uh what else does it have uh it's got uh growth hormone um let me think of another one it's got um i c s h which is interstitial cell stimulating hormone that's the one that makes sperm there's so many again if you have my study guide I have it simply put out for you in the table on the endocrine glands okay the next one is the thyroid the thyroid makes thyroxine and thyroxine I'm just going to put it down here is responsible for maintaining your metabolism right we're going to come back to thyroxine because that's a very popular one and in terms of an exam question and I'm going to explain it a bit more for you so you know what to do then under the pancreas I think we all know what they secrete that one is insulin and glucagon and remember that's sugar going up sugar going down the adrenal gland is a new one for us because that is adrenaline and adrenaline by the way just so that we are aware is often linked to the nervous system but we'll come back to that one too I'm going to elaborate a bit more so we've got the adrenaline and oh I forgot of course and aldosterone if you've forgotten aldosterone aldosterone is for salt regulation that's also a grade 11 topic and then the ovaries are going to be estrogen and the testes are going to be testosterone [Music] so I know it's a little bit messy here so let me just highlight a couple of things so you can see how they stand out so these are all of the hormones I'm just highlighting them in yellow here that we need to know and be aware of and what they do and then I'm just going to highlight in pink here their function so ADH is water these all have different functions I haven't listed here thyroxine is for metabolism insulin and glucoganoff or glucose aldosterone is for salt adrenaline we're going to come back to that one because that's a very unique um response so I'm going to explain that to you and I think we know what estrogen and testosterone do okay so the best way to study this particular section is using a table so I keep referring back to my cheat sheet and the study guide but the table makes it really easy to study because you just simply need to study the table and I've put everything you need to know in there the most important thing you actually need to be able to do with this is apply it to a process in other words how do these hormones maintain homeostasis because they're never going to ask you 8 10 12 marks on the hypothalamus asking you what is the name of the hormone and what it does that's only going to be about two marks you now have to take the knowledge about this these endocrine glands and the hormones they secrete and apply it to homeostasis so whenever we have a situation where we need to apply our knowledge of the endocrine system we are going to use the template answer to explain ourselves so let me show you what I mean again this is also available in the study guide and you will be able to find it I'm going to turn my page sideways this answer is actually a template for the nervous system the endocrine system and the homeostatic system they're all linked together I need you to see the big picture all three systems maintain your internal environment and your body's safety so when we construct an answer in the exam this is what we are going to do we always start off our answers with a stimulus now what is a stimulus or a stimuli a stimulus or a stimuli is in reference to something external or internal that has changed and it can be anything like temperature it can be pain it can be light it can be blood pressure there are so many different kinds of stimulus or stimuli that your body can experience so when you are explaining a homeostatic function we always start with the stimulus you find out what the stimulus is and they often tell you what it is in a paragraph then the next step in our answer is there is always going to be a receptor now the receptor is there to interpret the stimulus now receptors are often organs or cells and some examples of these can be the eye it can be your skin in terms of cells it can also be like the alpha cells in your pancreas right those are the ones that determine if you have enough insulin or enough glucagon and do you have enough glucose in your bloodstream is it too high or is it too low so the receptor picks up a stimulus now that receptor receives that information but unfortunately it can't do anything with it because it doesn't have the ability to what we call integrate or think so it sends that information to a control center now the control center again is multiples there are different kinds we could have the brain can be a control center the pancreas is also considered a control center when it comes to sugar let's think of another control center uh another control center could also be the adrenal gland these are parts of the body that sometimes also overlap elsewhere you'll see now when I go to the effectors there might be an overlap but it's because they are both integrative and responsive in other words they choose the decision and then they carry it out now the control center receives the information from the receptor so it's basically passing on a message there's a message in the form of a stimulus that goes to the receptor the receptor then sends that information to the control center the control center now makes a decision and we call that decision a corrective measure right now the corrective measure have obviously the corrective measure could be anything it could be secrete more secrete less make warmer make cooler and so the corrective measure is linked to returning back to homeostasis to a home myostatic level in other words returning back to normal right that's what the corrective measure is and again generally the words we associate with corrective measures are inhibit or secrete okay and you either secrete more or you secrete less you inhibit or you make more and so I'm just going to quickly go back and start from the beginning we start off with a stimulus that stimulus is received by a receptor that receptor sends on that information to the control center the control center makes a decision which we call a corrective measure and now from here the corrective measure needs to be sent to someone which in this case is going to be a effector now most often effectors are you may remember this they will be muscles or they will be glands and that's also why sometimes there's an overlap between the gland that is in the effector and the control center sometimes this is the same place okay in other words the control center is telling itself what to do and so some examples of glands that we link to effectors would be the pancreas but it could also be um regions of the brain um it can be your muscles when we speak about muscles we're also speaking about let's say the small little um arterials so let's talk about the dermal arterials those are the ones if you remember in your skin that that Therma regulate that either squeeze closed or or dilate when it's hot or cold the next step after um the effect is is going to be the response to the stimulus and returning to Norm and when we say return to Norm it means returning to normal and that's remember what we want we want the effector to allow the body to return to Norm now in your answer you actually have to write or state we are returning to normal but elaborate what return to normal means everyone please don't just say we return to Norm okay you need to actually say what's happening maybe we absorb more water for example or maybe we release more glucose maybe our blood sugar levels are low so you need to actually say we absorb more water returning to the norm now there is one final step in our Circle generally this is where the circle ends but sometimes there are a few that has a follow-on result like a domino effect and so sometimes there is one last little bit at the end here which I would call results and I'll show you when we use this one result often is linked to the return to Norm and so basically what's happened is for example you have absorbed more water in the kidneys and the results would be less urine is produced now as you can imagine that doesn't apply to all of these right doesn't apply to every single one of these actions it only applies to a few one of them being for example the um absorbing more water that one is a common one where you have to tell me that there is less urine you might even say there's less sweating and you associate those together those are all the results that happen if you absorb more water okay so again this is in our guideline if you want to access it what I'm going to do now and step into is some actual homeostatic Loops so you can see how they work because that was also requested and there are so many to pick from because there's osmo regulation thermoregulation salt regulation glucose carbon dioxide thyroid I think I'm going to do the thyroid one because it's most often the one that is mistaken if you have any questions or queries I would love for you to pop them in the chat now for me so I can have a quick look and see if there is anything you want me to go over while I just wait for you I want to set up our next point remember if you want to ask me anything you can put it in the chat foreign otherwise I'm going to go into Kai wants to do salt cool we can do salt aldosterone those are two tricky ones so what I'll do is I'll do thyroxine and then I will go into salt the reason why I really like doing thyroxine by the way if you weren't aware why I'm choosing it to do it first is because it's most often the um question or the homeostatic function they love to ask in the final paper it really is one of their favorite questions and most often it's a paragraph that you must read for example one year it was something about thyroxine in the growth of cattle and what happens if you give cattle more thyroxine than they need how does that affect their body and now you have to understand what thyroxine does so that if you get more thyroxine what happens you know if you get too much but I'm going to show you the most simple way to study thyroxine which is when there is low thyroxine and how we bring it back up to normal or how we bring it back up to homeostatic level okay so we're going to start off with that now the reason why a lot of people get also thyroxine wrong is because there's actually two hormones in this system which is unusual normally we only have one hormone at play Okay so let's go into what happens if you have low thyroxine so if we follow our answer from previous stimulus receptor control center corrective measure return to normal if we follow this system this is how we need to learn it starting off first of all with the stimulus so what happens is your thyroxine levels drop okay now what does that look like what does it look like when thyroxine drops thyroxine it affects your metabolism which means it affects your body's cellular respiration a lot of people think metabolism is digestion no it is not digestion metabolism is your body's ability to build up and break things down and what is the most important building up and breaking process you have cellular respiration and when cellular respiration slows down then your metabolism slows down so all of this is linked to your metabolism and how fast or slow your cellular respiration is occurring so what happens is your thyroxine levels drop for whatever reason now this is an example of negative feedback as well and so again many of us are uncomfortable with negative feedback because we don't know what to write if you write these Loops you are writing the correct answer okay so our thyroxine levels drop that's the stimulus now someone needs to receive that information remember there must be someone responsible for um experiencing the drop and the individual who is responsible for that is the pituitary gland now again what's unique about this is the pituitary gland is both the receptor and the control center so it receives this information how does it receive it through your bloodstream as your blood moves through your brain it can the pituitary gland picks up that there's not enough thyroxine in your bloodstream so now the pituitary gland is the receptor okay but it is also the control center so just in Brackets here I'm going to put here that it is the receptor but it is also the control center the CC so it does both at the same time and it registers there is a drop now it's got to create a corrective measure if we go back to my previous slide if it's being both of these at the same time the corrective measure or the choice must be made so the pituitary gland is now going to make a decision about what it needs to do and now it secretes a hormone and now this is where it is unique in that we actually secrete two hormones to get this um thyroxine to come up the pituitary gland secretes thyroid stimulating hormone TSH yes you can use the short hand you do not need to write it out in full every time the only time you have to write hormones out in full is if you are in the terminology section of your exam okay so the thyroid stimulating hormone is the corrective measure that is sent now to the effector who is the effector that is the thyroid gland right the thyroid gland is now going to be told you need to make more thyroxine so it goes off to make more thyroxine so this is our corrective measure acting out now and it releases more thyroxine remember keeping in mind and let me just highlight them in different colors TSH is a hormone and thyroxine is a hormone and that's why this is a unique Loop because it's got two hormones in it normally there's only one hormone and so the thyroid is going to release more thyroxine thyroxine goes up in the bloodstream now the moment it goes up in the bloodstream negative feedback is going to kick in in other words the levels of thyroxine were low now they've come back up again we don't need as much TSH so as the thyroid produces thyroxine TSH reduces why because of High levels of thyroxine and that's how negative feedback works as one hormone goes up the other hormone goes down as TSH increases and increases and increases because thyroxine is low it eventually gets to a point where it's so high that it triggers thyroxine to come back up as thyroxine comes back up it forces TSH to be reduced it's kind of like a little um a seesaw effect maybe your teachers have spoken about that before where if this is the set point the seesaw moves oh that is a horrible line it's undo that one and try it again the seesaw moves up and down in other words if there are high levels of thyroid stimulating hormone then eventually when it's so high this must come down so that thyroxine can go up and then it goes the other way when there's high levels of thyroxine and low levels of thyroid stimulating hormone then it must go the other way so that's why as one goes up the other goes down and it's a seesaw that happens now the final thing by the way we have to have an effect or a returning to normal which we haven't finished here yet is if thyroid stimulating hormone reduces and this is because of the high levels of thyroxine the final effect on the body is cellular respiration increases and remember that is your metabolism it's all about cellular respiration it is not about um like your ability to to digest food that is a big big misconception okay right please be again aware and weary of the fact that they love asking this one and so you also need to know what happens if you have too little or too much thyroxine most of the time in the final exam what they like to do is give you an instance where they are artificially giving someone thyroxine as I said to you before they gave a question about cattle the cattle were given more thyroxine than they needed what is the effect on their body well if you think about the Seesaw if the thyroxine levels are really really high so if I'm forcing the thyroxine up the cattle's bodies are going to try and secrete less thyroid stimulating hormone right because if this one is going up the thyroid stimulating hormone is going to go down the thing is if you consistently give them more and more and more thyroxine it means that their bodies become over stimulated and they have what we call hyperthyroidism hyper meaning high thyroidism meaning they make too much thyroxine and that has a negative impact on the metabolism likewise if you don't get enough thyroxine you have hypothyroidism or low secretions of thyroxine and so what they do in those questions is they like imitate diseases that you would see or glandular endocrine disorders as you would see and you need to know enough about this to apply it to a new situation okay right let's do aldosterone because that again is one where They Don't Really uh we don't really teach it again in grade um 12. so we're hoping as teachers that you remember it but aldosterone is for salt everyone if we're not so certain about that so aldosterone and this is salt again I have a lovely little summary for aldosterone and salt in my study guide as well if you want to have a look at that nice easy way to remember what we're doing here now okay so again we follow the formula we start with a stimulus what is the stimulus well the stimulus in this one would be a decrease in Oz molarity um ma'am what is osmolarity okay if we don't know what osmolarity is we do need to work on our terminology because you are expected to use that word in the final exam osmolarity is referenced to water and salt in other words their ratio how much water to Salt there is inside of you so in other words if there's a decrease in osmolarity there is a low amount of salt that's what that means in other words you're too watery on the inside and you don't have enough salt to balance it out okay so now how do you fix this problem so first things first if there's a decrease in osmolarity which is our stimulus now we need to talk about who is the receptor who's going to fix this problem again this is an unusual um receptor because it's not a gland it's not a region of the brain it is your afferent arterials now which afferent arterials now you need to go back into your grade 11 knowledge these are the arterials that go into the kidney and into the Nephron and I'm just pausing now because I did see a question Kai does thyroxine stop or reduce secretion thyroxine only stops being secreted if it's too high so in other words you're always secreting a small amount of every hormone it just seesaws up and down so and that's how all homeostasis works on the Seesaw as one hormone goes up the other goes down and then they reach a peak and they reach a bottom and they must go the other way and then now there's too much thyroxine too little thyroid stimulating hormones so then we go the other way now there's too much thyroid stimulating hormone not enough thyroxine so we go the other way and it's the same with aldosterone here aldosterone Works in exactly the same way if there's too much water not enough salt now we go the other way now there's too much salt not enough water now we go the other way so my hands are showing this negative feedback seesaw that happens and it's applicable to all homeostatic functions that are negative feedback which are actually all of the ones we learn in matric we don't learn positive feedback in metric we only learn negative feedback and there's always a seesaw so to reiterate the Seesaw in aldosterone What's Happening Here is if this is the Seesaw right now salt is low but water is high and this is problematic basically it means there is not enough salt in the blood and too much water and so if you married this with their hormones ADH is too high there's too much water aldosterone is too low so now we need to make the Seesaw go the other way the important part is no hormones are ever at zero so yes this is low but it's not at zero it's just very low in amounts aldosterone now what we need to do is secrete more aldosterone so that the Seesaw moves the other way and hopefully gets what we're aiming for remember is this balance like that but that's not how negative feedbacks works we never really get to a level like playing like this we actually then end up going this way as well where now the salt is too high and the water is too low and then we go back again and so it's a seesaw effect all the time I do see another question so I'm going to have a look at it the question is with osmolarity the receptor will always be the afferent arterials yes always they are the ones who are receiving the information so they are the little blood vessels that go into the nephron of the kidney I think you may remember them there's the afferent and the efferent afferent is the ones that go in I hope we all remember that now we've got the stimulus the receptor so now we need the control center now the control center is a weird one it's weird because the afferent arterials again are both the control center and the receptor just like the pituitary gland can be that as well it can be the control center and it can be the receptor at the same time and you'll see now why it is both because it is going to secrete a hormone now the afferent arterials receive that there is not enough salt now that they know there's not enough salt they now make a decision and their decision is to secrete a substance called renin now in the simplest way renin is a hormone in some of your textbooks it will say it's like a like a stimulant but for grade 12 we can just know that renin is a hormone and now renin is the first step in the corrective measure and again this is why this one is also really hard because there's actually two corrective measures there is this first corrective measure which is to secrete renum so Raiden is now in the bloodstream renin stimulates another secretion that occurs inside of the arterials which is to secrete another hormone called angio tensin so this one is a little bit harder everyone I'm not going to pretend like it's not interact your hair around this one salt has two corrective hormones that need to be secreted if you're wondering why it has to do with a complex system of hormones that are responsible for regulating not only your salt but your blood pressure in grade 12 we simplify this so much that all you really need to know is the afferent arterial secrete renin renin triggers the secretion of angiotensin you don't really need to know how they work and who they interact with you simply need to know that once the message comes from the afferent arterials you'll secrete renin and renin will cause the walls of the arterials to secrete Angiotensin and that's really all you need to know okay don't over complicate it don't over study this please it's a waste of your time because they're not going to ask you more detail than What's Happening Here now again this is where it's even more unique is I'm actually going to put a third hormone in this now so these are the corrective measures there are two corrective measures secrete renin and secrete Angiotensin Angiotensin is secreted into the bloodstream and that is sent to the effector the effector is the adrenal cortex now it's important to say adrenal cortex not just adrenaline gland that's also another key feature everybody why Ma'am why is that well this is the adrenal gland and there if I cut it in half there is an inside and outside layer the outside layer is the cortex that is where we make the next hormone we're going to talk about there is also the inside which is the medulla now the medulla makes a different hormone everybody so that's why you have to be specific and say adrenal cortex so Along Comes Angiotensin gets pumped through the bloodstream goes to the adrenal cortex the adrenaline gland and now the adrenaline gland and sorry the adrenal gland I beg your pardon the part of the cortex is going to secrete our third hormone and so what happens is adrenal cortex secretes l dos turo and that is now our third hormone I know it's a lot so there are actually three hormones in the system as I mentioned to you just earlier so now we have a third player in the mix aldosterone has an effect on salt and ultimately what happens is aldosterone is then sent via your bloodstream to the distal I'm not going to write it all out convoluted tubules do you remember those those are the the twisty twisty nephron tubes it's sent to the distal convoluted tubules and there we increase salt absorption because remember we had low salts in the beginning we want the salt to come back up again this one is tricky and I'm going to go over one more time because there are three hormones acting at the same time so one more time from the top there is a decrease in osmolarity which means the blood is more watery less salty okay we need the salt to increase so who picks that message up the afferent arterials of the Nephron in the kidney the walls of these artery arterials are sensitive to Salt levels they notice it's very low so the first thing they do is they secrete renin renin is a stimulating hormone it's a trigger response that response causes another hormone to be released out of the arterials called Angiotensin if you don't have renin then you can't have Angiotensin and so you've got to have one hormone be released first that then stimulates the cells to now secrete Angiotensin this hormone now goes in through the bloodstream and makes its way to the adrenal cortex which is remember the adrenal gland but the outside layer of the adrenal gland that is where we secrete aldosterone aldosterone is the hormone that is now going to be responsible for increasing our salt level aldosterone now goes back to the kidney it makes the distal convoluted tubules um more permeable to Salt which means salt can go back into your bloodstream and we absorb more salt into the blood increasing the salt level and then returning back to normal right and so now it would say up here at the end return to Norm or salt levels increase this is a tricky one um they did ask this one if I remember correctly last in one of the two last papers it was either in the supplementary of 2023 or in the final paper last year in 2022 um it doesn't mean they won't ask it this year again it just means that they hadn't asked it for a while and so they asked it sometimes certain questions are very popular and they ask it again and again and again so this one I really think you should know but don't over complicate it in your head I promise if you just know this series of events you will be able to explain it at the end of the year not forgetting that if you don't use terminology then you won't get it right you know if you don't say afferent arterial if you don't say Rin and Angiotensin if you don't say adrenal cortex those are your keywords that should be in your sentences okay we've got time for one more homeostatic and endocrine system to do and again I want to remind you these are all endocrine systems with homeostatic functions the endocrine gland that I'm talking about in here was the adrenal cortex if we go back one it was the pituitary gland so they are unseparable you cannot separate endocrine from homeostasis I think the last one we're going to do is thermoregulation I know that that was also a request there is two thermoregulations I'm going to do the one because if you know the one you know the other kind of situation if you know what to do when it's hot then you'll know what to do when it's cold um let's do a cold day that's a nice one to do okay because it also has like relevance now of us being in winter this is what's happening inside of your body so we're going to do thermoregulation and I'm going to focus in on what we call vasoconstriction remember if you have any questions go ahead and ask them well I just set this up so vasoconstriction remember everybody is a cold day response Vaso blood vessels constrict make small okay so again one last one starting with the stimulus and then going all the way around the beauty of learning thermoregulation is if you learn the one you know the other it's just the opposite so if one contracts the other relaxes if one increases your body temperature the other one will decrease your body temperature it's really that simple and so I wouldn't spend a huge amount of time learning both I would just learn one very well and know that the other one is just the opposite it's the opposite actions okay so let's start first things first remember we always start off with a stimulus and that stimulus in this instance is going to be cold weather right it's just going to be cold temperatures very simple external cold body temperature is going to stimulate your receptors and your receptors are in your skin what's uh what's great to know is you don't need to know any of the skin receptors names you just need to know they are receptors in the skin and they are responsible for maintaining your body temperature so we just call them skin receptors now the skin receptors receive that message were cold it's a cold environment and now they're going to send that information off to the control center and the control center is the hypothalamus oh I'm not gonna be able to squeeze it in oops hypothalamus okay so the hypothalamus is not just a gland in the sense that it secretes hormones it also is responsible for maintaining body temperature too and that makes sense because the hypothalamus is linked to hormones and enzymes and your metabolism and so if you get too cold on the inside then all of those functions can't work properly so the hypothalamus is important to keep you nice and toasty and so it sends uh impulse to oh no impulse excuse me it sends um a stimulus to the hypothalamus and the hypothalamus now tells your dermal arterials which are the very small blood vessels in the surface of your skin and they do two things the first thing if this is now the effector so the hypothalamus was the control center the effectors are the dermal arterials right so they're going to carry out the corrective measure that's going to happen now two things happen the hypothalamus tells the I'm going to have to do two arrows here the hypothalamus tells the circular muscles of the arterials to contract but it also tells the shunt vessels to relax now ma'am what does that mean okay let me make a very quick sketch if this is the surface of your skin this is the fat layer down here so this is fat tissue these are fat cells what we have is dermal arterials which sit in the fat layer come up to the surface and come back down into the fat layer like that essentially if I just draw this correctly and make sure I get this to continue down here as well like that and I haven't drawn this correctly now because it should actually Branch off and this should come down here too but essentially what happens is when blood is going through your skin it'll go through the fat layer up to the surface down and then back into the fat layer this loses a lot of heat if you're cold so when the circular muscles contract they are talking about this area here let me change color they're talking about this area here there's a circular muscle here so the circular muscles here contract and what that does is it makes this Loop smaller in other words it you'll actually physically see it shrink I'm trying to make it a little bit thinner so you can see so it won't be as wide it'll be thinner and one cut circulation off completely but it'll cut it off enough that not a lot of blood is going to the surface so instead of losing lots of heat if these arrows represent heat you're now only losing a little bit of heat to the surface of your skin so that's when the circular muscles contract the shunt vessels are in this lower level blood vessel that stays in the fat and so the shunt vessels are over here it's like a little squeezy Bridge a little area here on the sides at the bottom in the fat layer now they stay open so what happens is instead of the blood going up and losing its heat it stays down here in the fat layer retaining the warmth down here so we don't want the blood to go up into the surface of the skin we want it to stay low in the fat layer that is why the circular muscles relax sorry circular muscles contract so these little muscles here so that less blood goes to the surface as we can see in this side so that more blood remains in the lower level in the fat layer and to do that the shunt vessels they relax so it's literally the difference between squeezing something closed the circular muscles or the shunt vessels they stay open and they relax if you were explaining on a hot day this is just the opposite everything else is the same except it would be hot temperatures are received by the skin the hypothalamus tells the dermal arterials to on a hot day the circular muscles will relax and the shunt vessels will contract and that makes sense because on a hot day you want more blood going to the surface so more heat is lost and you want less blood in the fat tissue layer because you want to retain less heat because you're hot right and so the final step in this because remember we've got to have a result or a return to Norm is more blood is retained or sorry more um I shouldn't say is it more blood yeah more blood is retained to the sub Q utaneous and subcutaneous everyone is fat and yes you need to use the word subcutaneous I've been using the word fat to make it easy to understand but again you must use our terminology more blood is retained to the subcutaneous layer maintaining your heat one other thing before I look at the questions in the um chat is they like to marry this question with water now think about it for a hot second how does your thermoregulation link to water well if it's a hot day you're going to sweat more you're going to lose water on a cold day you're going to sweat less so what examiners love to do is they love to ask thermoregulation with water regulation and now you really need to be able to apply your knowledge this is the harder part of the life sciences content taking two systems and marrying them together being able to show that when you sweat more you urinate less on a cold day you'll sweat less but urinate more and that is all to do with your body temperature and then how much water you are losing and so you've got to be really on point when we study thermoregulation now I'm going to have a look at a question because I'm pretty sure I saw one pop up okay Sunita asks how does the diameter of the blood vessels Aid with thermoregulation I saw this in a question paper in an explained question so how do they uh I think the question is how do they aid the blood vessels Aid in thermoregulation so if it's an explain question remember we must make a statement and a reason so how do they aid they aid in changing the blood flow that's your statement they aid in changing the blood flow they can and now you need to explain right explaining would be the circular muscles can contract and relax allowing more blood to the surface and the shunt vessels can contract or relax of keeping more blood in the subcutaneous layer or allowing less blood into the subcutaneous layer so that's what they're sort of meaning when they say explain how the blood vessels Aid in thermoregulation they aid or assist it in either Contracting or relaxing and allowing more blood or less blood to the surface or more blood or less blood to the subcutaneous layer I would think that that answer probably has three marks I don't think it was for two if it was for two it's okay if you give them a little bit more information and you give them a full rounded answer remember in explain questions the markers have to look for the answer they can't just Mark the first two things that you write unless the question says explain to then you're stuck because you do have to say two things and they will Mark the first two things don't hide your answer in like a third and fourth point is what I'm getting at okay I think that's where we're going to stop for today I hope that this has been useful again I encourage all of the members to use their study guide extensively and please use the study guide with a past paper sitting next to you okay so while you're preparing for prelims and finals I would sit and I would have the study guide open and I would have a question paper with me and I would start attempting to answer the questions right using the study guide as assistance if you need it if you can't remember and then this is the important part open up the memos to those final papers to see how the memo aligns with the study guide remember I've written the study guide through my experience of marking final papers and what gets you marks and what doesn't get you mocks okay so that's really important and remember you can find lots of past papers on the website testpapers.co.za the last little thing from me is if you also need a little bit more assistance I do have flash cards available on my website there's a whole free set that you can go and try out and if you like them you can get the full set singita asks when are we going to have paper 2 revision lesson like this ma'am I think what I want to do from now until prelims is I want to do at least one live lesson a week before we get to prelims and then when we're in prelims I'm going to do a lot more revision lessons so make sure that you have your notifications turned on and so that you can see when I'm going to be posting more revision on um your final prelim work okay so we definitely going to have another one next week um singita says she enjoys the full set of flashcards the flashcards by the way complement the study guide they are they are written to be used together um and if you don't have the copy of the study guide then don't forget to go and look for the link in the community page for members and you can request it there it takes about 24 to 48 hours before I see your request so don't worry if I don't see it straight away I can give you access as soon as I see the request um but if you don't have the study guide I mean if you do have the study guide the flashcards are amazing and they make studying really fast and efficient but I think that's it for today I hope I've asked or answered all your questions and just helped a little bit in your understanding um and I will see you all again very soon and we're going to do another lesson next week one a week before we get into prelims and then when we're in prelims we're definitely going to have multiple lessons so make sure you join those and if you ever miss a lesson you can always watch the recorded version and I'm going to say goodbye everyone and I'll see you all again soon bye