hi everybody and welcome back today we're going to be looking at the menstrual cycle in particular we are going to be looking at the hormones and how they affect the ovary and the uterus and it's really important for us to understand how they work in terms of their negative feedback on each other and also i suggest that you take a look at some of my other videos in which i go through past papers and the questions that go along with these menstrual cycle topics because it's often one of the most difficult questions that we see in the exams so let's look into ac a few of our basics surrounding the menstrual cycle so it's roughly 28 days long and it's broken into two cycles what we call the ovarian cycle which obviously takes place in the ovary and then the uterine cycle which takes place in the uterus it's really important to know that whatever happens in the ovary affects the uterus now if you have a look at the diagram in front of you just so that you're aware of what you are looking at you will notice that we have our cycle broken down from day one to day 28 and i am going to go through this entire little graph in a lot more detail but just so that we have an overview of exactly what we're looking at so the lines on this graph represent the four main hormones that are involved in the menstrual cycle which i'll break down exactly what each one does now and then along with that each of these round bubble-like structures represent um what's happening in our uterine wall in terms of growing the endometrium and essentially this first section is what we call the period it's where we lose the lining of the uterus which is when the endometrium falls away then you'll notice there is something called the proliferative stage essentially that is a fancy way of saying that we are growing a primary follicle um that's where we're going to grow an egg cell and then we have something called ovulation ovulation is when an egg cell is released into the fallopian tube and then the secretory phase is essentially um maintaining the lining of the uterus and if the lining um doesn't need to be maintained because there is no pregnancy taking place then the lining will fall away and we start again at the period now this is just a brief overview i'm going to go into a lot of detail from here on out so a key starting point is looking at the hormones that are involved in the menstrual cycle where they came from and specifically what their functions are so the first set of hormones i want to take a look at are our pituitary gland hormones these hormones have come from the pituitary in the brain so first up is fsh or follicle stimulating hormone you can write it as fsh and essentially follicle stimulating hormone is the hormone that is sent to the ovary and it stimulates a follicle to grow remember a follicle is like a sac like structure that houses an undeveloped egg or ovum and we want to make that bigger and more robust so the only way to do that is to stimulate it with fsh now it's sister hormone if you like is called lh or luteinizing hormone and the luteinizing hormone matures the follicle even further it makes the follicle eventually grow into what we know as the graffian follicle um and eventually that graphene follicle needs to burst now that whole bursting action is what we call ovulation and the only way to ovulate is with lh and so lh needs to peak in order to cause ovulation now these are our two pituitary gland hormones they work in conjunction with two other sets of hormones and they're antagonistic in other words fsh and lh are related to one another they work together however they have a influence on other hormones which are the ovarian hormones now the second set of hormones is known as the ovarian hormones and that is estrogen and progesterone and they are exclusively secreted out of the ovary now these two hormones play a really important role in preparing the uterus now i know they come from the ovary but their purpose is to prepare the uterus for a possible pregnancy and so the first hormone that we need to be aware of is estrogen estrogen is secreted by the follicle if you remember the follicle is being made by fsh and the purpose of estrogen is to repair the endometrium because remember we lost the lining of the endometrium every month so we need to repair it and we need to thicken it so it does both of these jobs at the same time now just like fsh and lh are sister hormones if that's what you want to call them estrogen also has a sister hormone known as progesterone now progesterone is also secreted out of the ovary except it comes from a structure called the corpus luteum now the corpus luteum used to be the follicle that we spoke of earlier that secreted estrogen but now that the follicle is empty it shrivels and becomes the corpus luteum now the corpus luteum and this is very important makes the endometrium more vascular and glandular it's slightly different to what estrogen is doing vascular means more veins and arteries glandular means more glands in other words it makes the endometrium more like a sponge a softer setting which will allow the egg cell to sort of melt into and to settle into so that it can grow into a fetus we also call it the pregnancy hormone because if you do a pregnancy test this is the hormone that you are looking for to see whether or not you are pregnant now often you will be faced with different ways in which you are going to have to interpret the menstrual cycle with either graphs or diagrams now this one i have here is pretty useful because what it does is it lies three different pieces of information on top of each other we have some body temperature at the top we have what's happening inside the ovary and then we have the hormone level now for this hormone level graph this is very important to know and i know that there's a lot of information on the graph right now but in the next slide i'll be looking at the individual hormones and what exactly to look for to tell the difference because unfortunately in a lot of test settings and exams they don't label the hormones they expect you to know what each one is doing the easiest way to learn from these kinds of diagrams where they have lots of information on them on top of each other is to take a ruler and to cover up the rest of the information or even a page and to slowly drag the page from zero days at the beginning of the cycle and drag it over to 28 days and so what you can see is a nice overlap as to what's happening in each of and the stages and so for example if i were to draw a very rough line over the first seven days and we're only going to look at the beginning you will notice a couple of things you will see that the follicle is growing because of fsh and if you have a look down over here at the hormones you will see that the follicle stimulating hormone fsh in the green is starting to rise up slightly and that is because we need to be able to stimulate the follicle to grow you will also notice that luteinizing hormone which is in the orange sort of sitting here in the background that is also slowly starting to increase although it's fairly consistent at this point if we then migrate a little further and now we look at a very important day which is day 14 you will notice a number of hormones are peaking at this point you will notice that for example estrogen over here is peaking just before you will notice that our luteinizing hormone is peaking and you will also notice if you look very carefully in the green here follicle stimulating hormone is peaking and this is a very important process to know now once ovulation has happened you will notice that the uh the follicle starts to disintegrate and it becomes the structure called the corpus luteum now the hormone associated with that if we look down at the graph you will see is progesterone and that's because this structure is making progesterone but now how do we interpret these pictures how do we know what to look for well that's what we're going to cover now what i want you to know is can you tell me what happens at each stage roughly every seven days what is happening inside the menstrual cycle so i really like this graph because what it does is it's going to help us to identify the hormones from a graph and what they've done is they have separated the pituitary hormones from the ovarian hormones unlike the previous graph which had both sets sitting on top of each other which made it very difficult to tell the difference this too has been separated so let's say we're in an exam and now we need to interpret the graph we're given but they don't label any of the hormones how do we tell the difference between the hormones and why are they peaking or dropping at different points so let's always start our journey with fsh because it is the hormone that starts this whole process and as you can see from the diagram fsh which is represented by this paler purple line over here is very gentle in its increase and you will notice that it does a sort of dramatic peak just before ovulation now the reason for that is very simple you need a little extra peak of hormone because the fsh finally forces the egg to be released it's almost like it's telling the body there are lots and lots and lots of um fsh which means the follicle is ready to be released and so now we need to push it out of the ovary and we need to push it into the fallopian tube and it peaks just before ovulation so that's what you're going to look for you're going to look for this slightly lower level hormone it's quite low but it peaks just before our ovulation point now remember our hormones come in pairs and so the sister hormone to fsh is going to be lh luteinizing hormone and you can see by the graph that luteinizing hormone is very low in the beginning it's this darker purple line that's lower down here you will notice that the only time it truly peaks is this very very steep increase just before ovulation and that is the signifier that we are working with lh because both fsh and lh peak before ovulation they are the hormones that cause ovulation now often these are the hormones that we get confused with the ovarian hormones because if you look a little bit lower down you will notice that this hormone over here is also peaking but you will notice that the steepness of this lower ovarian hormone down here is not as dramatic not as quick to go up it's a little bit more gentle as it increases and i'll explain why now but it's important not to confuse these two hormones with each other so now let's take a look at our ovarian hormone levels remember these are the hormones that are going to be secreted by the ovary and the only reason why we are secreting these hormones is because of what is happening in this graph happening above here remember they work with each other so whatever happens with our follicle stimulating hormone and our luteinizing hormone will have an impact on what's happening with estrogen and progesterone now like i said before estrogen sometimes is the hormone that we confuse with lh because of this dramatic peak that happens just before ovulation but there's some key things that actually make it different that will make it easy for you to tell the difference if we put all the lines on top of each other so estrogen gradually increases over time and you can see that here in the beginning of the graph it's a very slow gradual increase over time but what makes it so different from lh is that it has two peaks and so if you are trying to tell the difference between estrogen and lh it has two different peaks one here that we've already labeled just before ovulation and you'll see there's a second peak around day 21. now that doesn't happen in lh there is no peak in lh at 21 it's flat now the reason why there is a peak before ovulation and then one just before menstruation is slightly different they have different functions the one before ovulation is telling the body that the endometrium is now thick and ready the second time estrogen peaks is because it's telling the body it is now time to rid of the endometrium in other words cause menstruation in other words a period and the reason why it has to peak is because of negative feedback negative feedback if we can't remember is a seesaw effect and the only way to see saw is to be pushed really high so that you can be then pushed back down again and so if you never push the hormone up it will never go back down and that's the point of peaking hormones so that they go down again and when they go down they then have outcomes in this case causing menstruation now the final hormone that we are looking at is progesterone the pregnancy hormone and you will notice looking throughout the graph it's this darker blue line and all the way from day zero to day seven and well past day 12 and into day 14 it's almost at zero there's almost nothing in the bloodstream and that makes sense because remember progesterone is a pregnancy hormone so you're not going to make it if you're not pregnant or you're not preparing to be pregnant however what you will notice at day 14 it starts to make a very serious and dramatic increase and that is because of what progesterone does progesterone is making our endometrium lining much much thicker glandular and vascular preparing for pregnancy so so we're doing we're putting a lot of pregnancy hormone to say to the body we are ready to be pregnant now you will yet again notice that it also peaks around day 21 along with estrogen and then dramatically drops after day 21 and that makes sense because if progesterone drops estrogen drops it will cause menstruation in other words it's a signifier to say to the body we aren't pregnant we can lose the endometrium lining and we can start the whole cycle again and why on day 21 well remember that day 2001 is essentially the beginning stages of menstruation you may not necessarily be losing any period or the endometrium might not be falling away yet but you're in the beginning stages of that you're going to build up to the beginning part of losing the lining and another important thing that i think a lot of students don't realize is with this whole graph day 0 on this graph is the first day you start your period in other words the first day bleeding is happening people often think that day zero is the day you stop bleeding or that you stop menstruating it's not day zero is the day that you start your menstruation and then from there you work towards what you can see in the graph all right so now we get to the more technical aspect of how to actually explain the menstrual cycle this is probably the thing that you've been waiting for because it's the most difficult part and don't worry about the words moving on the side of the page essentially i'm just organizing my words so that i can bring them in as i explain i suggest that you listen to this whole section of the video and then you pause it and you either draw your own version of what i'm about to draw for you or you take a photo and you use it as your study note because this is the easiest way to remember everything so we start our journey on explaining the mental cycle with the pituitary gland and the pituitary gland specifically is going to secrete our fsh now remember fsh is the follicle stimulating hormone now the follicle stimulating hormone is going to be sent to one of the primary follicles which is going to stimulate it in other words it's going to make it grow and get bigger now as the follicle develops it is going to start to produce our estrogen and so that estrogen and by the way i'm going to color code all of this is going to have an effect on the pituitary gland as well estrogen is now secreted out of the follicle and that information is sent back to the pituitary gland now what estrogen does is it stimulates the pituitary gland to start to secrete luteinizing hormone now this hormone comes from the pituitary gland and it is sent to the follicle because remember what is the purpose of luteinizing hormone it is to mature our follicle and to grow our follicle because essentially the luteinizing hormone is going to be the hormone that's going to help us grow our follicle bigger but it's also going to allow us to ovulate as well now all of these hormones and there's a lot going on here but we can't forget what's happening with estrogen estrogen did stimulate the pituitary gland but estrogen is also doing something in terms of the uterine cycle and that is that the estrogen is causing the endometrium to thicken and also to repair itself because remember we would have lost this layer during menstruation so now what is happening in terms of our follicle is this we have follicle stimulating hormone which is coming from the pituitary gland and we have our luteinizing hormone which is also coming from the pituitary gland both of these glands are affecting the growth of our follicle and it's getting bigger and it's going to change its name the primary follicle slowly but surely forms what we call a graffian follicle it's the biggest follicle and essentially sitting inside the graphene follicle we can see here is the egg cell now when these two hormones fsh and lh peak they are going to cause ovulation ovulation is the bursting and the releasing of our egg cell now after ovulation we are left with this shrunken follicle we can see here it's empty on the inside and it changed its name it becomes the corpus luteum and the corpus luteum plays a really important role because it is the structure that secretes progesterone now because the corpus luteum is secreting the hormone progesterone we can now maintain the lining of the endometrium a lot better and we can actually make it more glandular and we can make it thicker and that's essentially what it's doing it's making it more vascular and it thickens it now at the same time we cannot forget our original thickening hormone which is estrogen and so we have to bring another little arrow all the way across to show that both of these hormones both estrogen and progesterone are thickening it and in particular progesterone is making it more glandular and vascular meaning more glands and more blood vessels now here is the key turning points the parts where everyone gets just a little bit confused because remember in the beginning of the video i said that fsh and lh are sister hormones and estrogen and progesterone or sister hormones unfortunately these hormones can only work with their sisters they cannot work with other hormones at the same time in other words if they're on the sea saw one set of hormones must be high while the other set of hormones must be lower just for clarity this is what i mean by a sea sauce so remember see saw as a child when you're growing up perhaps you would have played on a seesaw and it's this like little device that when someone sits on the one side it goes down and then the person on the other side will go up and that's how these hormones work as one hormone goes up the others will go down but remember that the seesaw can also go the other way and that's important because once we're right at the bottom of the seesaw we push up from the bottom and now the seesaw goes the other way so the one side that was now lower goes up and the other side now seesaws and goes back down and this is how the two sets of the hormones work lh and fsh are together on the one side of the seesaw and on the opposite side is our estrogen and progesterone and they see saw backwards and forwards each one taking a turn at being the higher amount compared to the other set of hormones and so now because of this see-sawing effect what we end up having is both our estrogen coming back around to our pituitary gland and along with our progesterone and what that does is it tells the pituitary gland we have a very thick endometrium we are now ready for pregnancy don't make another follicle because if you make another follicle we'll have two babies maybe at different stages and you can only be pregnant one baby at a time obviously twins is different but what i mean is is that you can't have a baby that's six months old and then one baby that is four weeks old so we have to stop the production of fsh and so what we say is that these two hormones inhibit fsh and lh i'm just going to put that there and that's what the blue and yellow line represents is the two hormones inhibiting the pituitary gland from secreting fsh and lh this now will result in our fsh levels dropping which is important because remember as i said we don't want to uh cause another follicle to form now stay with me here because this is where we often get the confusion because fsh is dropping it slowly but surely drops and drops and drops and like that sea saw it's going down and it's lifting up the estrogen levels and lifting up progesterone and allowing those hormones to be at their maximum but the moment fsh gets very very low it then will have an impact on estrogen and it will cause estrogen to also drop because now it's going to go in the opposite way so estrogen is going to start dropping now as estrogen is linked to progesterone if one hormone is going down which is estrogen progesterone is also going to start decreasing but it starts decreasing not because of fsh it decreases because of the corpus luteum so if we go back to our corpus luteum diagram over here what's happening is that our corpus luteum is starting to degenerate now this is where estrogen and progesterone come together because as the corpus luteum degenerates it secretes less and less progesterone because remember progesterone is a pregnancy hormone and if we aren't pregnant we're not going to make any pregnancy hormone and because progesterone is dropping both of the progesterone levels dropping and estrogen i'm going to take the line all the way over and around here because of these two levels dropping at the same time it causes the endometrium to fall away and we start menstruation so i know we've covered a lot and there's a lot going on in this diagram but i'm going to number it for you very quickly so first things first we start off with number one the pituitary gland secretes fsh that gets stent to the ovary where we stimulate a follicle that follicle grows and produces estrogen estrogen is made by our follicle and that then stimulates the pituitary gland and the pituitary gland secretes luteinizing hormone from there our estrogen continues to thicken the endometrium which is step five and as we thicken the endometrium we are also growing our follicle which is step six while our follicle matures we can look down here we grow into a graphene follicle step seven that then leads to ovulation because it gets bigger step eight and step nine the corpus luteum secretes progesterone step 10 the endometrium thickens and becomes more vascular because of both the estrogen and the progesterone thickening it this then inhibits fsh and lh step 11. because we inhibit it if we go other side here fsh drops step 12. if fsh drops for long enough eventually it will pull down estrogen step 13 if estrogen drops if we go all the way over here the corpus luteum starts to decrease and it degenerates step 14 and if progesterone drops and estrogen drops then step 15 the endometrium falls away i know it's a lot to cover but i promise you if you can learn this and explain it you will know exactly what you need to say we have done a lot in this video and please yet again as i said draw this pause the video take it down label it use the colors the colors represent the different color different um substances that are influencing our menstrual cycle and i hope that i've been a help please ask your questions if you need any more assistance and i will see you all again next time bye