[Music] hi everyone welcome back to another educational video from med school eu my name is andre and today we will be discussing our last topic in our last lecture on the biology unit of imat specifications and so today we are going to talk about the menstrual cycle and the homeostasis of the menstrual cycle so first of all in terms of the menstrual cycle that's the typically known as the the period or the the 28 days of the female cycle that undergoes changes in its reproductive organs and so let's first of all talk about the organs that are involved and the hormones that are involved in the menstrual cycle so we're going to have the ovary that will be involved of course and that will have its own ovarian cycle and the ovary is going to release estrogen and progesterone so these are the the hormones that will be released by the ovary and they will be used to regulate different systems in terms of the ovarian cycle and the uterine cycle so we're going to have the uterus of course involved as well so we have two cycles they will be in sync with each other so one is going to correspond to the other and they will be maintained by hormones the two hormones that are primary in terms of after ovulation will be the estrogen and progesterone and they will be involved throughout the entire menstrual cycle however they're predominantly going to be in higher concentrations after ovulation and we'll talk about what ovulation means and what all of those things entail now the other uh system that involves releasing hormones in order to contribute to the menstrual cycle is going to be the anterior pituitary gland previously we we have talked about the posterior pituitary gland that releases our adh hormone that regulates the water pressure and and the water balance within the body and here we're talking about the anterior pituitary gland so it is located in the brain right underneath the hypothalamus and is going to be releasing two hormones one is called the follicle stimulating hormone and the other is called luteinizing hormone most commonly they will be called fsh for follicle stimulating hormone and lh for luteinizing hormone and these are the names that i will interchangeably use for the rest of this lecture so now let's take a look what kind of effects these will have when their levels are going to rise and when they're going to drop depending on the ovarian and the uterine cycle so let's take a look at both of those and how they work in sync in order to regulate the menstrual cycle so it's important to remember that the menstrual cycle involves the 28 days so it's the entire month that a female goes through in terms of their changes in the reproductive organs and this involves the menstruation it involves you know typically known as the period it involves their ovulation as well after the two weeks since the start of menstruation and we're going to talk about all of those and how they change and this is all attributed to the change in the hormone levels so let's see how this works one thing to remember is menstrual cycle begins at the onset of menstruation and of course menstruation is the typical period that lasts about four to eight days depending on on the female depending on on the month depending on a lot of different factors but on average four to eight days so this image that popped up over here involves the ovary and it's it's going to show the stages that lead up to ovulation and we're going to talk about what is ovulation and so this involves the ovarian cycle right here so the ovary is responsible for developing a follicle a follicle that is going to make a gamete and we talked about gametes in in the reproduction unit and when we talked about you know punnett squares and genetics and all of these things so here um this involves the ovarian cycle in the female that will produce its egg it's gamete and how it does it so first of all we are going to form a lot of potential female gametes that start to develop and they will be occurring in in this area right here so next it's going to develop into a primary follicle so the follicle that is listed right there would be called the primary follicle because it grows the biggest it takes the most nutrients and it grows the fastest and that is the one that will be selected until the next stage so the primary follicle will will become a secondary follicle right here now the secondary follicle will then grow and develop into an ovarian follicle which is the one that's larger over here and as you can see the ovarian follicle will now start to develop a gamete and as soon as it's ready at ovulation so typically at about 14 days since the start of the menstrual cycle since the onset of menstruation we are going to have ovulation where a gamete is going to be released in to the fallopian tube and we'll talk about that and how it corresponds to the uterine cycle so a quick summary of the ovarian cycle as we begin with uh plenty of potential female gametes that start to develop within the ovary then it would form into a secondary follicle once the primary follicle is selected it will then grow into an ovarian follicle and then as soon as it's ready it is going to form a is going to release a gamete at ovulation now what's remaining from the follicle is going to be called a corpus luteum and it's going to be very important to know this term corpus luteum for you to understand how a gamete is going to be fertilized and how it's going to maintain its structure after ovulation so here we will be talking about the uterine cycle so we'll begin here on the upper left hand corner where we're going to talk about the start of menstruation this is the beginning of menstruation as you can see the endometrium endometrium is the inner lining of the uterus is going to be shedding its capillaries that it made and this is why there is going to be bleeding involved within the menstruation and at this point in time we are going to have uh development of a follicle probably the primary follicle that will be developing primary into the secondary will be happening during this first stage during menstruation now in the second stage moving along to the right the new endometrium will start to slowly develop as you can see it's not as thick but it's starting to develop its capillaries it's starting to form and the endometrium just begins to develop there and here an ovarian follicle is produced so so this is going to be coordinated in sync with the ovarian cycle so in second stage once once menstruation is over maybe this is entering into the second week so closer and closer to ovulation we are going to start developing the endometrium and again i'm gonna name this endometrium the inner lining of of the uterus that will develop its capillaries and these red parts are gonna be the capillaries that are running there in step three of the uterine cycle the endometrium is going to be maintained so it's going to fully grow into its into its its shape and to all the capillaries it needs to make and it's going to be maintained the same way until the corpus luteum is formed and the corpus luteum is formed only after the gamete is released so in step four of the uterine cycle this is exactly what happens ovulation takes place an ovulation when it takes place the endometrium is most developed and contains many blood vessels so it's got its capillaries and now as you can see the gamete will be traveling in the fallopian tube and this is why it is mentioned that during ovulation is is the only time a female can get pregnant so during uh typically the the second week or 14 days after the start of their menstrual cycle that they can develop a gamete that will be released into the uterus where the uterus is finally formed to receive the gamete and to nurture the gamete and that is the the time when the female is most fertile so i wanted to go through the stages of how the hormones are going to be acting on the endometrium how it's going to be acting on the ovary and how the ovary will be releasing its hormones in order to develop into a proper gamete so let's talk about the menstrual cycle in terms of its hormones and here's a chart of the level of hormones so we are going to begin with menstruation so again the first step of the menstrual cycle is menstruation that is going to last four to eight days and during menstruation we are going to have a continuous release of lh and fsh from the anterior pituitary gland and as you can see the lh and the fsh right here will be rising and rising that will be contributing to their effects and what these hormones are going to do now because of their rising level is they will stimulate the secretion of estrogen from the follicle you can most often see this happening right here on this diagram as as the fsh and the lh levels are going to rise throughout those days they're slowly declining here as well but they will remain more or less constant in this area in these in these few days after the menstruation and at the end of menstruation that this is when the estrogen levels will be steadily rising because the lh and the fsh hormones will be stimulating the follicle the follicle is responsible for releasing estrogen now in the second part is the increased concentration of estrogen that is acting as an inhibitor so it's going to be inhibiting the production of lh and fsh another effect that increased a concentration of estrogen has is it stimulates the endometrium to grow thicken and develop its capillaries and what's what's kind of interesting and the way it happens and and this is still a little bit difficult to understand because estrogen is an inhibitor to lh and fsh but at very very high concentrations at its very peak it causes a spike in lh and fsh that is very very close to ovulation so it it is an inhibitor of the start but when estrogen has a high concentration it is going to promote a surge of of lh and fsh concentrations and finally the last part of the the first half of the cycle is that an ovulation occurs because of the increased concentration of luteinizing hormone and how this luteinizing hormone does its ovulation is it causes the dominant follicle to burst and shed the gamete into the oviduct and then the follicle will of course form the corpus luteum now because of the formation of the corpus luteum it is now going to be responsible for releasing progesterone and to some degree estrogen as well and and you can see those levels to be rising right here progesterone and the estrogen in the blue will also be rising after ovulation occurs and that is because of the formation of the corpus luteum it is responsible for those things and what is the function of progesterone and estrogen at that point is to maintain the lining of the uterus because it is ready to receive an embryo and this is why the menstruation doesn't occur immediately after ovulation or maybe a few days after ovulation occurs two weeks after is because of the high levels of progesterone and estrogen after ovulation as well this increased progesterone is going to inhibit fsh and what this means is that no more new follicles will be formed during this time so during this this time after ovulation no new follicles formed and this is why the fsh levels will continuously fall as well as the lh levels however this works as a negative feedback system because low fsh and low lh are going to cause a lower stimulation of the corpus luteum so the corpus luteum will not be stimulated as much therefore the the levels of progesterone and estrogen will begin to decrease and of course the corpus luteum will degenerate now as soon as the corpus luteum degenerates the progesterone levels and the estrogen levels will fall and because they fall they will stop inhibiting fsh and then the fsh and the lh will then again begin to rise and this will cause another cycle of menstruation and it will cause the endometrium to shed its lining and it will cause a period to occur and now the whole cycle begins all over again so this concludes our lecture for today and finally this is the last lecture for biology so in the next one guess what we're going to be moving on to chemistry the first topic in chemistry that we will cover for the imat is going to be the composition of matter so stay tuned and that video will be out soon as well [Music] you