in this video we're taking a look at the ovarian and menstrual cycle i've got this diagram on the left that we're going to use and then the right i'm going to take us through a flow chart that'll help us see the cause and effect relationship in each stage of the process here so let's start with this there's two main events in the ovarian and menstrual cycles first one is menstruation or the period and then the second event is ovulation which is going to take place later on in the cycles menstruation or the period is going to take place on the first day of the cycle and then ovulation is going to take place about two weeks later about on day 14. there's two phases that we're going to look at as well one is called the follicular phase that's all about the ovarian follicle or the the cells that support the egg that are going to be growing and then the second phase that's going to take place during the days 14 through 28 is called the luteal phase so there's our general timeline we have menstruation on day one the next two weeks or so are going to be the follicular phase then we'll have ovulation where the egg is released from the ovary and then the next two weeks are going to be the luteal phase and at the end of that we'll start back up at menstruation back to day one at the beginning of the cycle again so this is on average a 28-day cycle though that number can vary that's just an average that we use whenever talking about the cycle on the top of the diagram on the left we can see what's taking place in the ovary we'll see a follicle here which is basically an egg and all of the surrounding supporting cells of that egg we call that a follicle so the follicle will grow we call this the follicular phase the follicle will release the egg here we call it ovulation and then that follicle that remains is going to become something else that we call a corpus luteum and then that quartus lutein will degenerate or die off and that's what's taking place in the ovary the second thing on this diagram is what's happening in the uterus and so during menstruation we have the menstrual flow where the endometrium exits through the vaginal canal and that takes place over a few days then we have a couple phases there one's called the proliferative phase and the secretory phase but what's happening there is the endometrium is growing and developing and it's getting ready for a possible implantation if an egg cell gets fertilized then this endometrium needs to be ready for that fertilized zygote to implant and for it to support that fertilized zygote as it grows into an embryo and then a fetus and eventually birth now if fertilization does not occur then the endometrium once it gets to this point we'll just shed again and then we'll be back at the beginning of the process here now the other two graphs we see on here show hormone levels we're going to look at pituitary hormones and ovarian hormones now it's helpful to think of hormones as chemical messengers they're going to be a way for the pituitary gland the uterus and the ovaries to communicate back and forth and let each other know where they are in the process so hormones again are just messengers for these different organs to communicate back and forth with each other the pituitary hormones we're going to look at are fsh and lh fsh is follicle stimulating hormone lh is luteinizing hormone and those words should sound sort of familiar we just talked about the follicle and we just talked about something called a corpus luteum follicle stimulating hormone and luteinizing hormone this is how the pituitary gland tells the ovary what to do it tells the follicle to grow with follicle stimulating hormone and it tells the ovary to release the egg and therefore create this leftover structure called the corpus luteum with luteinizing hormone finally the other hormones we have are ovarian hormones one is estrogen this graph says estradiol which is a type of estrogen or the most common type of estrogen and progesterone and this is going to be how the ovary communicates with the pituitary and the uterus to tell those organs what's going on with it so let's jump back over to our timeline over here and take a look at what's happening in each stage of the ovarian and menstrual cycle so starting with menstruation of course the menstruation is when the endometrium is shed and this happens unless there's a pregnancy or something else going on the main reason that we start with that and our timeline is because of all of the stages this is the one that's observable it's easy for a woman to tell when she's menstruating it's not easy to tell what part of the follicular phase is happening what part of the luteal phase is happening sometimes a woman can tell if she's ovulating but often that's hard to tell exactly when that's happening and so we start with menstruation because it's easily observable so that's why we start with that as quote unquote day one of the timeline so after menstruation starts then we'll be in the follicular phase and in the follicular phase we're going to have to look at what's happening in the pituitary as well as what's happening in the ovaries so i have a couple boxes in my flow chart one for the pituitary one for the ovaries so that we can sort of compartmentalize what's happening where and how they communicate with each other so the pituitary gland at this beginning follicular phase is going to release a hormone called follicle stimulating hormone this is how the pituitary gland tells one of the follicles to grow in the ovary a follicle will start growing and as that follicle grows which we can see here right it starts off small it's going to get a little bit larger it's going to get a little bit larger so that follicle is growing the egg cell itself isn't growing larger but the cells the supporting cells around it are growing larger and as they grow larger they're going to start to make more estrogen so we can see these hormones that are taking place in these graphs right here we have increased follicle stimulating hormone from the pituitary gland right and that's going to tell the follicle to grow and towards the end of that stage the follicle is going to be producing more and more and more estrogen that estrogen is going to communicate back to the pituitary so that the pituitary knows that the follicle has grown sufficiently so that estrogen is released from the follicle and that'll travel back up through the bloodstream to the pituitary to tell the pituitary what's going on to tell the pituitary that the follicle has grown to a sufficient size we call it a secondary follicle or graffian follicle the pituitary now knows the state of the follicle and the pituitary is going to communicate back to the ovary to tell it to ovulate the pituitary is going to release a different hormone this one luteinizing hormone the pituitary releases that luteinizing hormone and it's going to tell the follicle to release the egg so the egg gets released from the follicle there and that's going to happen around day 14 and we call that event ovulation and that will mark the end of the follicular phase if we look on this graph right here we'll see right before ovulation occurs we see this spike in luteinizing hormone and we've got this kind of blue threshold line here that once there's enough luteinizing hormone to pass that threshold then the ovary knows all right time to ovulate and then that egg cell gets released that egg cell will travel through the fallopian tube or it has a chance to be fertilized if there's a sperm sub present in the fallopian tube all right quick recap of that menstruation marks day one the pituitary gland will start making follicle stimulating hormone that's going to stimulate the ovarian follicle to grow as the ovarian follicle grows it's going to make more and more estrogen the estrogen tells the pituitary gland hey i'm ready i'm ready to go and the pituitary gland will release luteinizing hormone that's going to be sort of the okay or the go-ahead for the egg to be released from the ovary so the luteinizing hormone will stimulate the ovarian follicle to release the egg into the fallopian tube to have a chance of being fertilized all right now let's take a look at what happens in the ludial phase this is going to be the second half of the ovarian cycle and we call it the luteal phase because the leftover cells of the follicle so not the egg sub but all those supporting cells that didn't get released those supporting cells are going to form something called the corpus luteum hence the name ludial phase the purpose of the corpus luteum is to hang out in the ovary and keep making a hormone called progesterone so let's take a look in our flow chart here what progesterone does and why we need so much of it so the follicle is going to become that corpus luteum and that's just going to be kind of the leftover remnant of the follicle we call that a corpus luteum and that's going to communicate to the uterus with progesterone the purpose of the progesterone is to tell the uterus or to tell the endometrium in the uterus to keep growing and not to menstruate so the progesterone tells the uterus hey keep developing the endometrium and don't get rid of it don't menstruate basically it's a way to tell the uterus hey we could still have a pregnancy we need you to be ready for it keep growing the endometrium we see the endometrium growing a lot thicker here in the second half of the ovarian cycle so that progesterone will keep getting released eventually that corpus luteum though is going to die off if there's no pregnancy so without a pregnancy the corporate solution is going to die off it's going to degenerate it's a very sad thing as you can see here poor little corpus luteum so when the corpus luteum dies though it's no longer going to be releasing progesterone and without that progesterone communication what's the uterus going to do well it's not going to keep growing the endometrium the corpus luteum dies no progesterone and therefore the endometrium is going to shed it's going to menstruate at that point where that corpus luteum has died now we're approaching day 28 the endometrium will shed and we're just back here at day one where menstruation starts again and so we'll just repeat this cycle over again now i'm not going to include this on the diagram but if there was a pregnancy well that fertilized zygote that's becoming an embryo it's going to release a separate hormone called human chorionic gonadotropin that separate hormone is going to tell the corpus luteum hey don't die stick around keep making progesterone so that there is no menstruation so that the embryo can keep growing in the endometrium but that's if a pregnancy occurs as long as the pregnancy doesn't occur the corpus luteum will die off and the endometrium gets shed so let's go back through all this as a recap in day one menstruation starts we mark that as day one because that's an observable event this begins the follicular phase in the follicular phase which lasts from days one through 14 the pituitary gland will release follicle stimulating hormone which will stimulate the follicle to grow the follicle remember is that egg cell in the ovary and all of its surrounding supporting cells so that follicle will start to grow that follicle will start making more and more estrogen which will signal to the pituitary hey the follicle is ready it's ready to release that egg the pituitary will respond by releasing luteinizing hormone luteinizing hormone tells the ovary hey go ahead release the egg from that follicle into the fallopian tube and we call that event ovulation at that point the leftover follicle so the egg's been released but the follicle that's still left in the ovary it's going to become something called the corpus luteum the corpus luteum's job is to make progesterone which is going to stimulate the endometrium to keep growing during the luteal phase but eventually near day 28 the corpus luteum will degenerate and die off there won't be any more progesterone and then the endometrium will be shed during menstruation the main thing that would stop this from happening would be for a pregnancy to occur and that embryo would release hcg and that would tell the corpus luteum to keep making progesterone so the endometrium can keep growing and support that developing embryo in the uterus all right so those were the stages of the ovarian and menstrual cycle i know there's a lot of things going on here but if you follow this flow chart and think about the cause and effect relationship of each step then it'll help you understand how all of these different organs work together to regulate the ovarian and menstrual cycle all right thanks for watching have a great day