all right we're live this is a re-recording of um a lecture that I gave way back when um and the audio actually cut out during my recording it was really sad and that's also unfortunate because this is a really really high yield concept on the MCAT this is female sexual development specifically we're going to be talking about the menstrual cycle okay this female sexual development this is part of General Biology Chapter 2 right so earlier in the chapter we talked about ovaries right ovaries are the functional sexual organs of females right and they are derived of embryonic structures the same embryonic structures of the testes because we already spoke about earlier in the chapter um male sexual development and they're also under the control of FSH and LH as a reminder since this is a re-recording FSH is follicle stimulating hormone FSH and LH is lutenizing hormone LH both of these are collectively referred to as the gonad tropins because they are Tropic to the gonads right meaning that they are the middlemen of The Messengers that they go to the gonads and the gonads release something else and something happens right so in men right in men what does FSH do does anyone remember it's the other way right so men don't have follicles right but the way I think of it men don't have follicles but if they did they'd make sperm right FSH spermatogenesis LH is for testosterone and you know that because it's opposite for men and women in women FSH makes estrogen and LH makes progesterone later down the line because remember progesterone isn't there in the beginning right it has to be induced so these are the good tropin right so we talked about men then we talked about women but one of those in both people in both types of people is Tropic meaning that they release something else to do their effects right these are called the ganat tropins and since they're the ganat tropins they releas is regulated by GnRH gonat tropin releasing hormone gonadotropin releasing hormone okay so let's draw out a little chart G n RH from the hypothalamus fires onto the anterior pituitary and this releases LH and FSH and since we're talking about female sexual development FSH is going to hit the ovaries and that's going to release estrogen and LH is going to hit the let's talk about it later so let's talk about the menstrual cycle because the menstrual cycle is basically the up and down action of these hormones over time and how that kind of influences the way that the female body works so just an overview the female body you've got a uterus right and that uterus is connected to two Fallopian tubes which connect to the ovaries right and here is the cervix the entrance to the uterus and here is the vagina or the birth canal right and inside of the uterus implantation of the fetus normally is going to occur like here so we need to thicken and thin and control the environment in which the the embryo is going to implant right inside the uterus that's the goal of the menstrual cycle right so the menstrual cycle is a cycle with multiple days it's like 28 30 days something like that right it begins when menstrual flow Starts day one is the first day of active menstrual bleeding right and when that happens it happens because well it's called shedding of the uter and lining right it happens because the levels of all these hormones drop off from the end of the last cycle right and when those hormones drop off you know that LH and FSH go back and turn off GNR back at the hypothalamus so when these drop off G&R gets turned back on and then your FSH and LH levels are once again allowed to rise so phase one increase G&R Ys yields increase FSH and LH and that's going to increase estrogen and this estrogen right leads to thickening of endometrium thickening of the endometrium it's going to make the blood vessels it's going to vascularize it's going to grow it's going to become more mucousy it's going to become a warm welcoming environment for the embryo and the estr also going to go back and shut down GnRH secretion right right but you can think of estrogen kind of growing in a delayed form right so even though it's it as it rises it turns off the G&R secretion there's still FSH floating around that's increasing the estrogen right so the second step is when estrogen levels Peak and this leads to a flip of the feedback which means it now positively impacts GN secretion which leads to massive spikes in G&R why I've asked the question so many times I still haven't gotten an answer that massive spike in G&R leads to a massive spike in LH or sorry a massive spike in FSH but more importantly a massive spike in LH and that LH spike is colloquially known as the LH Spike who knows what the LH Spike does not yet ovulation LH Spike leads to ovulation so all of that stuff in the first step right what was that doing it was stimulating the development of one of the ovam right and it's carried inside of a follicle and that f icle makes estrogen and blah blah blah whatever else right and when the LH spikes the egg it breaks out of the follicle the ruptured follicle right so when the LH spikes that that egg cell breaks out and now it's allowed to get fertilized that ovulation there's only one woman in the room right now but at around day 14 after um your last menstrual cycle began you may realize that you have abdominal pain out of nowhere right in the middle of your cycle between two cycles you're like day 14 day 15 there's abdominal pain that abdominal pain is called middle schms right it's called middle Schurz it's a German word I think right and it describes the pain that is associated with ovulation right that pain is called middle schmerz there and there are many women who that's actually incredibly painful so they go to the emergency room and they always ask the question when was your last Menses when were when were you last on your like when were you last on your period I like oh about two weeks ago classic middle Schurz all right so this first part is called the follicular phase the second part is called ovulation right and when that FSH goes up and the LH goes up right the FSH is just going to lead to more estrogen and estrogen is going to further deepen the endometrium right next is the ludal phase so LH now we're going to talk about what LH does so the LH stimulates the ruptured follicle to become the Corpus ludum and this Corp is ludum under the response of LH under the under the sorry under the control of LH continuously secretes progesterone and what does progesterone do if estrogen builds the lining progesterone maintains the lining which is why when women we'll we'll talk we'll talk about that in a bit so the LH what does it do Corpus ludum progesterone estrogen builds the lining progesterone maintains it which one's more important M maintenance because if you don't maintain it sheds where LH stimulates ruptured follicle to become the Corpus ludum H when LH goes down the shedding will happen and that progesterone is going to go back and negative feedback on G&R sorry Corpus ludum releases progesterone now the fun part there's two Pathways to go down now can I erase this yeah everyone I just asked if I could erase it all right there's two paths to go down after the ludal phase so let's say let's let's draw like two little things like this no implantation implantation if there's no implantation all the men in the room since we don't know anything what happens menes right the reason I said that is because um a bunch of people left uh after the last lecture because we're continuing and all of the men stayed in the room because we know nothing about the menstrual cycle one there's one female there's one female in the room thank you sure you get your thank you Laura she she's our fact Checker when no imp plation occurs if you don't become pregnant right basically what happens is that the Corpus Ludi becomes insensitive to LH which leads to a drop in progesterone which leads to shedding of the uterine lining and that drop that drop in progesterone is going to turn off the negative inhibition of G&R right and then that's going to restart the menstrual cycle the G&R is going to come back up and blah blah blah whatever whatever whatever right which one oh shedding of the uterine lining what a complex process if fertilization does occur an implantation does occur the embryo secretes a specific compound known as beta human chonic gatot tropin beta HCG that's what you're testing for in a pregnancy test beta HCG and beta HCG is an analog of LH but it's an analog of LH that the Corpus ludum cannot become insensitive to so it maintains the progesterone concentration until implantation and the placenta forms and then the placenta is able to maintain the pregnancy good one more thing menopause as a woman ages or ovaries become less and less sensitive to FSH and LH and the atrophy right which leads to decreases in estrogen decreases in progesterone and menstruation stops and you have increased FSH and LH with minimal response that is menopause right so so before we go let's just go over the whole thing one more time through dictation right so shedding of the uterine lining occurs from the previous cycle because of drops in progesterone the drop in progesterone takes off the negative feedback of G&R G&R goes up which releases FSH and LH FSH stimulates the follicle to allow the ovary to the allow the ovam to develop and the follicle begins to and you know the ovary begins to produce estrogen estrogen leads to thickening of the endometrium and specifically they use a term sometimes glandular isation of the decidua it's just like blood vessels and mucus mucus uh uh production inside of the um endometrium right we move on next the LH doesn't really do much yet but the estrogen is going to have negative feedback on the G&R but the estrogen is going to continue to climb because there's still FSH floating around the body right now now when the estrogen reaches a peak point that negative feedback is going to turn into positive feedback and you're going to spike in G&R a spike in F and more importantly a spike in LH that spike in LH causes ovulation so the ovam ruptures out of the follicle and that ruptured follicle under the control of LH turns into the corpus ludum now we enter the ludal phase where the Corpus ludum is being acted upon by LH in order to produce progesterone that progesterone is going to have negative feedback on GNR and decrease all of that but estrogen still working right still building the lining and now the Corpus ludum being controlled by LH is going to continuously secrete progesterone and progesterone is going to maintain the uterine lining right very important if you lose progesterone you lose the uterine lining right now one of two things can happen either the woman is never mind the fertilization occurs right which normally occurs inside of the fallopian 2o and you get the formation of an embryo that embryo can come in and implant and we can begin to secrete beta human chonic anatropin which is an analog of LH that the Corpus ludum cannot become resistant to right which means progesterone will continue to be produced until the placenta is formed and it takes over in the production of Ester and progesterone but if fertilization and implantation do not occur the Corpus ludum is going to become insensitive to the LH produced by the body and it's going to stop producing and that stopping of the producing progesterone leads to shedding of the uterine lining and once again the G&R increases restarting the cycle so that was the menstrual cycle and female sexual development hope you enjoyed and I'll see you guys next time have a good night