Transcript for:
Understanding the Female Reproductive System

hello class so this is a continuation of the reproductive system um in this video our focus will be on the female reproductive system so as always i'll start off with a very brief discussion on the female reproductive anatomy the basic structures and features related to that organ system but then the emphasis will then shift towards um understanding the physiology of the female reproductive system there's a lot of different hormones that i will discuss in this video um we will again revisit the hvg axis the hypothalamus its interaction with the anterior pituitary and then um the gonadal hormones which of course will be a little different here uh we're not focusing on androgens this time um here we will be focusing on estrogen and progesterone so we need to talk about the hvg axis and then really draw a comparison between two important cycles the ovarian cycle and the uterine cycle all the different changes that occur developmentally and the roles that are played by the different hormones in regulating those two different cycles and how those events progress so let's get started um when we talk about the female reproductive system uh in terms of the anatomy the female gonads are called the ovaries the male gonads were called the testes if you recall um so the ovaries um just like the testes they produce specific conatal hormones um the testes produce testosterone and we talked about the the leading cells or the interstitial endocrine cells that produced the testosterone when it came to the male reproductive system and the testes and the seminiferous tibials within the testes in the case of the ovaries um the two hormones that we need to talk about here would be estrogen and progesterone and so then what are the roles of these two hormones of course then the most important function would be how it plays a role in the whole development of especially estrogen are playing a huge role in the development of the female gametes which are called the ova or the ovum the whole follicle development as it occurs inside of the ovary to the point where it becomes a prominent uh or a dominant um follicle which is then ready for ovulation so all of that is really um orchestrated or modulated by estrogen and then after that after the ovulation occurs which is when the the oocyte is released from the ovary into the into the uterine tube when that happens then there's a transformation that occurs inside of the ovary where the the remnants of that follicle gets transformed into something called a corpus luteum and the corpus luteum immediately will start to release progesterone so obviously all of this is still happening inside the ovaries and that's why we're talking about these two hormones are being produced by the ovaries progesterone has a very different role to play it's going to feed back to the uterus where there's two different layers that we need to talk about the stratum-based alice and the stratum functionalist um that basically gets the stratum functionalist layer within the uterus ready for um implantation of a fertilized ovum should uh fertilization occur between the ovum and the and the sperm so we're gonna highlight the differences between those two hormones and the roles that they play uh first of all within the ovary but also within the uterus okay there's several different ligaments that we need to talk about here um the ovarian ligament is the ligament that's going to hold or kind of anchor the ovary towards the the uterus so it's immediately located and then the the suspensory ligament and the mesovariant these two are part of something which is called the broad ligament and the broad ligament is basically a a a broad canvas or a broad tent like tissue which supports the uterus the vaginal canal the urine tubes so it's it's a much much more expansive ligament and i'll show that to you i believe on the on the next slide we will also talk about different access redux so let's kind of get started when you're looking at um this view of the of the female reproductive anatomy so kind of starting from just to kind of orient you this would be towards the anterior aspect where you see the man's pupils all of that adipose tissue and of course towards the back there that would be the posterior aspect you can kind of see the very uh end of the vertebral column right there that will be the coccyx um and so uh kind of let's kind of start from the front and move towards the back um kind of towards the front you're going to see this would be the urinary bladder okay and you the urinary bladder is meant to store urine and when the urine needs to be released it will be released through that tube there called the urethra okay and that's going to open out into this region here which is part of the female external genitalia where you have a a larger lip like structure called the labia um and well the reddish structure here should be the the labia minus or the minora and the larger lip here on the outside would be the the majora or the mages um so urine stored in the urinary bladder is expelled through the urethra it's a very short urethra unlike what you saw with the male reproductive structures where you had different regions of the urethra um kind of like as it went through the prostate was called the prostatic urethra and then the intermediate part and then of course then the final structure which is the spongy urethra and of course if you remember the urethra and the male anatomy was a common conduit for both the passage of um urine as well as sperm in the case of the female anatomy urethra is is specific for the passage of urine now right behind it kind of medially located all of these structures kind of shown in red uh that's going to be okay you can kind of see the the ovary there one of the ovaries of course it's a paired set of structures but you're seeing only one one side of it so one view uh here's uh one of the ovaries and uh there's going we're going to talk about the follicle development occurring inside of the ovary but when the um kind of towards the mid part of the ovarian cycle um that mature oocyte gets released during the process of ovulation from the ovary right here and then enters uh through these finger-like processes which we call femri we will talk about that and even though you see kind of see where the the fimbri which is part of the urine tube it looks like as if it's directly in contact with the ovary but that's not true there's actually space between the finger and the um and the ovary the over the oversight that's released from the ovary literally has to make a little jump there and due to the different movements and electrical kind of like a like a current type movement um that oversight is guided through different regions of this initial part of the uterine tube ultimately it's going to make its way all the way through that uterine tube which then enters this structure which is obviously the uterus and so here and i think there's another schematic coming up where you will see a much better view a more enlarged more magnified view of this um of this uterus but for right now let's just kind of talk about um what we can kind of see from this particular schematic so that osi is going to make its way into the uterus we've got different regions uh the body of the uterus and of course that's the lumen of the uterus and if if fertilization between the oversight and the sperm were to occur that typically occurs here in the very very first part in the proximal part of that urine tube and then it makes a very long journey about five to seven days or so that fertilized ovum would then make its way uh into the uterus where in the wall of the uterus um you're gonna see an event occurring called implantation and that's really um what is required for a pregnancy to be achieved for a successful pregnancy to be achieved um and for um basically that fetus to continue to develop throughout the throughout the pregnancy um okay so the the rest of this uh the rest of these structures is this portion of the um uterus the kind of like the exit channel right there uh is basically um the cervix where you've got two important openings and let me kind of find it um you i it's got to be here somewhere but you got the internal and the external law so it's probably on the next picture probably okay i think it's uh it's better explained on the next schematic but that internal opening is called the internal loss and the portion here towards the outside is the external loss and that opens up into this long um channel right there or canal right there which is of course uh the the vagina or the vaginal canal and of course menstruation which is a release of um of tissue broken down tissue and of course blood and that occurs um that that obviously will occur through through the vaginal canal right there um sexual intercourse when that occurs obviously the deposition of sperm is basically right there in in the vaginal canal and of course that sperm then has to make its way up through the uterus and then through the uterine tube where fertilization of sperm and the oversight typically would occur right there like i said towards the proximal part of that uterine tube now what happens if fertilization does not occur and if a pregnancy is not achieved well then that that ovum that was not fertilized will then um basically be shared during menstruation um dur with through the through the vaginal canal of course the vaginal canal is also called the birth canal so the delivery of the baby also occurs um at the time of birth occurs via the vaginal canal in the case of a normal or normal pregnancy that does not require c-section okay so you've got the urinary batter up front uh medially located you have the uterus and the vaginal canal and then of course uh right here at the back you should be able to see um the rectum the anal uh canal um for obviously the elimination of feces so this you you've got to make sure that you understand the anatomy and the position of all of those different structures uh from the anterior aspect all the way towards the posterior aspect um so let's continue i think there's another schematic coming up where you see a better more magnified view of that uterus um along with you know all of the different openings and and the ducks and all the tubes um laid out a whole lot better in terms of the female duct system i've already talked to you a little bit about this um the urine tube does not directly contact the ovary um the oocyte when it is released from the ovary and it makes its kind of a jump or a leap into the uterine tube um most of the time it's it's an efficient process that works quite well but sometimes the oversight at the time of ovulation uh is lost in the perennial cavity where is not um where it does not make that successful leap into the uterine tube um so we'll talk about all of these different the fallopian tubes of the uterine tubes and then of course all the different regions especially in the wall of the uterus you need to talk about the three layers there and then of course the vaginal canal um so the uterine tube has different um different regions if you will okay we'll talk about the infundibulum and of course those finger like processes at the end of the infantibilium is called the the february and uh it is ciliated and so there's actual currents that are created that helps to move the ovulated oocyte uh into the uterine tube and then once the oocyte makes its way into the uterine tube it is propelled throughout the uterine tube by peristaltic movements very similar to what you saw in the digestive system and also the wall of the uterine tube is lined by a ciliated epithelium um so therefore the cilia or those hair like structures will literally walk the oversight um through its journey as it goes through the urine tip okay um like i mentioned the very um proximal part of the uterine tube is typically where uh the the the ovulated oversight if fertilized by sperm um that event fertilization typically occurs in that very first part of the uterine tube because the oversight that is released from the ovary during ovulation has a very short shelf life it is viable or it is possible to achieve a pregnancy it is it is fertile it is viable only for a period of about 12 to 24 hours okay so um fertilization typically occurs in in the uterine tube so let's look this is the schematic that i was talking about where you see a more enlarged more magnified view of the of the uterus kind of pointing to all the different uh regions and of course we need to talk about the um the wall of the uterus as well so let me let me start here with the with the ovary and make my way down into the uterus and then of course the vaginal canal so you're looking at um one of the ovaries right here in in white and of course a cross section of the other ovary here on on the other side so the ovary is uh anchored to the wall of the uterus uh with the help of that ligament right there which is called the ovarian ligament um and then you see this broad um kind of tissue like region that you kind of spans the uterus tube the uterine tube holds it in place uh and kind of anchors the ovary as well and then it kind of anchors the entire uterus um and everything together and this is basically what we call the broad ligament i'm not going into the individual sub layers uh just this entire expansive sheet is what we call the broad ligament and you can see obviously different ovarian vessels um the arteries and the veins um kind of included in as part of that broad ligament so like i was mentioning when the oocyte is released from the ovary during ovulation um this is then received by uh these finger-like processes which is called the film uh fimbry right there okay um let me actually move over here to this other side so i can kind of show you what's going on here uh cross-section of the ovary right here we will go into all of these details which is uh follicle development occurring inside of the ovary this part here is kind of showing you ovulation that's occurring and what's released here is a secondary oversight we'll discuss this when that oversight is released notice how it is propelled towards those finger-like processes namely the fimbrai and then leads into this very very first region here called the infundibulum which is kind of like a a funnel kind of shaped uh region okay um kind of a broader region and then it's going to start to narrow down okay and it kind of leads into the ampulla and then becomes much more narrow and then this entrance into the entire body of the uterus this region here is called the isthamus okay and then you're looking at the entire the fundus of the uterus kind of like the fungus of the stomach and then of course the entire body of the uterus and of course this will be the lumen um the actual opening inside the uterus so that of the oversight if fertilization with sperm occurs occurs pretty pretty close to this region right here and then it's going to make its journey about five to seven days uh by the time it enters the isthmus and then enters the the lumen of the uterus now when you're looking at the uterus the wall of the uterus consists of three different layers that innermost lighter pinkish uh kind of layer is the endometrium um and then you've got muscle here and this is a smooth muscle and this is the myometrium and then the outside the external most layer is the perimetering so if fertilization has occurred of the oocyte then the next step that needs to occur is basically implantation so the fertilized dome is going to try to find a nice part there in the endometrial layer to basically embed itself in there and find a nice home there for that developing fetus for the next um nine and a half to ten months throughout the end of the pregnancy i mean throughout the life of the pregnancy um distally located uh where you see this entire region is basically the cervix of the cervical canal uh this opening kind of opening into the lumen of the uterus this opening is called the internal loss and of course this is the cervical canal and then this opening which opens in the vaginal canal is the external loss and of course that's the vagina the vaginal canal beneath it so i think we've talked about let me scan this right quick um yeah i think we've talked about most of the anatomy of the female reproductive system so let's go ahead and add a few more details here um and then get to more of the the physiology so backing up just right a bit um we need to talk a little bit about the ovary um especially what are all of these different structures that you see here uh within the ovary and these are all called follicles and they all have different names start with primordial follicles and move on they talk about primary follicles secondary follicles tertiary follicles and then how that tertiary follicle has different names to it as well ultimately ovulation occurs and then um basically how it gets transformed what's left behind of that mature follicle gets transformed into this yellow kind of structure which is called the corpus luteum and then ultimately becomes scar tissue corpus albicans so that's what we need to talk about next is all the different changes occurring here within the ovary so let's get started um so the ovary has an outer region called the cortex and an inner region called the medulla so all of this is kind of very similar to the adrenal gland um to the lymph node structure to the kidney structure so there's always an outer cortex region and then an inner medulla region the cortex okay the cortex is really where all of the um the sex cells again it's the over all the different follicles um are located uh you're gonna see um different um you're going to see blood vessels and nerves within the medulla region so we're going to be focusing on all these different ovarian follicles and and basically work through the the progression of how they develop and the development process is a very very long process it takes many many years for this to occur all the all the way from the time um a female is born so from the time of birth all the way through um childhood and adolescence and then um the whole um when when you uh when menstruation starts to occur when the ovarian cycles start to become uh more regular and so we'll talk about all of those different changes that are occurring but it's a it's it's a process that takes many many years um by the time you actually get to using one of those oversights for the process of ovulation and of course for the process of for the purpose of achieving a pregnancy but before we go that much further uh there's a few things i want to talk about on the slide uh when you think about a follicle a follicle contains it's like a package okay um so this there's an outer layer or multiple layers of cells okay and of course these cells are protecting what's inside of it and what's inside of it is called an oversight the oocyte is where the dna is um and depending on what type of follicle we're talking about it first starts off with uh with a diploid number of chromosomes so 2n 46 chromosomes but by the time it gets ovulated when we talk about a secondary oocyte you only have half the number of chromosomes so you only have a a haploid number of chromosomes 23 chromosomes as opposed to diploid which is 46 chromosomes and how do we go from 46 chromosomes to 23 chromosomes well this is the process of meiosis uh which we kind of talked about with the male reproductive system okay okay so the oocyte is obviously precious commodity right and that's where the dna is located we've got to protect the oocyte well what's going to protect it it's the surrounding cell layers if there's only a single layer of cells then these are called follicular cells now as those follicular cells become multiple layers okay if there's more than one layer present then instead of calling them follicular cells we call them granulosa cells so we're going to talk about how they develop but bottom line is this when you're looking at a follicle you need to be focusing on where the dna is organized um and where the chromosomes are which is the oocyte there's changes that are occurring in the oocyte but accordingly there's also changes occurring in all of these cell layers that surround the oversight but again a follicle is nothing but an oversight and protecting that oversight you either have a single layer of follicular cells or multiple layers of granulosa cells okay okay so what are the different types of follicles well this is this is where it gets interesting there's so many different types of follicles when we begin with the most primitive kind and these uh this is these are called primordial follicles these are actually formed uh during field development even before a female is born okay so these are primordial follicles um that develop prenatally and then at the time of birth you have millions of these primordial follicles or the ovary contains primordial follicles and all throughout your uh childhood before you hit puberty uh before the female hits puberty um the primordial follicles they pretty much stay the same way um but and then they they mature a little bit um kind of becoming something called a primary follicle and then we'll talk a little bit about how those primary follicles become a secondary follicle which is slightly more mature with multiple layers of granulosa cells and then those secondary follicles ultimately develop with in response to hormones especially estrogen they develop into something called a vesicular follicle also called an android follicle or a tertiary follicle so there's three different names for this more mature follicle and this this uh tertiary follicle or anterior follicle um i think i'm going to call it the vesicular follicle um i'll um i'll tell you what it's going to look like but you know these these are names that can be used interchangeably this is the most mature um follicle uh the oocyte from within this mature follicle is what is released at the time of ovulation and of course it's released so remember all of this is inside the ovary so at the time of ovulation the oversight gets released uh from this vesicular follicle leaving behind all of those layers of cells or most of the layers of cells within the ovary and of course all of those remaining layers of cells is what gets transformed into this structure called the corpus luteum now what happens to that oocyte well it was ejected from the or from the ovary so now it's going to make its way through the uterine tube um and maybe fertilization will occur or maybe fertilization will not occur so it doesn't matter it still has been released from the ovary and it has already been released into the uterine tube okay so we're going to follow through with all of these different follicle development and then we'll talk to you a little bit about the corpus luteum and what is its role um mostly important for progesterone okay all right so you're looking at a cross-section of the ovary here this is a histology view of course and so you you're gonna see the outermost region here this is all the the cortex the medulla is deeper inside when you look in you're scanning the periphery of the cortex right here you'll see all of these tiny tiny little cells and these are all basically follicles um the smaller they are towards the periphery they are the primordial follicles as they mature i'll have to zoom in a little bit more kind of to show you there are other schematics coming up where you can see all the details a little better um this is where you're going to see maturation of these follicles ultimately becoming um a secondary follicle and then of course it starts to form uh a kind of a fluid filled chamber inside of that secondary follicle and that's that that fluid-filled chamber is what we call an antrum and that's why the tertiary follicle can also be called the antral follicle and so we will kind of track the entire development um of all of these follicles okay okay um before we get to that quickly about uh one of the homeostatic imbalances related to the uterine tube of course i said an oversight um is normally fertilized um in the urine tube it's fertilized by this by the sperm but the bottom line is in a normal pregnancy that fertilized ovum will then continue its journey down the uterine tube and make its way into the uterus where then implants in the wall of the uterus within the endometrium but in certain circumstances um there is an ectopic pregnancy that has occurred that occurs that typically refers to when the fertilized ovum um is fertilized in the uterine tube it's i'm sorry it is uh the fertilizer over implants in the uterine tube itself and starts to develop there and obviously that's a very narrow tube it is not designed to expand throughout the pregnancy it is it is not a hospitable home or an environment for a successful pregnancy so obviously in that case um this would uh this this would cause us severe discomfort and and could also result in um rupture of the tube which is which can be very very problematic because there will be substantial bleeding and could could result in infection and of course needs to be taken care of um immediately that would be a very dangerous situation so that would be an ectopic pregnancy if it was occurring inside of the uterine tube as opposed to its normal designated home which would be the uterus or the the body or the of the uterus um and and also this could be where uh the oversight gets fertilized uh somewhere in the peritoneal cavity which is also very dangerous a pid this is of obviously inflammation related to the reproductive tract um infections spreading from there into the peritoneal cavity can cause a lot of infertility issues so pelvic inflammatory disease the uterus the uterus like i said the wall of the uterus has different layers the middle layer called the myometrium has a lot of smooth muscle in it and that's going to be important for contractions especially labor contractions and in the helps with the delivery of the baby we the uterus in most females are antiverted meaning it kind of tilts forward a little bit as opposed to retroverted and which you do see in some some females where it is tilted backwards uh makes the delivery of the baby a little bit more challenging in the case of a retroverted um uterus because we talked about the cervix we talked about all of the openings the internal and the external arse um cervical glands will play a huge role in secreting mucus um cervical plug okay oftentimes uh well most of the times you're going to see throughout the ovarian cycle of the female there is a very thick plug oh there's considerable amount of mucus a thicker mucus more dense mucus that tends to block the cervical canal and this prevents pregnancy of course mid-cycle right before ovulation mostly prompted by a hormone called luminizing hormone or lh um that tends to thin out the cervical mucus which makes penetration by the sperm much more convenient or easier obviously for the purpose of achieving a pregnancy so you're going to see a cervical mucus change in consistency throughout the ovarian cycle and of course if a pregnancy has been achieved then there is a solid cervical plug or a mucus plug that is formed that kind of blocks after me under the cervix and prevents any um contaminants especially pathogens like microbes prevents us makes it much more less uh convenient for sperm in fact prevent sperm from entering if that is if the cervical plug is doing its job uh prevents the sperm and prevents bacteria and other contaminants from entering into the lumen of the of the uterus and prevents any kind of infection of the developing fetus so you're going to see these cervical glands play a huge role in kind of producing the mucus that's important for the cervix region uh kind of helps as a lubricant either allowing for penetration of the sperm or kind of acting as a deterrent in certain cases you're looking at the uterine wall there are three important layers like i pointed out on my previous schematic starting with the outside you've got the perimetrium um and then of course the muscle layer with the smooth muscle that's the myometrium and then of course the mucosa lining the lume of the uterus which is the endometrium now a little further in relation to the endometrium there's two important layers uh so deep to the close closer to the myometrium um deeper are you going to see the stratum basalis layer um and this is very important because it has all the stem cells in here the stratum basalis will start to undergo rapid mitosis and rapid cell division immediately after menstruation and it is important for regenerating this inner layer which is a stratum functionalist layer or the functional layer so the layer that responds to ovarian hormones like estrogen and progesterone is mostly the stratum functionalist layer this is the layer that is shared during menstruation this layer is rebuilt by the underlying basalis layer um because of all those stem cells that are able to regenerate that shed functionality i'll talk about this with respect to the uvaria i'm sorry the uterine cycle a little later on um two homo homeostatic imbalance situations um cervical cancer and then of course a little later on we'll also talk about breast cancer i think that comes up pretty quickly so case for cervical cancer this is um and the most commonly seen in women and between 30 to 50 years of age several different risk factors could result in cervical cancer like stis cervical inflammation you can easily detect cervical cancer by doing um by kind of obtaining cells from within the cervix and looking to see if they are starting to become abnormal um in morphology if you will and this can easily be done using a diagnostic test called a pap smear um so the screening ages are kind of shown right there um hpv is the most important cause of most cervical cancers a human papillomavirus and of course now there is a vaccine that protects against hpv this is called gardasil the next homostatic imbalance situation breast cancer so this is a pretty common malignancy in most females the second most important cause of cancer death in at least the u.s women this it typically can arise due to many different reasons but mostly it affects epithelial cells within like the the tubes of the ducts within the um within the breast tissue uh several different um risk factors of course um just like cervical cancer many different factors that predispose you for developing breast cancer early onset of menstruation is one of them late menopause is also uh thought to be um an influential factor uh towards the disposition of um breast cancer but of course family history that's and that's an important one as well almost most of the times you look for genes mutations in these genes and brca one and two um so normally if you do have mutations in the in those genes and that you you have a higher likelihood of developing breast cancer and you are monitored much more closely how do you uh diagnose breast cancer well all of us can do self-examination looking for any lumps or any uh anything that feels abnormal um any hardness of of the breast tissue of course uh a mammography is uh recommended for for women over the age of 40 and it's done every year um and so that kind of has your physician looking for um anything that looks abnormal and anything that may need it may need to be sent off for um for a biopsy to investigate further treatment of breast cancer most of this is chemo or radiation of course surgery and different different levels of surgery or intervention methods lumpectomy just exercises um the cancerous lump simple mastectomy removes just the breast tissue and some of the lymph nodes within the axillary region and of course a radical mastectomy would remove all the breast tissue all the muscles underlying it um fascia and most of your associated lymph nodes in many of the regions close to the breast tissue so those are the intervention methods in the case of breast cancer okay so i think we're now ready to kind of dive off into much more detail related to the physiology of the female reproductive system focusing on a concept called ovogenesis which is uh basically the whole follicle development within the within the female um so i'm gonna i'm gonna mostly use schematics to um put together most of these concepts as a there's quite a few word slides i've tried to highlight it certain um important concepts but i'm mostly gonna guide the rest of this discussion using the schematics to make sure that you understand uh the hormonal influence um guiding this whole process of oogenesis and of course we need to talk about the ovarian and the urine cycle and how they're related um and how they feed back upon each other to regulate the processes that occur within the ovary within the uterus okay okay so within the ovary um females are born with a lifetime supply of what we called um um primordial follicles uh like i said a follicle consists of an oversight at the core and of course that's surrounded by either a single layer of cells called follicular cells or multiple layers of cells called granulosa cells so when this begins this whole process of oogenesis which is basically maturation of these female gametes this can like i said take many many years to complete and sometimes it has it is not even fully complete and in fact most of the cases most of the primordial follicles uh most of the follicles as they develop they do not completely um finish the process and this will make sense when i get to uh my schematic um so it begins in the uh fetal period we begin with organia where you have your your supply of stem cells and these are all deployed in nature at this point 2n which is 46 chromosomes they just multiply by mitosis and that's how you develop all of these different stem cells that have the potential of maturing into our sites i'm sorry i'm maturing into uh yeah oocytes throughout the development of the uh throughout the lifetime of the female so we're going to talk about how this transformation occurs in the oocytes starting with a primary or site and then how they enter this phase of meiosis where do they get stalled or held up or arrested there's different phases that occur so let me um this is a words like kind of explaining um what really happened so this kind of begins um right at birth uh you've got all of your primary oocytes that are arrested in prophase one and then after you hit peer body each month a few of those primary oocytes will get selected and then they all undergo this rapid um the follicle the outside the layer of cells undergo this this change they develop um but only one of these follicles becomes what we call a dominant follicle um which leads to an ovulation event now of course there are there are certain times especially um prompted by um artificial methods or you know um there are there are ways by which you can bring about uh more than one dominant follicle or this may even occur naturally as in the case of um creation of twins or triplets or multiples of any sort um but typically i'm going to go with the normal scenario typically only one um oocyte is selected every month and it goes through this process of completing meiosis one and if you remember meiosis consists of four stages just like mitosis prophase metaphase anaphase and telophase and so we'll talk about how that one um primary oocyte completes the very first round of meiosis meiosis one where then becomes a secondary or site which is where that this is this is the most important cell and then there's another cell that's formed which is a much smaller cell called the first polar body now the secondary oocyte will then uh begin meiosis round two where then gets arrested in metaphase two and this is the part this is the the secondary oocyte arrested in metaphase two is what gets ovulated um middle variant cycle which is released into the uterine tube and then when that secondary oscillate if it encounters and if it is penetrated by sperm then that's when this secondary oocyte will complete pick up from here metaphase 2 go through anaphase and telophase and it's going to complete round 2 of meiosis after which it forms a functional ovum and a second polar body um so this is um an overview of the whole genesis process let's use this schematic to explain it okay so what you see here um is a description of two different set of events occurring but it's really it's the same structure so if you remember we said the follicle consists of the oocyte at its very center at the core and it is protected by either a single layer of cells or multiple layers of cells and the oocyte plus all of these surrounding layers is what we call a follicle right so i have this broken down here um this is before birth and then what happens throughout um childhood and then what happens when you hit puberty um and then as you start to odd as you start to go through ovarian cycles every month uh what's the changes that occur so on the left this is explaining all the meiotic events occurring within the oversight so that is at the center of this follicle right so that's kind of showing you all the changes occurring in the oocyte and then on the on the right here you're seeing all the changes that are occurring in the layers of cells surrounding this oocyte so that's the overall follicle development so let's start here on the top um again uh kind of to remember meiosis consists of really meiosis part one meiosis two and and each meiosis one and meuses two each each of those phases consists of these four subphases you've got the prophase metaphase anaphase and telophase so you're gonna start meiosis one go through all four phases um and then you're gonna start meiosis part two and then depending on the fate of that oh of that oversight it can either go through all phases or can get arrested in metaphase so we'll talk about that so right before birth this is what you a female is born with a lifetime supply of follicles and these follicles are all called primordial follicles at this point they are the most primitive type of follicles so what is a primordial follicle it's a single layer of cells and those single layer cells is called the the follicular cells or follicle cells and what's in the center well it's called an oversight what type of oxide this oocyte is basically uh the primary oocyte and notice it says 2n which means this is diploid it has 46 chromosomes now where did all these primordial follicles come from it came from basically stem cells stem cells that underwent rapid mitosis and you formed millions maybe billions of these primary oocytes each primary oocyte is protected inside of this single layer of cells and that the entire package is called a primordial follicle okay so that is what a female is born with now what happens throughout childhood um all the way to before puberty no change okay so what happens here is at the time of birth you have a primary oocyte within each primordial follicle right and the primary oocyte begins phase one of meiosis but it gets arrested right there at prophase one okay so throughout um this is what you see at birth and throughout infancy and childhood there's basically no change because the ovary at this point is functionally inactive it's not producing estrogen estrogen is going to be required to uh transform to to move this forward okay so prior to puberty estrogen levels are very very low um and this is why you're not seeing any changes uh developmentally in the primary osi there's no changes occurring to the outermost layer of cell so therefore we'll be talking about a primary oocyte arrested at prophase one sitting inside of this primordial follicle now every month after a female hits puberty all the way up to menopause every month um some of these primordial follicles get chosen and they become the primary follicle so it's pretty much the same structure if you will but notice what's happening um as so as the it continues to develop this is what's happening every month right in these chosen uh follicles um it could be about five or six of the follicles that are chosen every month it's going to rapidly become multiple layers there on the outside so those are all granulosa cells so this is called a secondary follicle at this point and then the secondary follicle starts to hollow out and there's a fluid filled chamber or cavity form which is called the antrum there's uh there's a few more things occurring right outside that oversight and so this is at this point called um a vesicular follicle so what happens to the oversight and during this process well not a whole lot it's still arrested in prophase one okay now about an ovarian cycle well a textbook ovarian cycle is about 28 days so right before the midpoint of that cycle which if you assume a 28-day cycle then you would assume halfway point would be 14 days right before that 14-day mark there's a very important hormone that is released and this is called luteinizing hormone lh um this is one of the hormones that's released from the anterior pituitary in response to this lh surge very very rapidly so this is about day 13 or so very rapidly this primary or site will basically complete this entire all of these phases which is part of meiosis part one and at the end of meiosis part one after it completes telophase you will end up with one secondary oocyte and a much smaller cell here called uh the polar body so when these two cells are formed now these are both n number of chromosomes they're all they're both haploid because this is meiosis meiosis is a reduction division where you go from 2n 46 chromosomes to an n or haploid number of chromosomes which is 23 chromosomes now what happens to this secondary oocyte here well it's going to obviously begin meiosis round two it's gonna go through prophase and gets arrested right there in metaphase two that's what you see uh so this is all in response to the lh surge which is typically about 24 hours prior to so it takes about 24 hours or so for all of those changes to occur and now you have a a secondary oocyte that's ready to go through this process called ovulation which occurs typically day 14 of the ovarian cycle when ovulation occurs which you kind of see over here so remember this is the the oversight and it's surrounded by a layer of cells or a few layers of cells called the zonoperlucida and then the corona radiator all of that gets ejected from the ovary from this uh tertiary or vesicular or andral follicle so the the secondary oocyte gets released where does it get released into the uterine tube and what's left behind of all of these granulosa cells this gets transformed inside of the ovary gets transformed into basically the corpus luteum so that remains in the ovary okay so let me come back to the the the oocyte that was released into the uterine tube right this now is not in the ovaries in the uterine tube remember if it is fertilized by sperm okay if fertilization occurs that's when okay uh this secondary oocyte is going remember it was arrested there in metaphase part two it's going to complete round two of meiosis and now becomes the the ovum okay and this is the fertilized ovum okay um and it so the the this secondary or site becomes the ovum and a second polar body and then that first polar body undergoes meiosis part two in itself resulting in two more polar bodies so this is a very unequal result at the end uh so one stem cell or one primary oocyte gives rise to four cells as is always the case in the case of meiosis but except in this case it's uh the cells are not equal in content and you have all of the major content of the cell located within the ovum and then these three smaller bodies or smaller cells called the polar bodies okay so so now the ovum is going to then remember this is in the uterine tube it's going to continue down its journey in the uterine tube um and reach the uterus now what's going on inside of the the ovary um that mature follicle after ovulation after it has released the secondary oocyte i said it gets re transformed into this structure called the the corpus luteum and then the corpus luteum releases progesterone and the progesterone helps to keep a pregnancy viable so now the corpus luteum is looking for a very important answer as we get closer to the end of that ovarian cycle the corpus luteum is asking two questions well really one question the question is has fertilization occurred with the sperm has this entire process occurred do we now have a fertilized ovum that needs to be implanted into um the wall of the the uterus and if that implantation event has also occurred um then the corpus luteum knows that it needs to continue releasing or secreting progesterone because that's going to as long as you have enough progesterone um the pregnancy is viable and that's that's a very important hormone to sustain the health of a pregnancy so therefore this corpus luteum continues to produce progesterone for the first three months until the placenta can take over now what if what if that ovulated uh secondary oocyte what if it was not penetrated what if it was not fertilized by sperm then obviously none of this will occur now this will occur we have a we have an uh secondary oocyte if no sperm has penetrated has has fertilized it then it's going to remain a secondary oocyte it's going to stay arrested in metaphase two and you have this one tiny little polar body and so as they reach the the uterus well obviously then the secondary oocyte will not need to implant um into the wall of the uterus and then that's going to um basically signal to the corpus luteum that it is time to start disintegrating or kind of falling apart and when that happens there's the the amount of progesterone that's released by the corpus lithium starts to drop and as a result that's going to signal um menstruation to occur and as a result the secondary oocyte gets flushed out in that case uh during menstruation so there's two different outcomes here depending on whether the secondary oocyte was fertilized by sperm if that's the case the corpus luteum stays alive if there was no penetration with sperm then it needs to abort that ovarian cycle and flush it out basically bring about menstruation and start the ovarian cycle all over again okay so we'll talk a little bit more about hormones and how they all fit in in a subsequent slide but i hope this kind of made sense in terms of the changes occurring in the follicle development as well as the oocyte this table here gives you a comparison between the processes of oogen assistance spermatogenesis and so we kind of already talked about quite a bit of this um so myogenesis you have four viable sperm uh from every spermatogonia from every stem cell um as a result of oh genesis you only it's a very unequal division so you only have one viable sperm but you have three polar bodies and they don't the polar bodies don't play a role in fertilization they they're not capable of achieving a pregnancy it's only the ovum that is fertilized by spa so in terms of cytoplasmic division uh equals cytoplasmic division here because you need four equal viable sperm in the case of the females unequal division most of the cytoplasmic content the nutrients and everything um is stuffed into the ovum and the polar bodies don't really get it a whole lot and of course the reason for that is of course the ovum is where the um is the part that needs or the cell or the gamut that needs to be fertilized and of course it needs all those nutrients because that fertilized organ needs to or the oocyte in general fertilized or not will still need uh to basically continue its journey um about a six to seven day journey um through the uterine tube before reaches the uterus this is pretty interesting spermatogenesis the error rate is much much lower three to four percent whereas in the case of oh genesis the error rate is actually pretty high um one in five ovum that is produced during an ovarian cycle has a chance of having some kind of mutations or something wrong with it in which case if you have um any kind of mutation or something where something went wrong with the ovum of the female gamete then if fertilization were to occur uh with the sperm that's obviously going to be recognized by the body as not being viable and therefore could result in uh in miscarriage especially um early pregnancies uh like first pregnancy you're gonna see um even though some some people or some couples are aware of um these things happening um because they're tracking it or they're they you know you get a positive test and then a positive pregnancy test and then shortly after that a negative pregnancy test or something happens or you see a delayed onset of a period or um of menstruation and so those are all indicators that maybe a pregnancy did occur and then something went wrong and so therefore it aborted um and in other cases you're not even aware of it you're completely oblivious of it but the the miscarriage rate is pretty high in the case of the females and a lot of it is not because of um sperm it could be but most of the times it is as you can see those those percentages and much higher percentage of where things could go wrong with oogenesis as opposed to spermatogenesis okay which then brings me to um more of the hormones and kind of put this into perspective in terms of the ovarian and the uterine cycle and so what is what's the ovarian cycle this is the monthly events or the changes that are occurring all the sequence of events are occurring in terms of the follicle development in the in terms of the maturation of the ovum um within the ovary and you can break this down if you think about again we're going to go over the textbook cycle most females will um will relate to the fact that um it's not always a 28-day cycle um maybe it is a 28-day cycle but in many cases it's shorter or maybe even longer so it really kind of depends from one person to another but if you go with a classic 28 day cycle you can break this down into two important phases um mid cycle day 14 being ovulation so everything prior to ovulation is called the follicular phase so that's basically days 1 through 14 and then or everything post ovulation which is days 15 or 14 or whatever to day 28 the end of the ovarian cycle is called the luteal phase so why is this first part called the follicular phase this is where you're going to see major transformation like we described just a while ago major transformation occurring in the development of the follicle going from primordial to primary to secondary to um enteral follicle so all of that's happening in the follicular phase and then once that or site gets released or ejected from the ovary that is ovulation which typically um there's a population after that occurs you this kind of moves into this next part which is uh the remainder of the ovarian cycle called the luteal phase and this is where remember we said um what's what gets left behind in the ovary uh the remnants of the the mature follicle after it has released its oversight uh its secondary oocyte what gets remain what gets left behind gets transformed of the corpus luteum and that's why uh this next phase is called the luteal phase because this is the activity related to the corpus luteum of all the phases um of of both those phases um the luteal phase is always going to be a constant so from the time of ovulation to the end of the ovarian cycle if fertilization of the ovum has not occurred and that is always the luteal phase is always going to be 14 days so any variability in females in their ovarian cycle really is here in this early phase the follicular phase this can be variable um depending on each person okay i've kind of broken it down here for you as a visual reminder of what these phases look like so if you're going with a 28-day cycle um midpoint right then this is when ovulation is occurring population has occurred in response to something called an lh surge again this is a hormone if you think back to the endocrine chapter it's released from the anterior pituitary so this part here is a zero through uh 14 days prior to ovulation all of this is called the follicular phase what's happening here well it's called the follicular phase because this is where the development of the follicles is occurring from primary to secondary to android follicle and ultimately the secondary oocyte gets released from the android follicle at the time of ovulation which that which then means the second part of the ovarian cycle 14 to 28 this is called the luteal phase because after ovulation the remnants of that android follicle gets converted into the corpus luteum and so since this is dictated by the activity of the corpus luteum this phase is called the luteal phase the importance of the corpus luteum is that it will very quickly ramp up the levels of progesterone and estrogen so that's the that's all the changes that are occurring inside of the ovary and that's why this is the ovarian cycle so we're going to add a little bit more detail here as to like how these changes occur um what what happens during ovulation and and kind of tie in hormonal influences on each of those phases so the next few slides um uh word slides explaining uh the follicular phase the luteal phase the whole concept of ovulation um and everything and i've highlighted a few things here for you but as we go through um the next few schematics i'm going to be putting all of these concepts together okay so let's start with the follicular phase so if you're looking at a cross section of the ovary right there uh let's say okay um these uh tiny little cells and kind of leading towards this over here and those are your primordial follicles remember this is what a female is born with um primordial follicles have a primary oocyte inside of it uh arrested in prophase one and just a single layer of cells and at the time of a variant during the ovarian cycle several of these primordial follicles can be selected and they're going to then mature into a primary follicle which is slightly larger and still only a single layer of follicular cells surrounding that oocyte in the center and of course remember this is called the primary oocyte arrested in prophase one now as you go through follicular development notice that single layer cell becomes multiple layers of cells and that's why this is called the secondary follicle then secondary follicle starts to develop these fluid filled cavities at first it's all patchy like this ultimately it'll all kind of fuse together to form one large fluid-filled cavity so this is a very early transformation of that secondary follicle into a vesicular follicle okay um and then you've got your outer kind of your layer of cells there which is called the thicker folliculi and this is going to be important and then you've got the cells here on the inside your granulosa cells um we'll talk about hormones that are released from these different um regions now this early vesicular follicle ultimately becomes something that looks like this so this structure right here resembles this and what you can see here is you get very defined andrew which is filled with fluid and so what's this this is going to be my um primary oocyte arrested in prophase one okay but then in response to the lh surge this primary oocyte will then rapidly undergo complete meiosis but one and becomes the secondary oocyte which then gets arrested in metaphase um two so this is this is right before ovulation and it is surrounded by the secondary oxide is surrounded by kind of a gelatinous translucent layer called the zona pellucida and then a few layers of cells here a few layers of those name granulosuc radiator and then of course the fluid-filled um antrim and then of course the rest of the granulosa cells this entire structure is now a very very mature tertiary follicle also called the vesicular follicle or because it has an antrum a fluid-filled cavity it's also called the antral follicle so now what happens um uh during ovulation as you can see here right that secondary oocyte along with the zona pellucida and the corona radiator this entire structure gets ejected out of the ovary into the uterine tube right and so then what happens here then is the rest of this structure um which is this part that's left behind gets transformed into the corpus luteum and then that kind of starts off the whole luteal phase um so for the next 10 days or so this this structure is going to continue producing uh progesterone and then it's going to check on the fate of this ejected secondary oscillate within the uterine tube to see if fertilization with sperm has a com has been accomplished and then even further has that um secondary or site actually been implanted within the wall of the within the wall of the uterus and if that has occurred then the corpus luteum will stay alive and continue producing progesterone but if a secondary oocyte has not been fertilized by the um sperm then this will shrivel up progesterone levels are going to start dropping and then ultimately gets transformed into something called a scar tissue okay all right so i i think i kind of explained all of these concepts already with the schematic just want to make sure that i've covered it all so with the follicular phase like i said um the ultimate goal is at the end of the follicular phase you have a mature vesicular follicle and then of course in response to towards the end in response to luteinizing hormone i said um this primary oocyte within the vesicular follicle will complete meiosis one gets transformed into a secondary oxide in the first polar body the secondary oocyte then gets released at the time of ovulation correct that's when the ovary wall kind of literally goes through an acute inflammation process and then it expels that secondary oocyte along with the corona radiator um which is then kind of received by those finger either finger like extensions the uterine tip um and like i mentioned some percentages of ovulations could release more than one secondary oocyte which of course could result in fraternal twins um identical twins is basically the fertilization of just one oocyte with us with one sperm and then shortly after that and there's a process that occurs called cleavage where it undergoes rapid mitotic divisions uh so very early on during those very early cleavage divisions um if that fertilized ovum splits into two then you have the creation of identical twins okay okay so after ovulation occurs um for the luteal phase this is where we said all of those um remaining cells of the antral follicle gets converted into the structure called the corpus luteum and the importance of this is to generate or secrete progesterone and estrogen to a certain extent but mostly progesterone and what's the importance of this if a pregnancy has occurred well then the corpus luteum will continue to produce the progesterone in order to sustain the pregnancy until the placenta could take over at three months or so but if there was no um fertilization no implantation no pregnancy then the corpus luteum will start to degenerate becomes scar tissue called alpha cans typically within 10 days 10 to 12 days or so and then that basically signals the end of this ovarian cycle it kind of starts or initiates menstruation which then kicks off the next ovarian cycle and we just rinse and repeat until um a successful pregnancy has been accomplished okay i think this kind of just shows you um a little bit more of the details here i think i explained the secondary or side here within this is right before ovulation and then during ovulation the secondary oversight gets ejected along with the corona radiator and the zona and then of course the transformation of the remaining cells into the corpus luteum and then the corpuscle begins if a pregnancy has not had not been achieved this is just showing you in post ovulation uh first the ruptured follicle fills with blood this is called the corpus hemorrhagicum and then after that it becomes packed with densely packed with cells which is when it's called the corpus lithium and then um after this if the corpus luteum is no longer needed and progesterone levels start to drop from this structure it gets transformed even further into scar tissue mostly collagen called corpus albicans okay so now that we talked about all the different events of the ovarian cycle let's let's add a little bit more detail related to uh the different hormones that control the regulation of the ovarian cycle so this is all related to the hpg axis that we talked about with the male reproductive system h for hypothalamus b for the pituitary and g for gonads since this is the female ghana gonads were talking about it would be the ovary so just like the male reproductive system hypothalamus will produce the gonadotropin releasing hormone gnrh which then prompts the anterior pituitary to release follicle stimulating hormone fsh and luminizing hormone lh which then prompts these two hormones will work on and the female gonad namely the ovary which prompts the release of estrogen and progesterone so it's it's a cycle also it's a pathway that needs to be followed one leading to the next hormone um so we're going to talk a little bit about the relationships between the hypothalamus the pituitary and these two hormones that are released by the ovary um the hypothalamus throughout um after a female is born and throughout childhood till right before puberty is reached um and the hypothalamus is kind of inhibited and is not allowed to produce to produce gnrh and that's why it doesn't produce fsh that's why you don't have estrogen and progesterone this is all prior to puberty at the time of puberty um there's an important hormone that is uh linked to the onset of puberty this is leptin leptin is produced by adipose tissue as more fat more adipose tissue accumulates in the female body leptin levels will increase which is going to release um gnrh from the hypothalamus so we'll talk a little bit about that um and so during um during childhood uh until puberty is reached the um there's very small amounts of estrogen that helps to inhibit the gnrh and without the gnrh you don't really have any fsh and lh and so on and so forth so it's a leptin that actually uh kind of releases the inability effect of the gnrh um i'm sorry the inhibitory effect of the estrogen on the jnrh and therefore allows more fsh and lh to produce and that's why more more and more estrogen is being produced so i think that the next schematic will kind of put that into perspective so when puberty is reached and used and a female starts ovarian cycles initially it's very irregular and can take about three years or so before everything becomes regular and all um ovarian cycles actually result in an ovulation event with the release of the secondary oocyte that's capable of being fertilized by the sperm and and therefore being capable of of a pregnancy um so it it takes about two to three years before things become more regular so this is the overall hpg access explained and inhibin is also important just like um with the male reproductive system so let me use this schematic to explain the whole process so this is very uh during the during the follicular phases so so through our childhood through our after birth and through our childhood before puberty there's a there's a very very small amount of estrogen and notice the dotted lines dotted lines are inhibitory whereas solid lines would be stimulation effects so that the estrogen notice has a negative effect on the hypothalamus so therefore the hypothalamus does not release the gnrh which does not allow the pituitary the anterior pituitary to release the fsh of the lh and that's what keeps the ovary suppressed and you don't have any follicle development you don't have an ovarian cycle and all of that throughout childhood but at the time of puberty in response to increasing fat content and increasing adipose tissue when leptin levels increase it's going to remove this inhibition effect and so now the hypothalamus can release gnrh which then prompts from the anterior pituitary it prompts the release of fsh and lh so every month during the ovarian cycle right so starting with day zero one two three four five that's where it says early to mid follicular phases what's happening is fsh and lh are being released by the anterior pituitary what is fsh2 follicle stimulating hormone so it's going to work on those primordial cells primordial follicles converting them into primary secondary follicles and so on and so forth and at that time the luminizing hormones going to work on the outermost layer of cells they call the thicker cells which prompts the release of androgens androgens like testosterone well that's no good for the for the ovary so that androgens are then converted by these cells here on the inside the granulosa cells it gets converted into estrogen so what you see is as more and more lh is released you're going to see more and more androgens being produced which is converted to estrogen and the increase in estrogen is going to prompt this follicular development to where it becomes this um android follicle or this vesicular follicle with the antrum being formed and so on and so forth so all this while i have this oversight here this is still my primary oversight arrested in prophase part one okay so all of this is happening during um on the follicular phase and all this while you're going to see an increasing amount of estrogen so what happens then is i'm going to talk about what what leads to ovulation next okay and we're going to talk about what lh does um and how does it actually trigger this whole ovulation event which is what's explained here and then what happens after ovulation okay so we talked with the corpus luteum needs to form so we need to talk about all of this what happens if there is a pregnancy that is it that is achieved and what happens if there is no pregnancy so all of that's kind of what's explained here i'm going to use the rest of my schematic to work my way through the rest of this material so as we get to almost the end of the follicular phase and if you remember my textbook cycle um so like about day 14 is when ovulation occurs so let's say around day 13 or so about 24 hours or so right before ovulation i have a very mature um vesicular or a natural follicle i have a secondary or side there that is arrested in prophase part one in response to lh okay so what's going to prompt the lh here's what happens day 13 or so this rapid increase in in estrogen is going to provide a a positive feedback back on the hypothalamus i just want to point out one more thing here when this is released fsh and lh it's days one two three four five ish or so and after that you don't need to produce any more of this because follicular development is already occurring you've got the androgens being produced the estrogen being produced which is going to keep this whole ball moving forward like rolling forward right so this this kind of feeds back to where it shuts this off temporarily but at about day 13 in response to high androgen i'm sorry estrogen content that's going to provide a temporary override on the hypothalamus allowing it to produce the gnrh which then produces the lh and the fsh but the lh plays a much bigger role in this at this stage than the fsh so what does the lh do the lh is going to work on this second uh this primary oocyte right there it's going to prompt it to complete meiosis part one converting it into the secondary oocyte and a polar body and it's also going to prompt the whole ovulation event which is where the secondary oscillator gets ejected from the ovary into the uterine tube what remains of the follicle gets converted into progesterone okay i'm sorry it gets converted into the corpus luteum and what does a corpus luteum do it's going to increase progesterone it's going to secrete progesterone it's also going to secrete estrogen to uh to a minor extent and inhibit what does the inhibition do pauline ben is going to get basically shut down this axis again because ovulation has already occurred uh this oocyte has been released into the urine tube so therefore the corpus luteum is going to shut down this whole hypothalamus pituitary because you do not need another ovulation event occurring in the same ovarian cycle you don't want multiple possibilities of pregnancies occurring um several days apart once ovulation has been has occurred then shut it down until the next ovarian cycle begins okay so what's the fate of this corpus luteum like i was saying um so this is around what so day 14 is ovulation so we're going to continue on the corpus luteum continues on until about for another 10 more days maybe 24 day 24 day 25 and then it's going to check to see what happened to that secondary oocyte if it was fertilized by sperm if implantation of that fertilized egg occurs inside of the uterine lining then we need to um sustain the pregnancy we need to keep that pregnancy marble in which case the corpus luteum will continue producing the progesterone for up to three months like we said and then the placenta will take over but if there was no fertilization event and no pregnancy that was achieved then the corpus luteum will start to degenerate um as progesterone levels start to decrease as estrogen levels start to decrease that's what's going to basically come back full circle here and of course the then prompt the um beginning of the next ovarian cycle which of course will trigger menstruation and then this whole thing happens all over again okay so it's really important for you to keep track of what exactly the role of the corpus luteum is so make sure you understand what happens if fertilization has occurred versus what happens when there is no fertilization so if there's no fertilization like i said the corpus luteum it does not have a role to play anymore if it is not required to sustain a pregnancy in the case of no fertilization so therefore it will degenerate and there's actually another hormone that plays a role in this process and it's hcg human chorionic gonadotropin that actually the corpus luteum is looking for those levels to keep rising which typically occurs only when implantation of the fertilized ovum has occurred inside of the lining of the of the uterus so when those levels actually start to increase that's really when the corpus luteum knows that a pregnancy has occurred in which case it will continue producing progesterone but when there is no implantation because there was no fertilization and there is no pregnancy then the corpus luteum does not detect those increasing levels of hcg and that's when it degenerates and as those levels of estrogen and progesterone start to drop that's when that's when um the the body knows that it's time to abort this uh ovarian cycle and do to trigger menstruation and then basically trigger the next ovarian cycle the oversight that was um activated um the whole oversight development um going from primary to secondary to to tertiary all of that actually does not occur within the same ovarian cycle not within the same month it was actually selected or activated the oversight gets activated or chosen about a year prior to the the month during which it's actually ovulated so it's kind of interesting and then it kind of slowly even though it's selected it then kind of goes through this whole process slowly and then really gets activated only about a year later even though it has been chosen or selected a year prior to the ovulation event so let's let's talk about these concepts one more time kind of discussing uh different hormones here as well so i'm going to focus here on these two tracings on the top and of course this is from the anterior pituitary luteinizing hormone in blue fsh in in red all of the different events occurring inside of the ovary in response to the lh and the fsh and then as these follicles develop during the ovarian cycle it's going to start to produce these hormones in orange estrogen and then as the corpus luteum is formed you're going to see the progesterone which is shown in green so let's start here with the top um in all three graphs here or all three schematics everything in blue refers to prior to ovulation so ovulation will be kind of right there at day 14 and then everything in green should be after ovulation so blue should be the follicular phase and green should be the luteal phase with the midpoint being day 14 which is ovulation so if you're gonna go with the um time frame of zero to 28 days day 14 would be ovulation uh everything prior to day 14 follicular phase everything from after ovulation to 28 luteal phase so let's kind of look at this so in response to gnrh from the hypothalamus which releases the lh and the fsh notice what's happening here we're selecting some of the primordial follicles which will then develop into primary follicles and secondary follicles then ultimately into your tertiary follicle or the chosen follicle now not all of your primordial follicles selected for that month will mature at the same rate and that's why only one typically becomes the dominant follicle for that month and then so if you can put this into perspective about 24 hours before to the ovulation event so about day 13 this is when you're seeing that lh surging quite dramatically so this is right right before ovulation fsh also surges but not to the same extent lh is considered uh the more important contributor to ovulation so in response to that nate surge what happens ovulation occurs right um the secondary oocyte gets released into the uterine tube um and then what remains of this follicle uh gets converted into the corpus luteum so then we begin this portion here in green which is the um luteal phase what happens to the lh and the fsh well that they're gonna come back down they're no longer needed because ovulation has already occurred i remember the hypothalamus is inhibited again gnrh is not released and that's why fsh and lh they both come back down but in the meantime from the the corpus luteum you're going to continue to see a rise in estrogen okay not not the same extent though prior to fall ovulation but still it's it's high but notice here prior to ovulation because there was no corpus luteum you have a flat line for progesterone right after ovulation in response to the corpus luteum being formed you're going to see those progesterone levels start to increase okay and they're the highest at about a week or so after ovulation and this is when the corpus luteum is trying to decide if a pregnancy has occurred if a pregnancy has not occurred what happens it starts to degenerate into the scar tissue corpuscle begins and as a result estrogen levels start to drop progesterone levels start to drop and when that happens that ends this ovarian cycle menstruation will begin and then we come back to d0 and start the next ovarian cycle all over again which then brings me to the uterine cycle also called the menstrual cycle so this is basically all the changes that are occurring within the uterine wall especially within the endometrial the innermost mucosal lining kind of lining the um the lumen uh of the uterus so all the changes occurring in the endometrium uh in response to everything that's occurring the in the ovary and this is kind of very very much correlated the changes occurring in the ovary with the changes occurring in the uterus i'm going to break this up into three main um phases the menstrual phase which is days one through five six through fourteen would be the proliferative phase and then um 15 through 28 would be the secretory phase so to put it into perspective i wanted to before going too much further i want to show you the correlation between the ovary and the eucharist i've already um i already have this drawn on a previous slide so if you remember the ovary goes i mean if you go with an ovarian cycle of 28 days ovulation occurring at day 14 so everything prior to that is the follicular phase everything after ovulation is the luteal phase and we talked about all the changes occurring here in the follicular phase uh lh surge occurs about 24 hours prior to ovulation which triggers this whole release of the oversight during ovulation um conversion of the remaining structure into the corpus lithium occurs uh during the later phase you know that progesterone levels estrogen levels start to increase we talked about this around about 10 days after the corpus luteum is formed so around day 25 or so corpus luteum is trying to decide if a pregnancy has occurred if it needs to remain active or if it needs to disintegrate if it disintegrates well that ends this ovarian cycle and then you start all over again so that's occurring the ovary right so corresponding to these changes what is going on in the uterus okay so when you back up remember this was broken in three phases so let me correlate that okay so remember days up to ovulation it was called the follicular phase and the ovary well the follicular phase corresponds to these first two phases in the uterine cycle sorry back up um menstruation can occur um three to five days or so so zero to five let's say is the menstrual phase and then after this uh leading up to ovulation is called the proliferative phaso menstrual and proliferative phase in the uterine cycle corresponds to the follicular phase within the ovarian cycle now the secretory phase is all of this which as you can see corresponds directly with the luteal phase of the ovarian cycle so in a nutshell what's really happening here in the uterus okay so during the menstrual phase uh the inner most lining of the endometrium namely the stratum functionalist layer is shed all the blood vessels are ruptured and so therefore you have bleeding occurring release of the endometrial lining everything is being shed during the proliferative phase basically the stratum basalis layer where you have the stem cells it divides rapidly rebuilding the stratum functionalist layer back to its normal thickness and in becomes ready in readiness for the ovulation event and then for um basically in preparation for a fertilized ovum so the rest of this phase here this is the secretory phase this is all the work that needs to be done by the functionalist layer it's going to continue rebuilding or building up secretions are going to be increased for nutrients for other secretions to kind of improve the health um the health of the of the layer in case implantation of a blastocyst were to occur uh during this time now during this time if implantation has occurred which typically is implantation the earliest would be a week or so after ovulation so say day 21 anywhere between day 21 to 25 that's typically when our um implantation could occur and as as implantation occurs well you're going to start to see hcg levels start to increase hcg is being released by this implanted blastocyst within the endomete and yeah endometrial lining of the uterus as these levels start to increase the corpus luteum can detect those levels and it knows that we've got a viable pregnancy and that's why it will prevent uh from disintegrating okay if there's no implantation of the blastocyst if there's no hcg levels then the corpus luteum starts to degenerate and these levels will start to drop here the progesterone estrogen and ends the ovarian cycle which obviously ends the uterine cycle okay so let's kind of put this back into perspective um kind of explained here um those those three phases that i have marked here on this uh schematic is explained here so obviously during the menstrual phase this is in response to dropping levels of estrogen and progesterone from the corpus luteum so obviously you understand this is a interrelationship between um the ovary and the uterus changes occurring in the ovary will dictate changes that need to occur in the uterus as well okay so all the hormonal changes here will relate to changes in the functionalist layer and the basalis layer and then there the whole prep work that needs to occur here in the uterine lining um so in response to the corpus luteum disintegrating estrogen levels are dropping progesterone levels are dropping that's what's going to prompt the shedding of the stratum functionalist layer um and then as the ovarian follicles continue to grow primary to secondary to tertiary as more and more estrogen is produced that's going to prompt all of these changes here in the proliferative phase which is basically regenerating the stratum functionalist layer preparing um upregulating kind of increased numbers of progesterone receptors um mucus production uh allowing for thinning out of the cervical mucus allowing for sperm passage um to achieve pregnancy and then of course at the end of the proliferative phase here ovulation is occurring um within the within the ovary in the secretory phase um yes this is the most constant time wise because it corresponds uh with the luteal phase in the ovary and what's going on here is of course the endometrium is preparing for uh implantation and for fetal development embryonic development since called the secretory phase because endometrial glands are producing a lot of nutrients a lot of secretions and of course formation of the cervical mucus plug in case our pregnancy has been achieved if fertilization does not occur we talked about this corpus luteum is going to degenerate as a result progesterone levels will fall and then as a result all of the arteries all the blood supply that was in preparation for the secretory phase all of that starts to kind of spasm and regress and the the layer becomes um unstable and weakened and as a result you're going to start to see rupture rupture of the blood vessels rupture of the functionalist layer which then brings about menstruation so we've talked about these three um schematics on a previous uh slide so just let's add the uterine part of it here on the bottom so again um during days zero to five menstruations occurring the entire functionalist layer is being shed during the proliferative phase right prior to ovulation and building up the functionalist layer and by the stratum basalis and then in the secretary phase notice enlargement of those blood vessels secretions um enrichment with nutrients and formation of the cervical plug all of that is is being facilitated during the secretary phase over here okay so that kind of puts into perspective the correlation between the ovarian cycle and the urine cycle and all the different hormones that play a role in sustaining follicle development corpus luteum um all the changes occurring in the endometrial lining within the uterus all of that are very very um interconnected okay a quick mention about the effects of estrogen and progesterone of course on the next slide uh estrogen of course promoto genesis follicle development in the ovary um secondary sex characteristics all of this at the time of puberty progesterone mostly regulating uterine cycle changes in the cervical mucus plays a role a little later on if pregnancy were to occur uh preparing for lactation in the case of mammary glands all of that would be the rules of progesterone um and to wrap up this discussion let's talk a little bit about uh some of the developmental aspects uh so every cell has 46 chromosomes organized as 23 pairs of which after 23 pairs one of the pairs is this is a pair of sex chromosomes which determines um the sex of an individual so after of the pair of sex chromosomes um females um have a combination of x x okay so there's two x chromosomes and the individual is a female if there's one x and one y chromosome then the individual is a male so that's how you determine genetic sex based on this pair of chromosomes not the other 22 pairs that pretty much has the same organization of genes and just variants obviously from individual to individual but this is what determines male versus female and the last few things i'm going to talk about here is of course puberty we already talked about this the onset of puberty is actually determined by leptin the accumulation of fat um in adipose tissue and then of course how that increases gnrh and how that increases fshlh and and that of course is going to obviously show an increase in gonadal hormones as well secondary sex characteristics all of that starts to emerge uh which then triggers a variance of varying cycles um and you have your first um menstrual cycle or monarchy right the opposite of puberty is when the female ends there um ovarian cycles this is menopause of course this is when you mensis has not occurred for an entire year that's when it's typically defined as a female reaching menopause so i think um that kind of wraps up my discussion of the female reproductive system pay attention to the anatomy especially kind of focusing on all the changes occurring in the ovary follicle development the ovarian cycle dictated by changes in gnrh fsh lh changes in estrogen progesterone and then finally changes occurring within the uterus definitely the interplay between the ovarian and the urine cycle will be very important to kind of focus on and make sure that you understand those details i hope this made sense to you i hope you found this useful thank you