foreign and the final lecture for the reproductive system and for the semester is the physiology of the female reproductive system and the physiology of the female reproductive system is a little bit more complex than that of the male system so we'll Begin by talking about the process of uu Genesis which is a production of female gametes we will describe the two female reproductive Cycles in the ovarian and the uterine Cycles we will describe the process of fertilization which is where an egg and a sperm will meet and then implantation which is where the fertilized egg implants into the lining of the uterus and then lastly we will briefly describe some of the hormonal and physiological changes that are associated with pregnancy so getting started learning objective number one to describe the process of urugu Genesis so the formation of female gametes or female reproductive cells is called uu Genesis in contrast to spermatogenesis which begins in males at puberty ooh Genesis begins in females before they're even born during early embryonic development germ cells migrate to the ovaries where they differentiate into our urugonia ugonia are stem cells that contain 46 chromosomes and we see that represented by the two n here now these ugonia will divide via mitosis and produce millions of these germ cells but even before birth most of these germ cells will degenerate the cells that are left remaining will develop into our primary oocytes these primary oocytes then enter the first phase of meiosis while still in this fetal development period however they do not complete this phase until after puberty now during this arrested stage or poor stage of development each primary oocyte is surrounded by a single layer of flat follicular cells and this entire structure is called a primordial follicle so I follicle is just the urusite and all of the structures that surround it now at Birth approximately 200 000 oocytes remain in each ovary of these about 40 000 are still present at puberty and around 400 will mature and ovulate during a female's reproductive lifetime the remainder of these primary oocytes will disintegrate and therefore the number of other sides that a person is born with is the highest number of other sites that that person will ever have now each month from puberty until menopause gonadotropin's follicle stimulating hormone and luteinizing hormone will stimulate the development of several primordial follicles although typically only one will reach the level of maturity that is needed for ovulation as our primordial follicles develop they become our primary follicles and each primary follicle consists of a primary oocyte that is surrounded by several layers of cells which we now call granulosa cells so taking a bit of a closer look at each of those follicles we have our primordial follicle here and then our primary follicle here and our granulosa cells are these purple bubble looking cells in the middle here the outermost layer of granulosa cells rests on the basement membrane and as the follicle grows it forms a clear glycoprotein layer called the Zona pellucida it sits between the primary oocyte and the granulosa cells at the same time we also have cells surrounding this basement membrane form the thika folliculi now as our primary follicle develops into our secondary follicle the thika folliculi differentiate into two layers we have the thika interna which is this grayish layer along here this is made up of Highly vascularized cuboidal secretory cells that actually secrete estrogen and then the thicker external layer so the very outer layer which is made up of cells and collagen fibers we also have our granulosa cells start to secrete a follicular fluid which fills a cavity called the Antrim and the presence of an Antrim is what actually differentiates a secondary and a mature follicle from a primordial and a late follicle so it's that cavity here and here now as this follicle develops those granulosa cells become firmly attached to that zone of lucida and we now call them the corona radiata that secondary follicle then grows even bigger and it turns into our mature follicle which is the follicle that is actually ovulated now I don't expect you to be able to identify each of these structures or each of the different follicles in the different stages of development but I will be using some of these terms as we go along so don't stress you're not going to be examined on these in part A of the lab exam but I do want your head to have at least known or heard some of these terms before so coming back to this image and just before ovulation we have our primary oocyte with our 46 chromosomes our primary oocyte then completes meiosis one and it produces two cells of unequal size each cell has 23 chromosomes we have our first smaller polar body which is made up mostly of discarded nuclear material so the stuff from the nucleus that's no longer needed and then our larger cell which is called the secondary oocyte once the secondary urocyte is formed it then Begins the second phase of meiosis but once again it then stops our mature follicle then ruptures and it releases that secondary oocyte that polar body and the corona radiata out into the pelvic cavity all things going to plan these are swept into the uterine tube if fertilization does not occur all of these cells will simply degenerate if sperm are present in the uterine tube and one penetrates the secondary oocyte however then that second phase of meiosis II will resume the secondary oocyte then splits into a further two cells once again of unequal size we have a secondary polar body and the ovum the nucleus of the sperm cell and the ovum then unite and form what we call a zygote and it's now a cell with a complete 46 chromosomes so one primary oocyte gives rise to one gamete or over in contrast to the process in males where one primary spermatocyte produces four gametes or sperm so looking at that process in text and again a bit more complicated than spermatogenesis but oogenesis is the formation of female gametes or female reproductive cells the process begins before birth but is then halted or paused until puberty is reached although we have hundreds of thousands to a million oocytes in each ovary only about 40 000 are still present at puberty and only around 400 will be mature or matured and then ovulated during a female's reproductive lifetime so who Genesis begins with those germ cells which differentiate into the urugonia they then develop into primary oocytes and begin the first phase of meiosis at this stage the primary oocyte and the cells surrounding it are called our primordial follicle once a female reaches puberty once a month the follicle stimulating hormone and luteinizing hormone will stimulate the development of several primordial follicles into our primary follicles a primary follicle is that primary oocyte surrounded by the granulosa cells the primary follicles continue to develop into secondary follicles where that thicker folliculi differentiates into the thika interna OR at secretes estrogen and thicker externa we have the development of the Antrim which is that cavity which is filled with follicular fluid the innermost layer of our granulosa cells now becomes firmly attached to that zone of pellucida and we call it the corona radiata finally the second secondary follicle becomes even larger and we now call it a mature follicle within the mature follicle the first phase of meiosis is completed and two cells of unequal size are produced the smaller cell is called the first polar body the larger cell is called the secondary oocyte once the secondary oocyte is formed it begins meiosis II or that second phase of meiosis but then again stops the mature follicle then ruptures and it releases the secondary oocyte in the process called ovulation if the secondary oocyte is not fertilized or not met by sperm then it will disintegrate however if a sperm penetrates the egg meiosis II or the second phase of meiosis will resume and two cells with 23 chromosomes are produced a smaller second polar body and then the larger ovum or the egg so moving on to learning objective number two which is to describe the female reproductive cycles and after puberty it's these Cycles which actually regulate some of the processes that we just talked about so during their reproductive years non-pregnant females will typically exhibit cyclical changes in both the ovaries and in the uterus each Cycle takes roughly a month and involves both eurogenesis and the preparation of the uterus to receive that fertilized ovum hormones secreted by the hypothalamus the anterior pituitary and the ovaries will control these two cycles and the ovarian cycle is a series of events that results in the maturation and the ovulation of a follicle and an oocyte in the ovaries the uterine which you may also hear termed the menstrual cycle is a series of concurrent changes that occurs in the endometrium of the uterus to prepare for the arrival of that fertilizer ovum so our ovarian cycle occurs in our ovaries a uterine cycle occurs in our uterus now before we get into each of those cycles and the specific events or phases of each cycle I just briefly wanted to mention the hormones that regulate the female reproductive Cycles as a whole so to begin these processes gonadotropin releasing hormone is released from the hypothalamus in turn that stimulates the anterior pituitary gland to release follicle stimulating hormone and luteinizing hormone follicle stimulating hormone as the name somewhat suggests stimulates follicular growth and development our luteinizing hormone also stimulates development of the follicles and both of these hormones stimulate the follicles to secrete estrogen now Midway through the female reproductive cycle luteinizing hormone which we'll talk about shortly will trigger ovulation once ovulation occurs the follicle that's left behind becomes the corpus luteum the corpus luteum will produce and secrete a number of hormones including estrogen progesterone relaxin and inhibit so estrogen secreted by both the follicles and the corpus luteum have several important functions they help develop and maintain the female reproductive structures as well as a secondary sexual characteristics and the breasts remembering the secondary sexual characteristics are those that make a person look like a particular sex but don't play a role in reproduction so in females this includes distribution of adipose tissue so to the breasts the abdomen the mons pubis and the hips it changes the pitch of The Voice widens the pelvis and also changes the pattern of hair growth on both the head and the body moderate levels of estrogen and please ignore the Americans falling here will actually inhibit the release of gonadotropin releasing hormone as well as inhibit the release of follicle stimulating hormone and luteinizing hormone directly or via negative feedback progesterone mainly secreted by cells of the corpus luteum actually works together with estrogen it helps prepare and maintain the endometrium so that inner layer of the uterus for implantation of a fertilized ovum it helps prepare the memory glands for milk secretion and high levels of progesterone also inhibit both gonadotrope and releasing hormone and luteinizing hormone relaxin is also secreted in small amounts during these Cycles by the corpus luteum as well as the placenta once an egg is fertilized during the normal non-pregnant monthly cycle it's believed that relaxin quietens or stops any minor contractions of the myometrium or that middle muscle layer of the uterus the thinking being that a quiet array still myometrium will help with the implantation of aovum during pregnancy when we have a lot more relaxant being produced and secreted by the placenta it will obviously help stop any contractions during the early stage of pregnancy it will increase the flexibility of the pubic symphysis and is also believed to help dilate the uterine cervix inhuman is released by the granulosa cells of the growing follicles and by the corpus luteum after ovulation it inhibits follicle stimulating hormone and to a lesser extent luteinizing hormone so a similar function to what it has in the male but getting back to our two specific Cycles so our ovarian and our uterine cycle and taking a look at the different phases within each cycle we're going to use this image and I appreciate that it looks like a lot and it is a lot but it also really nicely sums up visually the phases in each cycle how they relate to one another and then also the hormones that contribute to these changes so what I'm going to do is walk you through each of the Cycles using these images but as I did with the anatomy of the reproductive organs I will also put this into a text summary at the end so that you can just sit and listen and not have to worry about taking too many notes so the duration of both female reproductive Cycles typically ranges from 24 to 36 Days but for this discussion and if you take any textbooks they will assume a duration of 28 days so roughly a month now the first phase of a reproductive cycle is called the menstrual phase this is also called menstruation or Menzies and it lasts roughly for the first five days of a cycle so the first day of menstruation or the first day of bleeding is considered day one of our new cycle now during this time approximately 50 to 150 milliliters of blood tissue fluid mucus and epithelial cells are Shed from the endometrium and this discharge occurs because of declining levels of progesterone and estrogen so although we've got one long line here you have to think of this cycle as a bit of a circle so starts at zero goes up to 28 after 28 we go back to the start so at the end of our Cycles we have high levels of estrogen sorry progesterone and estrogen as these levels decline that's what actually stimulates menstruation and that cycle to begin again so those declining levels of progesterone and estrogen will stimulate the release of prostaglandins and that causes arterials in the endometrium and this image here is showing the endometrium to actually constrict as a result the cells that they Supply become oxygen deprived and they start to die eventually the entire stratum functionalis which is that very inner layer of the endometrium will Shed off and so that what we can see here during menstruation or that period of bleeding that endometrium will become thinner and thinner because that inner stratum functionality stratum functionalis layer will actually Shed off after menstruation so after those five or so days the endometrium is quite thin only about two to five millimeters because it's only that stratum basalus That Remains that menstrual flow passes from the uterine cavity through the cervix through the vagina and to the exterior of the body now at the same time we have follicle stimulating hormone being released by the anterior pituitary and we can see a slight increase in our follicle stimulating hormone here and this stimulates the development of our primordial follicles into our primary follicles and then our primary follicles into our secondary follicles this phase of the ovarian cycle is called our follicular phase so development of our follicles so once the follicles have developed into our secondary follicles they begin to secrete estrogen and also in heaven by about day six a single secondary follicle in one of the two ovaries has outgrown all of the others and it becomes our dominant follicle estrogen and inhibit secreted by this dominant dominant follicle then reduce the secretion of follicular stimulating hormone and we can see that slight decrease here which causes the other less well-developed follicles to actually stop growing and degenerate now normally the one dominant secondary follicle becomes the mature follicle and it continues to enlarge until it's about 20 millimeters in diameter and it's ready for ovulation so this follicle forms a bit of a a blister on the surface of the follicle oh sorry the surface of the ovary and it's due to this swelling of the Antrim during the very final maturation process that mature follicle increases its production of estrogen and within reference to the ovarian cycle this follicular phase lasts right up to ovulation so in the second half of the follicular phase the uterine cycle is undergoing the proliferative state so in our ovarian or in our ovaries our follicles are developing but down here in our uterus after we've shared that inner layer we need to build it back up again so during this phase estrogens are released into the blood by those growing follicles and it stimulates the repair of the endometrium so cells of the stratum basalis undergo mitosis and they produce a new stratum functionalis this phase is called the proliferative phase because that's the endometrium proliferating or multiplying getting bigger in size in the ovarian cycle we then have ovulation which is roughly day 14. here the mature follicle will rupture and expel that secondary urocyte into the pelvic cavity where it's swept into the uterine tube by those fimbriae or those little fingers on the end of the uterine tube a sharp increase in luteinizing hormone triggers ovulation and I'm sorry I'm not sure why it's not showing there but this is our luteinizing hormone and this is why when people take at-home ovulation tests they're testing for this hormone luteinizing hormone because that's what triggers the release of this secondary ubocyte now the final phase of the ovarian cycle is the luteal phase this is where after ovulation that mature follicle collapses and under the influence of luteinizing hormone becomes our corpus luteum so luteinizing hormone corpus luteum the corpuscle team as we've already talked about secretes progesterone estrogen relaxin and inhuman and then the later events that occur in the ovary depend on whether or not an oocyte has been fertilized so if the oocyte is not fertilized then this corpus luteum only has a lifespan of about two weeks then it's secretory activity will Decline and it degenerates into what we call the corpus albicans if the secondary oocyte is fertilized and it begins to divide this corpus luteum persists way past its normal two-week lifespan and it's rescued from degeneration by the hormone human chorionic gonadotropine so also called HCG this hormone is produced by the embryo and it begins about eight days after fertilization and it stimulates a secretory activity of the corpus luteum so the presence of HCG or human chorionic gonadotropin in blood or urine is the indicator of pregnancy and it's the hormone that's detected in an at-home pregnancy test now in the uterus the final stage of the uterine cycle is called the secretory phase so during this phase progesterone and estrogen levels are rising because it's being produced by the corpus luteum and it promotes the growth of the endometrial glands the blood vessels and the thickening of the endometrium and you can see that here this thickness is increasing we're sending all the blood and the nutrients to this layer just in case a fertilized egg is to implant these Preparatory changes Peak about one week after ovulation which is the time that a fertilized ovum might actually arrive in the uterus so remembering it does take a few days for that fertilized egg to travel down through the uterine tubes if fertilization does not occur then the levels of our progesterone and our estrogen will decline because our corpus luteum has disintegrated into our Corpus albicans it's no longer secreting those hormones the declining of these hormones remember is then what stimulates the first part of our cycle which is menstruation so recapping the ovarian cycle so what is happening in the ovaries Days 1 to 14 are the follicular phase and this is when our follicles are developing so follicle stimulating hormone stimulates the growth of our follicles we then have our mature follicle so creating estrogen this helps prepare the lining of the uterus for implantation at the middle point of that cycle is ovulation an increase or a spike in luteinizing hormone triggers ovulation and it causes that mature follicle to rupture and release a secondary oocyte into the pelvic cavity the second half of this phase from day 14 to 28 is called the luteal phase relating to the corpus luteum the Corpus lutein secretes progesterone alongside estrogen relaxin and in a human to a lesser extent the progesterone is what maintains and thickens up that endometrium just in case that fertilized egg or that fertilized ovum actually implants into the uterus so again looking at this image but now just looking at ovarian cycle so we have three phases or three events you know our ovarian cycle the follicular phase ovulation and the luteal phase so our follicular phase is when we have follicle stimulating hormone stimulating the development of our follicles we have a big spike in luteinizing hormone which triggers ovulation our mature follicle will rupture and expel that secondary herbicide into the pelvic cavity we then have our final luteal phase which is the development of the corpus luteum a corpus luteum secretes all of those hormones which acts on the endometrium of the uterus if that egg is fertilized then the corpus luteum remains functioning because of the hormone secreted by the embryo if that egg is unfertilized then the Corpus lutein will disintegrate into the corpus albicans and these Cycles Begin Again recapping the uterine or the menstrual cycle so remembering this is what happens within the uterus this is the the cycle that involves a period or the bleeding so days one to five and of course this can vary is menstruation suppose of those reduced levels of estrogen and progesterone we have shedding of that stratum functionalis that inner layer of the endometrium days 5 to 14 we have our proliferative phase so we have increased estrogen also a bit of increased progesterone it's building back up that stratum functionalis the second part is day 14 to 28 is our secretory phase so the increased levels of progesterone from the Corpus luteam will thicken and maintain the endometrium causes all the blood and nutrients to go to that layer just in case that fertilized egg implants so once more looking at that cycle but now just focusing on this middle bit here so if this is our endometrium the first phase of the cycle is our menstrual phase it's when we're bleeding and that stratum functionalis is being shed the second phase is the proliferative phase so we're building that layer back up we've got estrogen being secreted from our follicles which helps with this process we then have the last part which is our secretory phase so we've built this endometrium back up but now we're sending all the blood and the nutrients to this layer just in case that egg implants this will continue to stay nice and thick and nourished if the egg is fertilized and in plants if it doesn't then we have again those dropping layers of progesterone and estrogen which cause that menstruation process to happen again so ovarian cycle follicular phase ovulation luteal phase our uterine cycle is menstrual phase proliferative phase and secretory phase now following on from the ovarian and the uterine Cycles to talk about what happens if an ovulated secondary herocyte meets a sperm and is fertilized and then implants in the uterine wall so during fertilization the genetic material from a sperm containing 23 chromosomes and a secondary oocyte also containing 23 chromosomes merges into a single nucleus which contains our full set of 46 chromosomes of the 200 million sperm that are introduced into the vagina during intercourse fewer than 2 million or one percent will really will reach the cervix of the uterus and only about 200 will actually reach the secondary oocyte fertilization normally occurs in the uterine tube within 12 to 24 hours after ovulation but sperm can remain viable for about 48 hours after deposition into the female reproductive tract although a secondary oocyte is only viable for about 24 hours after ovulation so you really need to get the timing right to actually produce a baby so from the vagina sperm will swim into the cervix using whip-like movements of their tails or their flagella through the rest of the uterus and into the uterine tubes the passage of the sperm actually results mainly from contractions of the walls of these organs which are stimulated by prostaglandins in semen so as sperm move toward an oocyte secretions from the female reproductive tract actually prepare the sperm for fertilization and this first process is called capacitation so the secretions released by the female reproductive tract will improve the motility of sperm so how well they move it also removes cholesterol molecules embedded in the plasma membrane of the head of the sperm so it thins the membrane around the acrosome which remember is this this layer that kind of sits around the head of the sperm containing digestive enzymes which then helps the enzymes be released so the sperm can actually penetrate into the exterior layers of the oocyte once that contact is made so sperm must undergo this process of capacitation in order to have the capacity to fertilize an egg if they reach the oocyte before this capacitation process is complete they'll be unable to penetrate the oocytes thick outer layer of cells and therefore it can't fertilize that egg so as the fertilize over more the zygote moves along the uterine tube it then encounters these capacitated sperm so the sperm that have had the secretions from the female reproductive tract act upon it and the sperm moved towards the ovum in response to chemicals that are released by the cells of the corona radiator so it kind of calls the sperm towards the ovum remembering that a secondary oocyte is surrounded by two protective layers the corona radiata which is that layer of granulosa cells and then the underlining Zona pellucida which is that thick glycoprotein membrane that surrounds the actual secondary oocyte so to reach the oocyte and fertilize it with site the sperm must penetrate those two layers it must first burrow through the cells of the corona radiator and then upon contact with the Zona pellucida the sperm bind to receptors in this layer and this initiates a process called the acrosomal reaction the acrosomal reaction is just the release of those enzyme-filled acrosomes releases those stored digestive enzymes so it can burrow or eat away at some of these glycoprotein layers the enzymes will kind of clear a path through the Zona pelicitor that allow the sperm to reach the oocyte the sperm can then make contact with the receptors on the plasma membrane of the urocyte the plasma membrane of that sperm then fuses with the oocytes plasma membrane and the headpiece and the mid piece of that winning sperm actually enter the interior of the oocyte so we have chemicals being released by the corona radiator that attract all of the sperm the sperm then Burrows through that outer layer of those granulosa cells it then binds to the the Zona pellucida which causes the release of those enzymes also called the acrosomal reaction that sperm can then actually reach the membrane of the secondary oocyte the sperm binds to our receptor and then the nucleus of those two cells will merge now the process of fertilization doesn't actually end there when the first sperm fuses with the urocyte the oocyte deploys two mechanisms to prevent poly spermi which is the penetration by more than one sperm so this is important because if more than one sperm would actually fertilize the oocyte the resulting zygote would have 69 chromosomes which is not actually how twins are made but is actually incompatible with life so this process is actually really important so the first mechanism by which the oocyte acts to prevent polyspermy is called the fast block this involves a near instantaneous change in sodium ion permeability upon the first binding of sperm so this depolarizes the plasma membrane of the oocyte and it prevents the fusion of any additional sperm this fast block sets in almost immediately and it lasts for about a minute during which time we have an influx of calcium ions which triggers the second mechanism which is called the slow block so the slow block is also referred to as the cortical reaction in this reaction we have granules sitting just underneath the plasma membrane of the oocyte bind with the membrane and expel those granules that were contained within that vesicle these contain zonal inhibiting proteins and mucopolysaccharides they put these into the space between the plasma membrane and the Zona pellucida these cause the release of any other sperm that is still actually attached to the oocyte they also destroy the oocyte sperm respect receptors so no other sperm can continue to bind to the oocyte it also causes the zygote or that fertilized oocyte to form an impenetrable barrier together with the hardened zone of pellucida that we call the fertilization membrane the fertilization membrane is just like a really hard thick layer that prevents any sperm from actually continuing on into the oocyte so then after fertilization the zygote travels down the uterine tubes and remains free within the uterine cavity for about two days before it's attached to the uterine wall at this time the uterine cycle is in its secretory phase and the endometrium is nice and thick and highly vascularized about six days after fertilization the blastocyst which is now what we call that fertilized egg Loosely attaches to the endometrium this process is called implantation about seven days after fertilization it attaches to the endometrium more firmly the endometrial glands within this vicinity will enlarge the endometrium becomes even more vascularized the blastocyst secretes enzymes and it actually buries nice and deep into that endometrium to become completely surrounded by it so recapping that process for you because I get there's a lot of terms and processes for you learn for you to learn today so fertilization is the union of sperm containing 23 chromosomes and a secondary oocyte also contain containing 23 chromosomes sperm swim through the cervical Canal but then once inside the uterus move towards the urocyte largely due to contractions of the female reproductive tract as the sperm moves through the reproductive tract secretions act on the sperm to provide them the ability to actually fertilize the oocyte this process is called capacitation and it involves the removal of cholesterol from the sperm and the thinning of the plasma membrane covering the acrosome which is that that membrane that surrounds the head of the sperm that contains digestive enzymes sperm then move towards the Oracle urusite sorry on account of chemicals that are released by the corona radiata the sperm burrow into the granulosa cells and then once they reach the Zona pellucida they release the digestive enzymes from the acrosome which allows them to to reach the oocyte this process is called the aquasomal reaction and it's what allows a sperm to actually reach the membrane of the oocyte the sperm then binds to sperm receptors on the plasma membrane of the urocyte and the membranes of the two cells will fuse this causes the cortical reaction in which the uru site immediately depolarizes and we have an influx of calcium which causes the release of our zonal inhibiting proteins and our mucopolysaccharides these destroy the sperm receptors and Harden the Zona pellucida containing an implemental boundary called the fertilization membrane so a really tough thick boundary that sperm can't pass through and finally the last learning objective is to speak about the result of fertilization and implantation so in learning objective number four we will describe the physiological changes that are associated with pregnancy so Beginning by looking at the hormones that regulate pregnancy and during the first three to four months the corpus luteum and the ovaries will continue to secrete progesterone and estrogen which maintains the lining of the uterus and prepares the mammary glands to secrete milk the amount secreted by the corpus luteum however are only slightly more than what would be produced after ovulation in a normal menstrual cycle from about the third month so about 12 weeks the placenta itself provides the high levels of progesterone and estrogen which are required to maintain a pregnancy now as noted previously the embryo secretes human chorionic gonadotropin or HCG into the blood by about the eighth day after fertilization HCG can be detected in the blood and the urine of a pregnant woman Peak secretion of HCG occurs at about week nine and after about the fourth or the fifth month after fertilization that HCG starts to decline the function of HCG is to promote the secretion of estrogen and progesterone by the corpus luteum Beyond its normal two-week lifespan but when the placenta is fully formed the Corpus or team is no longer required and that's why we have that drop off of HCG now not shown on this image we also have relaxin which is also produced at first by the corpus luteum and then later by the placenta and remember that increases the flexibility of the pubic symphysis the joints in the pelvis as well as help dilate the cervix which can both Aid in the delivery of a baby so the hormones or the important hormones of pregnancy coming from the Corpus luteam are the estrogen and the progesterone which help maintain that lining of the uterus in the first three to four months these come primarily from the corporation the corpuscle team also secretes small amounts of relaxin the embryo after I think about seven or eight days will secrete HCG or human chorionic gonadotropin HCG promotes the endocrine function of the Corpus otam so it tells the corpuscle team to keep secreting the hormones after the first three to four months the placenta is now fully formed so we can stop secreting HCG to stop the corpuscle team producing these these hormones here the placenta then takes over so the placenta also secretes the estrogen and the progesterone from about month four till the end of the pregnancy towards the end of the pregnancy we also have a big increase in the secretion of relaxin which remember is the hormone that helps relax the joints and the cervix to help ease the aid of delivery of a baby looking next at the anatomical changes and near the end of the third month of pregnancy the uterus the uterus sorry occupies most of the pelvic having as the fetus continues to grow the uterus extends higher and higher up into the abdominal cavity so you can see the uterus is here and it's pushed all of these up organs up closer to the lungs towards the end of a full-term pregnancy the uterus feels nearly the entire abdominal cavity almost right up to the xiphoid process so that very bottom part of the sternum the fetus moves the maternal or the mother's intestines Livia and stomach superiorly it elevates the diaphragm which we talked about in the respiratory system and it can also widen the thoracic cavity in the pelvic cavity compression of the ureters and the urinary bladder can also occur which causes that that increase in the urgency to go to the bathroom physio physiologically pregnancy can also induce a number of changes so obviously there is weight gain owing to the increased weight of the fetus the amniotic fluid the placenta the enlargement of the uterus increase blood volume increase size of the breast thinking about cardiovascular changes we can have an increase in cardiac output by up to 20 to 30 percent an increase in blood volume by up to 50 percent and these changes arise due to the additional needs of the feeders for nutrition and energy with our urinary changes we can have an increase in our glomerular filtration rate by up to 40 percent and increase frequency and urgency of urination as well as stress incontinence so that's when blood when pressure is put on the bladder you're no longer able to to control those sphincters The increased glomerular filtration rate is what actually allows additional waste products by their fetus to be excreted quite quickly gastrointestinal changes can include an increase in appetite due to the additional nutritional needs of the fetus a decrease in the gastrointestinal tract motility which can cause things like constipation and a delaying of gastric emptying in turn this can produce things like nausea vomiting and heartburn respiratory function which we have talked about a little bit um is also changed of course to meet the added oxygen demands of a baby so tidal volume can actually increase by 30 to 40 percent as well as how frequently a person breathes so they'll take more breaths per minute however as we mentioned in our lab exam our total lung capacity is actually reduced due to the displacement of the diaphragm considering skin pregnant mothers can often have pigmentation on the face and of the stomach so a darkening of the skin stretch marks can also occur due to hormonal changes as well as the growing size of the fetus increase blood flow to the vagina and the vulva can also cause issues like swelling and discomfort and hormonal changes can lead to an increased risk of things like yeast infections and then after that glowing review of the wonderful changes that can occur with pregnancy that is US done for the reproductive system and for all of the lectures of this unit I know some of this content can be quite tricky so we will go over a lot of this content the ovarian and the uterine Cycles there's just one example in the labs but well done I'm getting through all of the content and good luck for your final exam