hello and welcome to the review of guyson and hall's medical physiology textbook this time we're going to go over chapter 82 covering female physiology if you've been following along these chapters and enjoy the videos please don't forget to subscribe as that's the main way that helps this channel grow so i'd really appreciate it if you do subscribe to the channel otherwise we can jump straight into the chapter starting off talking about female physiology and how we can divide the reproductive function of the female into two stages the first is preparation of the body for conception and pregnancy and then the second stage is actually the period of pregnancy so we'll be covering the first stage in this chapter so as everybody knows females provide the egg whilst the male provides the sperm to then create the child so the egg is actually first created in the embryonic development so you have this first developing egg called an oocyte that then differentiates into an ovum goes through mitotic replication and in the first stage of meiosis all within the first five months within fetal development so you actually create all of the eggs that are going to remain in the rest of the female body within the actual embryo once you have created all those eggs then which are called primordial ova they get surrounded by this ovarian stroma and that create this epithelial like cells that surround it called granulosa cells they just really help to develop the ovum through time so you're going to create this one to two million primary oocytes right within embryonic development and then following puberty you're going to complete the myotic division of all of those oocytes do you create two cells per egg but one of them is going to be the larger ovum and then the other one's going to be at what's called a polar body now that polar body just disintegrates so effectively you just end up with one ovum that may end up being fertilized and turned into a child following puberty that one to two million primary oocytes now have diminished down into three hundred thousand oocytes which will then be released around one at a time each monthly cycle which we also covered so this figure here just kind of goes through that development from our primordial germ cell into our primary oocyte it then goes through meiosis to create that first polar body which gets disintegrated in that secondary oocyte which then will eventually be fertilized by the sperm and then complete meiosis after fertilization to create your ovum or your zygote that's what gets turned into the child now you can see on the side here this is just showing you the development of the stromal layer or the germinal cell layer which creates a follicle that matures up which eventually releases the egg during ovulation and then those cell layers actually turn into the corpus luteum and this follicle and corpus luteum each produce some hormones which we'll cover and have their own function and then when it's all said and done only 400 to 500 primordial follicles actually develop enough to reach this end stage and actually be expelled and ovulated on a monthly basis so when it comes to our hormones it's very similar to the male we've got three hierarchies starting up in the hypothalamus that releases the releasing hormone which is g gnrh or gonodotropin releasing hormone that then stimulates the release of follicle stimulating hormone or fsh and luteinizing hormone or lh from the anterior pituitary gland which then affects the ovarian hormones and causes the release of estrogen and progesterone or two female sex hormones so we have that classic three tier system now gnrh does get released in short pulses approximately every 90 minutes and then we have more of a cycle with fsh and lh over our monthly basis and that corresponds to our estrogen and progesterone production as well we will dive a little bit deeper into each of these hormones as we go through this chapter so this rhythmic pattern is called the menstrual cycle and it lasts about 28 days and one single ovum on average now obviously these exceptions is going to get released each month and that's going to occur at this timing right here right in the middle of the cycle timing ovulation and as you can see we have that spike in lh which is what stimulates ovulation and causes that follicle to burst open and release the ovum into the fallopian tube you can see that we have a sudden reduction in estrogen at that time and then a steady increase in progesterone over that time due to the formation of the corpus luteum so starting off we're going to talk about fsh and lh fsh and lh really just activate the ovaries and make them active so as you could imagine in the absence of these hormones during childhood your ovaries are remaining inactive so once you hit puberty and you start to release some of these hormones the ovaries become active and you become sexually mature the easiest way to think about these two is that fsh follicle stimulating hormone is the one that's going to stimulate the follicle to develop so we turn this primordial follicle into a nice pre-ovulatory mature follicle so fsh has its main role at the beginning of the cycle to help prepare an ovary for ovulation by developing the follicle so fsh mainly does that now lh does have a small role there too but it's easier just to think that's what fsh's role is then luteinizing hormone comes in as a big spike just before ovulation to then cause the oocyte to get released from that mature follicle now we do also have fsh spiking here too so that also plays a role i think luteinizing hormone means to release the ovum whereas fsh stimulates the development of the follicle this developing follicle and all these granulosa cells actually start to produce more estrogen and estrogen has a role in positive feedback by increasing the numbers of fsh and lh receptors on that maturing follicle so then it's able to respond to both of those molecules when need be so it's a self-perpetuating cycle now each month only one follicle is actually going to reach maturity you're going to have about five to 11 competing to grow into that primary follicle but only one will remain and the rest will actually become atretic so you have this attrition of follicles that start to be developed but then do not win the race and then they actually become attractive within the ovary so then they lose the ability to ovulate that mature follicule then is going to respond to that lh surge which occurs about two days before ovulation and then that is going to tell the follicule to now burst open and release the ovum into the fallopian tube as we've mentioned and then also turn those granulosa cells into progesterone secreting cells so turning this follicular that's matured into a corpus luteum now luteinizing literally means to turn yellow and that's what the corpus luteum is it gets turned to this yellow structure that's going to produce progesterone now estrogen reduces around this time of ovulation because those granulosa cells which are releasing estrogen are getting turned into progesterone so estrogen is dropping the follicles rapidly growing and progesterone starting to get secreted all stimulated by the luteinizing hormone that then causes the release of the ovum and ovulation ovulation is able to occur because of two main events one proteolytic enzymes are going to get released so dissolving that follicle wall and then there's going to be a growth of new blood vessels within the follicular wall so then you get exudates into the wall it's becoming thinner and then eventually it just bursts open from all of the pressure we then get the creation of the corpus luteum which lasts about 12 days until it starts to atrophy and turn into something called the corpus albicans so you get the creation of this corpus luteum it's going to be producing a whole bunch of progesterone in addition to some estrogen but mainly progesterone and then eventually after 12 days it starts to actually reduce down and atrophy now it may actually stay if the ovum gets fertilized and then the placenta starts to grow because the placenta is going to produce chorionic gonodotropin which is going to actually keep that corpus luteum in place and prolong its life for another two to four months because you need that progesterone to maintain pregnancy which we'll cover in the next chapter so without pregnancy the corpus luteum just fades away after 12 days and that ends the 28 day cycle you get the first two weeks is going to be fsh creating those follicles at the end of the two weeks you get lh causing ovulation then you get the production of the corpus luteum and progesterone that's going to be increased in production for the next two weeks and then once the corpus luteum is gone you lose that progesterone effects and then you restart the cycle and then you've got estrogen working throughout to help to promote proliferation and growth of very specific cells mainly all your sexual cells and that's what creates the sexual characteristics of a female both internally and externally now there are several types of estrogens and different types of progesterones really the main type of estrogen is going to be beta estrodiol main progestin is going to be progesterone remember these are steroid molecules so they're made out of cholesterol they work within the actual cell itself receptors within the cell because it's able to cross the cell membrane because they are lipid soluble and they have to be bound by plasma proteins when transported around the body they then get degraded by the liver which then is going to spit it out either through the bile or through the urine so you can actually get an increased level of estrogen within the body if your liver function has been reduced and they end up with a situation like hyperestronicism so you result in increased characteristics promoted by estrogen which once again is proliferation of growth of your female sexual organs now it's important to note that estrogen increases the proliferation and growth of the sexual organs but it doesn't actually make them functional for instance the breast they're going to become functional due to progesterone actually creating all of the functional tissues within the breasts and then prolactin is actually going to be the hormone that results in milk let down so you have other organs as well having an influence on the sexual organs estrogen is that base layer hormone that gives and grows those female characteristics now estrogen does inhibit osteoclastic activity meaning that your bones are not being broken down by those osteoclasts so estrogen helps to stimulate bone growth so at puberty that's going to cause rapid growth during high estrogen levels but it also has a potent effect on the epiphysis of the shafts of the long bones so it's rapid growth but rapidly closing growth plates at the same time so you get rapid growth just a certain point but that's going to cease a lot earlier than the male now in the lack of estrogen so after the reproductive years of a female during menopause then you start to lose that protective effect against bone remodeling that estrogen provides so you start to break down the bones a lot easier when you lose those estrogens and then you can result in osteoporosis which just means thin and brittle bones estrogen also has a role to increase our total body protein and increase body metabolism but at the same time increasing fat depositions although metabolism is increased there's actually a stronger influence in helping fat be deposited within the body it has little effect on hair distribution and actually helps to develop the texture of the skin that is soft and smooth but it is thicker than that of a child incarcerated female so those are effects of estrogen progesterone on the other hand helps to increase the functional components of your sexual organs that helps to develop the secretory functions of the uterus and also the breasts as well now there is also maturation of the endometrium every month as well which is going to provide that fertile ground for a fertilized ovum to develop and that gets replenished every month and is what ultimately leads to a period every month so the first phase is going to be the proliferative phase and this is under the influence of estrogen once again just helping to promote the growth of those sexual organs we are involved in the proliferation of the endometrium then in the second half the secretary phase so this is after our ovulation we have both progesterone and estrogen available here so that causes much swelling and secretory development of the endometrium so then that's when the endometrial layer becomes the thickest and it's the most fertile and then as soon as the corpus luteum starts to fade away and disappears we lose our estrogen and our progesterones so then now those growth promoting hormones are gone so we end up with vasospasm of all the blood vessels and essentially necrosis of this entire area so then we end up with the menstrual phase where we lose all of our endometrial lining to then restart the phase after so this occurs roughly every 28 days and there's time so then ovulation is going to occur at the same time that we have this nice healthy bit of tissue and provide nutrients for that fertilized egg so the next part is going to talk about the positive and negative feedback mechanisms of these three main hormonal layers because remember gnrh is being released every 90 minutes roughly so you would think that that's going to cause the release of lh and fsh every 90 minutes now the difference is that yes fsh is going to be released initially to cause follicular growth but as estrogens start to be produced more by those follicles estrogen actually has a negative effect on the release of lh and fsh so this is an inhibitory effect of estrogen which is going to gradually increase as that follicle becomes more and more mature suppressing lh and fsh release eventually it gets to a point where we obviously have that lh spike to cause ovulation now it's a little bit unknown exactly why the lh spike occurs despite the presence of estrogen but there's two kind of thoughts estrogen seems to flip here and cause positive feedback on lh release but also we're getting a reduction in estrogen as those granulosa cells are starting to produce more progesterone instead regardless we get an lh spike we get ovulation and then we get the reproduction of progesterone and estrogen from the corpus luteum now progesterone also has a negative feedback loop on the anterior pituitary gland to prevent the production of lh and fsh so we don't have lh and fsh being released in that second half of the cycle while the corpus luteum is there then the corpus luteum has that designated time at 12 days where it's going to start to fade away and die off and then the progesterone and estrogen levels are going to reduce again that allows both fsh and lh to increase because we have that 90 minute pulsatile nature of g and rh release so that fsh and latch increase if sh causes follicles to start to grow again those follicles release estrogen negative feedback on lhfsh and the cycle continuous so that's how we get the cycle of hormones that's just causing follicular development ovulation once a month corpus luteum production which fades away and then fsh lh start to increase once again now that's going to happen during the reproductive years of a female now we obviously have times during childhood when you do not have the release of lh or fsh and you're also going to have a time point where females stop the cycle and that's usually after around 40 to 50 years of age and that's called menopause so you've run out of eggs or follicles to start to produce estrogen and slow down fsh and lh release and turn into a corpus luteum etc so it's literally just a loss of available follicles within the ovaries that result in menopause as a consequence you get very high fsh and lh because they are being uninhibited from release and you also get very low estrogens low estrogens in the body results in some physiological changes like hot flushes psychic sensations of dyspnea irritability fatigue anxiety decreased strength of the bones and these are all classic symptoms of menopause now interestingly if you just give estrogens after menopause then you actually increase the risk of cardiovascular disease but that risk is actually reduced if you start estrogen therapy just in early menopause so just as you start to go into menopause if you start estrogen at least according to this book you're going to reduce your risk of cardiovascular disease but also reduce your chances of some of these physiological changes from menopause now that thought process is the same if the ovaries never develop appropriately during embryology or if you have a lack of ovaries or genetically abnormal ovaries you can never produce those estrogens then you're going to have hypogonadism and a reduction in estrogen and reduction in the production of those female sexual characteristics that can also occur in the face of other endocrine diseases so in the case of hypothyroidism you may end up having some periods of having abnormal menstruation now in terms of the female sexual act and there are obviously both psychic and also local sexual stimulation factors they come into play but the main physiological cycle factor is that there is going to be high levels of estrogen around the time of ovulation and that's when there is going to be the greatest sexual stimulation so that's timing around the time when the ovum can be fertilized as with the male the sexual organs are mainly controlled by the parasympathetic nervous system that pass through from the sacral plexus and that's going to result in stimulation of the sexual organs and then also the secretion of mucus as well the female climax actually helps to promote fertilization by helping to increase uterine and fallopian tube motility which will help fertility but also in order to be the most fertile in the ova must be fertilized and within 24 hours of being expelled or else it just fades away sperm can last around five days within the reproductive tract so really intercourse needs to occur between four to five days before ovulation in a few hours afterwards that means that there is this rhythm method of contraception which is difficult to exactly predict because ovulation is not the same for everybody and everyone's not all on a 28 perfect day cycle so it's very hard to know exactly when ovulation is going to occur subsequently unintentional pregnancy can be as high as 20 to 25 other forms of contraception include the pill which is by administering really both estrogen and progesterone during the first half of the cycle which will inhibit ovulation from occurring and stop that surge of lh which stimulates the ovulation now some theta hormones are mainly used for the pill because natural hormones are going to be degraded by the liver on first pass metabolism and this form of contraception results in unintentional pregnancy about eight to nine percent per year there are also unfortunate cases where women are infertile and about five to ten percent of women and the most common reason for sterility is the failure of ovulation due to hyposecretion of eukanodotropic or hormones so you never end up with that lh surge and ovulation there is also another condition called endometriosis which is when the endometrial tissue is just very abnormal starts to grow and can menstruate into the actual pelvic cavity itself and that just causes massive fibrosis within the abdominal cavity and can unfortunately block the fallopian tubes and block the entrance of the ovum down into the uterus so that is the end of the chapter for today if you enjoyed the video please feel free to give it a like don't forget to subscribe to the channel as it does help us out greatly feel free to drop a comment otherwise we'll see in the next one