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Lecture 34

PHYSIOL 201 Lecture 34: Lecture 34

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Elizabeth Rust

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Lecture 34: Female Reproductive Tract Slide 2 17.13a.jpg The female has 3 different tubes -The urethra is the tube that is used by urine and semen but not at the same time -The urethra and the bladder are separate from the vagina and the uterus Slide 3 The ovaries developed from the primitive gonad Within the ovaries are what we call follicles that will develop at different times and go through different stages at different time from infancy to menopause -Follicles produce the hormones so they respond to LH and FSH that will produce estrogen for an example -They also have the oocyte that will be developing -Females have two ovaries The fallopian tube will transport an oocyte from the ovaries if it is released to the uterus -They are not physically connected -As the hormones are changing and getting closer to the ovulation time, the fallopian tube sits right over the top of the ovaries -The fimbriae which are finger like structures can move. They sweep fluid up through the fallopian tube and will increase this activity during ovulation -The oocyte is only viable for 24-48 hours -Takes 4-5 days to reach the uterus -So fertilization will have to occur in the fallopian tube The uterus is a very muscular organ -There is an endometrial lining that is not muscle cells -These are the cells that will change during every cycle and be ready for implantation The cervix is almost like a sphincter -Can be closed or open during penetration -Ejaculation will occur near the cervix Slide 4 One thing that is different in males and females is the process of generating the germ cells In males, once puberty occurs, it’s continuous In females, it is cyclical -Essentially after puberty, after each cycle only one ovum will be ovulated -Stages have breakpoints so it doesn’t go all the way to be an ovum The first part is called fetal life: -This is when the fetus is developing -In the ovaries, there are the oogonia which are similar to the spermatogonia in males -They undergo mitosis and begin to differentiate leading to multiplication of the oogonia -At about 7 months, all the oogonia replicate their DNA making all of them primary oocyte -None is left behind that can replace and make more primary oocyte after this point -But they don’t finish the first meiotic division -So we have all of these primary oocyte that are available at birth that have 2nx2 chromosomes so they have 46 chromosomes per cell and 2 chromatids per chromosome since they have not gone through the division yet -The primary oocyte is what is in the ovary -What’s ovulated is a secondary oocyte -They are stored in follicles that have cells around them that nourish the oocytes -But the oocyte will not do the first meiotic division until after puberty and the follicle is ready to go called the dominate follicle when the LH surge happens -So each cycle after puberty, a whole bunch of follicles will start to develop further but only one will make it to the dominant follicle and make it through the first meiotic division After the first meiotic division: -With sperm, after the first meiotic division, you get two daughter cells -After the first meiotic division occurs with the primary oocyte happens, you get a secondary oocyte -The nucleolus divides and the genetic material goes half and half to each cell and homologous chromosomes separate -But only one cell is a viable cell and this becomes the secondary oocyte -It gets all the cytoplasm while the other one is just the nucleolus without cytoplasm called the first polar body Then it will stop again -This is called meiotic arrest -Will not start again until the right hormones are around (referring to the first meiotic arrest that happens before creation of the primary oocyte) -The secondary oocyte will undergo the meiotic division and thus leave the 2 nd meiotic arrest only if fertilization occurs -Once the secondary oocyte is ovulated, if a sperm fertilizes it, it will underogo the second meiotic division and get only 1 viable cell and second polar body So the ovum exists only a brief period of time until the sperm and the ovum fuse to form the zygote The 2-4 million primary oocytes will degrade from infancy through childhood -Then at puberty, there’s a certain number left -Between puberty and menopause, there’s about 400 secondary oocytes being ovulated -Somebody who never has fertilization occur never produces an ovum Slide 5 LH surge causes the first meiosis division Fertilization causes the second meiosis division Slide 6 The oocytes that are present at birth are housed in follicles meaning they are surrounded by certain cells -The follicle is an oocyte that is surrounded by granulosa cells -As they mature, they began to be surrounded by these granulosa cells and theca cells The initial primary follicle is tiny and the oocyte is smaller -The growing of the oocyte to its full size doesn’t change the size of the nucleolus (it’s really just a volume change in the cytoplasm which increases the size of the oocyte) The white area is called the zona pelicuida and that’s a membrane that surrounds and protects the oocytes -There’s communication from the granulosa cells that are lining outside the zona peliucida -They can also secrete substances to nourish the oocyte Cells divide and differentiate overtime to generate a second layer of cells called theca cells Then a little more maturation can occur and you start to get a fluid filled cavity called antrum inside the follicle -This is called an early antral follicle -Has the primary oocyte, granulosa cells, couple layers of theca cells and the fluid filled cavity This process from the primodial follicle to the ealry antral follicle can happen at any time (for example, can happen right after birth or around age 5, etc) -If they don’t get exposed to LH and FSH in the early antral follicle state, at that point they will degrade -Lot of oocytes are lost before puberty -This stage does not require the input of any hormones Early antral follicle to mature follicle: -The granulosa cells are expressing FSH receptors and the theca cells are expressing LH receptors -At this point, in order to continue to develop, the cells need to have FSH and LH binding to those receptors and stimulating those cells -Will degrade if FSH and LH is not available (for example, with the five year old girl who has this early antral follicle will be degraded) -The process of degrading the early antral follicle is called is called atresia After puberty, there is cyclical changes in FSH and LH -So with each cycle, there will be somewhere between 10-20 follicles that are at the early antra follicle state -Those will then continue the process of developing into the mature follicle -However, only one of them will be able to make it to the continue the rest of the cycle into the secondary oocyte and the others will undergo atresia The mature follicle is also called the dominant follicle -Has the oocyte sticking out into the antrum -During ovulation, the oocyte and the layer of granulosa cells around it will be released from the ovaries Slide 7 Simple look at the cycle The first day of the cycle is when menstrual bleeding happens -This is the day the lining of the uterus is coming off and is based on hormonal changes -At this point, FSH and LH levels are beginning to rise -At this point, multiple follicles that are in the early or primordial state will continue to develop -Around 7 days into the cycle, one follicle will become the dominant follicle which is the follicle that is thought to be the most sensitive to FSH and LH -That one can keep going. The other ones that are less sensitive cannot and will undergo atresia -The dominant follicle will continue to get bigger and make more and more estrogen -That leads to ovulation Around day 14, ovulation occurs -After ovulation, the oocyte has been released into the fallopian tube -The follicular cells that are still in the ovaries become a different structure called the corpus luteum and make different hormones (make estrogen and progesterone) -This maintains the luteal phase -In this phase, if the oocyte is fertilized it can implant -If it doesn’t get fertilized, then the corpus luteum will degenerate -Progesterone and estrogen levels will go down and this will cause an increase in LH and FSH which will start the cycle all over again Slide 8 What are the hormones the ovaries are producing? The hypothalamus are releasing GnRH using pulsatile secretion -GnRH stimulates the release of LH and FSH -LH acts on the theca cells in the beginning -FSH acts on the granulosa cells all the time The theca cells actually synthesize androgens -The androgens, primary testosterone, diffuse to the granulose cells (which are the inner layer while the theca cells make up the outside layer) -The granulosa cells has an enzyme called aromatase which will convert the androgens into the estrogens So the granulose cells only have FSH receptors in the beginning -Then they start to express LH receptors -It’s thought that the one that has the most LH receptors will become the dominant follicle -The theca cells only have LH receptors Slide 10 In general, the upper diagram is a daily average -The anterior pituitary releases LH and FSH in response to GnRH -The ovarlian hormones estrongen and progesterone are showed on the bottom graph -This graph doesn’t show inhibn which is another important hormone produced by the granolusa cells and is important for inhibiting FSH levels Slide 11 We will start with the early follicular phase and think about what’s changing and what’s going on Shown on the previous slide, the ending of the cycle leads to the rise in FSH and LH and decrease in estrogen and progesterone and this is the key to starting the next cycle We will start at looking at the early and mid-follicular phase which is about 7 days into
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