Lecture 37 - Female Reproductive system II Flashcards
Name the layers of the uterine wall from outermost to innermost. Which layer is shed during menstruation?
Perimetrium, myometrium, endometrium
The endometrium is shed during menstruation
Which artery is associated with the female reproductive tract branches directly off the abdominal aorta? Which ligament does this artery run through?
Ovarian artery and it runs through the suspensory ligament
Name the fingerlike projections on the infundibulum. What is their purpose?
Fimbriae and they help to guide the oocyte to the opening of the uterine tube
Oogenesis
Formation and development of the oocyte (female gamete) from oogonia (stem cells)
Requires mitosis and meiosis
Lifetime supply of gametes produced before birth
Initiated before birth. Continues between puberty and menopause - cyclic with 1 ovulation approximately every 28 days (whereas in males, spermatogenesis is largely continuous)
Oocytes develop within ovarian follicles (1 oocyte per follicle) - as the oocyte develops the follicle surrounding it also develops
Oogonia vs oocyte
During oogenesis, the oogonia become primary oocytes (the oogonia are the stem cells and the oocyte is the daughter cell of it)
Follicles in oogenesis
Primordial ovarian follicles then primary ovarian follicle and then secondary ovarian follicle then tertiary follicle then a secondary oocyte is released by the rupturing of the follicle. Hopefully the oocyte is collected up by the fimbriae into the uterine tube. The follicle develops into a structure known a the corpus luteum following the release of a secondary oocyte from the follicle during ovulation. This is an important structure in terms of hormone production.
Mitosis of oogonium
Asymmetric division is a process of mitosis in which one oogonium divides unequally to produce one daughter cell that will eventually become an oocyte through the process of oogenesis, and one daughter cell that is an identical oogonium to the parent cell.
Before birth oogenesis
Oogonium is diploid (2n=46) in the gonad which is the ovary for females
Population of oogonia increase by mitosis (this stops before birth)
Oogonia differentiate to form primary oocytes (diploid, 2n=46)
Encased in a primordial follicle
Many primary oocytes undergo atresia
Primary oocytes start meiosis
Meiosis halts at prophase I
Halts until puberty begins
Atresia
Degeneration
In the event that the oocyte is not fertilised
From menarche till menopause oogenesis
At puberty females have approximately 300,000 oocytes - encased in the follicular cells ready to get started with the menstrual cycle
Under GnRH influence, small number of follicles recruited each ovarian/menstrual cycle
With the increasing production and secretion of GnRH that’s when we get the ovarian cycles kicking in which is where you get a small number of follicles that start developing and growing but usually only one of the growing oocytes goes on to ovulate and that oocyte is encased in what is known as the dominant follicle
Only one oocyte will complete development and ovulate (within the dominant follicle)
Primary oocyte completes meiosis I. Forms a secondary oocyte and 1st Polar body and both of these are haploid (n=23)
Although genetic division is equal, the cell division in terms of the cytoplasm, organelles etc is uneven which means that you end up with one oocyte and one cell that is known as a polar body, we don’t think their is a particular function to these polar bodies and in some instances they go on to complete meiosis 2 but ultimately these cells are going to undergo atresia and degenerate
Secondary oocyte starts meiosis II.
Halts at metaphase II
Suspended until fertilisation
Meiosis II resumes when the sperm penetrates the plasma membrane of the ovum at fertilisation
If not fertilised, will degenerate (called atresia) and therefore never complete meiosis.
Oocytes develop within _____
Follicles (one oocyte per follicle)
One primary oocyte ultimately forms ______ ova….
One
Three polar bodies also form - these undergo atresia (degeneration)
Primary vs secondary oocyte
Primary oocyte is a diploid cell formed in foetal ovary when the gamete mother cell, oogonia is arrested at prophase-I of meiosis. Secondary oocyte is the haploid cell formed from primary oocyte that starts meiosis II and halts at metaphase II until fertilisation.
Oogenesis occurs within _____
Developing follicle
Follicles are multilayered and multicellular - granulose cells and theca cells
Granulosa cells produce estradiol
Ovulation - oocyte and corona radiate released into the peritoneal cavity - when ovulation occurs the wall of the follicle ruptures and the oocyte with the corona radiata and the fluid known as the antrum are released out into the pelvic cavity and hopefully collected up by the fimbriae and into the uterine tube
Granulosa cells
Produce estradiol
Theca cells
Theca cells are a group of endocrine cells in the ovary made up of connective tissue surrounding the follicle.
Ovulation …
Ovulation - oocyte and corona radiate released into the peritoneal cavity - when ovulation occurs the wall of the follicle ruptures and the oocyte with the corona radiata and the fluid known as the antrum are released out into the pelvic cavity and hopefully collected up by the fimbriae and into the uterine tube
Which structure does oogenesis occur in?
Ovary and it is the process of oocyte formation from oogonia
The number of oogonia increases in the ovary by __________ before birth
Mitosis
Primary oocytes start meiosis prior to birth but….
The process halts at prophase I until puberty begins
After puberty, small groups of follicles start to …..
Grow each ovarian cycle - only one of these follicles goes on to ovulate (the dominant follicle)
Dominant follicle
The follicle that goes on to ovulate
The oocyte within the dominant follicle begins meiosis II but …
But the process halts at metaphase II until fertilisation occurs
Oocyte growth and development occurs within …
Ovarian follicles
Female reproductive hormones
Gonadotrophin Releasing hormone (GnRH) Follicle stimulating hormone (FSH) Lutenising hormone (LH) Estradiol Inhibin Progesterone
Female reproductive hormones - Hypothalamus
GnRH
Female reproductive hormones - anterior pituitary
FSH
LH
Female reproductive hormones - Ovary (follicles)
Estradiol
Inhibin
Female reproductive hormones - Ovary (corpus luteum )
Inhibin
Progesterone
GnRH function
Hypothalamus
Stimulates the release of FSH and LH from the anterior pituitary gland
FSH function
Anterior pituitary
Stimulates the growth of ovarian follicles
LH function
Anterior pituitary
Surge of LH involved in ovulation, formation of corpus luteum
Estradiol function
Developing follicles in the ovary
Assists follicle growth (with FSH); bone and muscle growth; endometrial growth, secondary sex characteristics, feedback to anterior pituitary, changes with reproductive tract particularly with the uterus
Inhibin function
Granulosa cells
Negative feedback to the anterior pituitary to suppress FSH
Progesterone function
Corpus luteum in the ovary
Negatively feedback to suppress GnRH (therefore LH and FSH); endometrial maturation (preparing the endometrium for the possibility of implantation); maintains pregnant state
Definition of the ovarian/menstrual cycle
The regular cyclic changes in the ovary and uterus that prepare an oocyte/ova for fertilisation and the endometrium for embryo implantation
Menarche
First menstrual period
Occurs at age of 12-13 years old on average
Part of puberty - orchestrated by increase in sex steroid production (estrogens ) by the gonads
Menopause
Cessation (stopping) of menstruation
Typically occurs in early 50s
Reduction of estradiol and progesterone due to absence of or lack of response by follicles (no hormones means no changes in the endometrium which means no menstrual cycle)
Anterior pituitary feedback no longer active therefore FSH/LH high
Menstrual cycles occurs on an approximately _______ basis
Monthly basis (average 28 days)
Two phases of the female reproductive cycle
Follicular (preovulatory phase) - Day 1 -14
Luteal (postovulatory phase) - Day 15-28
Follicular phase
Also called the preovulatory phase
Day 1-14
Increased FSH from the anterior pituitary - stimulates follicular growth
This surge stimulates ovulation - LH surge means that meiosis is completed and meiosis 2 is initiating and halting at metaphase II and then the oocyte is going to be ovulated out through the ovarian wall
Growing follicles secrete estradiol and inhibin.
Reduces FSH from anterior pituitary (negative feedback)
Growing follicles undergo atresia, except dominant follicle
Dominant follicle secretes large amounts of estradiol
Luteal phase
Also called the postovulatory phase
Day 15-28
Ovulated follicle collapses and forms the corpus luteum.
Secretes progesterone, estradiol, and inhibin
Produces hormones that together provide negative feedback to the hypothalamus and the anterior pituitary which keeps the gonadotropin levels really low too they keep other things in the ovary very quiet
These decrease FSH and LH secretion
Negative feedback on the hypothalamus
If fertilisation and implantation does not occur, the corpus luteum involutes/begins to breakdown in a process called luteolysis
Fall in progesterone and estradiol
Removes negative feedback on FSH and LH …..cycle starts again …..
Feedback and the hormones in the female reproductive cycle
Follicular phase
Ovary produces estradiol which provides negative feedback to the anterior pituitary and to the hypothalamus
Midcycle l(leading up to ovulation) Ovary produces estradiol which provides positive feedback to the anterior pituitary and to the hypothalamus Dominant follicle is producing lots of estradiol in this phase which sends a positive feedback message up to the hypothalamus and the pituitary and so you get the LH surge which is responsible for ovulation
Luteal phase (formation of the corpus luteum) Ovary produces progesterone which sends negative feedback up to the anterior pituitary and to the hypothalamus Negative feedback system that keeps FSH and LH levels low until the whole process can start again
Menstrual (endometrial) cycle
Menstrual and proliferative = Day 1-14
Secretory (and premenstrual) phase = Day 15-28
Menstrual phase and proliferative phase
Days 1-14
Endometrium breaks down and bleeds during menstruation
Estradiol stimulates endometrial growth from approx days 6-14
Rapid tissue growth, including growth of glands and vasculature
Levels of progesterone decreasing because the corpus Leuteum is breaking down then you will get the reduction of progesterone and without its support it means that the endometrial tissue specifically the functional layer will begin to breakdown and bleed which is the menstrual phase which you can tell is occurIng through blood loss down through the cervix and out through the vagina
After the menstrual phase the tissue begins to repairs and starts to grow in response to the estrogen specifically estradiol level being produced by the ovary and this is a rapid growth that happens in about day 6-14 and this is rapid tissue growth and we are talking about 4-7mm of growth happening each menstrual cycle
Menstrual phase - The uterine cycle begins with the menstrual phase. This phase is marked by the degeneration and shedding of the endometrial functional layer leading to menstruation, also called menses. This degeneration is caused by constriction of the spiral arteries which reduces endometrial blood flow. Eventually, the weakened arterial walls rupture, and blood pours into the connective tissues of the functional layer. Blood cells and degenerating tissues then break away and enter the uterine cavity, to be lost by passage through the external os and into the vagina. Menstuation generally lasts from 1-7 days.
Proliferative phase - The basal layer and the deepest uterine glands survive menstruation intact. The epithelial cells of the uterine glands then multiply and spread across the endometrial surface, restoring the uterine epithelium. During this reorganisation, the endometrium is in the proliferative phase. Estrogens secreted by the developing ovarian follicles stimulate and sustain the proliferative phase. By the time ovulation occurs, the functional layer is several millimetres thick, and prominent mucus glands extend to the border with the basal layer. At this time, the uterine glands are manufacturing a glycogen- rich mucus that can be metabolised by an early embryo
Secretory phase
Days 15-28 After ovulation (day 14) - corpus luteum secretes progesterone
Progesterone promotes endometrial maturation
Glands become secretory
Spiral arterioles grow and coil
Secretory phase - During the secretory phase, the uterine glands enlarge, accelerating their rate of secretion, and the arteries that supply the uterine wall elongate and spiral through the tissues of the functional layer. This activity occurs under combined stimulatory effects of progesterone and oestrogens from the corpus luteum . The secretory phase begins at the time of ovulation and lasts as long as the corpus lute stops producing stimulatory hormones, a new uterine cycle beings with the onset of menstruation and the disintegration of the functional layer
Secretory phase and back to …
If fertilisation and implantation does not occur:
Corpus luteum atrophies
Progesterone levels fall
Spiral arteries contact
Endometrial tissue breaks down and bleeding occurs
Shed tissue and blood removed via cervix and vagina (menstruation/menses)
A cohort of follicles begin to grow in response to signals from ….
The hypothalamus and pituitary - all but one of these follicles will undergo atresia
Secretion of large amounts of _______ by the ______ follicle will cause …….
Estradiol
Dominant follicle
Will cause the LH surge and subsequently ovulation and formation of the corpus luteum
The endometrium undergoes cyclic periods of growth, maturation and breakdown in response to cyclic patterns of what….?
Estradiol and progesterone
Hormones of the ovarian cycle
Release of Gonadotropin-releasing hormone - the ovarian cycle beings with the release of GnRH, which stimulates the production and secretion of FSH and the production - but not the secretion - of LH.
Follicular phase of the ovarian cycle
The follicular phase begins when FSH stimulates growth and development of a group of tertiary ovarian follicles. Usually only one follicle becomes dominant
As tertiary ovarian follicles develop, FSH levels decrease due to the negative feedback effects of inhibin
Developing ovarian follicles also secrete estrogens especially estradiol, the dominant hormone prior to ovulation
In low concentrations, oestrogen’s inhibit LH secretion. This inhibition gradually decreases as estrogen levels increase
Luteal phase of the ovarian cycle
The combination of increased GnRH pulse frequency and increased estrogen levels stimulates LH secretion
On or around day 14, a massive surge of LH tigers (1) the completion of meiosis I by the primary oocyte, (2) the forceful rupture of the follicular wall, (3) ovulation roughly 9 hours after the LH peaks, and (4) formation of the corpus luteum . The luteal phase begins at ovulation
The corpus lute secretes progesterone, which stimulates and sustains endometrial development
After ovulation, progesterone levels increase and estrogen levels decrease. This suppresses GnRH secretion. If pregnancy does not occurs, the corpus luteum will degenerate after 12 days. As progesterone levels decrease, GnRH secretion increases and a new cycle begins
Follicle maturation (tutorial) Ovulation
Follicle isn’t really responding to any FSH until secondary - starts responding to FSH and LH and start
Developed enough to respond to the levels of LH and FSH - theca produce estrogens and granules produces inhibin. Estrogens negatively feedsvack on GnRH and LH, inhibin negatively feedback on FSH
Estrogen changes to positive from negative to promote a rise in LH and then FSH which is going to cause a surge that causes ovulation
FSH is inhibited the whole time by inhibin but the FSH has some positive therefore has higher levels usually
Corpus lute doesn’t secrete oestrogen anymore and secretes progesterone instead, progesterone is going to negatively feedback. LH is needed for the corpus luteum to stay together. Goes to corpus albicans, doesn’t secrete progesterone therefore menstruation as progesterone keeps the endometrium in tact
LH surge causes ovulation, goes to corpus lute which secretes progesterone which cause LH drop, corpus albicans forms therefore no progesterone therefore menstrution yay
