Lecture 37: Female reproductive system 2 Flashcards
what is oogenesis?
formation and development of the oocyte from oogonia
what does oogenesis require?
mitosis and meiosis
what happens to gametes before birth?
lifetime supply of gametes produced before birth
when does oogenesis happen?
- initiate before birth
- continues between puberty and menopause
- it is cyclic so there is 1 ovulation every 28 days (average)
where do oocytes develop?
oocytes develop within ovarian follicles
- 1 oocyte per follicle
what part of oogenesis occurs before birth?
- oogonium (diploid) in the gonad
- population of oogonia increases by mitosis (this stops before birth)
- oogonia differentiate to form primary oocytes (diploid)
- primary oocytes are encased in primordial follicle
- many primary oocytes undergo atresia
- the primary oocytes start meiosis
- meiosis halts at prophase 1
- stops here until puberty begins
what happens when oogenesis resumes at puberty?
- at puberty, females have 300,000 oocytes
- under GnRH influence, a small number of follicle are recruited each ovarian/menstrual cycle
- only 1 oocyte will complete development and ovulate (within dominant follicle)
- primary oocyte completes meiosis 1.
- it forms a secondary oocyte and 1st polar body (both are haploid)
what happens after the secondary oocyte is formed?
- the secondary oocyte starts meiosis 2
- it halts at metaphase 2
- stops until fertilisation occurs
- meiosis 2 resumes when the sperm penetrates the plasma membrane of the ovum at fertilisation
- if not fertilised, it will degenerate through a process called atresia and never complete meiosis
what are the features of the follicles during oogenesis?
- oocyte develops within a developing follicle
- follicle are multilayered with granulosa cells and theca cells
- granulosa cells produce estradiol
- when ovulation occurs, the oocyte and corona radiata are released into the peritoneal cavity
what are the female reproductive hormones? what are the released by?
- GnRH (hypothalamus)
- FSH (anterior pituitary)
- LH (anterior pituitary)
- estradiol (ovary follicles)
- inhibin (ovary follicle and corpus luteum)
- progesterone (corpus leuteum)
what does GnRH stimulate in the female reproductive system?
- released in hypothalamus
- release of FSH and LH
what does FSH stimulate in the female reproductive system?
- released from anterior pituitary
- stimulates growth of ovarian follicles
what does LH stimulate in the female reproductive system?
- released from anterior pituitary
- surge of LH in ovulation
- formation of corpus luteum
what does estradiol stimulate in the female reproductive system?
- found in developing follicles
- assists follicle growth with FSH
- bone and muscle growth
- endometrial growth
- secondary sex characteristics
- feedback to anterior pituitary
what does inhibin stimulate in the female reproductive system?
negative feedback to anterior pituitary to suppress FSH
what does progesterone stimulate in the female reproductive system?
- released from corpus luteum
- negatively feeds back to suppress GnRH (therefore LH and FSH)
- endometrial maturation
- maintains pregnant state
what is the ovarian/menstrual cycle?
- the regular cyclic changes in the ovary and uterus that prepares an oocyte/ova for fertilisation and the endometrium from embryo implantation
when do the menstrual cycles occur?
on an approximate monthly basis (28 days) between menarche and menopause
what is menarche?
- first menstrual period
- occurs at age 12-13 on average
- part of puberty orchestrated by increase in sex steroid production (estrogens) by the gonads
what is menopause?
- cessation of menstruation
- reduction of estradiol and progesterone due to absence of or lack of response by follicles
- anterior pituitary feedback no longer active, therefor FSH and LH is high
what are the 2 ovarian cycles?
- follicular (preovulatory phase)
- luteal (postovulatory phase)
when does the follicular (preovulatory) phase occur?
Day 1-14
when does the luteal (postovulatory) phase occur?
day 15-28
what happens in the follicular (preovulatory phase)
- increased FSH from anterior pituitary
- this stimulates follicular growth
- the growing follicle secrete estradiol and inhibin
- this reduces FSH from anterior pituitary by negative feedback
- growing follicles undergo atresia, except the dominant follicle
- the dominant follicle secretes large amounts of estradiol
- this stimulates a surge of LH by positive feedback
- the follicle rupture and ovulation occurs
- the oocyte enters the peritoneal space/collected into uterine tube
what happens in the luteal (postovulatory phase)?
- ovulated follicle collapses and forms corpus luteum
- it secrete progesterone, estradiol and inhibin
- these decrease FSH and LH secretion by negative feedback on the hypothalamus (GnRH)
- if fertilisation and implantation do not occur, the corpus luteum involutes (luteolysis)
- this results in a fall in progesterone and estradiol
- this removed negative feedback of FSH and LH and the cycle starts again
what are the 2 menstrual cycles?
- menstrual and proliferative phase
- secretory (and premenstrual) phase
when does the menstrual and proliferative phase occur?
Day 1-14
what does the secretory (and premenstrual) phase occur?
Day 15-28
what happens in the menstrual and proliferative phase?
- the endometrium breaks down and bleeds during menstruation
- estradiol stimulates endometrial growth from days 6-14
- involves rapid tissue growth, including growth of glands and vasculature
what happens in the secretory phase?
- after ovulation (day 14), the corpus luteum secretes progesterone
- progesterone promotes endometrial maturation
- glands become secretory
- spiral arterioles grow and coil
what happens after the secretory phase if fertilisation and implantation do not occur?
- corpus luteum atrophies
- progesterone levels fall
- spiral arteries contract
- endometrial tissue breaks down and bleeding occurs
- shed tissue and blood removed via cervix and vegina (menstruation)
- cycle continues until fertilisation occurs
