Reproductive system 4 Flashcards
What is Oogenesis
Formation and development of female gamete (oocyte) from oogonia
What does Oogenesis require
Mitosis and meiosis
When does Oogenesis occur
Lifetime supply produced before birth
Continues between puberty and menopause
Where do Oocytes develop
Within ovarian follicles - 1 per follicle
How often is each cycle
1 ovulation every 28 days (average)
Describe Oogenesis before birth
Oogonium in gonad - 46 (2n)
Pop. of oogonia increase by mitosis (stops before birth)
Differentiate to form primary oocytes - 46 (2n)
Primary oocytes undergo atresia - start meiosis (halts at prophase 1 until puberty)
Where are primary oocytes encased
In primordial follicle
How many oocytes do females have at puberty
300,000
What does GnRH influence
Small number of follicles recruited each ovarian/menstrual cycle
How many oocytes will complete development and ovulate
Only one - within dominant follicles
What happens when the primary Oocyte completes meiosis 1
Forms a secondary oocyte and 1st polar body - haploid n=23
What start meiosis 2
Secondary oocytes - halts at metaphase 2 - suspended until fertilation
When does meiosis 2 resume
When the sperm penetrates plasma membrane of the ovum at fertilisation
What happens if fertilisation doesn’t occur
Will degenerate - atresia - and never complete meiosis
Describe developing follicle
Multi-layered
Granulosa cells
Theca cells
What do granulosa cells produce
oestradiol
What happens during ovulation
Oocyte and corona radiata released into peritoneal cavity
What are the female reproductive hormones
GnRH FSH LH Estradiol Inhibin Progesterone
Where is GnRH released
Hypothalamus
Where is FSH and LH produced
Anterior pituitary
Where is Estradiol, inhibin and progesterone produced
Ovary
Follicles - Estradiol and inhibin
Corpus luteum - Inhibin and progesterone
What does GnRH do
release of FSH and LH
What does FSH do
Stimulates growth of ovarian follicles
What does LH do
Surge of LH involved in ovulation - formation of corpus luteum
What does estradiol do
Assists follicle growth Bone and muscle growth Endometrial growth Secondary sex characteristics Feedback to anterior pituitary
What does inhibin do
Negative feedback of anterior pituitary to suppress FSH
What does progesterone do
Negative feeds back to suppress GnRH
Endometrial maturation
Maintains pregnant state
What does the ovarian/menstrual cycle do
Cyclic changes in ovary and uterus that prepare an oocyte/ova for fertilisation and the endometrium for embryo implantation
Describe menarche (menstrual period)
Part of puberty - increase in sex steroid production (estrogens)
Why does menopause occur
Reduction of estradiol and progesterone due to absence of or lack of response by follicles
Anterior pituitary feedback no longer active (FSH/LH high)
What are the two phases of the reproductive cycle
Follicular - preovulatory phase: day 1-14
Luteal - postovulatory: day 15-28
Describe the follicular (preovulatory) phase
Increased FSH from AP - stimulates follicular growth - secrete estradiol and inhibin - reduces FSH (negative feedback) - follicles undergo atresia, except dominant follicle - secretes large amounts of estradiol (positive feedback) - surge of LH
Follicle ruptures and ovulation occurs - oocyte enters peritoneal space/collected into uterine tube
Describe luteal (postovulatory) phase
Ovulation follicle collapses and forms corpus luteum - secretes progesterone, estradiol and inhibin - Decrease FSH and LH - Negative feed back to hypothalamus
What happens if fertilisation doesn’t in the luteal (postovulatory) phase
If fertilisation and implantation don’t occur corpus luteum involutes (luteolysis)
Fall in progesterone and estradiol
Removes negative feedback on FSH and LH and cycle starts again
Describe the menstrual and proliferative phase
Endometrium breaks down and bleeds
Estradiol stimulates endometrial growth (days 6-14)
Rapid tissue growth - growth of glands and vasculature
Describe secretory phase
Days 15-28
After ovulation corpus luteum secretes progesterone
Progesterone promotes endometrial maturation
- glands become secretory
- Spiral arterioles grow and coil
Describe secretory phase if fertilisation and implantation doesn’t 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 vagina
