Lecture 6: ovary part 2 Flashcards
features of a primordal follicle (found near tunica albuginea)
- basement laminae
- single simple squamous granulosa cells
Features of a primary follicle
- single cuboidal granulosa cells
- zona pellucida (formed by secretions of glycoprotein from oocyte)
Features of a secondary follicle
- granulosa cells (more layers added)
- zona pellucida
- theca interna (vascular)
- theca externa (fibrous capsule)
Features of a tertiary follicle
- Multiple layers of granulosa cells
- zona pellucida
- corona radiata (innermost layer of granulosa cell attached to zona pellucida)
- theca interna and externa
- antrum!
Features of a graafian (mature) follicle
Multiple layers of granulosa cells
zona pellucida
theca interna and externa
antrum
cumulus oophorous (tree trunk)
Features of the corpus luteum
After the rupture, everything breaks down and the remaining body of follicle undergoes luteinisation + increase in progestagen. Granulosa cells stop dividing and get huge to form large lutein cells (rich in mitochondria, smooth endoplasmic reticulum, lipid droplet, golgi bodies and carotenoid pigment, lutein. t
Features of corpus albican
progressive cell death and decrease in progesterone. white scar tissue. body is reabsorbed back into stromal tissue in a few weeks- months
During ovulation, what happens to the follicle in the cortex of ovary?
starts to increase in size and bulge out from ovarian surface
follicle will rupture at the stigma from the ovary slowly, carrying the oocyte and cumulus cells to protect it. follicle is then collected by fimbria of the oviduct, which sweeps up the cumulus mass into oviduct.
What is mittelschmerz?
period cramps, from small amount of blood htat leaks into pelvic floor from the rupturing follicle
what is Gametogenesis
Primary germ cells take 3 weeks in the yolk sac to develop and then migrate to the genital ridge. After 6 weeks of migration, the primary germ cells can for the gonad and undergo mitotic proliferation
What stops the corpus luteum from breaking down if the oocyte is fertilised?
human chorionic gonadotropin (hCG). it is produced by the chorion of embryo 8 days after fertilisation. It is this hormone that pregnancy tests pick up.
Why do we have menstrual cycle (theories)?
1) cleanse the tract from harmful bacteria that may have entered with sperm
2) old endometrium is too bulky for reabsorption
3) more energy efficient to shed endometrium than keep it for the next cycle
what are the two function of the female reproductive tract?
1) produce egg
2) incubate embryo
There are 2 phases in ovarian cycle, what are they?
- follicular (day 1- ovulation)
2. luteal phase (ovulation - mensturation)
there are 3 phases of endometrium cycle, what are they?
- menstural
- proliferation
- secretory
How much blood + mucus + tissue fluid etc usually comes out?
50-150 mL
Which layer sheds in menstrual cycle?
stratum functionalis
Which follicular phase does NOT change between women?
luteal phase. always 14 days!
Go through steps of menstrual cycle (10 steps)
- Corpus luteum gets smaller, oestrogen and progesterone levels are low but FSH levels start to increase
- FSH stimulations causes the follicle to grow bigger
- At day 6-7, dominant follicle is chosen and causes an increase in estrogen and inhibin. (the follicle produces oestrogen)
- oestrodial and inhibin start to dampen FSH and LH production in the anterior pituitary (negative feedback loop.
- oestrogen levels increase by day 12, it reaches a threshold concentration and exceeds it. If the level stays above the threshold for 36 hours without progesterone to support it, the feedback loop will switch from negative to positive.
- its high levels of oestrogen (and inhibin) that supports the positive feedback, which triggers a rise in GnRH leading to the LH surge
- LH surge induces ovulation!
- corpus luteum forms and contributes to the rising progesterone levels.
- High progesterone levels prevent GnRH production and therefore decreases FSH and LH
- Corpus luteum dies, and leaves a corpus albican
What is the two cell -two gonadotrophin hypothesis?
In the early follicular phase, there is high FSH and LH
- FSH acts on follicles to help them develop and increase the layers of granulosa cells
- LH acts on the follicle to help increase the number of thecal cells
How are androgens made by the follicle?
The cells responsible for androgen production is the thecal cells.
- Androstenedione
- testosterone
What stimulates steroidogenesis?
- LH acts on the receptor of the thecal cell
- triggers a cascade of signalling via the rate limiting cholesterol side-chain cleavage enzyme
- androstenedione crosses the basement membrane and gets converted into estrone, then estradiol 17b and is released into the blood.
- FSH acts on granulosa cells and causes the aromatisation of androgens to oestrogen ( androstenedione → estrone → estradiol 17b
FSH acts on what cell? of follicle?
granulosa
LH acts on what cell?
thecal
at 5 month gestation, how many oogonia are there in the ovaries?
6-7 million
- new borns girls have 1-2 million that reduces to 3-400,000 by the time she enters puberty.
- follicles just start to deplete, its inevitable
- Approximately, only 400 follicles reach adulthood!
How are follicles recruited?
- everyday, 20-30 follicles grow and die.
- Follicular maturation is controlled/regulated by survival and cell death
- At the start of puberty, there is regular recruitement of primordial follicles into a pool of growing preantral (all the type of follicles)
- every month, 20-30 are recruited to potentially devleop and grow, but only ONE becomes dominant (this is around day 7)
- the initial growth depends on FSH and also requires GDF, GDF9, BMP, BMP15
- So, this dominant follicle will undergo pre-ovulatory growth, make itself some LH receptors on the thecal cells and eventually is able to ovulate when there is a LH surge
- If follicle doesnt get stimulated by FSH, it will die.
- Remember, a mature follicle produces oestradiol (and inhibin) which inhbits FSH from developing the the weak follicles! (basically poisoning the others!)
How does FSH threshold affect number of follicles?
- When FSH surpasses its threshold in a normal cycle (typically 10-30 %), it will start to trigger the growth of a small number of antral follicles → it starts getting bigger in size (this occurs around 0-6 days)
- The length of time that the threshold is exceeded may potentially determine how many preantral follicles are chosen in the pool prize to start developing.
- The number of follicles recruited can increase if endogenous FSH (your body makes it) are higher than exogenous FSH.
