Lecture 6: ovary part 2

Question 1

features of a primordal follicle (found near tunica albuginea)

Answer 1

• basement laminae

- single simple squamous granulosa cells

Question 2

Features of a primary follicle

Answer 2

• single cuboidal granulosa cells

- zona pellucida (formed by secretions of glycoprotein from oocyte)

Question 3

Features of a secondary follicle

Answer 3

• granulosa cells (more layers added)
• zona pellucida
• theca interna (vascular)
• theca externa (fibrous capsule)

Question 4

Features of a tertiary follicle

Answer 4

• Multiple layers of granulosa cells
• zona pellucida
• corona radiata (innermost layer of granulosa cell attached to zona pellucida)
• theca interna and externa
• antrum!

Question 5

Features of a graafian (mature) follicle

Answer 5

Multiple layers of granulosa cells

zona pellucida

theca interna and externa

antrum

cumulus oophorous (tree trunk)

Question 6

Features of the corpus luteum

Answer 6

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

Question 7

Features of corpus albican

Answer 7

progressive cell death and decrease in progesterone. white scar tissue. body is reabsorbed back into stromal tissue in a few weeks- months

Question 8

During ovulation, what happens to the follicle in the cortex of ovary?

Answer 8

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.

Question 9

What is mittelschmerz?

Answer 9

period cramps, from small amount of blood htat leaks into pelvic floor from the rupturing follicle

Question 10

what is Gametogenesis

Answer 10

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

Question 11

What stops the corpus luteum from breaking down if the oocyte is fertilised?

Answer 11

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.

Question 12

Why do we have menstrual cycle (theories)?

Answer 12

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

Question 13

what are the two function of the female reproductive tract?

Answer 13

1) produce egg

2) incubate embryo

Question 14

There are 2 phases in ovarian cycle, what are they?

Answer 14

1. follicular (day 1- ovulation)

2. luteal phase (ovulation - mensturation)

Question 15

there are 3 phases of endometrium cycle, what are they?

Answer 15

1. menstural
2. proliferation
3. secretory

Question 16

How much blood + mucus + tissue fluid etc usually comes out?

Answer 16

50-150 mL

Question 17

Which layer sheds in menstrual cycle?

Answer 17

stratum functionalis

Question 18

Which follicular phase does NOT change between women?

Answer 18

luteal phase. always 14 days!

Question 19

Go through steps of menstrual cycle (10 steps)

Answer 19

1. Corpus luteum gets smaller, oestrogen and progesterone levels are low but FSH levels start to increase
2. FSH stimulations causes the follicle to grow bigger
3. At day 6-7, dominant follicle is chosen and causes an increase in estrogen and inhibin. (the follicle produces oestrogen)
4. oestrodial and inhibin start to dampen FSH and LH production in the anterior pituitary (negative feedback loop.
5. 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.
6. its high levels of oestrogen (and inhibin) that supports the positive feedback, which triggers a rise in GnRH leading to the LH surge
7. LH surge induces ovulation!
8. corpus luteum forms and contributes to the rising progesterone levels.
9. High progesterone levels prevent GnRH production and therefore decreases FSH and LH
10. Corpus luteum dies, and leaves a corpus albican

Question 20

What is the two cell -two gonadotrophin hypothesis?

Answer 20

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

Question 21

How are androgens made by the follicle?

Answer 21

The cells responsible for androgen production is the thecal cells.

• Androstenedione
• testosterone

Question 22

What stimulates steroidogenesis?

Answer 22

• 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

Question 23

FSH acts on what cell? of follicle?

Answer 23

granulosa

Question 24

LH acts on what cell?

Answer 24

thecal

Question 25

at 5 month gestation, how many oogonia are there in the ovaries?

Answer 25

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!

Question 26

How are follicles recruited?

Answer 26

• 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!)

Question 27

How does FSH threshold affect number of follicles?

Answer 27

• 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.