Lecture 3: Ovary and Ovarian cycle

Question 1

How does germ cells become tertiary follicle that is ovulated and what is the time period for these 6 steps

Answer 1

1. Primordial Germ cells migrate from the yolk sac to the genital ridge where they differentiate into Oogonium
2. Oogonium undergo mitotic division to make 6-7 mil primordial follicles by 6 months of gestation.
3. Primordial follicles (aka 1’ oocytes) start meiosis but are stopped at the end of prophase 1- arrested for 12-50 years.
4. Following puberty, primordial follicles can respond to FSH are recruited to become 1’ follicles and start to undergo 2-12 months slow growth to become 2ndary follicles
5. In menstrual cycle 2ndary follicles are stimulated to grow rapidly in 2 weeks due to upregulation of FSH receptors: become 3’ follicles
6. One follicle is dominant (3’) and causes major atresia of the others (as well as on other ovary): 3’ Follicle is ovulated

Question 2

Why are only a small amount of oocytes ovulated 400-500 throughout reproductive life compared to 7mil at 6mo gest?

Answer 2

There is a big loss from 6-9mo gestation.

From the time that follicles are formed a smaller number of them become activated through unknown process until menopause.

Before puberty all activated follicles die (atresia)

After puberty the follicles are recruited in waves to grow: 30-50 follicles at a time, with only 15-20 progressing to 2ndary follicle and then only one/two 3’ follicle so Major loss by atresia every ovarian cycle.

Question 3

What are the cell features of primordial and primary follicle

Answer 3

Primordial follicle: A single layer of flattened granulosa cells on the outside of the ooplasm with surrounding stromal cells

1’ follicle: granulosa cells are single layer cuboidal- slow developing follicles

Question 4

What are the cell features of secondary follicle

Answer 4

• zona pellucida (dark ring closest to ooplasm)
• multilayered cuboidal granulosa cells surrounding
• Outside of that layer are Theca cells- not stromal cells anymore - making androgen

Question 5

What are the cell features of tertiary follicle

Answer 5

• antrum filled with follicular fluid
• cumulous oophorous: group of granular cells closely attached to the oocyte which adds bulk, allowing it to be swept by fallopian tube easier, connected to rest of granulosa by stalk
• zona pellucida
• surrounding thin layer of theca cells

Question 6

What is the structure and function of zona pellucida

Answer 6

A dark staining membrane around the ooplasm made of ZP1 glycoproteins (in primordial follicle) and ZP2 and ZP3 added to activated follicles.
Important for filtering normal sperm in and blocking polyspermy.

Question 7

What substances do granulosa cells and theca cells produce in secondary follicles, what hormones do they respond to and how do they relate to each other

Answer 7

Theca cells respond to LH. they produce androgen (androstenedione) from cholesterol->progesterone.

Granulosa cells respond to FSH. They make Oestrogen (estradiol) from this androgen. This has (-) feedback to both ant pit and hypothalamus
They also make inhibin which feeds back to FSH secretion and Anti-Mullerian Hormone which helps sex determination and prevents recruitment of early stage follicles

Question 8

How is the oocyte released in ovulation - adverb, and what happens to basal body temperature after this

Answer 8

Gently - from the dominant follicle the stigma pops out the follicular fluid containing the oocyte complex.

Following ovulation, basal body temperature increases: fertile phase

Question 9

What happens to the follicle after the egg is released

Answer 9

Undergoes lutenisation: rapid proliferation of granulosa cells (and theca cells) over ~10 day period to become the corpus luteum. This has a thick wall and is a highly vascularised tissue.
The granulosa cells make progesterone (and estrogen for inhib feedback): SM relaxant to stop miscarriage of the potential fetus

If egg not fertilised, It will regress into the corpus albicans: atretic corpus luteum

Question 10

How do gonadotropic hormones and ovarian hormone levels change in the first phase of ovarian cycle and what stage of uterine cycle does this match?
What about middle peak and 2nd stage?

Answer 10

1st: Follicular phase (development of follicle) = menstruation->proliferative phase of uterine cycle
- FSH is higher than LH. Estrogens are dominant over progesterone, inhibin in the middle

Middle: Ovulation
- Large spike in LH and estrogen. mini peak in FSH and inhibin.

2nd: Luteal phase (development of corpus luteum) = secretory phase

-Rising high Progesterone, rising inhibin both to peaks, with low estrogen.
LH and FSH are flat lines.

Question 11

What are the 5 regions of the fallopian tube from distal to proximal, and which is the site of fertilisation mainly

Answer 11

1. Fimbria, 2. infundibulum 3. Ampulla (main site of fertilisation- high SA for embryo nutrients)
2. Isthmus 5. Intramural/interstitial portion joined to the uterus

Question 12

What is tissue layers of the fallopian tube

Answer 12

1. Epithelial lining:
   a)ciliated for movement of the sperm, embryo, oocyte b)secretory for nourishing the embryo
   differential response to steroid hormones
2. Muscular coat: inner circ and outer long.
3. Serosal coat

Question 13

Compare the effect of oestrogen (E2) and progesterone (P2) in the fallopian tube and why

Answer 13

E2 promotes cillia increase, increased in secretory activity, and increase in muscular activity - to help the sperm reach the egg

P2 promotes decrease in muscular activity, decrease in cillia but increase in the beat frequency after estrogen priming, decrease in volume of secretions- to help the embryo go to the uterus