folliculogenesis

Question 1

what are primordial germ cells

Answer 1

common origins of spermatozoa and oocytes

produced by 3week post-conception

Question 2

what do primordial germ cells form

Answer 2

mitosis (to inc their number)->migrate to genital ridge. development of PGC here depend on whether the genital ridge becomes the gonad (testis or ovary)

Question 3

what happens to primordial germ cells if genital ridge develops into ovaries

Answer 3

germ cells enter into ovary and become oogonia

Question 4

what are oogonia

Answer 4

egg precursors. still diploid.
increase their number by mitosis (increases upto 7m)
then oogonia stop dividing by mitosis->enter meiosis 1 & arrest at anaphase .
these are primary oocyte. remain arrested until ovulated (or death)

Question 5

what is meant by a women’s defined fertility

Answer 5

all eggs ever made are in embryology (by primordial germ cells) initially 7m.
decreases to 500,000 – 1,000,000 due loss of primary oocytes by apoptosis at birth

Question 6

when does the primary oocyte complete meiosis 1

Answer 6

at ovulation.

Question 7

what happens to oocyte at ovulation

Answer 7

completes meiosis 1.

homologues split, oocyte= haploid.

Question 8

how is teh oocyte protected

Answer 8

is surrounded by many protective layers which also nourish it with the nutrients it needs to survive.

Question 9

what happens to the surrounding cells in the foetal ovary

Answer 9

surrounding cells condense around the oocyte and differentiate into the granulosa cell

form a single flattened layer around the oocyte

Question 10

what is the role of the granulosa cells of the oocyte

Answer 10

secrete an acellular layer called the basal lamina. the whole structure is called the primordial follicle

Question 11

what is folliculogenesis

Answer 11

the growth and development of follicles from the their earliest “resting” stages as they were laid down in the foetus through to ovulation

Question 12

what is an ovarian follicle

Answer 12

fluid-filled sac that contains an immature egg, or oocyte

Question 13

how do follicles grow

Answer 13

follicles grow by multiplication of the granulosa cells
oocyte itself grows by synthesising protein etc. as the egg grows it lays down z.pellucida (a protective acellular layer)
second layer of cells that differentiate around the basal lamina (called rheca cells)

Question 14

what are the layers of the follicle from outside to inside

Answer 14

Theca cells -> Basal lamina -> Granulosa cells -> zona pellucida -> primary oocyte

Question 15

what drives folliculogenesis

Answer 15

early growth - local factors (independent of FSH)

most of folliculogenesis is driven by FSH

Question 16

how do we know that early stages of folliculogenesis is independent of FSH

Answer 16

• patients with mutation in FSH or FSH receptor, still have early stage growing follicles
• when FSH is supressed (eg oral contraceptive pill) still get early growth of follicle but eventually die as they need FSH to progress.

Question 17

how does the ovarian antrum form

Answer 17

as follicle grows =increase in diameter. granulosa cell divisions increase.
as this occurs, gaps form between granulosa cells. fluid moves through these gaps to form fluid filled spaces that combine to form an antrum.

Question 18

what are the two phases of follicular growth

Answer 18

1. pre-antral phase

2. antral phase

Question 19

what is the pre-antral phase

Answer 19

before the antrum is formed

pre-antral follicle growth is gonadotrophin independent

Question 20

what is the antral phase

Answer 20

after formation of antrum.
antral follicle (secondary follicle) growth is dependent on gonadotropins soon after formation.
if there is a lack of gonadotrophins, follicle will die.

Question 21

how does the antrum form

Answer 21

primordial follicle

• > cohorts grow under influence of local factors
• > oocyte grows. granulosa cells multiply. theca cells condense around it.
• > fluid filled spaces form between granulosa cells
• > fluid filled spaces join together to form larger fluid filled space (antrum) and oocyte is pushed to the edge

Question 22

what are cumulous cells

Answer 22

specialised granulosa cells that surround oocyte.

Question 23

what is an aretic follicle

Answer 23

Typically around 20 follicles mature each month but only a single follicle is ovulated.
rest are aretic follicles and degraded and reabsorbed.

Question 24

what happens in folliculogenesis

Answer 24

1 - follicle initiation - a cohort of early follicles leae resting pool and start to grow continuously.
2 - follicles that manage to reach right size when FSH is at its peak are recruited into menstrual cycle. rest will die.
3 - human pelvis can only carry one fetus so from that group only one is selected for ovulation
4 - selected follicle grows to form graafian follicle

Question 25

what is the graafian follicle

Answer 25

a fluid-filled structure in the mammalian ovary within which an ovum develops prior to ovulation

Question 26

why can the follicle respond to circulating hormones

Answer 26

due to theca being well vascularised

Question 27

what happens to granulosa cells in the dominant follicle

Answer 27

multiply drastically

Question 28

What is the 2-cell 2-gonadotrophin theory

Answer 28

LH stimulates thecal cells to produce androgens

-FSH stimulates granulosa cells to produce estrogens from androgens.

Question 29

how dos LH stimulate theca cells to produce androgens

Answer 29

theca cells surrounded by blood supply
have LH receptors on their surface.
LH binds to receptor and cause synthesis of androstenedione (androgens) from cholesterol
androgens are send around the body in the circulation and some move into granulosa cells.
here androstenedioine -> estradiol by aromatase

Question 30

how dos FSH stimulate granulosa cells to produce androgens

Answer 30

FSH binds to FSH receptors on granulosa cells.
cause synthesis of androstenedione from cholesterol.
Aromatase converts androstenedione to estradiol.

Question 31

where are the LH receptors

Answer 31

only on theca cells until just before ovulation.

LH receptors will appear on granulosa cells just before ovulation to enable them to produce progesterone

Question 32

what do oestrogens do

Answer 32

oestrogens drive granulosa cell multiplication and increased follicle growth
also feeds back to the HPG.

Question 33

what is the starting point of steroid synthesis

Answer 33

cholesterol.

converted to steroids through reactions with various enzymes inc. cytochrome P450 enzymes.

Question 34

how is folliculogenesis controlled

Answer 34

steroids produced by the ovary feedback on the HPG axis and control release of gonadotrophins