Folliculogenesis Flashcards
What needs to be achieved to reproduce?
differentiation into male and female in embryo stage
sexual maturation (puberty)
good production, storage and release of egg/sperm
right chromosome number
What are the primordial germ cells the origin of (what do the PGC’s become)?
egg and sperm
3 weeks after conception, where is the primordial germ cell seen?
in the yolk sac of the foetus
What do the primordial germ cells do in the yolk sac of the foetus?
divide by mitosis to increase its number
After mitosis of the primordial germ cells, where do they go?
from yolk sac to genital ridge
What does the genital ridge form?
gonads
What is the word for primordial germ cells?
bipotential- they can become egg or sperm
when they reach the genital ridge form, then they can become egg or sperm accrording to the gonad formed
When the germ cells enter an ovary, what do they become?
- they become oocyte
- primordial germ cells colonize the area
- divide by mitosis
- then becomes oogonia (diploid)
- oogonia colonizes the ovary
- oogonia makes mitosis stop and meiosis begin
What is an oogonia?
egg precursor
have 46 chromosomes
multiply by mitosis- 7,00,000 formed
What does the oogonia do?
colonizes the ovary
mitosis stops and meiosis begins
At what stage does the oogonia arrest and what are they known as?
when oogonia enters first stage of meiosis, it arrests
known as primary oocytes
Till when does the primary oocyte remain arrested?
arrested in meiosis I (anaphase) till ovulation
Women have defined fertility/ true ovarian reserve. What does this mean?
=Women are born with all the eggs they will ever have
=eggs are laid down in foetal life
Why are mitotic divisions important?
The number of mitotic divisions will define how many eggs are laid down in the female ovary
At menopause, how many eggs will the female have left?
1,000
What happens in oogenesis?
- oogonia replication by mitosis
- forms primary oocytes
- when reach ovary, mitosis stops and meiosis begins
- arrest in first stage
- during LH surge and ovulation, meiosis I completes.
- meiosis arrests again at second stage (MEIOSIS II)
- after egg fertilises, meiosis II finishes
When is meiosis I complete?
ovulation
When is meiosis II complete?
after the egg fertilises
Before mitosis, how many chromatids are there per chromosome?
1
After replication there are 2 chromatids per chromosome
after mitosis, one chromatid per chromosome
What are spindles formed from?
centrioles
Where are primary oocytes packed in the ovary?
outer layer of the ovary (cortex)
What is a primordial follicle?
the oocyte needs to be protected
so is surrounded by protective layers and cells
the follicle comprises of granulosa cells
these granulosa cells secrete an acellular layer (no cells) around the oocyte called the basal lamina
What do the granulosa cells do to protect the primordial follicle?
these granulosa cells secrete an acellular layer (no cells) around the oocyte called the basal lamina
What is folliculogenesis?
growth and development of follicles at puberty from the earliest resting stages as laid down in the foetus through to ovulation
What happens as the follicles start to grow?
granulosa cells multiply
shape become cuboidal
oocyte also grows in size
What is the zona pelucida?
oocytes secrete a protective acellular layer
REMAINS attached to oocyte after ovulation
What is the zona pelucida made of?
proteins ZP1, 2, 3
What are theca cells?
once the follicle grows, there is another layer of cells differentiate around basal lamina
What is the order of protection outside the oocyte?
OOCYTE, ZONA PELUCIDA, GRANULOSA CELLS, BASEMENT LAMINA, THECA CELLS
What happens to the growth of the follicles if on the contraceptive pill?
the follicles continue to grow but die later bc later growth is dependent on FSH
What happens when follicles start to grow?
diameter increase
granulosa cell division
gaps form in granulosa cell layer (consist of fluid spaces forming antrum)
What are the fluid spaces in the granulosa called and filled with?
antrum
follicular fluid
What are the 2 stages of follicle growth?
pre antral follicle growth
antral follicle growth
What happens when the antrum continues to grow?
continues to grow
pushes some of the cell to the edge of the follicle
granulosa cells on the edge known as mural granulosa cells
Where are the cumulus granulosa cells?
the ones surrounding the egg
When the egg ovulates, what leaves the ovary and what is left?
cumulus oocyte complex leaves (CUMULUS GRANULOSA CELLS AND THE EGG)
WHAT IS LEFT= mural granulosa, theca cells and basal lamina
To develop an antral follicle, what does it need to be under the influence of?
FSH
How long does the initiation, recruitment, and selection of the follicle take?
90 days to occur
What kind of blood supply does a follicle have?
avascular until theca cells form
What steroid does the theca cell produce?
progestogens and androgens derived from cholesterol and is under the influence of LH
What receptors do theca cells have?
LH
How does oestrogen influence granulosa cells?
to drive granulosa cell proliferation
What is aromatase influenced by?
FSH
What receptors do granulosa cells have?
FSH
they acquire LH receptors in the dominant follicle
What is the 2 cell, 2 gonadotrophin theory?
- Initially theca cells produce progestogens and androgens in response to LH
- androgens are converted into oestrogen in the granulosa cells in response to FSH
- dominant follicle acquires LH receptors and starts responding to LH and produces progestogens in the later stages
What is the graafian follicle?
The single selected follicle will then grow very massively into the Graafian follicle.
What happens in the 2 cell, 2 gonadotrophin theory?
- LH binds to LH receptors and stimulates androgen and progesterone production FROM CHOLESTROL
- Androgens enter the circulation and either go into circulation (deep) or go into granulosa cells
- In granulosa cells= convert to oestrodiol by aromatase
- Aromatase is stimulated by FSH binding to its receptor
What is aromatase stimulated by?
FSH binding to receptor
Explain the different LH and FSH receptors and where they go?
FSH receptors on granulosa cells (androgen to oestrodiol)
LH receptors on theca cells (cholestrol to androgens)= NEVER HAS FSH receptors
THE FOLLICLE which becomes destined ovulating follicle (dominant) acquires LH receptors on granulosa cells
