folliculogenesis Flashcards
(34 cards)
what are primordial germ cells
common origins of spermatozoa and oocytes
produced by 3week post-conception
what do primordial germ cells form
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)
what happens to primordial germ cells if genital ridge develops into ovaries
germ cells enter into ovary and become oogonia
what are oogonia
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)
what is meant by a women’s defined fertility
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
when does the primary oocyte complete meiosis 1
at ovulation.
what happens to oocyte at ovulation
completes meiosis 1.
homologues split, oocyte= haploid.
how is teh oocyte protected
is surrounded by many protective layers which also nourish it with the nutrients it needs to survive.
what happens to the surrounding cells in the foetal ovary
surrounding cells condense around the oocyte and differentiate into the granulosa cell
form a single flattened layer around the oocyte
what is the role of the granulosa cells of the oocyte
secrete an acellular layer called the basal lamina. the whole structure is called the primordial follicle
what is folliculogenesis
the growth and development of follicles from the their earliest “resting” stages as they were laid down in the foetus through to ovulation
what is an ovarian follicle
fluid-filled sac that contains an immature egg, or oocyte
how do follicles grow
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)
what are the layers of the follicle from outside to inside
Theca cells -> Basal lamina -> Granulosa cells -> zona pellucida -> primary oocyte
what drives folliculogenesis
early growth - local factors (independent of FSH)
most of folliculogenesis is driven by FSH
how do we know that early stages of folliculogenesis is independent of FSH
- 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.
how does the ovarian antrum form
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.
what are the two phases of follicular growth
- pre-antral phase
2. antral phase
what is the pre-antral phase
before the antrum is formed
pre-antral follicle growth is gonadotrophin independent
what is the antral phase
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.
how does the antrum form
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
what are cumulous cells
specialised granulosa cells that surround oocyte.
what is an aretic follicle
Typically around 20 follicles mature each month but only a single follicle is ovulated.
rest are aretic follicles and degraded and reabsorbed.
what happens in folliculogenesis
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
