Folliculogenisis Flashcards
where are the primordial germ cells found - at what week are they producerd?
in the yolk sac at 3w GA
what happens to the primordial germ cells once they have been produced in the yolk sac?
divide by mitosis and migrate to the genital ridge - differentiate into oogonia or spermatocytes
once the oogonia are within the ovary - how do they divide?
replicate by mitosis and then undergo meiosis I - arrested at metaphase - become primary oocytes
what is the development of a primary oocyte from arrest before birth?
when they reach puberty - a few primary oocytes are selected from the cortex - (outer layer of the cortex) - become surrounded by granulosa cells - secrete acellular basal lamina to protect and nourish - also forms the zona pellucida
how does the primary follicle become the secondary follicle?
undergoes meiosis II - forms a mature ovum and a polar body - cumulus cells surround the oocyte
what are the three phases which prepare a cell to enter cell division?
cell growth - G1
chromosome replication - S phase
preparation for divison - G2
what does the basal lamina differentiate in to when it is selected?
becomes the Theca - becomes vascularised
what is the FSH independent stage of folliculogenisis?
local growth factors cause basal growth - there is an change from resting to preantral size
this is initiation
know it occurs because people with FSH deficiency or receptor mutations are still able to reproduce
what is the FSH dependant stage of folliculogenisis?
oocytes which have reached the threshold size during initiation then enter this stage
rapid increase in diameter
increase in granulosa cells - become flatter and gaps open up in between them
antrum forms
oocyte is displaced to one side
the follicles move to the centre of the ovary
one follicle is selected – GRAFFIAN FOLLICLE
why are older mothers more likely to have babies with chromosomal defects?
oocytes have been arrested in metaphase I for too long - susceptible to mutation and DNA damage
what is the 2 cell 2 gonadotrophin theory?
LH acts on theca cells –> produce androgens - then enter circulation OR enter granulosa cells - converted to oestrogen using AROMATASE
FSH acts on granulosa cells - causing production of oestrogen
Late in the cycle - LH is able to act on granulosa cells - causing progesterone production
how is the release of oestrogen and progesterone controlled within the cycle?
oestrogen and progesterone are released into the blood stream - act on the hypothalamus and pituitary - decrease GnRH - cause a decrease in LH and FSH - consequential decrease in oestrogen and progesterone production
NEGATIVE FEEDBACK
how large is the graaffian follicle?
up to 20mm diameter
