Folliculogenesis Flashcards
Where do germ cells enter into?
Enter the gonads
What are cells called that will become eggs or sperm?
These are called primordial germ cells
When are primordial germ cells first identifiable?
First identifiable in the yolk sac of the developing foetus at 3 weeks after conception
What do primordial germ cells undergo and migrate to where?
PGC undergo many cycles of mitosis and migrate to the genital ridge in the foetus
What becomes the gonad?
The genital ridge becomes the gonad
What does further differentiation of the PGC depend on?
Depends on the development of the gonad
What do primordial germ cells become when they enter the ovary and how?
If PGCs enter the ovary, they become oocytes.
- Germ cells become oogonia when in the ovary
- Oogonia are egg-precursors, diploid and multiply by mitosis
- Once mitosis stops and they enter into meiosis, they’re known as primary oocytes
How does duplication of chromatids occur?
- Chromosomes replicate during s-phase of the cell cycle
- Chromatids remain attached at the centromere
- Each copy known as a chromatid
Mitosis and Meiosis steps
LOOK OVER IN DETAIL IN OWN TIME
Where are primary oocytes packed into?
Primary oocytes are packed into the outer layer of the ovary:the cortex
How do we go from primary oocyte to primordial follicles?
-Primary oocytes are in the vulnerable 1st meiotic phase for many years
-Therefore each one becomes surrounded by
protective layers and protective cells
-In the foetal ovary, the surrounding cells condensate around the oocyte and differentiate into the granulosa cells
-The granulosa cells then secrete an acellular layer
called the basal lamina
-This whole structure is called the primordial follicle
What is folliculogenesis?
It is the growth of the follicle
What is folliculogenesis defined as?
Defined as the growth and development of follicles from the earliest resting stages as laid down in the foetus, through to ovulation
Comment on the growth of follicles after puberty?
Most of the follicles in the ovary are not growing after puberty, after puberty only a few grow
What happens a s the follicles start to grow?
As the follicles start to grow, the granulosa cells multiply and the oocyte secretes another protective acellular layer called the zona pellucida which stays attached after ovulation
What else grows once growth of the follicles start?
Once growth of the follicles has started, a second layer of cells then differentiate around the basal lamina:the theca
What drives most of folliculogenesis and early follicle growth ?
FSH drives most of folliculogenesis but early growth is independent of FSH and is driven by local factors
What happens when FSH is suppressed in follicle growth?
When FSH is suppressed, the follicles will still continue early growth but then die
What happens as follicles start to grow and what do they consist of?
As follicles start to grow, it increases rapidly in diameter and granulosa cell division increase, but gaps begin to form in the granulosa cell layers
-These gaps consist of fluid filled space which form an antrum and are filled with follicular fluid
What are follicles known as before an antrum and what do they have?
Before the antrum, they’re known as pre antral follicles and just have a layer of granulosa cells with theca
What are follicles known as after the formation of the antrum?
After the formation of an antrum, they’re known as secondary follicles
What happens to the oocyte as the follicle grows?
As the follicle grow, the oocyte is displaced to one side
What is follicle initiation?
It is where a cohort of early follicles leave the resting pool and grow continuously
What is follicle recruitment?
When follicles see FSH at the the right time and are recruited by the menstrual cycle for continuous growth
What is the follicular phase of the menstrual cycle?
It is the phase just after the formation of the antryma and just before ovulation
What do ovarian follicles produce and what is this called
Produce steroids
and is called the 2 cell 2 gonadotropin theory
What is the 2 cell 2 gonadotropin theory?
-LH binds to LH receptor on theca cell and produces the androgen
-These androgens go into circulation but also cross the granulosa membrane and are converted into oestrogen
-Oestrogen will drive granulosa cells in the follicle and
go out in circulation
-FSH binds to FSH receptor and catalyses the conversion of androgens in to oestrogens
