The Ovary: Ovarian Follicle Development Flashcards
What is a PGC (primordial germ cell)
This is the cell before it goes down either male or female pathway
When the PGC get to the female gonad they become what?
Oogonia
When mitotic division stops and meiosis starts the oogonia is called what?
Oocyte
What is an oocyte called after ovulation but before fertilisation?
Egg
In the developing fetal ovary what are oogonia surrounded in?
Somatic cells which form nests
What are found within the stromal nests in a developing ovary?
There are cysts of germ cells with cytoplasmic connection to each other due to incomplete cytokinesis - this means there is cytoplasmic movements
What do the mesonephrones secrete to tell the ooconia to stop undergoing mitosis and to start meiosis?
Retinoic acid (in males this would just be ignored)
What stage does retinoic acid happen?
Fetal ovary stage
Retinoic stops mitosis which means what?
There will be no more new oogonia (she can only lose them).
Can you make new germ cells from ovary in vitro?
Yes - but you cant do it in the body
How does mioisis work in females?
One cell replicates its DNA. This is now called an oocyte and is maintained in meiotic arrest.
Eventually it will ressume and undergo meiotic division. The DNA split leaving a cell with 2 chromosomes and a polar body with 2 chromosomes
The 2nd meiotic then occurs and you are left with one cell with 1 chromosome and 2 polar bodies.
How many haploid germ cells do you get from males?
4
How many germ cells do you get from female meiosis?
1 and 2 polar bodies
When do oocytes stay in meiotic arrest?
From when it first becomes a follicle (before birth) and comes out of it after ovulation.
What happens after oocytes begin meiosis and are still surrounded by the nest?
Somatic cells now invade cysts and surround individual oocytes
Somatic cells invading cysts and surrounding oocytes are called primordial follicles. What are primordial follicles?
Oocytes surrounded by single layer of granulosa cells (this is accompanied by lots of cell death).
What also forms between oocyte and granulosa cells in a primordial follicle?
Zona pellucida
When do follicles form in humans?
Just around mid pregnancy
Once a follicle formation is complete do the ovary have an endless pool?
No
Are primordial follicles able to stay in a resting state until ovulation (which could be around 45)?
Yes
Are primordial follicles the only follicles made before birth?
Yes -
When does the menapause occur?
When there is not enough promordial follicles
What happens once a primordial follicles form?
They will eventually be activated or could be eliminated (although this is rare).
What happens when primordial follicles begin to grow?
Granulosa cells round up and can undergo mitosis and the oocyte gets bigger
What initiates growth of primordial follicles?
PTEN signalling pathway
What does PTEN signalling do?
They keep primordial follicles as primordial follicles and if you disrupt this all the follicles will grow and be lost.
What happens in the early stages of follicle development?
Granulosa’s continue to divide and oocyte grows.
A basement membrane is now made and surrounds this.
Thecal cells form around the basement membrane.
What is a basement membrane?
A round follicle (barrier to blood vessels and large molecules but can let small molecules through.
What are the early stages of follicle growth called?
Pre-antral stages
What is an antral follicle (early stage growth does not have this)?
Follicles with fluid-filled antral cavity
What happens in antral follicles?
Granulosa cells continue to undergo mitosis but the oocyte will be fully grown but will still have its double set of chromosomes producing lots of mRNA and proteins which will later help support the egg.
Still has a basement membrane
Why do we have antral cavaties?
Acts as a blood supply when the oocyte is too big not to have one. Takes waste away and gives nutrients too it.
When granulosa cells have divided enough what two types of cells do they differentiate into?
Cumulus cells (interact will oocyte)
Mural granulosa cells (very steroidogenically active - interact with rest of ovary).
What is the Graafian follicle?
When antral follicle is fully grown, ready to ovulate it is called a pre-ovulatory or graafian follicle
When does meiosis resume?
When follicle is ready to ovulate
What is the other signal which causes the primordial cells to stay at resting stage most of the time?
AMH
What do granulosa cells secrete inhibiting the primordial follicles from growing?
AMH
What would AMH secretion mean if there wasnt many growing follicles?
There would be less AMH and therefore more growth initiation in the resting pool
What is the self regulatory loop between AMH and primordial growth?
If there is lots of early growing follicles there would be less AMH leading to less growth (as there is less primordial follicles in the resting pool), in order to replenish stocks.
However if there is only a few growing follicles more AMH will be secreted (as there is more primordial follicles in the resting pool), encouraging growth.
What are the hormones in follicle development?
FSH and LH
What is FSH required for?
Antral follicle Growth
What does LH stimulate?
Final stage follicle development and required for ovulation.
Do we need FSH and LH for early follicle growth?
No
Does the endocrine system regulate antral follicles?
No
Does the pill affect the timing of primordial follicle loss?
No
Why do women ovulate one oocyte?
Follicle dominance
Why does follicle dominance happen?
To regulate how many oocytes are ovulated to maintain better pregnancies
What makes a follicle dominant?
Within a group of growing follicles at the mid-antral stage some are more ahead developmentally
- they have more blood vessels in their thecal layer making FSH more able to cross basement membrane.
- They have more FSH receptors
- mural granulosa cells have started to express LH receptors.
Why do dominant follicles survive?
FSH levels drop and they have more receptors and can transition into LH more readily - surviving.
What happens to the non-dominant follicles?
Subordinate follicles die as they cant get enough FSH or LH when FSH levels drop.
Do the dominant follicles bring about the fall in FSH?
Yes through the endocrine loop. Dominant follicles secrete oestrogen and inhibins which have a negative feedback on FSH reducing the FSH in the cell.
Does oestrogen and inhibin affect LH?
No
