The Ovary: Ovarian Follicle Development

Question 1

What is a PGC (primordial germ cell)

Answer 1

This is the cell before it goes down either male or female pathway

Question 2

When the PGC get to the female gonad they become what?

Answer 2

Oogonia

Question 3

When mitotic division stops and meiosis starts the oogonia is called what?

Answer 3

Oocyte

Question 4

What is an oocyte called after ovulation but before fertilisation?

Answer 4

Egg

Question 5

In the developing fetal ovary what are oogonia surrounded in?

Answer 5

Somatic cells which form nests

Question 6

What are found within the stromal nests in a developing ovary?

Answer 6

There are cysts of germ cells with cytoplasmic connection to each other due to incomplete cytokinesis - this means there is cytoplasmic movements

Question 7

What do the mesonephrones secrete to tell the ooconia to stop undergoing mitosis and to start meiosis?

Answer 7

Retinoic acid (in males this would just be ignored)

Question 8

What stage does retinoic acid happen?

Answer 8

Fetal ovary stage

Question 9

Retinoic stops mitosis which means what?

Answer 9

There will be no more new oogonia (she can only lose them).

Question 10

Can you make new germ cells from ovary in vitro?

Answer 10

Yes - but you cant do it in the body

Question 11

How does mioisis work in females?

Answer 11

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.

Question 12

How many haploid germ cells do you get from males?

Answer 12

4

Question 13

How many germ cells do you get from female meiosis?

Answer 13

1 and 2 polar bodies

Question 14

When do oocytes stay in meiotic arrest?

Answer 14

From when it first becomes a follicle (before birth) and comes out of it after ovulation.

Question 15

What happens after oocytes begin meiosis and are still surrounded by the nest?

Answer 15

Somatic cells now invade cysts and surround individual oocytes

Question 16

Somatic cells invading cysts and surrounding oocytes are called primordial follicles. What are primordial follicles?

Answer 16

Oocytes surrounded by single layer of granulosa cells (this is accompanied by lots of cell death).

Question 17

What also forms between oocyte and granulosa cells in a primordial follicle?

Answer 17

Zona pellucida

Question 18

When do follicles form in humans?

Answer 18

Just around mid pregnancy

Question 19

Once a follicle formation is complete do the ovary have an endless pool?

Answer 19

No

Question 20

Are primordial follicles able to stay in a resting state until ovulation (which could be around 45)?

Answer 20

Yes

Question 21

Are primordial follicles the only follicles made before birth?

Answer 21

Yes -

Question 22

When does the menapause occur?

Answer 22

When there is not enough promordial follicles

Question 23

What happens once a primordial follicles form?

Answer 23

They will eventually be activated or could be eliminated (although this is rare).

Question 24

What happens when primordial follicles begin to grow?

Answer 24

Granulosa cells round up and can undergo mitosis and the oocyte gets bigger

Question 25

What initiates growth of primordial follicles?

Answer 25

PTEN signalling pathway

Question 26

What does PTEN signalling do?

Answer 26

They keep primordial follicles as primordial follicles and if you disrupt this all the follicles will grow and be lost.

Question 27

What happens in the early stages of follicle development?

Answer 27

Granulosa's continue to divide and oocyte grows. A basement membrane is now made and surrounds this. Thecal cells form around the basement membrane.

Question 28

What is a basement membrane?

Answer 28

A round follicle (barrier to blood vessels and large molecules but can let small molecules through.

Question 29

What are the early stages of follicle growth called?

Answer 29

Pre-antral stages

Question 30

What is an antral follicle (early stage growth does not have this)?

Answer 30

Follicles with fluid-filled antral cavity

Question 31

What happens in antral follicles?

Answer 31

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

Question 32

Why do we have antral cavaties?

Answer 32

Acts as a blood supply when the oocyte is too big not to have one. Takes waste away and gives nutrients too it.

Question 33

When granulosa cells have divided enough what two types of cells do they differentiate into?

Answer 33

Cumulus cells (interact will oocyte) Mural granulosa cells (very steroidogenically active - interact with rest of ovary).

Question 34

What is the Graafian follicle?

Answer 34

When antral follicle is fully grown, ready to ovulate it is called a pre-ovulatory or graafian follicle

Question 35

When does meiosis resume?

Answer 35

When follicle is ready to ovulate

Question 36

What is the other signal which causes the primordial cells to stay at resting stage most of the time?

Answer 36

AMH

Question 37

What do granulosa cells secrete inhibiting the primordial follicles from growing?

Answer 37

AMH

Question 38

What would AMH secretion mean if there wasnt many growing follicles?

Answer 38

There would be less AMH and therefore more growth initiation in the resting pool

Question 39

What is the self regulatory loop between AMH and primordial growth?

Answer 39

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.

Question 40

What are the hormones in follicle development?

Answer 40

FSH and LH

Question 41

What is FSH required for?

Answer 41

Antral follicle Growth

Question 42

What does LH stimulate?

Answer 42

Final stage follicle development and required for ovulation.

Question 43

Do we need FSH and LH for early follicle growth?

Answer 43

No

Question 44

Does the endocrine system regulate antral follicles?

Answer 44

No

Question 45

Does the pill affect the timing of primordial follicle loss?

Answer 45

No

Question 46

Why do women ovulate one oocyte?

Answer 46

Follicle dominance

Question 47

Why does follicle dominance happen?

Answer 47

To regulate how many oocytes are ovulated to maintain better pregnancies

Question 48

What makes a follicle dominant?

Answer 48

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.

Question 49

Why do dominant follicles survive?

Answer 49

FSH levels drop and they have more receptors and can transition into LH more readily - surviving.

Question 50

What happens to the non-dominant follicles?

Answer 50

Subordinate follicles die as they cant get enough FSH or LH when FSH levels drop.

Question 51

Do the dominant follicles bring about the fall in FSH?

Answer 51

Yes through the endocrine loop. Dominant follicles secrete oestrogen and inhibins which have a negative feedback on FSH reducing the FSH in the cell.

Question 52

Does oestrogen and inhibin affect LH?

Answer 52

No