Oogenesis, ovulation and corpus luteum Flashcards
What is oogenesis
Formation and development of the female gamete from undifferentiated germ cell to highly differentiated oocyte ready to be fertilised
When does oogenesis begin and end
Begins in foetal life and ends with fertilisation.
Where do the primordial follicles sit in the ovaries?
They sit within the ovarian cortex.
Describe the maturity of the following cumulus cells:
1. expanded cumulus cells
2. unexpanded cumulus cells
- Mature oocyte
- Immature oocyte
(however, all eggs will still be fertilised)
What is a germinal vescile?
The term germinal vesicle describes the nucelus of an oocyte that is arrested in prophase I. Once germinal vescile breakdown occurs meiosis I can be completed and will result in the first polar body formation,
How mature is the oocyte if you can see the germinal vescile?
Immature
How mature is the oocyte if you cannot see the germinal vesicle but no polar body is present?
Assume the oocyte is undergoing meiosis I
How mature is the oocyte if there is a polar body present?
Fully mature, the oocyte is ready for fertilisation to help complete meiosis II.
Should an IVF collected oocyte be thrown away if it’s too small or too large?
> 200 um oocytes should be thrown away as its either the fusion of two cells or it contains too much cytoplasm and therefore DNA from a polar body
Which out of the following oocyte dimorphisms should be discarded?
- cytoplasm granularity
-vacuoles
- Smooth endoplasmic reticulum discs
Smooth endoplasmic reticulum discs
What name is given to the primordial germ cells when they arrive at the genital ridges
Oogonia (gonocytes)
When do the oogonia start meiosis?
when the pre-granulosa cells surround them
When are oogonia called primary oocytes
When they enter meiosis
When is the first stage that germs cells are lost in the developing ovary
Before birth, when connections break down between primary oocytes
Describe a primordial follicle
A primary oocyte surrounded by a thin layer of pre-granulosa cells
How do we describe ovarian reserve?
quiescent primordial follciles
How often are primordial follicles activated?
A handful every day
What is the difference between a primordial follicle and a primary follicle
Primordial contains a thin layer of pre-granulosa cells surrounding the primary oocyte.
Primary follicles contain a cuboidal layer of granulosa cells surrounding the primary oocyte
Describe a secondary follicle
Primary oocyte surrounded by 2 layers of cuboidal granulosa cells
What happens to the secondary follicle before puberty?
They undergo atresia due to lack of hormone stimulation
What causes the secondary follicle to develop into an antral follicle
FSH
At what stage does the ZP form and the ability to cytodifferentiation is acquired?
Development from primary follicle to secondary follicle
How long does the phase of development from primary follicle to secondary follicle last?
120 days
Describe how the antrum appears
small cavities appear between granulosa cells and then they coalese to form the follicular antrum
What are mural granulosa cells
Granulosa cells that sit around the edge of the antrum
What are cumulus oophorus cells?
Granulosa cell stalk that the oocyte is attached too
At what stages of the oocyte DNA nucleus start to become less active and compacts
At the antral phase
How long does the antral phase last?
8-12 days
Describe the 2 somatic layers surrounding the follicle at the antral stage
- Theca externa - vascular layer
- Theca interna - thick fibrotic layer
Which receptors are present on theca interna cells?
And what hormone production do they stimulate?
LH
Cholesterol to Androgens
Which receptors are present on granulosa cells during antral follicle stage?
And what hormone production do they stimulate?
FSH
Androgens to oestrogen
Which hormones stimulate granulosa cells to grow at antral follicle stage?
Androgens and oestrogen
(as well as FSH and LH)
At what point are there also LH receptors on granulosa cells?
When there are high levels of LH
Describe the selection of the dominant (graafian) follicle
The most mature follicle develops LH receptors on the granulosa cells so when FSH levels drop, this follicle can rely on this to still recieve hormonal input to grow. Whereas the rest can’t and so die off
Describe other features of adaptation that help graafian follicle to survive in the FSH drop:
Dominant follicle more fit to cope with declining FSH levels
- high FSH receptor levels
- increased vascularity in the theca layer (preferential delivery of FSH to this follicle)
- LH receptor in granulosa cells
Does oestrogen or progesterone increase the frequency of GnRH pulses
Oestrogen increases
Progesterone decreases
Does high frequency GnRH pulses stimulate the release of LH or FSH
LH
What effect does the LH surge have on the oocyte and the follicle?
- ovulation
- final maturation of the oocyte (via progesterone also) - DNA condensation
- differentiation of theca and granulosa cells to luteal cells (lutinisation)
What do theca cells secrete
progesterone
At what point is an oocyte called secondary oocyte
Once it has completed the first meiotic division and has produced a polar body
What enzymes help with ovulation?
Matrix metalloproteinases digest proteins to make the surface of the ovary thin
