Ovarian function and its control Flashcards
What is a corpus luteum?
-Forms once a dominant follicle has ruptured.
-It is highly vascularised
-Transient endocrine gland
Produces progesterone
Describe early germ cell development
- Primordial germ cells migrate–> from yolk sac to hind gut to developing gonad.
- Proliferate by mitosis to become oogonia
- Oogonia develop in clusters and then enter meiosis to develop into primary oocytes
What stimulates primordial follicles to develop into primary follicles?
Intra ovarian factors. NOT gonadotrophins
What initiates follicle recruitment?
FSH wave
Describe the key points of oestradiol production
- Involves theca and granulosa layers
- Main enzyme= Aromatase= converts testosterone to oestradiol
- Stimulated by FSH and LH
- Theca cells stimulated by LH produce testosterone, testosterone moves to the granulosa cells where it is converted into oestradiol
What stimulates the LH surge before ovulation occurs?
Oestradiol (and progesterone suppresses it)
When is meiosis 2 activated?
At fertilisation due to influx of calcium
How does the LH surge allow meiosis 1 to be completed?
LH surge removes meiotic inhibitors
Describe luteinisation
- Basement membrane breaksdown
- Granulosa cells hypertrophy= large luteal cell
- Theca cells proliferate= small luteal cell
- Intense angiogenesis
- Steroidogenesis switches secretion from oestradiol to progesterone
What does the hormone Luteotroph do?
Support the growth/ function of the CL
What is StAR?
- Steroid acute regulatory factor
- It is a transport protein that regulated cholesterol transfer to the mitochondria
- Rate limiting step in the production of steroid hormones
What does luteolysis enable?
- Follicular development
- Return to oestrus
What is the key luteolytic hormone?
PGF2a
What is the counter current system of PGF2a in the ovary especially important in the sheep?
- Because majority of PGF2a produced goes directly to the ovary via to ovarian artery to cause luteolysis.
- In the sheep almost all of the PGF2a is denatured by one pass through the lungs, so it must be able to bypass general circulation.
Describe the mechanism of luteolysis incows
-Oxytocin released by the CL and posterior pituitary gland activated the oxytocin receptors in the endometrium of the uterus. Stimulates endometrium to release PGF2a which then acts n the CL to cause luteolysis and further release of oxytocin.