Ovarian function and its control

Question 1

What is a corpus luteum?

Answer 1

-Forms once a dominant follicle has ruptured.
-It is highly vascularised
-Transient endocrine gland
Produces progesterone

Question 2

Describe early germ cell development

Answer 2

• 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

Question 3

What stimulates primordial follicles to develop into primary follicles?

Answer 3

Intra ovarian factors. NOT gonadotrophins

Question 4

What initiates follicle recruitment?

Answer 4

FSH wave

Question 5

Describe the key points of oestradiol production

Answer 5

• 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

Question 6

What stimulates the LH surge before ovulation occurs?

Answer 6

Oestradiol (and progesterone suppresses it)

Question 7

When is meiosis 2 activated?

Answer 7

At fertilisation due to influx of calcium

Question 8

How does the LH surge allow meiosis 1 to be completed?

Answer 8

LH surge removes meiotic inhibitors

Question 9

Describe luteinisation

Answer 9

• Basement membrane breaksdown
• Granulosa cells hypertrophy= large luteal cell
• Theca cells proliferate= small luteal cell
• Intense angiogenesis
• Steroidogenesis switches secretion from oestradiol to progesterone

Question 10

What does the hormone Luteotroph do?

Answer 10

Support the growth/ function of the CL

Question 11

What is StAR?

Answer 11

• 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

Question 12

What does luteolysis enable?

Answer 12

• Follicular development

- Return to oestrus

Question 13

What is the key luteolytic hormone?

Answer 13

PGF2a

Question 14

What is the counter current system of PGF2a in the ovary especially important in the sheep?

Answer 14

• 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.

Question 15

Describe the mechanism of luteolysis incows

Answer 15

-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.