Folliculogenesis

1. Define ovarian folliculogenesis. 

ovarian follicular growth and degeneration occurs continuously throughout the entire estrous cycle

2. Characterize the four processes of ovarian folliculogenesis. 

Recruitment: group of small follicles start to grow and release estradiol.

Selection: follicles selected to be dominant rest go through atresia (they die)

Dominance: preovulatory follicles keep growing

Ovulation: follicle ruptures to release oocyte during ovulation.

3. What is the fate of most of the recruited follicles during folliculogenesis? 

most of the recruited follicles will degenerate (undergo atresia)

4. Compare the basal secretion of GnRH and the preovulatory secretion of GnRH.  Which is the site of production of each of these types of GnRH secretion? What do  they stimulate? What is the profile of each type of GnRH secretion? 

tonic center: responsible for basal secretion of GnRH.

-stimulate basal FSH and LH secretion

-this pattern of secretion of GnRH in small pulses is called episodic profile

surge center: responsible for the preovulatory secretion of GnRH

-stimulates a surge of LH

-secretes basal levels of GnRH until it receives the appropriate positive stimulus of estradiol above a threshold concentration in absence of progesterone

5. How do ovarian steroids regulate the release of GnRH (positive and negative  feedback during the follicular and luteal phases)? 

negative feedback: during the luteal phase (metestrus and diestrus), the corpus luteum secretes P4.

- P4 will prevent high quantities of GnRH to be released from the tonic and surge center of the hypothalamus (negative feedback) which will only allow basal levels levels of FSH and LH to be released.

Low E2 reduces the degree of GnRH neurons firing in the surge center – negative feedback

positive feedback: during the follicular phase (proestrus and estrus), there is no corpus luteum to secrete P4 P4 does not prevent GnRH secretion

-E2 stimulate firing by GnRH neurons in the surge center when is higher than threshold

the preovulatory surge of GnRH occurs, which results in final follicular growth and ovulation

6. What are the roles of each gonadotropin during folliculogenesis? 

FSH

-important for recruitment and secretion of E2

FSH stimulates E2 production so small follicles grow to release E2

LH

-promotes final growth and maturation of dominant follicles and ovulation

7. Explain the hormonal regulation of gonadotropins secretion? 

FSH: its release from the anterior pituitary is inhibited by estradiol and inhibin released by the antral follicles

LH: regulated by GnRH pulse frequency from the hypothalamus, which is inhibited by progesterone.

8. Which types of ovarian follicles are FSH- or LH-dependent? 

FSH: recruited and early selected follicles

LH: dominant and late selection follicles