The Follicular Phase of the Estrous Cycle Flashcards
what are the 4 major events of the follicular phase?
- elevated gonadotropin secretion from anterior pituitary
- follicular growth and preparation for ovulation
- sexual receptivity
- ovulation
what is the driving force for initation of the follicular phase?
luteolysis (of previous CL)
list the cascade of events that occur in response to luteolysis
- decreased progesterone
- negative feedback removed
- increased amplitude (concentration) and frequency of GnRH
- initial increase of FSH and LH
- increased estradiol
what triggers the LH surge in spontaneous ovulators?
high levels of E2
what triggers the LH surge in induced ovulators?
high levels of E2 and neurological stimulation
does a follicle have to be at a certain stage to undergo atresia?
no, any follcile at any stage can undergo atresia
what percent of monovulatory follicles undergo atresia?
99%
what is superovulation?
the process of rescuing follicles from undergoing atresia with FSH treatment
about how many follicles is a cow born with?
100,000
how many follicles does a cow have at 100 days of gestation (pre-birth)?
2.9 million
how many follicles does a cow have at 12 months of age?
75,000
how many follicles does a cow have between 4-6 years old, her peak breeding years?
21,000
how many follicles does an aged cow have?
2,500
what does a cow enter at 20-25 years of age?
reproductive scenesence, equivalent to menopause
what is cyclic recruitment, or emergence?
phase when a group (cohort) of a small antral follicles begin to grow and secrete estradiol
what is selection?
recruited follicles get selected to become dominant or undergo atresia
what is dominance?
large antral follicle in final stage of maturation
what happens to a dominant follicle in the presence of high LH?
ovulation
what happens to a dominant follicle in the presence of low LH?
atresia
describe the difference between atresia and necrosis?
atresia is the moderated, clean, organized, non-infectious process of destroying follicles through apoptosis; necrosis is never good!!
what is atresia?
degeneration of follicle prior to ovulation
what are the 2 stages of initial follicular growth?
- initial recruitment
2. cyclic recruitment
which phase of follicular growth is gonadotropin independent?
initial recruitment
how long does initial recruitment last?
50-60 days
how long does cyclic recruitment last?
only a few days
what does gonadotropin independent mean for follicular growth?
does not require LH or FSH
when does cyclic recruitment begin?
when small antral follciles get FSH receptors
what are follcilular waves in accordance with?
CL lifespan
what happens if the dominant follicle is ready when a CL is still present?
no signal to ovulate, leading to atresia and a new wave
what intiates recruitment?
high levels of FSH
describe FSH, E2, and inhibin levels during selection
FSH low from negative feedback, high E2 and inhibin furhter lower FSH
describe FSH, E2, and inhibin levels during dominance
FSH is VERY low, E2 and inhibin are VERY high
decribe FSH levels after atresia
FSH increasing again
what happens to the developing follicle during dominance?
follicle starts getting LH receptors in granulosa cells; follicle can now respond to LH for continued growth
will a 2-wave or a 3-wave cycle have longer follicular waves?
2- wave cycle
list the steps of LH producing E2 (3)
- LH signals to theca cells to produce testosterone using cAMP pathway
- testosterone diffuses into granulosa cell
- FSH drives conversion of testosterone to E2 using the cAMP pathway