Principles of Ovarian Follicular & Luteal Dynamics Flashcards
What is the history of female reproduction?
- in the 5th century BC, HIPPOCRATES suggested that generation of a new lifer was the action of 2 kinds of semen (male ejaculate & female menstrual blood)
- a century later, ARISTOTLE characterized the ovary as an imperfect vestige of the male testis w/ no apparent function
- in the mid-1600s, a Dutch physician, REGNIER DE GRAAF, recognized the ovary as an organ for egg production
- all of these early modern scientists, however, held the mistaken belief that the follicle itself was the egg
- in 1827, Estonian physician, KARL ERNST VON BAER, provided the 1st description of a mammalian egg from his microscopic study of ovarian vesicles (follicles) in the ovary of a dog
What is continuous follicular dynamics?
follicular growth & regression is a continuous pattern & is independent of the phase of the reproductive cycle
What is wave pattern follicular dynamics?
a reservoir of antral follicles remains in a resting stage, & at a particular time in each sp, 1 or several of these follicles begin to grow & reach maturity during the ensuing estrus
What are more than 95% of bovine estrus cycles composed of?
either 2 or 3 follicular waves
What 4 things do follicular dynamics consist of?
- recruitment
- selection
- dominance
- atresia
How do dominant follicles work in monotocous vs polytocous spp?
in monotocous sp (giving birth to a single offspring) ex: cow, mare, & woman, most reproductive physiologists consider that a single follicle is selected & will develop dominance. however, in polytocous spp (litter bearers), multiple dominant follicles are present
GnRH release & follicular dynamics
- tonic & surge centers in the hypothalamus control GnRH release
- the release of GnRH from the tonic center neurons occurs spontaneously in a rhythmic fashion
- antral follicles of various sizes develop on response to tonic levels of FSH & LH & these antral follicles are always present
- GnRH RELEASE FROM THE SURGE CENTER IS CONTROLLED BY HIGH ESTROGEN (which comes from growing antral follicles in the form of estradiol) ACCOMPANIED BY LOW PROGESTERONE. (it is essential to turn on the surge center to achieve ovulation)
The dynamics of follicles are synchronized by the interaction of which 4 hormones?
- FSH (follicle stimulating hormone)
- LH (luteinizing hormone)
- estradiol
- P4 (progesterone)
What is recruitment?
- SMALL ANTRAL FOLLICLES ARE RECRUITED FROM THE OVARIAN POOL & PRODUCE SMALL AMTS OF E2
- the phase of follicular development in which a cohort (group) of small antral follicles begins to grow
- EMERGENCE OF A FOLLICULAR WAVE IS PRECEDED BY A SURGE IN PLASMA FSH CONCENTRATIONS (peak concentrations of FSH on the day before the follicular wave emergence)
What is selection?
- follicles are selected from previously recruited small follicles & either become atretic or develop further
- selected follicles produce moderate amounts of E2
- follicles (not all) start shifting their dependence from FSH to LH, so they acquire LH responsiveness
What is dominance?
- The dominant follicle of a wave is defined as the one that reaches the largest diameter
- SELECTED FOLLICLES THAT DO NOT BECOME ATRETIC BECOME DOMINANT FOLLICLES THAT PRODUCE LARGE QUANTITIES OF E2
- DOMINANT FOLLICLES WILL OVULATE
- IN POLYTOCOUS SPP, MORE THAN ONE FOLLICLE IS SELECTED. HOWEVER IN MONOTOCOUS SPP ONLY A SINGLE FOLLICLE IS SELECTED.
What is atresia?
degeneration of antral follicles
How does the dominant follicle become dominant?
- FSH starts the follicular wave
- IN THE FACE OF THE POSTSURGE DECLINE IN FSH, THE GROWTH OF MOST OF THE FOLLICLES IN OF A WAVE STOPS, & THEY BEGIN TO REGRESS w/in 2 to 5 days of emergence
- the transient rise in FSH permits sufficient follicular growth so that some (not all) follicles acquire LH responsiveness
- the ability of the dominant follicle to transition from FSH to LH is critical for the selection of a single dominant follicle in cattle
- THE DOMINANT FOLLICLE MAINTAINS ITS GROWTH BY TRANSITIONING ITS DEPENDENCE FROM FSH TO LH
How are dominant follicles ovulated?
- dominant follicle produces increasing amts of estradiol (estrogen), which causes positive feedback to the anterior pituitary
- ONCE ESTROGEN LEVELS REACH A THRESHOLD LEVEL, A SURGE OF LH (at least 10x greater than tonic levels) results in ovulation
- peak estradiol concentration in the follicular fluid of the ovulatory follicle is twice as high as the peak in anovulatory dominant follicles
What happens when estradiol crosses its threshold?
- it turns its negative feedback on GnRH secretion to positive feedback; resulting in LH surge for ovulation
Follicular phase: - hypothalamus -> releases GnRH -> acts on anterior pituitary -> releases FSH & LH -> act on follicles in ovaries (PITUITARY HORMONE EFFECT: LH & FSH stimulate several follicles to grow) -> Estradiol negative feedback on hypothalamus (OVARIAN HORMONE EFFECTS: follicles produce low levels of estradiol that inhibit GnRH secretion by the hypothalamus, keeping LH & FSH levels low)
Ovulation: - hypothalamus -> releases GnRH -> acts on the anterior pituitary -> releases FSH & LH -> act on follicles in ovaries (PITUITARY HORMONE EFFECT: LH & FSH stimulate maturation of 1 of the growing follicles) -> estradiol positive feedback on hypothalamus (OVARIAN HORMONE EFFECTS: growing follicles begin to produce high levels of estradiol which stimulate GnRH secretion by the hypothalamus. LH & FSH levels rise, resulting in ovulation about a day later
