Control of the ovaries Flashcards
Control of the Ovaries
- Sequence of events depends on pulsatile secretion of GnRH from the hypothalamus
- Frequency and amplitude of these changes over the course of the menstrual cycle
- Responsiveness of the anterior pituitary gland to GnRH and ovaries to LH and FSH differ over the course of the menstrual cycle
What is The Ovarian Cycle?
Day 1-5: GnRH increases FSH and LH secretion, this causes primordial follicles to mature into primary follicles
Days 6-15: small # of primary folllicles form secondary follicles, the dominat follicle matures
~ 2 days before ovulation: small surge in LH and FSH, causes follicle to expand and form swelling on surface of ovary
~ 16 gours before ovulation: Surge is FSH and LH leads to final maturation of the follicle. Follicle ruptures and oocyte released
What is the Uterine Cycle?
What is HCG?
human chorionic gonadotropin (HCG)-
prevents degeneration of the corpus luteum
progesterone and estrogen levels are maintained
What are the roles of FSH and LH during the Early follicular phase?
FSH:
- causes proliferation of granulosa cells
- leads to an enlargement of the antrum
- increases estrogen
LH
- proliferation of theca cells
- production of androgens (primarily
androstenedione)
make into two seprate acrds
What are the roles of FSH and LH during the Early follicular phase?
What occurs in the Early and Middle Follicular Phase?
- Dominant follicle formed, developing follicles have undergone atresia
- Dominant follicle matures and LH receptors appear on its granulosa cells
- Increase in plasma [estrogen]
- Reduced release of GnRH from hypothalamus and reduced sensitivity of anterior pituitary to GnRH
- Reduction in plasma [FSH and LH]. [FSH] decreases more than LH due to inhibin release from granulosa cells.
Early and Middle Follicular Phase Negative Feedback Loop:
What occurs in the Late Follicular Phase?
- Primary follicle continues to increase plasma [estrogen]
- Positive feedback of estrogen on anterior pituitary
- Increased release of GnRH from hypothalamus and increased
sensitivity of anterior pituitary to GnRH - FSH and LH surge
- Ovulation and formation of corpus luteum
- Reduction in FSH and LH as soon as ovulation occurs
Late Follicular Phase Positive Feedback Loop:
What occurs in the Luteal Phase?
- Corpus luteum maintained by low but adequate [LH] (for about 14 days)
- Increased plasma [estrogen] and [progesterone]
- Reduced FSH and LH release from anterior pituitary (no fertilization)
- Degradation of corpus luteum
- Reduced plasma [estrogen] and [progesterone]
- Increased plasma [FSH] and [LH]
Luteal Phase Negative Feedback Loop:
An endurance athlete undergoes amenorrhea for two years while she trains for the olympics. What hormone(s) might contribute to this? What do you hypothesize is the evolutionary mechanism for this?
GnRh, LH, FSH
Energy efficency and weight loss due to not meeting caloric needs
