SDN members see fewer ads and full resolution images. Join our non-profit community!


Discussion in 'MCAT Study Question Q&A' started by Farcus, Jun 2, 2008.

  1. Farcus

    Farcus 10+ Year Member

    Nov 28, 2007
    My Bed
    Is menstruation both a positive and negative feedback process? Like during the follicular phase its positive feedback with estrogen leading to more LH causing follicle to actually explode and form corpus lectum. The negative feedback is when the high amount of progesterone with low estrogen brings a negative feedback on the FSH and LH so there wouldn't be more than 1 ova in the oviduct.
  2. SDN Members don't see this ad. About the ads.
  3. RySerr21

    RySerr21 i aint kinda hot Im sauna 7+ Year Member

    Dec 22, 2007
    you are a little confused. during the follicular phase, low levels of estrogen actually inhibit release of FSH and LH. this occurs so that no more than one follicle is maturing.

    Its not til you get really high levels of estrogen that you see the surge in LH. take a look at a graph of the hormones, it will make more sense. if you type in menstruation to wikipedia it has one.
  4. DrMattOglesby

    DrMattOglesby Grand Master Moderator Emeritus 7+ Year Member

    Aug 15, 2007
    i studied this thing and it helped me figure out what happens.
    in short, the follicular phase is thus:

    1. FSH will stimulate Theca cells (on the outer perimeter of the ovum)
    2. Theca cells will then produce an Androgenic Precursor
    3. Androgenic Precursor will go to the Granulosa cells lining the inside of the follicle
    4. ...thus enabling the production of Estrogen by the granulosa cells
    5. and when the [estrogen] is high...then that will trigger a surge of Luteinizing Hormone!
    that is when you see the peak on the graph...often referred to as a LH surge.
    This will be the then trigger the ovulation (ie the ovum leaves the ovary).
    the graph on the bottom of this image depicts the LH surge

    now you are dealing with the remaining follicle that is missing its is called the Corpus Luteum
    since we called it the corpus luteum, it makes sense that this next phase of the cycle is referred to as the luteal phase.
    during luteal phase:
    *if there is fertilization of the egg --> the pregnancy hormone (hCG = human chorionic gonadotropin) will keep the corpus luteum from falling apart.
    it is important that the corpus luteum does not fall apart because it is the source of another hormone: progestorone -- one of the hormones we see rising in the luteal phase.
    progesterone will work to maintain the integrity of the endometrium and ensure that it wont be sloughed off as would be the case during a menstruation.
    *the graph on the top of this image portrays the rising levels of progesterone -- in this instance no fertilization occurred because the progesterone values declined
  5. Farcus

    Farcus 10+ Year Member

    Nov 28, 2007
    My Bed
    So in the follicular phase there is both positive and negative feedback then? ones from low Estrogen that inhibits FSH/LH but when Estrogen is high it stimulates LH and cause ovulation.
  6. Vihsadas

    Vihsadas No summer Moderator Emeritus Lifetime Donor Classifieds Approved 5+ Year Member

    Oct 17, 2007
    An Igloo
    That's the current working theory. There's a cutoff point where this switches. I don't remember exactly why, but I do remember being able to rationalize it once. Maybe someone else knows..
  7. atalkinghead

    atalkinghead 5+ Year Member

    Jun 23, 2007
    From my notes:

    • Menstrual cycle
      • Day 0 --> onset of menses (bleeding) --> progesterone levels are low, endometrium is sloughed
      • Day 1-14 --> follicular phase --> one or more follicles respond to increases in FSH/LH from anterior pituitary
      • Day 14 --> midcycle LH surge --> due to switch of estrogen having negative feedback on hypothalamus/anterior pituitary -->LH surge triggers ovulation (movement of the oocyte out of the follicle and then out of the ovary)
      • Day 14-28 --> luteal phase --> leftover follicle after ovulation (corpus luteum) secretes progesterone --> keeps endometrium intact and stops ovulation (by blocking GT production)
      • Day 28 --> no pregnancy --> corpus luteum degrades -->progesterone drops, menses occurs --> GT start being secreted again

Share This Page