progesterone

   This is the hormone secreted after ovulation by the corpus luteum. It is a steroid (a cholesterol with a funny hat), enters receptive cells to stimulate their growth, and acts as an anabolic agent. Estrogen should be viewed as the primary coat underneath all the cycles during a woman's reproductive years, with progesterone, its antagonist, surging for ten or twelve days in ovulatory months. Most of the actions of progesterone cannot occur without estrogen having previously induced the growth of progesterone-receptive binding sites. In the estrus cycle, estrogen stimulates the thickening of membranes (the proliferative phase), and progesterone stimulates their sophistication into organized and secreting mucosa (the secretory phase). The new secretions contain anticoagulants, antimicrobials, and rich mucus fluids. If there is pregnancy, the uterine membranes are fully structured for the long haul; if menses occurs, the thickened tissues can erode away without clotting, becoming infected, or flowing poorly. If there is not enough estrogen, the corpus luteum will not mature. If the corpus luteum is weak, menses becomes disorganized, clotty, and painful. It is also the first part of the cycle to become disorganized in early menopause, since the available ovarian proto-follicles have been reduced over the years to only a few. In earlier years, dozens of potential follicles may attempt maturity each month, with only the strongest one able to reach dominance, form a corpus luteum and an ovum...the rest disintegrating. In a manner of speaking, the better the follicle, the better the corpus luteum and (presumably) the sounder the ovum. Since the number of potential follicles is fixed at birth, by early menopause those that still remain contain a high number of hormone-resistant and unsound proto-follicles, resulting in more and more cycles having less predictable estrogen and especially progesterone levels.