The Menstrual Cycle

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  • Created by: chloe
  • Created on: 29-04-13 18:23
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  • Menstrual Cycle
    • lasts about 28 days but can vary
    • cycle is continuous with the one that went before and the one that will follow
    • first day of menstruation is considered as 'day 1' of the cycle
      • menstruation is the loss of the inner layer of the endometrium accompanied by a small volume of blood
    • made up of 2 phases
      • follicular
        • FSH from anterior pituitary stimulates the development and maturation of Graafian follicle and production of oestrogen by the ovarian tissues
        • as the concentration of oestrogen builds up, it brings about repair and proliferation of the endometrium
        • eventually the high concentration of oestrogen triggers a surge in production of LH by the anterior pituitary at about day 14
        • the surge of LH is the direct cause of ovulation since it makes the blister like wall of the graafian follicle rupture and release the egg
        • egg is then moved slowly along the oviduct, during a short period of about 3 to 4 days , fertilisation may occur if the egg meets a sperm
      • luteal
        • follows ovulation
        • LH stimulates the graafian follicle to become the corpus luteum which secretes progesterone and oestrogen
        • the rise in progesterone concentration stimulates further development of the endometrium
          • it becomes thick, vascular and spongy, ready to accept  and nourish an embryo, if fertilisation takes place and the embryo becomes implanted
        • combined high levels of oestrogen and progesterone during this luteal phase also trigger an inhibitory efect on the anterior pituitary
        • concentrations of FSH and LH drop as a result and no new follicles develop at this time
        • lack of LH leads to the degeneration of the corpus luteum by about day 22, this is followed by a rapid drop in progesterone
        • by day 28 these ovarian hormones are at such a low level that the endometrium can no longer be maintaines and menstruation begins


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