Menstrual Cycle process

• • It is the cyclic events starting from one menstruation till the next that take place during the reproductive period (from puberty to menopause) of a woman’s life. Its duration is 28 or 29 days.
  •  Menstrual cycle is also seen in other primates.
    Menstrual cycle includes
    a. Ovarian cycle: Changes in ovary.
    b. Uterine cycle: Changes in uterus, oviduct and vagina.
    Menstrual cycle has the following phases
    I. Menstrual phase: 1-5th day
  • The cycle starts with menstrual flow (bleeding).
  •  It lasts for 3-5 days.
  • It is due to the breakdown of the endometrial lining and blood vessels of the uterus that comes out through the vagina.
  • Menstruation occurs if the released ovum is not fertilized.
  • Lack of menstruation may be indicative of pregnancy.
  • It may also be caused due to stress, poor health etc.
    II. Follicular (Proliferative) phase: 5-13th day
  • It starts on 5th day after menstruation and completed within 8-12 days.
  •  In this phase, the action of gonadotropins (FSH &LH) from pituitary occurs. FSH stimulates
  • 1. Development of primary follicles into Graafian follicles.
  • 2. Secretion of oestrogens by Graafian follicles.
  • Oestrogens stimulate
    1. Proliferation of ruptured uterine endometrium and mucous lining of oviduct & vagina.
    2. Development of secondary sexual characters.
    3. Suppression of FSH secretion.
    4. Secretion of LH (Luteinizing hormone).
    III. Ovulatory phase: 14th day
  • LH & FSH attain a peak level in the middle of cycle.
  • Rapid secretion of LH (LH surge) induces rupture of Graafian follicle and thereby ovulation (on 14th day).

IV. Secretory (Luteal) phase: 15-28th day

•  After ovulation, Graafian follicle is transformed into a yellow endocrine mass called Corpus luteum. It secretes progesterone. By the action of progesterone,
• Endometrium attains maximum vascularity, thickness and softness. Thus the uterus gets ready for implantation.
• FSH secretion is inhibited to prevent development of a second ovarian follicle.
• During pregnancy all events of menstrual cycle stop and there is no menstruation.
• If fertilization does not occur, corpus luteum degenerates and becomes a whitish mass (corpus albicans). As it has no secretory ability, progesterone level in blood decreases. It leads to menstruation indicating a new cycle.
  1. Menarche: The first menstruation during puberty.
  2.Menopause: Stopping of menstrual cycle (at about 50 yrs of age).
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