Human Reproduction - Notes | Class 12 | Part 5: Menstrual Cycle

Menstrual Cycle (Reproductive Cycle)

Menstrual Cycle (Reproductive Cycle)

  • It is the cyclic events in female reproductive system starting from one menstruation till the next during the reproductive period (from puberty to menopause).
  • Its duration is 28 or 29 days.
  • Menstrual cycle is also seen in other primates.
  • Menstrual cycle includes Ovarian cycle (changes in ovary) & Uterine cycle (changes in uterus, oviduct & 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.
  • Menstruation occurs if the released ovum is not fertilized. It results in breakdown of endometrial lining and its blood vessels that comes out through vagina.
  • Lack of menstruation indicates pregnancy. It may also be caused due to stress, poor health etc.
  • Menarche: The first menstruation during puberty.

II. Follicular (Proliferative) Phase: 5-13th Day

  • It starts from 5th day after menstruation and completed within 8-12 days.
  • In this phase, the action of gonadotropins (FSH & LH) from pituitary occurs. FSH stimulates:
    • Development of primary follicles into Graafian follicles.
    • Secretion of oestrogens by Graafian follicles.
  • Oestrogens stimulate:
    • Proliferation of ruptured uterine endometrium and mucus lining of oviduct & vagina.
    • Development of secondary sexual characters.
    • Suppression of FSH secretion.
    • 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 to a yellow endocrine mass called Corpus luteum. It secretes progesterone.
  • Functions of progesterone:
    • Makes the endometrium maximum vascular, thick and soft. Thus, the uterus gets ready for implantation.
    • Inhibits the FSH secretion to prevent development of a second ovarian follicle.
  • If fertilization does not occur, corpus luteum degenerates. It causes disintegration of endometrium. It leads to next menstruation and new cycle.
  • If a woman becomes pregnant, all events of menstrual cycle stop and there is no menstruation.
  • Menstrual cycle ceases around 50 years of age. It is called Menopause.

Menstrual Hygiene

  • Take bath and clean body regularly.
  • Use sanitary napkins or clean homemade pads.
  • Change them after every 4–5 hrs as per the requirement.
  • Dispose the used napkins or pads properly. Do not throw them in the drainpipe of toilets or in the open area.
  • After handling the napkin, wash hands with soap.

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