Human Reproduction - Notes | Class 12 | Part 5: Menstrual 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: 1-5^th 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: 5-13^th Day

• It starts from 5^th 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: 14^th 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 14^th day).

IV. Secretory (Luteal) Phase: 15-28^th 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.

Select Next Topic 👇

• Topic 1: Male Reproductive System
• Topic 2: Female Reproductive System
• Topic 3: Spermatogenesis
• Topic 4: Oogenesis
• Topic 6: Fertilization and Implantation
• Topic 7: Pregnancy, Embryonic Development, Parturition, Lactation

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