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.
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