Sunday, July 26, 2020

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

o Development of primary follicles into Graafian follicles.

o Secretion of oestrogens by Graafian follicles.

-    Oestrogens stimulate

o  Proliferation of ruptured uterine endometrium and mucus lining of oviduct & vagina.

o  Development of secondary sexual characters.

o  Suppression of FSH secretion.

o  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:

o  Makes the endometrium maximum vascular, thick and soft. Thus, the uterus gets ready for implantation.

o  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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