3. HUMAN REPRODUCTION
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
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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