TNPSC Free Notes Biology -Menstrual cycle

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

Menstrual cycle

The menstrual or ovarian cycle occurs approximately once in every 28/29 days
during the reproductive life of the female from menarche (puberty) to menopause
except during pregnancy
Menstrual cycle comprises of the following phases
1. Menstrual phase
2. Follicular or proliferative phase
3. Ovulatory phase
4. Luteal or secretory phase
1. Menstrual phase
• The cycle starts with the menstrual phase when menstrual flow occurs and lasts
for 3-5 days.
• Menstrual flow is due to the breakdown of endometrial lining of the uterus, and
its blood vessels due to decline in the level of progesterone and oestrogen.
• Menstruation occurs only if the released ovum is not fertilized.
2. Follicular or proliferative phase
• The follicular phase extends from the 5th day of the cycle until the time of
ovulation.

• During this phase, the primary follicle in the ovary grows to become a fully
mature Graafian follicle and simultaneously, the endometrium regenerates through
proliferation.
3. Ovulatory phase
• Both LH and FSH attain peak level in the middle of the cycle (about the 14th
day).
• Maximum secretion of LH during the mid-cycle called LH surge induces the
rupture of the Graafian follicle and the release of the ovum (secondary oocyte)
from the ovary wall into the peritoneal cavity.
• This process is called as ovulation.
4. Luteal or secretory phase
• During luteal phase, the remaining part of the Graafian follicle is transformed
into a transitory endocrine gland called corpus luteum.
• The corpus luteum secretes large amount of progesterone which is essential for
the maintenance of the endometrium.
• In the absence of fertilisation, the corpus luteum degenerates completely and
leaves a scar tissue called corpus albicans.
• It also initiates the disintegration of the endometrium leading to menstruation,
marking the next cycle.

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