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The Menstrual Cycle: A Comprehensive Overview
The menstrual cycle is a reproductive cycle occurring in female primates (e.g., monkeys, apes, and humans). In human females, menstruation is repeated at an average interval of about 28/29 days.
1. Menstrual Phase (Days 1–5)
Trigger: Lack of fertilization leads to the degeneration of the Corpus Luteum.
Action: Progesterone levels fall, causing the breakdown of the endometrial lining of the uterus and its blood vessels.
Result: Menstrual flow (blood and tissue) exits through the vagina.
2. Follicular Phase / Proliferative Phase (Days 6–13)
Ovarian Changes: Primary follicles in the ovary grow to become a fully mature Graafian follicle under the influence of FSH (Follicle Stimulating Hormone).
Uterine Changes: The endometrium regenerates through proliferation, stimulated by Estrogen.
Hormones: Both LH and FSH increase gradually.
3. Ovulatory Phase (Day 14)
The Peak: Both LH and FSH attain a peak level in the middle of the cycle.
LH Surge: Rapid secretion of LH induces the rupture of the Graafian follicle.
Result: The release of the secondary oocyte (Ovulation).
4. Luteal Phase / Secretory Phase (Days 15–28)
Formation: The remaining parts of the Graafian follicle transform into the Corpus Luteum.
Progesterone: The Corpus Luteum secretes large amounts of Progesterone, which is essential for maintaining the endometrium (necessary for implantation).
Fate:
If Fertilization occurs: The endometrium is maintained; the cycle stops (Pregnancy).
If Fertilization does NOT occur: The Corpus Luteum degenerates, leading to the next menstrual phase.
Menarche: The first menstruation at puberty.
Menopause: The permanent cessation of menstruation (usually around age 50).
LH Surge: The specific trigger for ovulati#NEETBiology #MenstrualCycle #Class12Biology #HumanReproduction #NEET2025 #BiologyWithDipti #NCERTBiology #MedicalAspirants
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NEET Tip: Focus on the graph in the NCERT textbook. Pay close attention to which hormone peaks first (Estrogen) and which peaks highest during the Luteal phase (Progesterone)