A duration of 28 days in the female reproductive cycle is divided into 4 phases –
- Menstrual Phase
- Preovulatory Phase
- Ovulatory Phase
- Post-Ovulatory Phase
(A) Menstrual Phase [ First 5 days of the cycle / menses=month / Menstruation]
As the Influence of FSH (Follicle stimulating hormone)
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Primordial follicles develop & then into
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Primary follicles & then change into secondary follicles in the ovaries
(A follicle that begins to develop in a particular cycle may ovulate after several cycles later)
Menstrual flow is about 50-150 ml occurs through the uterus
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as a decline in progesterone & estrogen level
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which causes the release of prostaglandins
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Arterioles become constrict & O2 deprived cells begin to die
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Stratum functionalis ( functional layer) sloughs off
(B) Preovulatory Phase [Proliferative Phase]-
[ Time between the end of menstruation & ovulation / 6-13 days in 28 days cycle]
secondary follicles secrete estrogen (1 from both ovaries)
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Become dominant follicle
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Estrogen decreases secretion of FSH by dominant follicles
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stop the growth of other follicles
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One mature dominant (Graafian follicle) continue to enlarge (>20 mm in diameter)
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estrogen within the follicle stimulate and repair the endometrial wall
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Mitosis in the cells of stratum basalis & produce a new stratum functionalis (4-10 mm diameter)
(C) Ovulation – [Rupture of Graafian follicle & release of 2˚ oocyte, on the 14th day of cycle]
High level of estrogen in the last part of the pre-ovulatory phase
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Exert positive feedback on a cell that secretes LH & GnRH ( Gonadotropin-releasing hormone )
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GnRH promote the release of FSH & LH by the anterior pituitary
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LH causes rupture of the Graafian follicle
Note – Expulsion of 2˚ oocyte about 9 hours after the peak of the LH surge.
(D) Post Ovulatory Phase –
[ Secretory Phase / Luteal Phase / Time between the ovulation & onset of next menses / from 15-28 days in a 28-day cycle.]
After ovulation mature follicle collapses
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Basement membrane between granulosa cell & theca cell breaks down and change into corpus luteum
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Corpus luteum secretes progesterone, estrogen, relaxin, inhibin [Luteal phase]
* If 2˚ oocyte not fertilized corpus luteum has a lifespan of 2 weeks, becomes corpus albicans
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Progesterone, estrogen, inhibin decreases & GnRH, FSH & LH increases due to loss of negative feedback suppression by ovarian hormones
* If 2˚ oocyte fertilized
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Corpus luteum persists past its normal 2-week life span
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Rescued from degeneration by hCG
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hCG (Human chorionic gonadotropin) produced from chorion of an embryo after the 8th day of fertilization
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Progesterone, estrogen produced by corpus luteum promote the growth of the endometrial gland
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Secretory activity of endometrial gland increases
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which secretes glycogen [in secretory phase for the nourishment of fetus]
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