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Menstrual cycle
The menstrual cycle involves changes in the ovaries and uterus across approximately 28 days. In the ovaries, a follicle grows and matures, culminating in ovulation around day 14 when the mature egg is released. After ovulation, the ruptured follicle transforms into the corpus luteum which secretes progesterone and estrogen to prepare the uterus in case of fertilization. If fertilization does not occur, progesterone and estrogen levels drop and the endometrial lining is shed through menstruation, starting a new cycle.
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Menstrual cycle
- 1.
- 2. Onset of menstruation Day 1 Day 1 0 4 8 12 16 20 24 28 Menstruation
- 3. Key events inovarian cycle Day 1 LH 1. Follicular growth 0 4 8 12 16 20 24 28 Oestradiol Ovulation Menstruation
- 4. LH surge Day 1 LH Day 1 Days before Days after Follicular phase Luteal phase 0 4 8 12 16 20 24 28 Ovulation Menstruation
- 5. Key events inovarian cycle LH 2. Ovulation Day 1 1. Follicular growth 0 4 8 12 16 20 24 28 Oestradiol Ovulation Menstruation
- 6. When does ovulationoccur? The timing of ovulation varies with the length of a woman's menstrual cycle. In the average 28 day menstrual cycle, the LH surge usually occurs between cycle days 11-13 and ovulation follows about 36-48 hours later, on or close to cycle day 14.
- 7. Key events inovarian cycle LH 2. Ovulation Day 1 1. Follicular growth 3. Luteal function 0 4 8 12 16 20 24 28 Oestradiol Oestradiol (& Progesterone) Ovulation Menstruation
- 8. Key events inovarian cycle LH 2. Ovulation Day 1 1. Follicular growth 3. Luteal function 4. Luteal regression 0 4 8 12 16 20 24 28 Oestradiol Oestradiol (& Progesterone) Ovulation Menstruation
- 9. The follicle isthe fundamental element of the ovary Cumulus Oocyte cells Antrum Zona pellucida
- 10. What control follicular growth? Hypothalamus GnRH Pituitary Steroid LH feedback FSH Ovary Estradiol Reproductive tract
- 11. What control follicular growth? ????? Gonadotropin independent Ovulation 4 8 12 16 20 24 28 0 Oestradiol Menstruation As each follicle grows, it produces increasing amt of Estradiol
- 12. The follicle isthe fundamental element of the ovary LH Androgens are converted (aromatized) to estradiol by granulosa cells Androgens FSH Oestradiol Inhibin
- 13. Hypothalamus Increasing GnRH –ve feedback - Pituitary mechanism Inhibin suppress Increasing amount of LH ↓FSH FSH estradiol + Ovary Estradiol + Reproductive tract
- 14. FSH As the follicle grow, FSH level fall due to the –ve feedback mechanism Estradiol 0 4 8 12 16 20 24 28
- 15. Why is onlyone selected & become dominant ? Many follicles at the start of the cycle Ovulation 4 8 12 16 20 24 28 0 Menstruation
- 16. Hypothalamus Increasing GnRH –ve feedback - Pituitary mechanism Inhibin suppress Oestradiol ↓FSH FSH + Small folicle Ovary Large folicle very dependent independent on on FSH FSH Growth factor estradiol X Dominant + + follicle
- 17. FSH secretion suppressed FSH Estradiol Dominant follicle (s) can survive Insufficient FSH to keep smaller follicle going to become atretic 0 4 8 12 16 20 24 28
- 18. What causes ovulation? Oestradiol What effects does it have ? What causes LH surge ? 0 4 8 12 16 20 24 28
- 19. Hypothalamus For most ofthe cycle negative feedback GnRH mechanism - operates Pituitary ↓ LH & FSH LH Inhibited by FSH estradiol Estradiol Ovary
- 20. Hypothalamus ↑GnRH But, with high level of estradiol GnRH maintained for + ↑Sensitivity to GnRH long enough Pituitary + LH surge Estradiol Ovary
- 21. How does theLH surge affects the follicle ? About 36 h between LH surge & oocyte release…..
- 22. Oocyte Loosening ofthe cumulus cells Enzyme induction in the follicle wall Oocyte
- 23. Transformation of rupturedfollicle into corpus luteum Mature follicle become Corpus luteum Steroid secretion changes Progesterone + Estradiol
- 24. What maintains the CL ? Follicular phase Luteal phase Estradiol domination Progesterone domination Why does the CL degenerates at the end of the cycle ? 0 4 8 12 16 20 24 28 Ovulation
- 25. What maintains the CL ? Hypothalamus ~8 h between LH pulses GnRH Pituitary LH very low levels CL CL very sensitive Progesterone + to LH E2
- 26. What maintains the CL ? Hypothalamus - GnRH Steroid negative feedback keeps Pituitary LH & FSH level relatively low - LH (low levels in CL + luteal phase) Progesterone + E2 CL very sensitive Reproductive to LH tract etc
- 27. Towards the end Hypothalamus of the cycle, the sensitivity to LH reduces GnRH Pituitary The low level of LH are insufficient to keeps the CL LH going CL degenerates Progesterone + E2
- 28. Hypothalamus GnRH As CL degenerates Pituitary steroid negative feedback reduces ↑ FSH + LH Progesterone +of folicles A new wave stimulated by rising FSH & LH E2
- 32. Other changes inthe cycle 1. Outer muscles layer the myometrium 3. Inner glandular layer mucusa the endometrium
- 33. Uterine changes inmenstrual cycle Endometrial depth Estradiol cause an ↑ in More secretion from the thickness gland, hence the term (the proliferative phase) secretory phase 0 4 8 12 16 20 24 28 Opt time for Ovulation implantation
- 34. Time course ofmenstruation Onset of menstruation is rapid Probably, 95% women have a total blood loss of less than 60 ml This blood loss can represent as a significant loss of iron (leading to anemia)- especially in women on marginal diet
- 35. Menstruation….Why ? In preparationof pregnancy, the human uterine stromal cells go through complex changes and the stromal cells terminal differentiate If implantation and pregnancy do not occur, this tissue is lost and the uterus prepares itself again for another possible pregnancy
- 36. Key events inovarian cycle LH 2. Ovulation Day 1 1. Follicular growth 3. Luteal function 4. Luteal regression 0 4 8 12 16 20 24 28 Oestradiol Oestradiol (& Progesterone) Ovulation Menstruation
- 37.
Editor's Notes
- #7 (It is the mid-cycle surge of the hormone LH that causes the dominant follicle to rupture and release the mature egg.)