Regulatory circuit of gonads

Female Reproductive System

Menstrual Cycle

Image Female Reproductive and Menstrual Cycle System used under license from Shutterstock.com.

  1. Early chromosome and SRY tests (1960s–1990s)
  • At the Olympic Games from 1968 onwards, the IOC introduced mandatory “sex tests.”
  • Initially simple physical examinations, then chromatin tests (Barr bodies), and later also SRY gene tests.
  • Reason: To prevent men from competing in women’s competitions.
  1. Ewa Kłobukowska (Poland, 1967)
  • European champion, Olympic medalist in athletics.
  • Failed an early chromosome test → she had XX/XY mosaicism (intersex variation).
  • Result: Lifetime ban, even though she bore no responsibility.
  1. María José Martínez-Patiño (Spain, 1985)
  • Hurdler.
  • Chromosome test showed 46,XY → she had the SRY gene and Androgen Insensitivity Syndrome (AIS).
  • Her body developed as female, and she had no advantage from testosterone (because the androgen receptors did not function).
  • Nevertheless, she was excluded from competition.
  • Later, she strongly campaigned against these tests – with success: in 1999, the IOC abolished blanket chromosome testing.
  1. Caster Semenya (South Africa, since 2009)
  • 800m runner, multiple world and Olympic champion.
  • Examinations revealed 46,XY with functional SRY → testes produced testosterone.
  • The International Association of Athletics Federations (IAAF, now World Athletics) therefore introduced testosterone limits:
    • Female athletes with XY/DSD and SRY must lower their testosterone levels medically in order to compete.
  • Semenya today (as of 2025) is no longer allowed to compete in her preferred events because she does not want to take medication.
  1. Other known cases
  • Several anonymous DSD athletes at World Championships and Olympic Games have been flagged in recent decades, but their names were often not disclosed (privacy protection).
  • The issue was always the same: SRY gene present → development with increased testosterone → athletic advantage in women’s category.
  1. Conclusion
  • The presence of the SRY gene was decisive in some cases for top-level performances in women’s sport.
  • Most famous examples:
    • Martínez-Patiño (AIS, Spain) → no advantages, but excluded.
    • Caster Semenya (XY with SRY, South Africa) → likely advantages due to higher androgen effects.

 

Hormones of the Menstrual Cycle


Summary
The menstrual cycle is regulated by a complex interaction of several hormones from the pituitary gland and the ovaries.

  • FSH rises at the beginning of the cycle to stimulate follicle maturation.
  • Estrogen increases during the follicular phase and drops slightly after ovulation before rising again in the luteal phase.
  • LH peaks during ovulation.
  • Progesterone dominates the luteal phase, stabilizes the uterine lining, and decreases at the end of the cycle if no fertilization occurs.
    This sequential pattern of hormonal changes is essential for regulating the menstrual cycle and fertility.

The menstrual cycle is regulated by a complex interaction of several hormones. The most important hormones involved in the menstrual cycle are:

  1. Gonadotropin-Releasing Hormone (GnRH):
    • Produced by: Hypothalamus
    • Function: GnRH stimulates the pituitary gland to release FSH and LH.
  2. Follicle-Stimulating Hormone (FSH):
    • Produced by: Pituitary gland
    • Function: FSH promotes the growth and maturation of follicles in the ovaries.
  3. Luteinizing Hormone (LH):
    • Produced by: Pituitary gland
    • Function: A sharp increase in LH (the “LH peak”) triggers ovulation and promotes the formation of the corpus luteum.
  4. Estrogen (particularly Estradiol):
    • Produced by: Maturing follicles in the ovaries
    • Function: Estrogen promotes the growth of the uterine lining and has a feedback effect on the pituitary gland, influencing the production of FSH and LH.
  5. Progesterone:
    • Produced by: Corpus luteum after ovulation
    • Function: Progesterone stabilizes the uterine lining to prepare it for the potential implantation of a fertilized egg and inhibits the production of GnRH, FSH, and LH.
    • growth of the uterine lining. Estrogen levels peak just before ovulation.
    • LH: Estrogen has a positive feedback effect on the pituitary gland, leading to a rise in LH levels.
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Amenorrhea
Amenorrhea refers to the absence of menstruation in women of childbearing age. It can be divided into two main categories: primary amenorrhea and secondary amenorrhea.

Hormonal Changes During the Menstrual Cycle

The menstrual cycle is divided into four main phases:

  1. Menstrual Phase (Days 1-5):
    • Hormones: Estrogen and progesterone levels are low, causing the breakdown and shedding of the uterine lining.
    • FSH: FSH levels begin to rise slightly to stimulate the development of the next follicles.
  2. Follicular Phase (Days 1-13):
    • FSH: FSH stimulates the growth of follicles in the ovaries. One follicle becomes dominant and continues to mature.
    • Estrogen: The dominant follicle produces increasing amounts of estrogen, which promotes the growth of the uterine lining. Estrogen levels peak just before ovulation.
    • LH: Estrogen has a positive feedback effect on the pituitary gland, leading to a rise in LH levels.
  3. Ovulation Phase (Day 14, approximately mid-cycle):
    • LH: The rapid rise in LH (LH peak) triggers ovulation, releasing the mature egg from the follicle.
    • Estrogen: Estrogen levels peak just before the LH surge and then drop.
  4. Luteal Phase (Days 15-28):
    • Progesterone: After ovulation, the empty follicle transforms into the corpus luteum, which produces progesterone. Progesterone prepares the uterine lining for the implantation of a fertilized egg and suppresses the release of GnRH, FSH, and LH.
    • Estrogen: Estrogen levels rise slightly again but remain lower than in the follicular phase.
    • End of the cycle: If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen levels. This ultimately results in menstruation and the start of a new cycle.