Understanding the Menstrual Cycle and Hormones

Aug 18, 2024

Lecture Notes: The Menstrual Cycle and Homeostasis

Overview

  • Topic: Menstrual Cycle and Homeostasis
  • Lecturer: Andre from Med School EU
  • Context: Last lecture in the Biology unit for IMAT specifications

Menstrual Cycle

  • Duration: Typically 28 days
  • Processes:
    • Changes in female reproductive organs
    • Involves two main cycles:
      • Ovarian Cycle
      • Uterine Cycle

Key Organs and Hormones

  • Organs:
    • Ovary
      • Releases estrogen and progesterone
      • Has its own ovarian cycle
    • Uterus
      • Involved in the uterine cycle
  • Hormones:
    • Estrogen and Progesterone
      • Main hormones after ovulation
    • Anterior Pituitary Gland
      • Releases Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)

Hormonal Effects and Cycles

  • Ovarian Cycle

    • Development of follicles and gametes
    • Cycle:
      • Formation of potential female gametes
      • Development into primary follicle
      • Growth into secondary follicle
      • Ovarian follicle formation
      • Ovulation (release of gamete into the fallopian tube)
      • Formation of corpus luteum

  • Uterine Cycle

    • Corresponds with ovarian cycle
    • Stages:
      1. Start of menstruation (shedding of endometrium)
      2. Development of new endometrium
      3. Maintenance and development of capillaries
      4. Ovulation (most fertile time)

Hormonal Regulation

  • Menstruation

    • Lasts 4-8 days
    • Continuous release of LH and FSH
    • Rising estrogen levels stimulate endometrium growth

  • Post-Menstruation

    • Estrogen inhibits LH and FSH at moderate levels
    • At high estrogen levels, a spike in LH and FSH occurs (leading to ovulation)

  • Post-Ovulation

    • Formation of corpus luteum
    • Increased progesterone and estrogen maintain uterine lining
    • Progesterone inhibits FSH (preventing new follicles)
    • Negative feedback decreases LH and FSH, leading to corpus luteum degeneration

Conclusion

  • Cycle Reset: Fall in progesterone and estrogen leads to rise in FSH and LH, restarting menstruation.
  • Next Topic: Transition to Chemistry, covering the composition of matter.