Female Reproductive Cycle | Menstrual Cycle

Hormonal Overview

  • Key hormones: Estrogen and Progesterone

  • Production occurs in the corpus luteum.

Phases of the Menstrual Cycle

1. Menstruation Phase

  • Description: Shedding phase of the uterine lining.

  • Duration: Days 1-5 (average).

  • Endometrium Composition:

    • Stratum Functionalis: The layer shed during menstruation; composed of simple columnar epithelial tissue.

    • Stratum Basalis: The deeper layer remaining after menstruation.

  • Blood Loss: Blood loss occurs through spirally coiled arteries in the stratum functionalis.

  • Key Point: The stratum basalis and straight arteries remain.

2. Proliferative Phase

  • Description: Regeneration of the stratum functionalis after shedding.

  • Duration: Days 6-14.

  • Hormonal Influence: Estrogen promotes regeneration.

  • Processes:

    • Regeneration of Stratum Functionalis: Growth of the inner uterine lining.

    • Anigogenesis: Formation of new spirally coiled arteries.

    • Uterine Glands Formation: Start of producing glands that will secrete fluids later.

    • Cervical Mucus Production: Estrogen causes the production of thin mucus to facilitate sperm movement for potential fertilization.

3. Secretory Phase

  • Description: Prepares the uterus for possible implantation of a fertilized egg.

  • Duration: Days 15-28.

  • Hormonal Influence: Progesterone from the corpus luteum secreted.

  • Processes:

    • Thickening of the Stratum Functionalis: Increased blood supply and thickness.

    • Further Angiogenesis: Development of more spirally coiled arteries.

    • Uterine Glands Activity: Glands begin secreting nutrient-rich substances containing glycogen and lipids.

    • Cervical Mucus Change: Progesterone thickens cervical mucus to block any potential access into the uterus, protecting a possible embryo.

If Fertilization Does Not Occur

  • Lack of Signals: Absence of human chorionic gonadotropin leads to corpus luteum regression.

  • Effects on Blood Supply:

    • Vasoconstriction of spiral arteries occurs, leading to weakness and rupture of these blood vessels.

    • Blood from ruptured arteries accumulates in the stratum functionalis, causing ischemia and necrosis of tissue.

    • Resulting shedding of this tissue is the next menstruation phase.

  • Cycle Reset: Cycle begins anew at day 1 with menstruation.

If Fertilization Occurs

  • Continued Hormonal Support: Corresponding hormonal signals maintain corpus luteum activity to sustain progesterone production.

  • Formation of Corpus Albicans: If no fertilization occurs, the corpus luteum turns into scar tissue (corpus albicans) post-cycle.

Conclusion

  • Recap of the intricate processes in the female reproductive cycle leading to menstruation, regeneration, and preparation for potential pregnancy.