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The Menstrual Cycle

Introduction to the Menstrual Cycle

  • Importance of understanding the female reproductive system.

  • Overview of the effects of female hormones:
      - a. Estrogen
      - b. Progesterone
      - c. Prostaglandins

Neurohormonal Basis of the Female Reproductive Cycle

  • Consists of:
      - a. Ovarian Cycle
      - b. Menstrual Cycle

Key Definitions

  • Uterus: Hollow organ where an embryo develops.

  • Fundus: The top portion of the uterus, opposite the cervix.

  • Fallopian Tubes: Tubes through which eggs travel from the ovaries to the uterus.

  • Ovaries: Organs that produce eggs and hormones (estrogen and progesterone).

  • Estrogen: A hormone essential for sexual and reproductive development.

  • Progesterone: Hormone responsible for maintaining the uterine lining.

  • FSH (Follicle Stimulating Hormone): Hormone that stimulates follicle growth in ovaries.

  • LH (Luteinizing Hormone): Hormone that triggers ovulation and development of the corpus luteum.

Internal Organs of the Female Reproductive System

  • Suspensory Ligament: Supports the ovaries.

  • Fimbriae: Finger-like projections at the end of fallopian tubes that help guide the egg.

  • Uterine Structures:
      - Fundus of uterus
      - Sacrum
      - Perimetrium (outer layer of uterus)

  • Supporting Structures:
      - Round ligament, Urinary bladder, Mons pubis, Urethra, Clitoris, Labium minus, Labium majus, Pouch of Douglas, Posterior fornix, Cervix, Anterior fornix, Rectum, Vagina, Urogenital diaphragm, Anus, Bartholin's gland, Perineal body.

Further Details of Internal Organs

  • Examination of specific parts:
      - Fundus: Upper part of the uterus where it meets the fallopian tubes.
      - Uterine Cavity: The interior space of the uterus.
      - Cornua: The rounded parts of the uterus joining the fallopian tubes.
      - Isthmus of Fallopian Tube: Narrowed section of the fallopian tube.
      - Uterine Body: Central part of the uterus.
      - Myometrium: Middle muscle layer of the uterine wall.
      - Endometrium: Inner lining of the uterus.

  • Cervix: Lower part of the uterus opening into the vagina.

  • External and Internal Os: Opening of the cervix into the vagina and the uterine cavity respectively.

Female Reproductive System Overview

  • Hormones: Key players in regulating the cycles (Estrogen and Progesterone).

  • Ovarian Cycle: Includes the maturation of the ovum and its controlled timing.

  • Menstrual Cycle: Encompasses phases including:
      - Proliferative Phase
      - Secretory Phase
      - Ischemic Phase

Ovarian Cycle

  • Processes within the ovarian cycle include:
      - Maturation of Ovum: Triggered by hormones FSH and LH.
      - LH Surge: Marks the progression towards ovulation.
      - Follicular Development:
        - Primary follicle development into secondary and Graafian follicles.
      - Ovulation: Release of the ovum from the ovary, typically occurring around day 14 of the menstrual cycle.
      - Luteal Phase: Forming of the corpus luteum post-ovulation, which secretes progesterone.

Menstrual Cycle Phases

  • Changes in endometrial lining are driven by ovarian hormones:
      - Estrogen: Dominant hormone during the proliferative phase.
      - Progesterone: High levels mark the secretory phase, preparing the endometrium for potential implantation.

  • Phases of the Uterine Cycle include:
      - Menses (the shedding of the uterine lining)
      - Proliferative Phase (thickening of the endometrium)
      - Secretory Phase (preparation for implantation)
      - Ischemic Phase (if no pregnancy occurs, the lining breaks down).

Timeline of the Menstrual Cycle

  • Cycle Duration: Average of 28 days.

  • Day 1-7: Menses phase; shedding the uterine lining.

  • Day 8-14: Proliferative phase; endometrium rebuilds due to rising estrogen levels.

  • Day 15-21: Secretory phase; preparation for embryo implantation increases progesterone levels.

  • Day 22-28: If not pregnant, the cycle moves into the ischemic phase leading to menstruation again.

Summary of Ovarian and Uterine Phases

  • During each cycle, the interplay of FSH and LH results in the development of follicles in the ovaries and corresponding changes in the endometrium, encapsulating hormonal regulation and anatomical responses.