Female Reproductive

Mechanism of Female Birth Control Pills

• Functionality:

  • Hold estrogen and progesterone at steady moderate levels.

  • Main Actions:

  • Prevent Ovulation: Inhibits the release of eggs from the ovaries.

  • Inhospitable Uterine Lining: Alters the uterine lining to prevent implantation.

  • Mimic Infertile State: Creates a hormonal environment similar to pregnancy, which suppresses the uterine cycle.

Hormonal Regulation in the Female Reproductive Cycle

• Endometrium: The inner lining of the uterus that prepares for potential pregnancy.

• Ovarian Cycle: Relates to the maturation of oocytes in the ovaries.

  • Ovarian Events and Hormone Levels: Graphical representation indicates hormone levels during the cycle including:

  • Luteinizing Hormone (LH)

  • Follicle Stimulating Hormone (FSH)

  • Estradiol: Dominant hormone during the follicular phase.

  • Progesterone: Important for the maintenance of the endometrium in the luteal phase.

Cycle Phases

1. Follicular Phase: Develops follicles, secretes estrogen. Growing follicles release FSH and LH.

   • Dominance of Estradiol.

2. Ovulation: Triggered by a surge in LH, leading to the release of a mature oocyte.

3. Luteal Phase: After ovulation, the corpus luteum forms and secretes progesterone and estradiol.

4. Menstruation: If no fertilization occurs, the corpus luteum degenerates, leading to menstruation.

Hormonal Feedback Control

• Hypothalamus: Secretes Gonadotropin-Releasing Hormone (GnRH) to signal the pituitary gland.

  • Negative Feedback Loop:

  • High levels of estrogen and progesterone inhibit further GnRH production.

• Pituitary Gland: Releases FSH and LH to regulate ovarian function.

• Connections to Endocrine Glands:

  • Interaction with parathyroid glands, pancreas, testes (in males), and ovaries (in females).

Graphical Overview of Hormone Levels

• Cycle Illustration:

  • Days of Cycle: Depicted fluctuations of hormones over a typical 28-day cycle.

  • Follicular Phase: Days 1-14, characterized by increasing estradiol.

  • Ovulation: Day 14.

  • Luteal Phase: Days 14-28, dominated by progesterone.

• Uterine Cycle: Divided into phases:

  • Proliferative Phase (estrogen-dominated).

  • Secretory Phase (progesterone-dominated, maintenance of endometrium).

  • Menstrual Flow Phase (course of menstruation).

Ovarian Cycle Details

• Comparative Stability:

  • The ovarian cycle is variable; hormonal levels fluctuate.

• Menstrual Cycle Example: Average 28-day cycle with detailed hormones' levels depicted throughout different phases.

Meiosis and Oocyte Development

• Oocyte Production:

  • Meiosis process initiates during fetal development, where germ cells divide to form primary oocytes.

  • At birth: millions of primary oocytes present in prophase I of meiosis.

  • Daily Cycle: Each cycle, one primary oocyte completes meiosis I.

• Fertilization Process:

  • Upon fertilization, secondary oocyte completes meiosis II and forms a zygote.

Post-Ovulation Events

• Development of Corpus Luteum: After ovulation, the ruptured follicle develops into the corpus luteum which secretes hormones.

• Hormonal Changes:

  • If fertilization occurs, the blastocyst secretes human chorionic gonadotropin (hCG) to maintain the corpus luteum and hormone levels.

• Unfertilized Egg:

  • Discharged during menstruation, or reabsorbed by the body if not fertilized.

Summary of Hormonal Sequence during Menstrual Cycle

1. Initial estrogen levels trigger the release of GnRH from the hypothalamus.

2. GnRH prompts the pituitary to release FSH and LH.

3. FSH drives maturation of follicles which in turn secrete estrogen and progesterone.

4. Increased estrogen induces an LH surge, leading to ovulation.

5. The corpus luteum forms and secretes hormones critical for supporting the endometrium.

6. If no implantation occurs, corpus luteum degenerates, resulting in menstruation.

7. If implantation occurs, hCG maintains the corpus luteum preventing degeneration.