Hormonal Regulation of the Female Reproductive Cycle

Introduction

• Focus on the menstrual cycle and its hormonal regulation.
• Involves hypothalamus and pituitary glands, particularly the anterior pituitary.

Key Hormones and Their Roles

• Gonadotropin-Releasing Hormone (GnRH): Produced by the hypothalamus, travels to the anterior pituitary.
• Follicle-Stimulating Hormone (FSH) & Luteinizing Hormone (LH): Produced by the anterior pituitary, travel to the ovaries to stimulate egg production.

Female Reproductive Anatomy

• Ovaries: Connected to the uterus via the fallopian/uterine tube.
• Contain many follicles; each month, some mature but only one typically ovulates.

Menstrual Cycle Phases

• Follicular Phase: First 14 days, characterized by follicle maturation.
• Luteal Phase: Last 14 days, involves corpus luteum formation.

Hormonal Changes During the Cycle

Follicular Phase

• Increasing GnRH causes a rise in FSH and LH.
• FSH stimulates follicle maturation.
• Estrogen: Produced by maturing follicles, initially inhibits LH at low concentrations, causing steady LH levels in blood.
• FSH levels drop due to rising estrogen levels.

Luteal Phase

• LH Surge: High estrogen levels lead to positive feedback, spiking LH and triggering ovulation.
• Post-ovulation, LH, GnRH, and FSH levels drop.
• Corpus Luteum: Formed from ovulated follicle, secretes estrogen, inhibin, and progesterone.

Functions of Hormones in the Luteal Phase

• Inhibin: Suppresses FSH to prevent further follicle maturation.
• Progesterone: Inhibits GnRH, hence reducing LH and FSH release, stimulates endometrial growth.

End of Menstrual Cycle

• Corpus luteum degenerates if no fertilization occurs, decreasing hormone levels.
• Low progesterone allows increase in GnRH, starting new cycle.
• Decrease in estrogen and progesterone leads to shedding of the endometrial lining, known as menstruation.

Conclusion

• The cycle restarts with the increase in GnRH, continuing the hormonal regulation process.