Ovarian Cycle Lecture

Introduction

• Ovaries: Two structures in the female reproductive system producing eggs.
• Ovarian Cycle: Maturation process of eggs, creating a secondary oocyte for potential fertilization.
• Menstrual Cycle: Tied to the ovarian cycle.

Egg Maturation Process

• Primary oocytes develop in the ovaries and complete meiosis one before ovulation.
• Ejection: Secondary oocyte is ejected from the ovary, picked up by fimbriae, and swept into the uterine tube for possible fertilization.

Follicles and Granulosa Cells

• Primordial Follicles: Initial stage; primary oocyte surrounded by granulosa cells.
• Primary Follicles: Developing stage with more granulosa cells and the formation of the zona pellucida.
• Pre-Antral Follicles: Granulosa cells multiply, and a layer called the theca forms.
• Antrum Formation: Fluid-filled space created by granulosa cells, causing follicle expansion.

Hormone Production

• Granulosa cells secrete Estrogen, Progesterone, and Inhibin.
• Theca cells produce androstenedione (precursor to estrogen) in response to luteinizing hormone (LH).

Timeline

• Day 0: Primordial follicle starts developing.
• Day 13: Follicles mature; hormone levels rise.
• Day 14: Ovulation occurs; secondary oocyte ejected.
• Days 15–28: Follicle transitions back to primordial stage.

Development of Dominant Follicle

• Multiple follicles form, but only one dominant follicle ovulates.
• Other follicles undergo atresia (degeneration).
• Dominant Follicle: Enlarges due to expanding antrum and formation of cumulus oophorus (granulosa cell mound).
• Mature Follicle: Breaks ovarian wall, releasing the egg.

Corpus Luteum Formation

• Post-ovulation: Follicle collapses and becomes the corpus luteum.
• Corpus Luteum: Produces more estrogen, progesterone, and inhibin.
• If no fertilization: Corpus luteum degenerates by day 25.
• If fertilized: Corpus luteum persists, supporting the endometrium for implantation.

Menopause

• Age 50–51: Menstrual cycles become irregular and cease (menopause).
• Cause: Ovarian failure; ovaries stop responding to LH and FSH due to follicle atresia.

Key Terms

• Fimbriae: Finger-like projections that sweep the oocyte into the uterine tube.
• Zona Pellucida: Layer separating granulosa cells and the egg.
• Gap Junctions: Channels that allow nutrient exchange.
• Luteinizing Hormone (LH): Stimulates theca cells.
• Atresia: Degeneration of non-dominant follicles.
• Cumulus Oophorus: Mound of granulosa cells around the egg.
• Corpus Luteum: Post-ovulation structure producing hormones.
• Endometrium: Inner lining of the uterus where implantation occurs.
• Apoptosis: Programmed cell death process.

Quick Recap

• 28-day cycle involving the development, maturation, and release of an egg.
• Hormonal changes drive the process, preparing the body for potential pregnancy.
• Menstrual cycle ends with menopause, driven by ovarian failure.