Lecture 6: Ovaries and Oogenesis

Overview of Ovarian Structure

• Germinal Epithelium: Outermost layer.
• Tunica Albigenia: Beneath the germinal epithelium, similar to that in testes and penis.
• Cortex: External region containing ovarian follicles.
• Medulla: Internal region with blood vessels, lymphatics, and nerves.

Ovarian Follicles

• Contain oocytes at various developmental stages.
• Mature follicles are called Graafian Follicles.
• Ovulation: Release of a secondary oocyte from the ovary.
• Post-ovulation, follicles become:
  • Corpus Luteum: Produces progesterone, estrogens, relaxin, and inhibin.
  • Corpus Albicans: Degenerated corpus luteum, forms scar tissue.

Oogenesis

• Formation of haploid secondary oocyte.
• Involves:
  • Meiosis I (Reduction division)
  • Meiosis II (Equatorial division)
  • Maturation

Developmental Stages of Follicles

1. Primordial Follicle
2. Primary Follicle
3. Secondary Follicle
4. Mature (Graafian) Follicle
5. Corpus Hemorrhagicum: Post-ovulation, bloody stage.
6. Corpus Luteum
7. Corpus Albicans

Ovulation and Meiotic Arrest

• Ovulation involves the rupture of the follicle wall.
• Polar Bodies: Mechanism to discard excess DNA.
• Secondary oocyte pauses at Metaphase of Meiosis II until fertilization.
  • Fertilization triggers completion of Meiosis II.

Female Germ Cell Development

• Oogonia: Migrate to ovaries in a female fetus.
• Atresia: Degeneration of oogonia, only a fraction mature.
  • At birth, 200,000 to 2 million present, reduced to 40,000 by puberty.
  • Only ~400 mature during a woman's life.

Monthly Hormonal Cycle

• Hormones induce Meiosis I resumption.
  • Proceeds to Metaphase, Anaphase, Telophase, Cytokinesis, creating the first polar body.
• Meiosis II begins and arrests at Metaphase until sperm penetration.

Miscellaneous

• Ovarian Cysts: Fluid-filled sacs, common and usually benign.
• Scar Tissue: Formed post-ovulation; indicative of age and ovulation history.