Just as the testes have a specific cellular architecture for sperm production, the ovary is organized into an outer cortex (containing follicles) and an inner medulla (containing blood vessels and nerves). The cells within these regions are responsible for egg maturation and the secretion of female sex hormones.
1. Germ Cells (Oogenic Cells)
These are the cells that will eventually become the mature ovum.
- Oogonia: The diploid stem cells. In females, these multiply only during fetal development; a woman is born with her lifetime supply of potential eggs.
- Primary Oocytes: Oogonia that have entered Meiosis I but are “arrested” in Prophase I until puberty.
- Secondary Oocytes: Following the LH surge, the primary oocyte completes Meiosis I. This is the stage at which the egg is actually ovulated.
- Ovum: The final mature haploid gamete, formed only after fertilization by a sperm triggers the completion of Meiosis II.
2. Somatic Supporting Cells (Follicular Cells)
These cells surround the developing oocyte and change significantly as the follicle matures.
Granulosa Cells
These are the most prominent supporting cells, analogous to Sertoli cells in the male.
- Hormone Production: They convert androgens (from theca cells) into Estrogens (estradiol) using the enzyme aromatase.
- Support: They provide nutrients to the oocyte and secrete follicular fluid to create the antrum.
- Corona Radiata: The innermost layer of granulosa cells that remains attached to the oocyte after ovulation.
Theca Cells
Located on the outside of the follicle, these are analogous to Leydig cells.
- Theca Interna: Highly vascularized cells that produce androstenedione (an androgen) in response to LH.
- Theca Externa: A fibrous outer layer containing smooth muscle-like cells that help the follicle contract during ovulation.
3. Luteal Cells (Post-Ovulation)
After the egg is released, the remnants of the follicle transform into the Corpus Luteum.
- Granulosa Lutein Cells: Derived from granulosa cells; they become large and secrete massive amounts of Progesterone.
- Theca Lutein Cells: Derived from theca cells; they continue to produce androgens and some progesterone.
4. Other Specialized Cells
- Hilus Cells: Found in the medulla (hilum) of the ovary. These are histologically identical to Leydig cells and secrete small amounts of androgens.
- Interstitial Cells: Present in the stroma; they contribute to the production of ovarian hormones, particularly during early development.
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