Follicle-Stimulating Hormone and Follicle Development

What is a Follicle?

• A follicle is a structure in the ovary.
• Surrounds a primary oocyte.
• During oogenesis, a primary oocyte is formed.
• Women have about 500,000 oocytes per ovary.
• Oocytes are frozen in the primary oocyte stage within a primordial follicle.

Role of Follicle-Stimulating Hormone (FSH)

• Stimulates the growth of follicles in the ovaries.
• Over 14 days, under FSH influence, follicles grow.
• Affects up to 20 follicles initially, but usually only one matures.

Follicle Development Stages

• Primordial Follicle:
  • Contains a primary oocyte surrounded by flat cells.
• Mature Follicle:
  • Contains a secondary oocyte.
  • Surrounded by granulosa cells.
  • Granulosa cells are stimulated by FSH and produce fluid in the antrum.
  • The antrum is a fluid-filled space within the mature follicle.

Role of Granulosa and Thecal Cells

• Granulosa Cells:
  • Stimulated by FSH.
  • Produce fluid and ovarian hormones.
  • Work with thecal cells to produce estrogen.
• Thecal Cells:
  • Stimulated by luteinizing hormone (LH).
  • Produce precursors to estrogen.
  • Surround the mature follicle.

Estrogen Production

• Thecal cells produce molecules converted to estrogen by granulosa cells.
• Estrogen levels increase as follicles mature.

Summary

• FSH stimulates follicle growth and the production of granulosa cells.
• LH stimulates thecal cells to produce estrogen precursors.
• Estrogen levels rise due to the cooperative function of granulosa and thecal cells.