Female Reproductive Cycle Lecture Notes

Overview

• This lecture focuses on the female reproductive cycle, specifically the ovulatory cycle.
• It highlights the hormonal interactions starting from the hypothalamus and their role in the reproductive processes.

Hormonal Regulation

• Hypothalamus:
  • Houses nuclei that secrete hormones:
    • Preoptic Nucleus
    • Arcuate Nucleus
  • Secretes Gonadotropin Releasing Hormone (GnRH).
• Anterior Pituitary:
  • Responds to GnRH by releasing:
    • FSH (Follicle Stimulating Hormone)
    • LH (Luteinizing Hormone)

Ovary and Follicle Development

• Birth to Puberty:
  • Females are born with oogonia, diploid stem cells.
  • Oogonia convert to primordial follicles pre-puberty, still diploid and frozen in prophase 1 of meiosis.
• Puberty Onset:
  • Primordial follicles are stimulated by local androgens to become primary follicles.

Follicular Development Phases

• Primary Follicle:
  • Contains a primary oocyte in prophase 1.
  • Surrounded by a single layer of cuboidal/columnar cells.
  • FSH stimulates:
    • Proliferation to multiple granulosa cell layers.
    • Formation of zona pellucida.
    • Estrogen production.
• Early Secondary Follicle:
  • FSH causes further proliferation and production of follicular fluid.
  • Estrogen continues to be produced.
• Late Secondary Follicle:
  • Further FSH and LH stimulation.
  • More granulosa layers, increased follicular fluid forming pockets.
  • Still a primary oocyte.
• Graafian (Tertiary) Follicle:
  • Undergoes meiosis 1 to form a secondary oocyte.
  • Formation of a large antrum.
  • Prepares for ovulation.

Ovulatory Phase

• Triggered by an LH surge around day 14-15.
• Results in ovulation:
  • Secondary oocyte is released.
  • Fimbriae create fluid currents to guide oocyte to fallopian tubes.

Luteal Phase

• Occurs days 15-28.
• Graafian follicle transforms into the corpus luteum under LH influence.
• Corpus luteum produces progesterone.

Feedback Mechanisms

• Estrogen:
  • Mid-follicular phase: Negative feedback on hypothalamus and anterior pituitary.
  • Late follicular phase: Positive feedback causing LH surge.
• Inhibin: Inhibits FSH release from the anterior pituitary.

Summary

• The ovulatory cycle involves a complex interplay of hormonal signals starting from the hypothalamus to the ovaries, which prepares the female body for potential fertilization.
• The next lecture will focus on the menstrual cycle and its interactions with estrogen and progesterone.