Female Reproductive Cycle

Overview

• Discussion focused on how the auditory cycle and the menstrual cycle are interconnected.
• Importance of understanding how these cycles work together.

Hormonal Pathway

• The cycles depend on hormones produced by the hypothalamus.
• Key nuclei in the hypothalamus:
  • Pre optic nucleus (red)
  • Arcuate nucleus (orange)

Gonadotropin Releasing Hormone (GnRH)

• Secreted by the hypothalamus.
• Acts on the anterior pituitary.

Anterior Pituitary Hormones

• Contains gonadotropes that secrete:
  • FSH (Follicle Stimulating Hormone)
  • LH (Luteinizing Hormone)
• These hormones play a crucial role in ovarian function.

Oocytes Development

• Females are born with oogonia (stem cells, diploid 2n).
• Oogonia develop into primordial follicles during childhood (pre-puberty).

Hormonal Transition at Puberty

• Upon reaching puberty, primordial follicles convert into primary follicles.
• Localized androgens stimulate development of primary follicles.

Primary Follicle Characteristics

• Primary oocyte is still diploid, frozen in prophase I of meiosis.

Follicular Development Stages

1. Primary Follicle:
   • Has a single layer of cells around it.
2. Early Secondary Follicle:
   • FSH stimulates proliferation of granulosa cells, forming multiple layers.
   • Produces zona pellucida (glycoprotein membrane).
   • Granulosa cells produce estrogen.
3. Late Secondary Follicle:
   • Continued FSH and LH stimulation increases layers and pockets of follicular fluid (rich in hyaluronic acid).
4. Graafian Follicle:
   • Secondary oocyte (haploid, metaphase II).
   • Surrounded by corona radiata cells.
   • Dominates the follicular phase.

Phases of the Ovarian Cycle

Follicular Phase

• Days 1-14: formation of follicles, increasing estrogen levels.
• Estrogen levels rise, providing negative feedback to hypothalamus and anterior pituitary, leading to decreased FSH/LH initially.
• As estrogen peaks (around day 14), it triggers positive feedback on the hypothalamus to release more GnRH.
• LH Surge: stimulates final maturation of the Graafian follicle and triggers ovulation.

Ovulation

• Occurs around day 14 or 15: release of secondary oocyte into the fallopian tubes.
• Triggered by the LH surge which increases blood flow and follicular fluid.

Luteal Phase

• Days 15-28: Graafian follicle transforms into corpus luteum.
• LH stimulates corpus luteum, promoting production of progesterone.
• Inhibin B produced by graafian follicle inhibits FSH production.

Summary

• Important phases: Pre-puberty, Puberty (hormonal changes), Follicular Phase, Ovulation, Luteal Phase.
• Next steps involve understanding the menstrual cycle and the effects of estrogen and progesterone on the uterus.