Ovaries and the Ovarian Cycle

Overview of Ovaries

• Primary female reproductive organs.
• Located on either side of the uterus.
• Produce gametes: oocytes (egg cells).
• Secrete hormones: estrogen and progesterone, crucial for reproduction.

The Ovarian Cycle Phases

1. Follicular Phase
2. Ovulation
3. Luteal Phase

Follicular Phase

• Follicles and Oocytes

  • Primary Oocytes: Form during fetal development.
    • Begin meiosis but pause at prophase 1.
  • Primordial Follicles: Contain primary oocytes.
  • Maturation Process:
    • At puberty, primordial follicles mature into primary follicles with Follicle Stimulating Hormone (FSH).
    • ~20 primordial follicles mature monthly into primary follicles.
    • One primary follicle matures further to a secondary follicle.

• Secondary Follicle

  • Contains a secondary oocyte (23-chromosome cell completing meiosis 1).
  • Develops into a vesicular follicle a few days before ovulation.
  • Vesicular follicle has antrum (fluid-filled space).

Ovulation

• The vesicular follicle ruptures releasing:
  • Antrum contents.
  • Secondary oocyte.
• Oocyte travels down the uterine tube.
• Potential Outcomes:
  • Fertilization: Oocyte meets sperm.
    • Completes meiosis 2.
    • Develops into a zygote.
  • No Fertilization: Travels to uterus, exits during menstrual period.

Luteal Phase

• Corpus Luteum Formation: Post-ovulation from follicle remnants.
  • Releases estrogen and progesterone.
  • Without Fertilization: Luteolysis starts ~10 days after, forming corpus albicans (scar).
  • With Fertilization: Continues progesterone production for ~12 weeks until placenta takes over.

Additional Resources

• Visible Body Suite: 3D models and animations for reproductive system anatomy and physiology.
  • visiblebody.com/vbsuite