Fertilization Process: From Ovulation to Implantation

Overview

• Lecture by Armando Hasudungan on Fertilization
• Female reproductive organs involved: uterus and ovaries.
• Series covers the fertilization stages.

Female Reproductive System

• Ovaries: Female gonads producing the egg.
• Menstrual Cycle: Monthly cycle involving ovulation and egg release.
• Ovulation: Release of the egg (secondary oocyte).

Structure of Secondary Oocyte

• Zona Pellucida (ZP): Thick protective membrane.
  • Contains sperm recognition proteins (ZP3).
• Corona Radiata: Layer of cells surrounding the ZP.

Egg Fertilization

• Egg must be fertilized within 24 hours; otherwise, menstruation occurs.
• Capacitation: Sperm preparation in the vagina.
• Acrosome Reaction: Initiated upon docking with ZP3 proteins.

Formation of Zygote

• Meiosis II: Secondary oocyte undergoes Mei2 forming a polar body and an Ovum.
• Ovum incorporates sperm genes forming a zygote (Day 1 of development).
• Zona Pellucida: Remains protecting the Morula, sheds later on.

Cleavage and Blastocyst Formation

• Days 2-3: Cleavage
  • Zygote divides into multiple cells (2, 4, 8, etc.).
  • Cytoplasm amount remains the same during cleavage.
• Day 4: Morula
  • Cleavage results in a ball of 16 cells.
• Day 5: Blastocyst
  • 16-cell Morula cleaves into a 32-cell Blastocyst.
  • ZP surrounds the blastocyst.

Implantation

• Day 7: Shedding of Zona Pellucida
  • Occurs just before implantation.
  • Blastocyst is a hollow sphere with a cell lump binding to the endometrium.

Key Points

• Coordination of cellular events and timings is crucial for successful fertilization and implantation.
• The Zona Pellucida plays a vital role in protecting developing cells until implantation.