Lecture Notes: Fertilization Process

Introduction

• Fertilization involves the journey of sperm from ejaculation in the male to the fusion with the female egg.
• Copulation: The process where sperm is ejaculated into the female genital tract.

Female Reproductive Anatomy

• Fallopian Tube: The site where fertilization occurs.
  • Ampulla: The location within the fallopian tube where the egg waits for sperm.
• Graafian Follicle: Releases the secondary oocyte during ovulation.
  • Influenced by Luteinizing Hormone.
  • Secondary oocyte is halted in metaphase 2.

Male Contribution

• Seminal Vesicles:
  • Produce 60-70% of seminal fluid.
  • Key components include fructose (energy source), prostaglandins, and coagulase.
• Prostate Gland:
  • Produces about 30-40% of seminal fluid.
  • Provides citrate (energy source), fibrinogen, and prostate-specific antigen (marker for BPH).

Sperm Structure

• Head: Contains nucleus (23 chromosomes), and acrosome (enzymes like acrosin and proteases).
• Midpiece: Packed with mitochondria for ATP production.
• Tail (Flagellum): For movement; structured in a 9+2 microtubule arrangement.

Journey of Sperm

• Sperm travels through female tract, using seminal fluid nutrients.
• Fructose: Provides energy for mitochondrial ATP production.
• Prostaglandins: Stimulate uterine contractions (retroperistalsis) to help sperm move towards the egg.

Sperm-Egg Interaction

1. Capacitation:

   • Sperm undergoes changes in the female tract.
   • Removal of cholesterol and glycoproteins from the sperm head.
   • Induces hypermotility.

2. Acrosomal Reaction:

   • Sperm binding to Zona Pellucida (ZP3 receptors) triggers calcium influx.
   • Causes release of acrosin and proteases to digest the egg's protective layers.

3. Penetration & Fast Block to Polyspermy:

   • Sodium influx prevents other sperm from binding.

4. Fusion & Slow Block to Polyspermy:

   • Cortical Reaction: Smooth ER releases calcium, activating cortical granules.
   • Harden the egg membrane and degrade ZP proteins.

Completion of Meiosis and Zygote Formation

• Calcium stimulates the secondary oocyte to complete meiosis II.
• Formation of definitive ovum and polar body.
• Fusion of male and female pronuclei forms a zygote (2N).

Key Takeaways

• Capacitation and acrosomal reaction are crucial for fertilization.
• Blocks to polyspermy ensure only one sperm fertilizes the egg.
• The union of sperm and egg nuclei marks the beginning of embryogenesis.

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End of Lecture Notes