Lecture Notes: Understanding Semen and Sperm

Key Concepts

• Semen vs. Sperm
  • Sperm: Male sex cells produced in the testes, carrying half the DNA needed for reproduction.
  • Semen: A complex mixture of proteins, lipids, fluids, and sperm.

Composition of Semen

• Sources of Semen Components
  • Seminal Vesicles: Produce a fructose-rich fluid, making up about 70% of semen.
  • Prostate: Adds enzymes, citric acid, phosphates, and lipids.
  • Bulbourethral Glands: Secrete lubrication for sperm passage.
• Sperm Content
  • Only 1-5% of semen is sperm.
  • An average ejaculation contains 200-500 million sperm cells.

Function and Misconceptions

• Protective Role

  • Semen protects sperm from the acidic environment of the vagina and the female's immune system.
  • Semen also protects sperm from the male's immune system after leaving the testes.

• Pre-Ejaculate

  • Secreted by Cowper’s gland, not semen.
  • Used for lubrication; typically does not contain sperm.
  • Can potentially lead to pregnancy if sperm remains in the urethra after previous ejaculation.

Vasectomy and Semen Quality

• Vasectomy

  • Involves cutting the vas deferens, preventing sperm from mixing with semen.
  • Post-vasectomy, men still ejaculate semen without sperm.
  • Does not prevent STD transmission.

• Sperm Quality

  • Only about 50% of sperm are functional; many are misshapen (e.g., two heads/tails).
  • One testicle can suffice for fertility.
  • Load size does not correlate with fertility; average ejaculation is about a teaspoon.

Additional Facts

• Sperm Necessity
  • Sperm is uniquely produced in one body but meant to survive in another, highlighting its role in reproduction beyond the male body.

Conclusion

• Semen plays a crucial role in protecting sperm and facilitating fertilization.
• Despite common misconceptions, the composition and functionality of semen are more complex than often thought.
• Vasectomies alter sperm presence but not semen volume or STD risk.

Suggested Further Reading

• "Weird Facts About Testicles"
• "Weird Facts about Male Body"