Lecture on Human Sexual Response and Fertilization

Introduction

• Focus on human sexual intercourse leading to fertilization
• Excludes: STIs, sexual behavior, mate selection
• Discusses contraception in terms of preventing fertilization
• Historical context: Masters and Johnson's research in the 1950s-60s

Masters and Johnson's Human Sexual Response Cycle

• Four Phases:
  • Excitement:
    • Arousal triggers parasympathetic reflex
    • External genitalia blood vessels dilate
  • Plateau:
    • Increased muscle tension, heart rate, blood pressure, breathing
    • Male urethral sphincter contracts
  • Orgasm:
    • Pelvic muscles contract
    • Male ejaculation releases sperm
    • Female orgasm helps sperm retention (not required for conception)
  • Resolution:
    • Male refractory period
    • Females may experience multiple orgasms

Fertilization Process

• Ovulation:
  • Secondary oocyte released, viable for ~1 day
  • Sperm viable in female reproductive tract for 3-5 days
• Sperm Journey:
  • Ejaculation into vaginal canal
  • Acidic environment and immune response reduce sperm numbers
  • Sperm capacitation required for penetration
• Penetration Process:
  • Sperm must pass through granulosa cells and zona pellucida
  • Calcium ion influx triggers acrosomal reaction
• Formation of Zygote:
  • Sperm and oocyte membranes fuse
  • Oocyte completes meiosis II
  • Formation of male and female pronuclei
  • Pronuclei fusion creates diploid zygote

Contraception Methods

• Sterilization:
  • Permanent methods (tubal ligation, vasectomy)
• Barrier Methods:
  • Condoms, diaphragms, female condoms
• Hormonal Methods:
  • Birth control pills, shots, patches, rings
  • Prevent ovulation, alter uterine lining, cervical mucus
• IUDs:
  • Prevent zygote implantation

Conclusion

• Overview of the human sexual response cycle and fertilization
• Various contraception methods to prevent fertilization
• Next discussion topic: zygote implantation

Acknowledgements

• Support from Patreon patrons
• Production team credits