Lecture 1: Introduction to Development and Fertilization

Overview of Development

• Steps from Fertilization to Birth:
  • Fertilization
  • Implantation of fertilized egg
  • Placenta development
  • Fetal development
  • Gestation
  • Labor and Parturition (Birth)
• Developmental Periods:
  • Embryonic Development: First 2 months post-fertilization
  • Fetal Development: From Week 9 until birth
  • Gestation Period: Approximately 40 weeks (38-40 weeks)
  • Prenatal Period: Before birth
  • Neonatal Period: First month and a half after birth

Embryonic Development

• Critical time for organ development
• Importance of avoiding teratogenic substances (e.g., drugs, alcohol)
• Often occurs before pregnancy is detected

Fields of Study

• Developmental Anatomy: Study of developmental stages
• Embryology: Fertilization to fetal period
• Obstetrics: Deals with pregnancy, labor, neonatal period

Fertilization Process

• Occurs within 12-24 hours after ovulation
• Sperm viability: 24-48 hours after ejaculation
• Key Steps:
  • Ovulation
  • Fertilization in the uterine tube
  • Cleavage producing morula
  • Differentiation into blastocyst
  • Implantation (6 days post-fertilization)

Mechanism of Fertilization

• Merging of sperm and egg (haploid gametes) to form diploid zygote
• Location: Uterine tube, typically a third of the way to the uterus

Sperm Journey

• Transported by peristaltic contractions and cilia movement
• Sperm swims up through the uterus to the uterine tube
  • Capacitation: Final maturation of sperm in female tract
• Acrosomal Reaction: Enzymes from sperm digest path through zona pellucida

Prevention of Polyspermy

• Fast Block: Membrane depolarization prevents additional sperm fusion
• Slow Block: Calcium-induced hardening of zona pellucida

Completion of Meiosis

• Sperm entry triggers completion of oocyte meiosis
• Formation of male and female pronuclei
• Fusion leads to zygote formation

Types of Twins

• Dizygotic (Fraternal): Two oocytes fertilized by separate sperm
• Monozygotic (Identical): One fertilized egg splits post-fertilization
• Conjoined Twins: Incomplete separation after fertilization

Goals for Lecture

• List and describe development stages from fertilization to birth
• Draw a secondary oocyte and label:
  • Zona Pellucida
  • Corona Radiata
  • Cytoplasmic Membrane
• Describe fertilization process using terms:
  • Capacitation
  • Acrosomal Reaction
  • Polyspermy (Fast and Slow Block)
  • Syngamy
  • Pronucleus
  • Zygote
  • Types of Twins (Monozygotic, Dizygotic, Conjoined)