Human Development and Pregnancy

Introduction

• Human growth: From the size of a pinhead (zygote) to a full-grown human (approx. 1.7 meters)
• Focus on physiological processes of pregnancy

Hormonal Influence

• Pregnancy is controlled by hormones
• Begins with fertilization: sperm and egg form a zygote
• Hormones involved: estrogen, progesterone, and hCG

Early Development Stages

1. Cleavage Phase

   • Zygote divides into blastomeres (16 cells)
   • Cells divide quickly without growing, increasing surface area

2. Morula Stage

   • A berry-shaped cluster of cells
   • Transition to the blastocyst stage

3. Blastocyst Formation

   • Hollow sphere of cells, with outer trophoblast layer and inner cell mass
   • Trophoblasts form placenta; inner cells develop into embryo

Implantation

• Blastocyst reaches uterus, begins implantation
• Involves hormones: estrogen and progesterone
• Trophoblasts produce hCG to maintain pregnancy

Maternal Adaptations

• Anatomical and physiological changes
  • Breasts swell, uterus expands, blood volume increases by 40%
  • Hormones involved: relaxin, human placental lactogen (hPL)
  • Effects include: increased glucose storage, greater urine production, and cardiovascular changes

Labor and Birth

1. Hormonal Preparation
   • Placenta reduces progesterone, increases estrogen
   • Fetal release of hormones like cortisol triggers estrogen release
2. Labor Stages
   • Dilation: Cervix thins and dilates, contractions begin
   • Expulsion: Baby is delivered through cervix and vagina
   • Placental Stage: Placenta is delivered as "afterbirth"

Conclusion

• The cycle of human development: from zygote to independent human
• Importance of hormones in pregnancy and childbirth
• Summary of anatomical and hormonal changes during pregnancy

Additional Information

• Crash Course episode credits and contributors