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Understanding Conception and Fetal Development: Key Processes and Stages

This study guide explores the critical processes of fertilization, conception, and fetal development. It details the journey of the ovum and sperm, the moment of fertilization, the establishment of the zygote, and subsequent implantation within the uterine wall. The guide outlines the three developmental stages: preembryonic, embryonic, and fetal. It also highlights the functions and structures of fetal membranes, the placenta, and umbilical cord, along with the dynamics of twin formation. This comprehensive overview serves as a valuable resource for understanding human development.

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Understanding Conception and Fetal Development: Key Processes and Stages

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  1. Chapter 8: Conception and Fetal Development Study Guide

  2. Process of Fertilization • Ovum are released into the fallopian tubes • fertile for 12 – 24 hours • Sperm deposited into vagina • Viable for 48 – 72 hours • Fertilization takes place in the ampulla • Sperm penetration causes a chemical reaction that blocks more sperm and causes oocyte to complete 2nd division

  3. Moment of Fertilization • Zygote – when ovum and sperm unite • True fertilization – when nuclei unite • Union restores diploid number • Sex determined at this time • Twenty-third pair is sex chromosomes • XX = female; XY = male

  4. Implantation • Between 6-8 days after conception • Posterior uterine wall most common site • Chorionic villi • Decidua

  5. Pregnancy • 10 lunar months • 9 calendar months • 40 weeks • 280 days • Computed from last menstrual period (LMP)

  6. Intrauterine Development • Three stages: • Preembryonic stage • Embryonic stage • Fetal stage

  7. Preembryonic Development • First 14 days after fertilization • Two stages: • Cell Multiplication • Call Differentiation

  8. Primary Germ Layers • Three primary germ layers • Ectoderm • Mesoderm • Endoderm

  9. Embryonic Stage • From 3 weeks to 8 weeks gestation • Most vulnerable to teratogens during this period

  10. Fetal Membranes • Two fetal membranes: • Chorion • Amnion

  11. Amniotic Fluid • Amniotic fluid • Many functions • Oligohydraminos • (Poly) Hydraminos • Aminocentensis

  12. Yolk Sac • Yolk Sac • Produces primitive red blood cells • Incorporates into the umbilical cord

  13. Umbilical Cord • Umbilical Cord • Develops from amnion • Two arteries and one vein • Wharton’s jelly • Nuchal Cord- when it is around the neck of the fetus

  14. Placenta • Placental Development • Begins development at about the third week of embryonic development • Usually implants at the site where the embryo attached to the uterus • Stops growing at 20 weeks, then only thickens • Placenta has two parts • Maternal: red flesh-like • Fetal: shiny and gray

  15. Placental Function • Respiration • Nutrition • Excretion • Protection • Storage • Hormonal production

  16. Fetal Circulation • Ductus venosus • Ductus arteriosus • Foramen oval

  17. Fraternal Twins (dizygotic) • Two separate ova fertilized by two separate sperm • Two placentas, two chorions and two amnions • Sometimes placentas fuse • No more alike than siblings • May be same or different sex

  18. Identical Twins ( Monozygotic) • Divide from single fertilized ovum • Same sex • Not affected by environment, race, physical characteristics or fertility treatments • Single placenta • # of amnions and chorions depends on timing of division

  19. Identical Twins (con’t) • If division occurs: • within 3 days of fertilization- two embryos, two chorions, two amnions • within about 5 days- two embryos, one common chorion, two amnions • within about 7-13 days- two embryos, one chorion, one amnion

  20. Fetal Stage • Nine to 40 weeks

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