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Chapter 8: Conception and Fetal Development

Chapter 8: Conception and Fetal Development. Study Guide. 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

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Chapter 8: Conception and Fetal Development

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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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