1. Chapter 4
Prenatal Development

2. From Conception to Birth
Period of the Zygote (Weeks 1-2)
Period of the Embryo (Weeks 3-8)
Period of the Fetus (Weeks 9-38) 2

3. From Conception to Birth
Ova travels from ovary to Fallopian tube
Penetration by 1 of sperm
Outcome: single-celled ZYGOTE 3

4. Periods of Prenatal Development
Period of the Zygote (Weeks 1-2)
After fertilization, the zygote travels down the fallopian tube and is implanted in the uterine wall (IMPLANTATION – period stops!)
Period of the Embryo (Weeks 3-8)
Body structures, internal organs, and the three layers of the embryo (ectoderm, mesoderm, & endoderm) develop
The amniotic sac fills with fluid and the umbilical cord connects the embryo to the placenta
Know. Weeks 1-2.
Period of Zygote: Called zygote until attached to urine wall. After which is called embryo. During zygote CANNOT be affected by teratogens (toxins) - zygote divides for the first time at 36 HOURS
At this point: Zygote may SPLIT = IDENTICAL TWINS (more common to have FRATERNAL TWINS – two eggs fertilized by two sperms)
Small cluster of cells near zygote – GERM DISC
layers of cells (on GERM DISC) CLOSEST to UTERINE WALL becomes the PLACENTA (for nutrient transfer)
Period of Embryo: zygote completely embedded in uterine wall
Initially a SALAMANDER, then a differentiated being with organs (NO sex organs yet)
UMBILICAL CORD present and blood vessels of umbilical cord transfers nutrients from mother’s blood vessels (they are NOT connected however: diffusion)
Ectoderm: becomes hair, outer skin, and NS
Mesoderm: muscles, bones, circulatory system
Endoderm: digestive system, lungs 4

5. Prenatal Development: Period of the Zygote
Figure 4.2 Schematic representation of the events of the first week of human development .

6. Prenatal Development: Period of the Embryo
Figure 4.4 Human ovum and embryo showing growth and body form from three to eight weeks. Adapted from Textbook of Embryology, 5th ed. (p. 87), by H. E. Jordan and J. E. Kindred, 1948, New York: Appleton-Century-Crofts. Copyright © 1948 by Appleton-Century-Crofts. 6

7. 7

8. Neural Tube App 3 weeks 8

9. Abnormalities Migratory Problems (in Corticogenesis) Corpus callosum
Neurulation: formation & closure of neural tube
(app 25th day of gestation)
Posterior: Spina bifida
Anterior: Anencephaly
Migratory Problems (in Corticogenesis) Corpus callosum
Subcortical 9

10. Periods of Prenatal Development
Period of the Fetus (Week 9-Birth)
Week 9- Differentiation of the ovaries and testes
Week 12- Circulatory system begins to function
Week 16- Movement felt by mother
Week 23- Age of viability 10

11. 11

12. Prenatal Environment
Figure 4.5 Maternal structures that support the embryo and fetus include the placental villi, amniotic sac, placenta, and umbilical cord. 12

13. Teratology
Teratogens: agents that cause abnormal development in the fetus
Can have physical effects (malformation) or psychological effects (intelligence, temperament, activity)
Types of teratogens
Drugs (e.g. Thalidomide---phocomelia; other therapeutic drugs, street drugs, caffeine, nicotine, alcohol)
Maternal infectious diseases
Natural “teratogens”
Environmental chemicals (e.g., mercury, lead, and PCBs )

14. Possible Consequences of Some Teratogens
Thalidomide
Malformations of internal organs and eyes, ears, fingers and toes
Other therapeutics
Fetal malformations and newborn death
Street Drugs
Babies of drug-addicted mothers are born addicted and are likely to have developmental problems
Caffeine
May be associated with miscarriage, premature birth or low birth weight
Nicotine
Can affect growth, increase risk of premature delivery, premature birth or low birth weight
Alcohol
Can lead to Fetal Alcohol Syndrome
Environmental Chemicals
Increase risk of miscarriages and developmental disabilities
Maternal Infectious Diseases
Can damage the CNS, cause brain abnormalities and blindness, and produce facial abnormalities
Vitamin A is a teratogen (ACCUTANE for acne contains vitamin A) and if you are pregnant u must stop taking it.

15. Principles of Teratology
The effect of a teratogen depends on the genetic makeup of the exposed organism
Teratogen effects on development depend on timing (period of 2–8 weeks (EMBRYO) is particularly sensitive)
The effect of a teratogen may be unique
The impact of teratogens may be severe
Teratogens differ in how they gain access to the fetus
Teratogen dosage is related to degree of abnormal development

17. Preventing, Detecting, and Treating Birth Defects
Prevention
Prenatal Care: Proper nutrition and abstinence from drugs and alcohol
Genetic Counseling: Through genetic testing and interviews with prospective parents, the risk for certain genetic defects is assessed

18. Preventing, Detecting, and Treating Birth Defects
Screening for Abnormalities
Ultrasound Imaging: Uses ultrasound to monitor the development of the fetus
Amniocentesis: Samples amniotic fluids for cells that are examined for markers of genetic defects
Chorionic Villus Sampling: Collects cells from a portion of the placenta for genetic analysis
Test-Tube Screening: In vitro embryos can be screened for genetic defects

19. Preventing, Detecting, and Treating Birth Defects
Treatment
Medical Therapy: Vitamins and drugs provided to mother and/or fetus
Surgery: Conducting surgery in utero on unborn fetus
Genetic Engineering: Gene therapy involving correcting defective gene by replacing or altering it