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Prenatal Development

Prenatal Development. In which we examine the three stages of development from conception to birth, and the causes of congenital defects that can occur during that time. Stages of Prenatal Development. Zygotic (or Germinal) Stage 0-2 weeks Embryonic Stage 2-8 weeks Fetal Stage 9-40 weeks.

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Prenatal Development

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  1. Prenatal Development In which we examine the three stages of development from conception to birth, and the causes of congenital defects that can occur during that time.

  2. Stages of Prenatal Development • Zygotic (or Germinal) Stage 0-2 weeks • Embryonic Stage 2-8 weeks • Fetal Stage 9-40 weeks

  3. Part 1: Zygotic Stage

  4. Zygotic Stage • Major tasks: Cell division and implantation • Rate of cell division: 36 hours 2 cells 48 hours 8 cells 72 hours 32 cells 96 hours 70 cells • After 4th day, cells arranged in a hollow sphere, called the blastocyst. • Cells are undifferentiated (not yet specialized for function)

  5. Zygotic Stage, continued • Zygote develops from an area of blastocyst called the embryonic disk • At 2 weeks, the embryonic disk as 3 layers: • Entoderm: from which develops pharynx, tonsils, thyroid, trachea, lungs, digestive system, bladder, urethra • Mesoderm: from which develops muscles, bones, circulatory system, lymph system, kidneys, gonads • Ectoderm: from which develops skin, hair, nails, sense organs, nervous tissue

  6. Zygotic Stage: Week 2 Come to class to see slide!

  7. Critical Periods • Critical Period: specific time when a given event, or its absence, has the greatest impact on development • Development = differentiation, then growth • Differentiation: the process in embryonic development during which unspecialized cells or tissues become specialized for particular functions. (Ex: pre-gonadal tissue differentiates into pre-ovarian or pre-testicular tissue) • Growth: Once the cells have differentiated, the structure grows • The critical period for prenatal defects is during differentiation

  8. Critical Periods of Various Embryonic Structures

  9. Part 2: Embryonic Stage

  10. Embryonic Stage • Major Task: Differentiation of all body systems except cerebral cortex and sensory system. • Trends in differentiation of cells • Size and structure: from uniformity to diversity; from simplicity to complexity • Shape: from irregular to regular; from vagueness to definiteness • Adaptability: from plasticity to rigidity

  11. Embryonic Stage, continued • 3 weeks: neural groove closes; thyroid differentiates; liver differentiates; urinary duct begins to form; primitive heart begins beating • 4 weeks: limb buds appear; tongue bud appears; lung bud appears; esophagus, stomach and intestine are single tube; nerves begin to form; optic cup appears • 5 weeks: nasal pits appear; jaws begin to form; premuscle masses appear; genital buds appear; pre-gonadal tissue present; intestine begins looping; circulatory system extends to head and limbs

  12. Embryo: Week 4 Come to class to see slide!

  13. Embryo: Week 4

  14. Embryonic Stage, continued • 6 weeks: external ear appears; limbs recognizable; lobes of lungs appear; bronchi dividing • 7 weeks: back straightens; tail begins to disappear; larynx developing; muscles begin to differentiate • 8 weeks: head elevating; digits formed; epidermis in 3 layers; taste buds appear; lymph system developing; testes and ovaries identifiable; skeletal systems begins to ossify; brain attains general structure, with lower brain more developed

  15. Embryo: Week 8 Come to class to see slide!

  16. Embryo: Week 9

  17. Development of Three Species Early stages in the development of a guinea pig (left column), a monkey (middle column), and a human embryo (right column).

  18. Part 3: Fetal Stage

  19. Fetal Stage • Major Tasks: Differentiation of neocortex, sensory systems, and overall growth • Neocortex and sensory systems • The old brain develops early in the embryonic stage. Needed to control circulatory system. • The midbrain develops later in embryonic stage. • The neocortex doesn’t develop until fetal stage. All structures not present until after first year of life. • Sensory systems are intricately connected to neocortex and so develop at same time.

  20. Brain Development

  21. Brain Development, continued

  22. Fetal Growth 2 months 1” long 1/13 ounce 3 months 3” long 1 ounce 4 months 9” long 6 ounces 5 months 12” long 14 ounces 6 months 14” long 20 ounces 7 months 16” long 3-4 pounds 8 months 18” long 5-6 pounds 9 months 20” long 7.5 pounds

  23. Part 5: Congenital Defects

  24. Teratogens & Congenital Defects Teratogen: achemical or physical agent which can lead to malformations in the fetus Congenital Defect: a defect present at birth caused by a teratogen.

  25. Categories of Teratogens • Metabolic (Diseases) • Chemicals • Drugs • Alcohol, Heroin, Narcotics, Nicotine • Maternal malnutrition • Radiation

  26. Metabolic Teratogens

  27. Chemical Teratogens

  28. Alcohol, Nicotine & Other Addictive Substances • The most common defect of addictive substances, including nicotine, is low birth weight • Infants born to addicted women will also be addicted. • Fetal Alcohol Syndrome • Growth deficiencies • Skeletal and facial deformities • Organ deformities: heart defects; genital malformations; kidney and urinary defects. • Central nervous system handicaps: small brain; mental retardation learning disabilities; hyperactivity, poor coordination.

  29. Child with FAS

  30. Malnutrition & Radiation • Most common effect of material malnutrition is low birth weight. • Radiation may prevent organs from developing and may cause mutations.

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