04 teratogenics
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THE CRITICAL THE CRITICAL PERIODS AND PERIODS AND TERATOGENICSTERATOGENICS
Critical PeriodsCritical PeriodsThe critical periods are times during
which certain environmental influences can have an impact on the development of a child.
The most likely time for a miscarriage, or spontaneous abortion, is in the first three months, as the organs are forming and first becoming functional.
15-20% end in miscarriage
Definition of TeratogenicsDefinition of TeratogenicsAny agent that causes a birth
defect (from the Greek word teras meaning ‘monster’)
Includes drugs, chemicals, viruses – any substance or factor that can cause a defect.
The Thalidomide DisasterThe Thalidomide Disaster
Early 1960sPrescribed as sedative to
control nausea4th-6th weeks –
abnormalities. Fused fingers and toes,
dislocated hips, missing limbs, hands and feet attached to torso, facial malfunctions, malformed organs.
10, 000 children worldwide before detection.
Effects of teratogenic agents Effects of teratogenic agents on prenatal developmenton prenatal development1) Sensitive periods: Varies with organ systems
developing at different times. Germinal period - zygote may
be completely destroyed.Embryonic period –most
vulnerable in structural abnormality
Foetal period – more likely function than structure.
2) Tissue-specific effectEach teratogen acts in a specific
way on specific developing tissue E.g. thalidomide – limb
deformation, while mercury causes brain damage.
3) Dose-response relationship* > concentration of teratogenic =
> risk of abnormal development
4) Individual differences in effect
Response depends to some degree on its genotype and that of its mother.
Mother’s age, nutrition, hormonal balance can all affect the action of teratogens
Influences and EffectsInfluences and EffectsMalnutritionDrug and alcohol intakeIllnessesExternal environmental hazards
MalnutritionMalnutrition
Higher chance of premature or low-birthweight infants
Affects developing brain – can contain as few as 60% of normal number of cells
Major concern for low socio-economic families
Drug IntakeDrug IntakeDrugs can cross the placentaStrongest effect in early
pregnancyIdeally no medication should be
prescribed for pregnant or breastfeeding women unless it is absolutely essential for her health or that of her child.
Drug Effects
Aspirin Increased risk of bleeding for mother and baby; harm to circulatory system
Oral contraceptives
Increased risk of birth defects
Marijuana Irritability, nervousness, tremors; easily disturbed, startles
Alcohol Foetal alcohol syndrome (FAS) – mental retardation, delayed growth, facial malformation; learning difficulties, smaller head
Opiates Likely to bear premature babies addicted to the drugs in the womb
Nicotine Miscarriage, low birth weight, stillbirth, short stature, mental retardation, learning disabilities
Caffeine Miscarriage, low birth weight
Cocaine Decreased height, low birth weight, respiratory problems, seizures, learning difficulties; addiction
IllnessesIllnessesDisease producing organisms in the
mother’s blood can sometiems infect the foetus via the placenta
Minor effects on the mother can still have serious effects on the foetus.
E.g. rubella can cause blindness, deafness or heart disease in the foetus in first four weeks of pregnancy
Other diseases that can be transmitted include: chicken pox, mumps, malaria, syphilis, herpes and AIDS.
External Environmental External Environmental HazardsHazardsRadiation – gene mutations,
higher incidence of cancers, physical deformities
High temperatures – increased chance of neural tube defects, such as spinal bifida