Prenatal Development

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Prenatal Development

• The structure and function of the nervous system
  and sensory organs undergo a major part of their
  development before birth
• we will look at the sequence of normal
  development from conception to birth, as well as
  expore how adverse environmental events can
  impact this development

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Prenatal Development A Global Look

• At Conception the organism is two microscopic
  germ cells
• At Birth the organism is on average 7.5 lbs and
  20 in length
• the organism develops from a mass of
  undifferentiated identical cells to a highly
  differentiated organism with distinct structures
  and characteristics HOW

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Microscopic Germ Cells
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Full Term Fetus
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3 Aspects of Prenatal Development

• When a structure emerges
• Stages of the Prenatal Period (Ovum, Embryo,
  Fetus)
• growth and functional maturity of the structure
• behavior associated with different phases of
  development

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The Period of the Ovum

• Conception to Layering (10-14 days)
• Organism is called Blastocyst
• Characterized by rapid cell division and early
  differentiation
• Implantation and embryonic disk (cluster of cells
  on one side from which embryo will develop) by 5
  days

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Implantation
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Blastocyst
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Period of the Ovum, Contd

• Layering of cells at approximately 12 days in the
  embryonic disk
• ectoderm (skin, hair, nervous system, sensory)
• endoderm (digestive, respiratory)
• mesoderm ( circulatory, muscular)
• Disk is bounded by 2 fluid filled cavities and
  surrounded by chorionic cavity
• amniotic cavity
• yolk sac (initial supply of nurtrients and blood
  cells prior to placenta)

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Period of the Ovum, Contd

• Later developments
• yolk sac disappears by 40 days
• amniotic cavity becomes amniotic sac
• fluid environment within which the embryo
  develops
• chorionic cavity taken up by developing fetus
  leaving chorionic membrane fused with amniotic
  membrane
• bounding the fluid environment

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Period of the Embryo

• Layering until 8 weeks gestation
• major developments
• development of connections between the organism
  and maternal systems (placenta)
• differentiation of major neural, organ, and
  physical structures

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Period of the Embryo Placenta

• Earliest form is villi on blastocyst
• Blood vessels form by 2 weeks
• Mass of blood vessels from fetus and maternal
  systems come together to form placenta
• Not a direct connection blood pools around villi
  containing embryonic blood vessels

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Period of the Embryo Placenta contd

• Functions
• anchor embryo
• transport food, respiratory gases
• transports embryonic waste (acts as liver,
  kidney, lungs)
• manufactures hormones to prevent miscarriage,
  prepare breasts for milk production
• partial barrier for toxins

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Period of the Embryo Brain Heart

• Neural groove begins to form and becomes fused
  (neural tube) at 22-26 days
• Brain cells proliferate and migrate to cell
  addresses along microscopic threads
• Layering and differentiation of brain structures
  begins
• Heart is a straight tube at 20 days
• Primitive 4-chamber heart with heartbeat at 4
  weeks

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Period of the Embryo Limbs, Eyes, Ears, Mouth

• Buds
• Arms (26 days), legs (32 Days)
• Paddles
• Arms (43 days), legs (43 Days)
• Digits
• Arms (50 days), legs (57 Days)
• Primitive at 6 wks (eyes, ears,mouth)
• Differentiated at 8 wks

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Period of the Embryo Behavior

• Responds to touch, esp around mouth and soles of
  feet
• Tiny fluttering movements by 8 weeks
• Major organ structures differentiated, not yet
  fully functioning, but possiblity for harm is
  great
• Organism is approximately 2.5 cm, 1 gm

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Fetus
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Period of the Fetus

• Structures become further differentiated and more
  refined
• Structures begin to develop and functioning is
  fine tuned, sometimes in response to stimulation
  (e.g., audition, swallowing reponse)

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Period of the Fetus Brain

• By 6 mos all neurons made and in place
• Glial cells continue to be made until 3 yrs after
  Birth
• Mylenization occurs until 3 yrs
• 6-9 mos cortex enlarges and behaviors become more
  complex

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Period of the Fetus Brain Behavior

• 8-12 weeks organized behaviors such as kicking
  feet, bending arms, forming fist, curl toes, open
  mouth, suck thumb, exapnd/contract lungs
• 20 weeks shield eyes if light introduced as in
  fetoscopy
• 28 weeks strong response to sounds
• 36 weeks response to mothers voice

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Period of the Fetus Circulatory

• Heart becomes more refined chambers and valves
  formed
• lungs and liver bypassed until birth
• placenta acts as organ of respiration until birth

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Period of the Fetus Sensory

• Optic nerve formed by 9 weeks
• retinal layering in period of 12-28 weeks
• eyelids sealed from 8-28 weeks, light can be
  perceived by 28 weeks, when lids open again
• last link in auditory development is ossification
  of inner ear bones by 20 weeks, auditory
  perception possible then

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Period of the Fetus Global

• Fetus receives antibodies from mothers system
• Period of most rapid growth in prenatal
  development
• in 3rd month fetus grows from 9 to 18 cm
• in 5th month fetus reaches half full term size
• weight gain begins in 7th month fat deposits
  help temperature regulation
• at Birth newborn is approx 7.5lb (3-4 kg) and 20
  in (50 cm) long

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Teratology Negative Environmental Influences

• study of birth defects that are caused by
  environmental, not genetic, factors
• a variety of factors influence the effects these
  environmental influences can have
• timing of the event
• type of teratogen
• dosage or degree of exposure
• genetic makeup of mother and fetus
• synergistic effects

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Teratology Drugs

• Drugs pass the placental barrier easily
• when this occurs early in prenatal development
  damage is structural
• when this occurs later, damage is typically
  functional, but could also be structural

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Teratology Drugs Cocaine, Heroin, Methadone

• Prematurity
• low birth weight
• physical defects
• respiratory difficulties, including respiratory
  distress at birth leading to perinatal death
• addiction and withdrawal, putting at risk for
  early death
• abnormal cry and vocalization patterns

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Teratology Drugs-Specifics for Cocaine

• Genital, urinary tract, heart, kidney deformities
• low responsivity to stimulation 1 yr or more
• increased risk for SIDs
• attentional and motor development lags
• crack cocaine effects more severe
• animal research suggest short term effects except
  when combined with alcohol abuse, then long term
• research correlational, synergistic effects

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Teratology Drugs-Specifics for Nicotine

• Increased rate of spontaneous abortion
• rate of stillbirth doubles
• low birth weight
• increased chance of cleft palate, mental
  retardation, hyperactivity
• causes placenta to grow abnormally, displaces O2
  from red blood cells
• effects increase with increased dosage, higher in
  breast milk than moms system

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Teratology Drugs-Specifics for Alcohol

• Fetal Alcohol Syndrome(FAS) results from heavy
  use of alcohol during pregnancy, can also be
  triggered by binge drinking during sensitive
  period, the particlar symptoms that manifest
  depend on timing and dosage
• symptoms
• growth deficiencies
• physical abnormalities including microencephaly,
  short eye opening, joint,limb, cardiac, motor
  dysfunction, hypperactivity, increased risk of
  stillbirth, prematurity

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• Sulik (1981)
• mice exposed to alcohol
• timing and dose manipulated
• find sensitive period Day 7 (mesoderm) 3 wk
  human gestation
• amount needed to produce effect small, timing
  crucial

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Teratology Drugs-FAS Research

• Astley et al (1992) study with humans
• point out difficulties of this research relies
  on reports, correlational in nature, often use of
  alcohol combined with other drugs
• find timing is critical as little as 2 oz per
  day can cause full FAS
• withdrawal at birth also contributes to symptoms
  of FAS

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Other Common Drugs

• Caffeine
• gt3 cups/day associated with prematurity
• Poorer neuromuscular reflex functioning
• Marijuana
• Respiratory problems
• Attentional learning disabilities
• Aspirin
• Linked to subcutaneous bleeding in newborn

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Rx Drugs Hormones

• Thalidomide
• Rx taken by moms to prevent morning sickness
• Limb and heart deformities immediate effects
• DES
• Hormone taken to prevent miscarriage 1948-69
• Sleeper effects
• Cervical cancer, infertility, problem pregnancy
  in women around childbearing age
• Cysts in sperm storage, low sperm count, abnormal
  sperm shape if taken 6-8 weeks of pregnancy

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Environmental Toxins

• Radiation
• Miscarriage, slow physical growth, underdeveloped
  brain, malformed skeleton, sleeper effects like
  childhood cancer
• Agent Orange (dioxin)
• Multiple deformities in host and offspring
• PCBs
• Lower birthweight, smaller heads, learning
  disabilities
• Mercury and Lead (even low dose danger)
• Mental retardation, slower speech development,
  uncoordinated movements, low birth weight,
  prematurity

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Maternal Disease

• Ruebella
• Blindness, deafness, heart abnormality, heart
  defects, urinary tract deformities, mental
  retardation, most danger 1st trimester
• Toxoplasmosis
• Eye and brain damage, caused by parasite found in
  uncooked meat
• AIDS
• Reduced birthweight, HIV which leads to increased
  chance of infectious disease early in life,
  abnormal immune system, low life expectancy

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Other Maternal Factors

• Age
• Over 35 at risk for genetic abnormalities
• Under 15 at risk for low birthweight, perinatal
  death
• Risk moderated by fitness and health level
• Emotional State
• Prolonged severe anxiety at risk for prematurity,
  heightened fetal activity, n executive monkey
  syndrome associated with higher levels of
  adrenalin

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Nutrition

• Two stages of brain growth
• 10-18 wks cell proliferation, 20 wk connections
  and myelinization, continuing until 3 yrs
• Animal studies
• Malnourishment leads to smaller brains, less
  myelinization, 40 reduction of connections,
  irreversible effects after 3 yrs

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Nutrition, contd

• Human Studies
• Cravioto
• 1966 study in rural Mexico during severe
  malnourishment
• Lag in general language development and verbal
  concept comprehension
• Richardson
• Jamaican children also malnourished early in
  development
• Poor academic achievement increased by
  impoverished environments
• MalnDeprived 52.9
• MalnEnriched 62.7
• HealthyDeprived 60.5
• HealthyEnriched 71.4

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Nutrition, contd

• Chavez
• Supplementary food program for parents and
  children (prenatal till 3 yrs)
• Newborns on average 8 heavier, infants and
  children had superior language dev, physical
  activity and physical developmental milestones
• Stein
• Famine in Holland during occupation, number of
  births halved, birthweight decreased by 10, not
  long term