Download Prenatal Development

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
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
Microscopic Germ Cells
Full Term Fetus
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
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
Implantation
Blastocyst
Period of the Ovum, Cont’d
• 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)
Period of the Ovum, Cont’d
• 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
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
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
Period of the Embryo: Placenta
cont’d
• 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
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
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
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
Fetus
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)
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
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 mother’s voice
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
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
Period of the Fetus: Global
• Fetus receives antibodies from mother’s
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
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
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
Teratology: Drugs
Cocaine, Heroin, Methadone
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•
•
•
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
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
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 mom’s system
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
• 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
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
Other Common Drugs
• Caffeine
– >3 cups/day associated with prematurity
– Poorer neuromuscular & reflex functioning
• Marijuana
– Respiratory problems
– Attentional & learning disabilities
• Aspirin
– Linked to subcutaneous bleeding in newborn
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
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
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
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
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
Nutrition, cont’d
• 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
Nutrition, cont’d
• 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