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Prenatal Development

Prenatal Development. The structure and function of the nervous system and sensory organs undergo a major part of their development before birth

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Prenatal Development

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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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)

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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)

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

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