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Prenatal Development Truth or Fiction?

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Chapter 3 Prenatal Development Newly fertilized egg cells survive without any nourishment from the mother for more than a week. Your heart started beating when you ... – PowerPoint PPT presentation

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Title: Prenatal Development Truth or Fiction?


1
Chapter 3 Prenatal Development
2
Prenatal Development Truth or Fiction?
  • Newly fertilized egg cells survive without any
    nourishment from the mother for more than a
    week.
  • Your heart started beating when you were only
    one-fourth of an inch and weighed a fraction of
    an ounce.

3
Prenatal Development Truth or Fiction?
  • If it were not for the secretion of male sex
    hormones a few weeks after conception, we would
    all develop external sex organs that look like
    those of females.
  • Fetuses suck their thumbs and hiccough, sometimes
    for hours on end.

4
Prenatal Development Truth or Fiction?
  • It is harmless to the embryo and fetus for a
    pregnant woman to have a couple glasses of wine
    in the evening.
  • The same disease organism or chemical agent that
    can do serious damage to a 6-week-old embryo may
    have no effect on a 4-month-old fetus.

5
Prenatal Development Truth or Fiction?
  • Babies can be born addicted to narcotics and
    other drugs.

6
The Germinal Stage
  • Wanderings

7
What Happens During the Germinal Stage?
  • Period from conception to implantation
    (approximately 2 weeks)
  • Zygote repeatedly divides but does not gain in
    mass
  • Travels down Fallopian tube to uterus
  • After 3 or 4 days, implants in uterine wall
  • Takes form of blastocyst
  • Trophoblast, outer membrane of blastocyst,
    differentiates into membranes that will protect
    and nourish the embryo

8
Figure 3.1 The Ovarian Cycle, Conception and the
Early Days of the Germinal Stage
9
How Does the Dividing Mass of Cells Obtain
Nourishment During the Germinal Stage?
  • Prior to implantation, the dividing cells are
    nourished by the yolk of the original egg
  • Once implanted, nourishment is obtained from the
    mother

10
The Embryonic Stage
11
What Happens During the Embryonic Stage of
Prenatal Development?
  • Begins with implantation (3rd week) through 8th
    week
  • Major organs systems differentiate
  • Developmental trends
  • Cephalocaudal head takes precedence over lower
    parts of the body
  • Proximodistal central axis of body outward

12
Figure 3.2 Human Embryos and Fetuses at Various
Stages of Development
13
What Happens During the Embryonic Stage of
Prenatal Development?
  • Embryonic disk
  • Ectoderm (outer layer) develops into nervous
    system, sensory organs, nails, hair, teeth and
    skin
  • Endoderm (inner layer) forms the digestive and
    respiratory systems, liver, and pancreas
  • Mesoderm (middle layer) develops into the
    excretory, reproductive and circulatory system,
    muscles, skeleton and inner layer of skin

14
When Does the Heart Begin to Beat?
  • Heart begins to beat (4th week)
  • Arm buds and leg buds appear (4th week)
  • Eyes, ears, nose and mouth begin to take shape
  • Limbs are elongating, facial features become
    distinct (8th week)
  • Teeth buds, working kidneys and liver (8th week)

15
Sexual Differentiation
  • Nondescript sex organs formed (5 to 6 weeks)
  • Internal and external genitals at this stage
    resemble female structures
  • Sex organs begin to differentiate, based on
    genetic code (7th week)
  • Y chromosome causes testes to differentiate
  • No Y chromosome causes ovaries to differentiate

16
Figure 3.3 Development of the Internal Genital
Organs from an Age of 5-6 Weeks Following
Conception
17
Figure 3.4 Development of the External Genital
Organs from an Undifferentiated Stage at 5-6
Weeks Following Conception
18
Sex Hormones and Sexual Differentiation
  • Male hormonal influences
  • Testes produce androgens
  • Testosterone differentiates male duct system
    (Wolffian)
  • DHT (dihydrotestosterone) triggers development of
    male external genital organs

19
Sex Hormones and Sexual Differentiation
  • Female hormonal influences
  • Small amounts of androgens are produced
  • play a role in secondary sexual characteristics
    in adolescence
  • important in sex drive of females
  • Wolffian ducts degenerate and Mullerian ducts
    develop into Fallopian tubes, uterus and inner
    part of the vagina

20
A Closer Look
  • Genetic Factors in Sexual Differentiation

21
How Does the Embryo Get Nourishment from the
Mother?
  • Amniotic Sac
  • Protects the embryo/fetus within the uterus
  • Sac is surrounded by amniotic fluid
  • Placenta
  • Mass of tissue exchanges nutrients and wastes
    between embryo/fetus and mother
  • Umbilical Cord
  • Connects the fetus to the placenta

22
Do Germs or Drugs in the Mother Pass Through the
Placenta and Affect the Baby?
  • Placenta acts as a filter between the bloodstream
    of the mother and the bloodstream of the
    embryo/fetus
  • Oxygen and nutrients reach the embryo
  • Carbon dioxide and waste pass to the mother
  • Many germs and drugs may also reach the embryo

23
The Fetal Stage
24
What Happens during the Fetal Stage of Prenatal
Development?
  • Third month through birth
  • End of first trimester
  • Major organ systems formed
  • Fingers and toes formed
  • Eyes can be distinguished
  • Sex of fetus can be determined visually

25
What Happens during the Fetal Stage of Prenatal
Development?
  • End of second trimester
  • Opens and shuts eyes
  • Sucks thumb
  • Alternates between sleep and wakefulness
  • Responds to light and sound

26
What Happens during the Fetal Stage of Prenatal
Development?
  • End of third trimester
  • Heart and lungs increasingly able to sustain life
  • Gains in weight and length
  • During 7th month, fetus turns upside down in
    uterus
  • Born at end of 7th month 90 survival rate

27
Fetal Perception
  • Sound
  • 13th week fetus responds to sound waves
  • During third trimester can discriminate pitch
  • The Cat in the Hat study (DeCasper and Fifer,
    1980)
  • During final six weeks of pregnancy, Mothers read
    The Cat in the Hat twice daily
  • Using a special pacifier, newborns chose The Cat
    in the Hat read by their mother
  • Newborns prefer Mothers voice

28
When Does the Mother Begin to Detect Fetal
Movements?
  • Middle of 4th month detect first fetal
    movements
  • End of second trimester
  • Fetus moves vigorously, turns somersaults
  • Begins slow squirming movements
  • Begins sharp jabbing and kicking movements
  • As fetus grows, movements becomes restricted
  • Prenatal activity predicts activity levels after
    birth

29
Environmental Influences on Prenatal Development
30
How Does the Nutrition of the Mother Affect
Prenatal Development?
  • Malnutrition in mother (esp. during last
    trimester)
  • Low birthweight, prematurity, stunted growth,
    retardation of brain development, cognitive
    deficiencies, behavioral problems
  • Overly slender mother
  • Risk preterm deliveries and low birthweight
  • Maternal obesity
  • Linked to higher risk of stillbirth

31
How Does the Nutrition of the Mother Affect
Prenatal Development?
  • Folic acid supplements
  • Reduce risk of neural tube defects
  • Obesity during pregnancy
  • Increases risk of neural tube defects
  • Mother can expect to gain 25 to 35 pounds during
    pregnancy
  • Inadequate weight gain increase chance of
    premature or low-birth-weight baby

32
How do Teratogens Affect Prenatal Development?
  • Teratogen environmental agents that can harm
    embryo or fetus
  • Drug ingested by mother
  • Substance produced by mother
  • Heavy metals such as lead and mercury
  • Excessive hormones
  • Radiation
  • Pathogens bacteria and viruses

33
Does it Matter When, during Pregnancy, a Women
is Exposed to a Teratogen?
  • Critical periods of exposure to teratogens
  • Based on development of organs
  • Embryo is more vulnerable than fetus due to major
    organ systems differentiating

34
Figure 3.5 Critical Periods in Prenatal
Development
35
A Closer Look
  • Spacing Children the Goldilocks Way What is
    Just Right?

36
What are the Effects of Maternal Health Problems?
  • Sexually Transmitted Infections (STIs)
  • Syphilis can cause miscarriage, stillbirth, or
    congenital syphilis
  • About one-quarter babies born to HIV/AIDS
    infected mothers are infected also
  • Many are infected during childbirth
  • HIV is also found in breast milk

37
A Closer Look
  • Preventing Ones Baby from Being Infected with HIV

38
What are the Effects of Maternal Health Problems?
  • Rubella (German measles)
  • Viral infection may cause birth defects
  • Toxemia
  • Characterized by high blood pressure, may be
    linked to malnutrition
  • May cause premature or undersized babies
  • Cause of maternal death
  • Rh Incompatibility
  • Transfer of maternal antibodies that may cause
    brain damage or death

39
What are the Effects of Drugs Taken by the Mother?
  • Thalidomide
  • missing or stunted limbs
  • Antibiotics
  • Tetracycline may lead to yellowed teeth and bone
    abnormalities
  • Hormones
  • Progestin can masculinize external sex organs of
    female embryo
  • DES can cause cervical and testicular cancer

40
What are the Effects of Drugs Taken by the Mother?
  • Vitamins
  • High doses of vitamins A and D are associated
    with central nervous system damage, small head
    size and heart defects
  • Heroin and Methadone
  • Maternal addiction linked to low birthweight,
    prematurity and toxemia
  • Baby may be born addicted
  • Marijuana
  • Risk of low birthweight, immature development of
    nervous system

41
What are the Effects of Drugs Taken by the Mother?
  • Cocaine
  • Maternal use of cocaine increases risk of
    stillbirth, low birthweight, and birth defects
  • In utero exposure results in problems throughout
    childhood
  • Alcohol
  • Alcohol passes through placenta and poses risks
    for death of fetus and neonate, malformations,
    growth deficiencies
  • Fetal Alcohol Syndrome (FAS)
  • physical and psychological defects

42
What are the Effects of Drugs Taken by the Mother?
  • Caffeine
  • Connected with miscarriage and low-birthweight
  • Cigarettes
  • Nicotine and carbon monoxide pass through the
    placenta
  • nicotine stimulates fetus
  • carbon monoxide is toxic and decreases oxygen to
    fetus

43
What are the Effects of Environmental Hazards?
  • Heavy metals (lead, zinc, mercury)
  • Threatens cognitive development
  • Prenatal exposure to PCBs
  • Connected with smaller, less responsive babies
  • More likely to develop cognitive deficits
  • Fetal exposure to radiation
  • Risks for neural and skeletal problems
  • Fathers exposure to heavy metals and radiation
    may also cause abnormalities in baby

44
What are the Effects of Maternal Stress?
  • Maternal stress linked to secretion of hormones
  • Adrenaline passes through placenta
  • Connected to complications during pregnancy and
    labor
  • Connected to low preterm, low-birthweight, and
    irritable babies

45
Is the Parents Age Connected with the Outcome
of Pregnancy?
  • Teenage mothers
  • Higher incidence of infant mortality and
    low-birthweight children
  • Women over age 30
  • Increasing risk of chromosomal abnormalities,
    stillborn or preterm babies
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