Download Prenatal Development

CONCEPTION AND PRENATAL
DEVELOPMENT
OT 500 : Child Behavior and
Development
Spring 2016
Figure 2.9
WHAT PROCESS BRINGS TOGETHER
THE GENES FROM EACH PARENT?
 Only
one sperm enters the zona pellucida
 Sperm secrete enzyme hyaluronidase to
allow penetration of the zona pellucida
 When one sperm enters, the zona
pellucida thickens, locking out other
sperm
 Chromosomes from sperm and egg
combine to form 23 new pairs
MISCARRIAGE

Spontaneous abortion
 Before 20 weeks pregnancy
 Usually due to mutation/ problem with
chromosomal pairing
 Estimated over 50% of fertilized eggs die, often
before a woman is aware of pregnancy
 At 4 -5 weeks pregnancy, miscarriage rate is
20%
 Can be related to stress, environmental toxins,
and maternal health issues and more common
in older women, and women who have had
prior miscarriage
INFERTILITY
Fertility problems among men
 Low sperm count
 Deformed sperm
 Low sperm motility
 Diseases
 Direct trauma to testes
 Autoimmune responses
 Causes
 Genetic factors, environmental poisons, diabetes,
STI’s, overheating testes, pressure to testes,
aging and effects of drugs

INFERTILITY

Major fertility problems among women
 Irregular or failure to ovulate
 Fertility drugs are used to cause women to
ovulate
 Declining hormone levels due to aging
 Infections
 Pelvic inflammatory disease (PID)
 Endometriosis
 Obstruct fallopian tubes
 Barriers or disorders in passageways (i.e.
Fallopian tubes)
OTHER WAYS OF BECOMING
PARENTS
 Surrogate
Mothers
 Surrogate “substitutes” bring babies to
term for another woman
 Adoption
 Greater diversity of adopted children
and adoptive parents
 Consideration of adopted children needs
OTHER WAYS OF BECOMING PARENTS
HOW ARE COUPLES HELPED TO HAVE
CHILDREN?
Artificial Insemination
 Sperm injected into mother’s uterus
 In Vitro Fertilization
 Ova and sperm are fertilized, then implanted
in mother’s uterus
 Donor IVF
 Ovum harvested from donor woman; fertilized
in vitro and implanted in recipient’s uterus
 Embryonic transplant

PRENATAL DEVELOPMENT
3
Phases
 Germinal Stage: Period from
conception to implantation
(approximately 2 weeks)
 Embryonic Stage: Period from
implantation to the 2nd month
 Fetal Stage: Period from the beginning
of the third month until birth
THE
GERMINAL STAGE
 Zygote
repeatedly divides but does not gain
in mass as it moves, taking about 3-4 days to
reach the uterus
 Within 3 days, the mass of dividing cells is
about 32 cells, and is called a Blastocyst
 The blastocyst shoes cell differentiation
 Inner layer or part of blastocyst is called
the embryonic disk (becomes embryo and
fetus)
 Outer part of the blastocyst is called the
trophoblast (protects and nourishes);
blood cells, umbilical cord, placenta
EARLY DAYS OF THE GERMINAL STAGE
Figure 3.1
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
FAILED PREGNANCY
 Miscarriage
(spontaneous abortion)
 Usually
stems from abnormalities
in development
 Approximately
one-third of all
pregnancies result in miscarriage
THE EMBRYONIC STAGE
WHAT HAPPENS DURING THE EMBRYONIC
STAGE OF PRENATAL DEVELOPMENT?
 Begins
with implantation (3rd week)
through 8th week
 Major
organ systems differentiate
 Developmental
trends
 Cephalocaudal
– head takes
precedence over lower parts of the
body
 Proximodistal
outward
– central axis of body
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; Neural tube develops into brain and
spinal cord

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
THE EMBRYO: WEEKS THREE
THROUGH EIGHT

Specialized layers of cells
 Ectoderm
 Mesoderm
 Endoderm
HUMAN EMBRYOS AND FETUSES
Figure 3.2
WHEN DOES THE HEART BEGIN TO
BEAT?
 Heart
begins to beat (4rd week); when you
were about ¼ inch long!!!
 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
week)
buds, working kidneys and liver (8th
DEVELOPMENT OF THE
NERVOUS SYSTEM
 By
end of first month, the neural tube is
producing 400 million neurons/nerve cells
per day
 Neurons
form cerebral hemispheres (5th
week)
 Cells
in the nervous system begin to
release neurotransmitters (2nd month)
SEXUAL DIFFERENTIATION


Nondescript sex organs formed (5 to 6 weeks)
Internal and external genitals at this stage
resemble female structures



Müllerian (female) ducts and Wolffian (male)
ducts
Sex organs begin to differentiate, based on
genetic code (7th week)

Y chromosome causes testes to differentiate

No Y chromosome causes ovaries to
differentiate
Distinct external genital structures (4 months)
BOY OR GIRL?

Prenatal sexual development
 Stage 1 – male and female have similar
gonadal streak, Müllerianducts, and Wolffian
ducts
 Stage 2 – physiological differences emerge
 Stage 3 – external genitals form; testosterone
stimulates development of testicles and penis
 Stage 4 – testosterone inhibits the cycles of the
hypothalamus and pituitary, which regulate
female ovulation
DEVELOPMENT
Figure 3.4
OF INTERNAL
GENITAL ORGANS
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

Müllerian inhibiting substance (MIS)
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
Müllerian ducts develop into Fallopian
tubes, uterus, and inner part of the
vagina
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
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 (alcohol, aspirin, narcotics)
Secretes hormones that prepare breasts for
nursing, and stimulate contractions that prompt
childbirth
The EMBRYO IS VERY SUSCEPTIBLE
THE FETAL STAGE
WHAT HAPPENS DURING THE FETAL STAGE
OF PRENATAL DEVELOPMENT?
 Third
 End
month through birth
of first trimester

Major organ systems formed

Fingers and toes formed

Eyes can be distinguished

Sex of fetus can be determined visually
WHAT HAPPENS DURING THE FETAL STAGE
OF PRENATAL DEVELOPMENT?
 End
of second trimester

Opens and shuts eyes

Sucks thumb

Alternates between sleep and
wakefulness; mother feels baby moving
around 4 months

Responds to light and sound
 At
22 to 25 weeks gestation, about 50%
babies born will survive
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
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
ENVIRONMENTAL INFLUENCES
ON PRENATAL DEVELOPMENT
HOW DOES THE NUTRITION OF THE MOTHER
AFFECT PRENATAL DEVELOPMENT?
Malnutrition in mother (esp. during last
trimester)
 Low-birth-weight, prematurity, stunted
growth, retardation of brain development,
cognitive deficiencies, behavioral problems,
cardiovascular disease
 Some effects of fetal malnutrition can be
overcome by supportive, care-giving
environments
 Maternal obesity
 Linked to higher risk of still-birth
 Increases risk of neural tube defects

WHAT SHOULD A PREGNANT WOMAN EAT?


Well rounded diet including protein, vitamins, minerals,
calcium, and calories
Folic acid supplements


Reduce risk of neural tube defects
Mother can expect to gain 25 to 35 pounds during
pregnancy

Inadequate weight gain increases chance of premature or
low-birth-weight baby
TERATOGENS AND HEALTH PROBLEMS OF THE
MOTHER
 Teratogens
– 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
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
CRITICAL PERIODS IN PRENATAL DEVELOPMENT
Figure 3.5
SENSITIVE PERIODS IN PRENATAL DEVELOPMENT
WHAT ARE THE EFFECTS OF MATERNAL HEALTH
PROBLEMS?

Sexually Transmitted Infections (STIs)

Syphilis can cause miscarriage, stillbirth, or
congenital syphilis

Infected mother can be treated with antibiotics
before 8th week

Infected mother not treated


Baby 40-70% chance of being infected in
utero
Babies with congenital syphilis
WHAT ARE THE EFFECTS OF MATERNAL HEALTH
PROBLEMS?

Sexually Transmitted Infections (STIs)


HIV/AIDS (human immunodeficiency
virus/acquired immunodeficiency syndrome)

Disables body’s immune system

Lethal unless treated
About one-quarter of babies born to HIV/AIDSinfected mothers are infected also

Many are infected during childbirth

HIV is also found in breast milk
WHAT ARE THE EFFECTS OF DRUGS TAKEN BY THE
MOTHER?


Accutane

Prescribed for difficult cases of acne

Linked to numerous abnormalities during first trimester
Thalidomide


Antibiotics


Missing or stunted limbs
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
WHAT ARE THE EFFECTS OF MATERNAL HEALTH
PROBLEMS?

Influenza (Flu)


Rubella (German measles)



Impacts mother’s respiratory system
Viral infection may cause birth defects
Toxemia

May cause premature or undersized babies

Cause of maternal death
Rh Incompatibility

Transfer of maternal antibodies that may cause brain
damage or death
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-birth-weight,
prematurity, and toxemia

Baby may be born addicted
Marijuana

Risk of low-birth-weight, immature development of
nervous system

Predisposes offspring to dependence on opiates, even in
adulthood
WHAT ARE THE EFFECTS OF DRUGS TAKEN BY THE
MOTHER?


Cocaine

Maternal use of cocaine increases risk of stillbirth, lowbirth-weight, 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, and growth
deficiencies

Fetal Alcohol Spectrum Disorders

Fetal Alcohol Syndrome (FAS)

Physical and psychological defects

Fetal Alcohol Effect (FAE)
FETAL ALCOHOL SYNDROME
WHAT ARE THE EFFECTS OF DRUGS TAKEN BY THE
MOTHER?

Caffeine


Connected with miscarriage and low-birth-weight
Cigarettes


Nicotine and carbon monoxide pass through the placenta

Nicotine stimulates fetus

Carbon monoxide is toxic and decreases oxygen to fetus
More likely to deliver smaller babies


Long-term effects


More likely to be stillborn or die soon after birth
Short attention spans, hyperactivity, lower cognitive scores,
poor grades
Men who smoke are more likely to produce abnormal sperm
WHAT ARE THE EFFECTS OF ENVIRONMENTAL HAZARDS?


Prenatal exposure to PCBs

Connected with smaller, less responsive babies

More likely to develop cognitive deficits
Heavy metals (lead, zinc, mercury)


Fetal exposure to radiation


Threatens cognitive development
Risks for neural and skeletal problems
Father’s exposure to heavy metals and radiation
may also cause abnormalities in baby
WHAT ARE THE EFFECTS OF MATERNAL STRESS?
 Maternal
stress linked to secretion of
hormones

Adrenaline passes through placenta
CNN week of Jan 25/2016: Zika Virus
linked to birth defect in newborns..3-4
million cases in the Americas (mostly
Brazil); spreading explosively..by
mosquitos..can result in microcephaly in
newborns