Human Growth and Development Chapter Four

Human Growth
Chapter Four
Prenatal Development and Birth
PowerPoints prepared by Cathie Robertson, Grossmont College
Revised by Jenni Fauchier, Metropolitan Community College
From Zygote to Newborn
• Germinal period—first 14 days
• Embryonic period—3rd through 8th
• Fetal period—9th week through birth
Process of Conception
Germinal: The First 14 Days
• Zygote divides and keep dividing (at least
though 3rd doubling they are the same)
• At this stage (8 cells) differentiation begins
- early “stem” cells take on distinct
- they gravitate to locations,
foreshadowing the type of cells they
will become
Germinal: The First 14 Days, cont.
• At about a week after conception the multiplying
cells separate into two masses
- outer layer forms a shell (later the placenta) and
the inner cells from a nucleus (later the embryo)
- first task of out cells to achieve implantation—
embed themselves into the nuturant environment
of the uterus
• 60% of all natural conceptions fail to implant; 70%
of in vitro procedures fail to implant
Embryo: From the Third
to the Eighth Week
• First sign of human structure: thin line down
the middle (22 days) that becomes the neural
tube, which eventually forms the central
nervous system, including brain and spinal
– fourth week
• head begins to take shape
• heart begins with a miniscule blood
vessel that begins to pulsate
Embryo: From the Third to the Eighth
Week, cont.
– fifth week
• arm and leg buds appear
• tail-like appendage extends from the spine
– eighth week
• embryo weighs 1 gram and is 1 inch long
• head more rounded; face formed
• all basic organs and body parts (but for
sex) present
– 20% of all embryos spontaneously abort now
Fetus: From the Ninth
Week Until Birth
• Called a fetus from 9th week on
Third Month
• Sex organs take shape (Y cell sends signal
to male sex organs; for females, no signal
- genital organs fully shaped by 12th week
• All body parts present
• Fetus can move every part of body
• Fetus weighs 3 ounces and is 3 inches long
Middle Three Months:
Preparing to Survive
• Heartbeat stronger
• Digestive and excretory systems
develop more fully
• Impressive brain growth (6X in size
and responsive)
- new neurons develop (neurogenesis)
- synapses—connections between
neurons (synaptogenesis)
Middle Three Months: Preparing
to Survive, cont.
• Age of viability—age at which
preterm baby can possibly survive
(22 weeks)
- 26 weeks survival rate about 50%
. brain maturation critical to viability
. weight critical to viability
- 28 weeks survival rate about 95%
Fetal Brain Maturation
Final Three Months—
Viability to Full Term
• Maturation of the respiratory
and cardiovascular systems
-critical difference
• Gains weight—4.5 lbs. in last 10
Risk Reduction
• Despite complexity, most babies are born
• Most hazards are avoidable
• Teratology—study of birth defects
– teratogens—broad range of substances
that can cause environmental insults
that may cause prenatal abnormalities
or later learning abilities
Determining Risk
• Risk analysis—weighing of factors that
affect likelihood of teratogen causing
Timing of Exposure
• Critical period—in prenatal
development, the time when a
particular organ or other body
part is most susceptible to
teratogenic damage
-entire embryonic period is
Amount of Exposure
• Dose and/or frequency
• Threshold effect—teratogen relatively
harmless until exposure reaches a
certain level
Amount of Exposure, cont.
• Interaction effect—risk of
harm increases if exposure to
teratogen occurs at the same
time as exposure to another
teratogen or risk
Genetic Vulnerability
• Genetic susceptibilities: product of
genes combined with stress
• Folic-acid deficiency may cause
neural- tube defects
- occurs most commonly in certain
ethnic groups and less often in
• Males are more genetically vulnerable
Specific Teratogens
• No way to predict risk on an individual basis
• Research has shown possible effects of most
common and damaging teratogens
• AIDS and alcohol extremely damaging
– pregnant women with AIDS transmit it
to their newborns; high doses of alcohol
cause FAS; alcohol + drug use increase
risk to developing organism
Low Birthweight
• Low Birthweight (LBW)
– less than 5 1/2 lbs.
• grows too slowly or weighs less than
• more common than 10 years ago
• second most common cause of neonatal
• Preterm
– birth occurs 3 or more weeks before
standard 38 weeks
Low Birthweight, cont.
• Small for Gestational Age (SGA)
– maternal illness
– maternal behavior
• cigarette smoking (25% of SGA
– maternal malnutrition
• poorly nourished before and during
• underweight, undereating, and
smoking tend to occur together
Low Birthweight, cont.
• Factors that affect normal prenatal
– quality of medical care, education,
social support, and cultural
The Birth Process
• Hormones in mother’s brain signals
• Contractions begin: strong and regular
at 10 minutes apart
– average labor for first births is 8
The Birth Process
The Newborn’s First Minutes
• Assessment—Apgar scale
– five factors, 2 points each
• heart rate
• breathing
• color
• muscle tone
• reflexes
– score of 7 or better: normal
– score under 7: needs help breathing
– score under 4: needs urgent critical care
• Parents Reaction
– preparation for birth, physical and
emotional support, position and size of
fetus, and practices of mother’s culture
• Medical Attention
– birth in every developed nation has
medical attention
– 22% of births in U.S. are cesarean section
• removal of fetus via incisions in mother’s
abdomen and uterus
– is medical intervention always necessary?
Birth Complications
• Cerebral Palsy—brain damage causing
difficulties in muscle control, possibly
affecting speech or other body
• Anoxia—lack of oxygen that, if
prolonged, can cause brain damage or
First Intensive Care . . .
Then Home
• At the Hospital
– many hospitals provide regular
massage and soothing stimulation;
ideally, parents share in caregiving
• At Home
– complications, e.g., minor medical
– cognitive difficulties may emerge,
but high-risk infants can develop
Mothers, Fathers and a
Good Start
• Strong family support (familia)
• Fathers play a crucial role
– may help wives abstain from drugs
or alcohol
– can reduce maternal stress
• Parental alliance—commitment by both
parents to cooperate in raising child
– helps alleviate postpartum
Mothers, Fathers and a Good
Start, cont.
• Parent-infant bond—strong, loving
connection that forms as parents hold,
examine, and feed their newborn
– immediate contact not needed for
this to occur