An 17th Century View of
Conception
Prenatal Development
Early Views
•Preformation—life begins with a new individual already
preformed
OR
•Epigenesis (Aristotle)—new structures and functions emerge
during development
Conclusion
•Embryology—the study of prenatal development
 Showed the existence of genes and cells
 Techniques for studying physical and behavioral
development in the womb
Conception
What: Gametes or Germ Cells
How: Through the process of conception the egg
and a sperm unite
Prenatal Development:
Period of the Zygote
Female reproductive system
A simplified illustration of the female reproductive system, with a fetus developing in
the uterus (womb). The umbilical cord runs from the fetus to the placenta, which is
burrowed deeply into the wall of the uterus. The fetus is floating in amniotic fluid inside
the amniotic sac.
Periods of Prenatal Development
•Zygote
Rapid cell division
Blastocyst
•Embryo
 gastrulation
 Cell division
 Cell migration
 Cell differentiation
 Cell death/apoptosis
 Hormones
•Fetus
Stages of prenatal development
Prenatal Development:
Period of the Embryo
(Figure adapted with permission from Textbook of Embryology, 5th ed. (p. 87), by H.E. Jordan and J.E.
Kindred, 1948, New York: Appleton-Century-Crofts.Copyright © 1948 by Appleton-Century-Crofts.)
Prenatal Environment
Fetal Experience
Touch
Taste
• Grasping, sucking, rubbing,
bumping walls of uterus
• Swallows amniotic fluid
• Fetus has a sweet tooth
Smell
• Amniotic fluid has odor of what mom ate
• During fetal breathing, amniotic fluid comes into contact
with olfactory receptors
Sight
• Negligible
Hearing
• Internally generated sounds (mom’s heartbeat, breathing, etc.)
• Externally generated sounds (mom’s voice and people talking to her)
• Fetus reacts by changes in heartbeat and movement
Fetal Learning
•Habituation
Before Birth
After Birth
•Around 32 weeks the fetus
shows signs of habituation
•Hearing: “The Cat in the Hat,”
recognizes mom’s voice, languages
heard in the womb
•Around 37 weeks the fetus
shows signs of long-term
memory and learning
•Smell: Prefers own amniotic
fluid
•Habituation is measured by •Taste: Recognizes carrot juice
changes in heartbeat
exposed as a fetus, but not since
birth
Teratology
• Teratogens
– Classes of teratogens include
– Drugs
– Infectious diseases
– Mother’s age
– Poor nutrition
– Other environmental agents
Principles of Teratology
1.
2.
3.
4.
5.
6.
The effect of a teratogen depends on the
genetic makeup of the exposed organism
Teratogen effects on development depend on
timing (period of 2-8 weeks is particularly
sensitive)
The effect of a teratogen may be unique
The impact of teratogens may be severe
Teratogens differ in how they gain access to
the fetus
Teratogen dosage is related to degree of
abnormal development
Consequences of Teratogens
Street Drugs
Therapeutics
Caffeine
Nicotine
Alcohol
Environmental
Chemicals
Babies of drug-addicted mothers are
born addicted and are likely to have
developmental problems
Drugs such as thalidomide may
induce abnormalities
Some risk is associated with caffeine
Can affect growth, increase risk of
premature delivery
Can lead to Fetal Alcohol Syndrome
Mercury, lead, and PCBs are harmful
to the fetus
Natural Teratogens
• Maternal infectious diseases
– Rubella can damage the CNS of the fetus,
sensitive period is 2-8 weeks
– Herpes virus can cause brain abnormalities
and blindness
– HIV can produce facial abnormalities
• Nutrition
– Poor prenatal nutrition results in unfavorable
development, low brain weight, and higher
rates of spontaneous abortion
Parental Age Effects
(Figure reprinted with permission from:
“Paternal Age Effect” by J.M. Friedman,
Obstetrics and Gynecology, vol 57, 1981,
p 746.)
Fetal Alcohol Syndrome
• Alcohol is the most widely used drug known
to harm the fetus
– Third major cause of birth defects
– Leading cause of congenital mental retardation
• Consumption of alcohol during pregnancy
can result in Fetal Alcohol Syndrome (FAS)
• Constellation of limb and facial deformations, failure
to thrive, mental retardation, and learning disabilities
• Chronic use of alcohol increases the risk of FAS to
50%; Risks associated with low levels of alcohol are
unknown
Screening Methods
•
•
•
•
Ultrasound Imaging
Amniocentesis
Chorionic Villus Sampling
Test-tube Screening
Birth
•Is being born as painful as giving birth?
The baby experiences squeezing
Reduces size of head to pass through mother’s pelvic bones
Stimulates the production of hormones which help
withstand hypoxia and regulate breathing
Inhibits the fetus from breathing until out
of birth canal
Squeezing of infant’s body forces amniotic fluid
from lungs to prepare for first breath
•Diversity of Childbirth Practices
Stages of Birth
“At Risk” Issues
• Babies may have two different risks:
– Risk for major physical malformations
– At risk for developmental delays, and for
cognitive and social problems
• Indicators of at risk status
Newborn Assessments
• Apgar exam
• Prechtl test
• Brazelton Neonatal Behavioral Assessment
Scale
The Newborn
•States
•Sleep
REM Sleep
50% of a newborn’s total daily sleep
•Sudden Infant Death Syndrome (SIDS)
Newborn states
The average proportion of time, in a 24-hour day, that Western newborns spend in each
of six states. There are substantial individual and cultural differences in how much time
babies spend in the different states.
Total sleep and proportion of REM and non-REM sleep
across the life span
•Crying
How Much?
What Does It Mean?
What Should You Do?
Newborn Reflexes
• Some reflexes are evident at birth but
disappear by age one; These reflexes can
index the development of the infant
– Rooting reflex
– Palmar reflex
– Moro reflex
Motor Development
• Postural development and locomotion
• Prehension
– Proximodistal direction
– Cephalocaudal direction
Physical Growth
(Figure adapted with permission from “Standards for Growth and Growth Velocity” by
J.M. Tanner, R.H. Whitehouse, and M Takaishi, 1966, Archives of Disease in Childhood,
41, p 467. Copyright © 1966 by Archives of Disease in Childhood)
Development of Locomotion
(Figure adapted with permission from “Early Development of Locomotion: Significance of Prematurity,
Cerebral Palsy, and Sex” by R.H. Largo, L. Molinari, M. Weber, L.C. Pinto, and G. Duc, 1985, Developmental
Medicine and Child Neurology, 27, pp 183-191, figure 2. Copyright © 1985 by MacKeith Press.)
Brain Development
• Three phases of brain
development:
– Cell production
– Cell migration
– Cell elaboration
Cortical Function
Negative Outcomes at Birth
•Infant Mortality
Poverty
Healthcare
•Low Birth Weight (LBW)—less than 5½ pounds
at birth
Types
Premature—less than or equal to 35 weeks gestation
Small for gestational age (SGA)—weight less for
gestational age whether preterm or full-term
•Long-term Outcomes
 As a group LBW babies have more developmental problems
(cognitive, social, and/or behavioral)
 Majority of LBW babies turn out fine
•Risk
Multiple Risk Model
Poverty
Resilience
Developmental Resilience
Responsive care from someone
Personal characteristics (intelligence, responsiveness to
others, believe can achieve goals)
Multiple risk factors
Children who grow up in families
with multiple risk factors are
more likely to develop
psychiatric disorders than
children from families with only
one or two problematic
characteristics (Rutter, 1979).
Descargar

An 17th Century View of Conception