PSYC 2450 Chapter Notes - Chapter 4: Intrauterine Growth Restriction, Fetal Alcohol Spectrum Disorder, Congenital Heart Defect
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CH4 Prenatal Development, Birth, and Newborns' Readiness for Life
-prenatal development-development that occurs between moment of conception and birth
- Inside womb, three stages as well, but stages pass quickly as organism becomes a zygote, then embryo,
and finally fetus.
- transition from embryo to fetus occurs at 8 weeks,
- full month before pregnant woman enters second trimester of pregnancy often, before aware
she is pregnant.
-foundations for all of embryo's major organs formed
-rest of the prenatal period time of growth, developing function, and refinement of organs and
From Conception to Birth
-moment of conception, take approximately 266 days for zygote to become a fetus ready to be born.
-period of zygote (or germinal period), lasts from conception through implantation, when zygote becomes firmly
attached to wall of uterus
- 10 to 14 days
-period of the embryo, beginning of third week through end of eighth
-all major organs formed , heart begins to beat
-period of fetus, lasts from ninth week of pregnancy until child is born
The Period of the Zygote
-two cells and all resulting cells continue to divide, forming ball-shaped structure, blastocyst, contain 60 to 80 cells
w/in4 days of conception
-inner layer of blastocyst, embryonic disk, becomes embryo, whereas outer layer of cells develop into
tissues that protect and nourish embryo
-blastocyst approaches uterus 6 to 10 days after conception, small, burrlike tendrils emerge from outer surface
tapping mother's blood supply
-This is implantation
-" window of implantation" during which blastocyst must communicate (biologically) with uterine wall,
-takes about 48 hours , occurs 7 to 10 days after ovulation, entire process completing about 10 to
days after ovulation
-nearly three zygotes out of four, including most of abnormal ones, fail to survive initial phase of
Development of Support Systems
-blastocyst's outer layer rapidly forms four major support structures that protect and nourish
-One membrane, amnion, watertight sac fills w/ fluid from mother's tissues
-purposes of sac and its amniotic fluid : cushion against blows, regulate temperature, provide weightless
environment for embryo to move
-in watery environment is balloon-shaped yolk sac
- produces blood cells until embryo capable of producing its own.
-attached to third membrane, the chorion, surrounds amnion , eventually becomes lining of
-allantois, forms embryo's umbilical cord.
Purpose of the Placenta
-fed by blood vessels from mother and embryo, although hairlike villi act as barrier prevents these two bloodstreams
-barrier is semipermeable,
-umbilical cord transports carbon dioxide and metabolic wastes from embryo.
-waste products cross placental barrier, enter mother's bloodstream, eventually expelled
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The Period of the Embryo
-lasts from implantation (roughly third week) through eighth week of pregnancy.
-third week, embryonic disk rapidly differentiating into three cell layers.
-ectoderm, will become nervous system, skin, and hair.
-mesoderm, will become muscles, bones, and circulatory system
-endoderm, will become digestive system, lungs, urinary tract, and other vital organs
-portion of the ectoderm folds into neural tube
- becomes the brain and spinal cord
-end of fourth week, heart has formed and begun to beat.
-embryo about .6 cm but already 10 000 times size of zygote
The Second Month
-becomes much more human in appearance
-grows about 1 mm per day
-primitive tail appears, soon enclosed by protective tissue , becomes tip of backbone, the coccyx
-middle of fifth week, eyes have corneas and lenses
-seventh week, ears well formed, embryo has rudimentary skeleton.
-Limbs developing from body outward; upper arms appear first, followed by forearms, hands,
-seventh and eighth embryo's sexual development begins w/ appearance of genital ridge indifferent gonad.
-end of second month, embryo slightly more than 2.5 cm long and weighs less than 7.0 g.
Period of the Fetus
-seven months of pregnancy, or period of fetus
-all major organ systems begin to function and fetus begins to move, sense , behave
-individuality emerges as different fetuses develop unique characteristics, ex different patterns of
movement and different facial expressions.
The Third Month
-organ systems formed earlier continue growth , become interconnected
-coordination b/w nervous and muscular systems allow fetus to perform many interesting
-male testes secrete testosterone-male sex hormone responsible for development of a penis and scrotum
-end of third month, sex of a fetus detected by ultrasound
The Second Trimester: The Fourth through Sixth Months
-13th through 24th weeks of pregnancy; second trimester.
-16 weeks, fetus approximately 20 to 25 em long , weighs about 170 g.
-15 or 16 weeks through 24 or 25, simple movements of tongue, lips, pharynx, and larynx increase in
complexity and coordination
-Infants born prematurely may have difficulty breathing suckling ; exit womb early stage in
development of these skill ; haven't had enough time to practice
-fetus begins kicking may be strong enough to be felt by pregnant woman.
-end of 16th week, fetus assumed distinctly human appearance, although stands virtually no chance of
surviving outside womb
-fifth and sixth months, nails harden, skin thickens, and eyebrows, eyelashes, and scalp hair appear.
-20 weeks, sweat glands functioning, heartbeat often strong enough to be heard
-fetus now covered w/ white cheesy substance called vernix and fine layer of body hair lanugo
-Vernix protects skin against chapping exposure to amniotic fluid
-lanugo helps vernix stick to skin.
-end of sixth month, fetus's visual and auditory senses clearly functional.
- some ability to discriminate b/w sounds.
- ability may indicate presence of a rudimentary, short-term memory system
The Third Trimester: The Seventh through Ninth Months
-all organ systems mature rapidly, preparing fetus for birth
-22 and 28 weeks after conception (usually seventh month), fetuses reach age of viability- point which
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survival outside uterus is possible
-28- to 32-week-old begin to show better organized and predictable cycles of heart rate activity; gross
motor activity; and sleepiness/waking activity
-indicate developing nervous systems sufficiently well organized to allow survival should birth be
-many fetuses born require oxygen assistance
-pulmonary alveoli (air sacs) in lungs too immature to inflate and exchange oxygen for
carbon dioxide on their own
-end of seventh month, weighs just over 1.8 kg and about 40.0 to 43.0 em long.
- month later grown to 46.0 em and put on another 0.5 to 1.0 kg.
-comes from a padding of fat deposited beneath skin later helps to insulate newborn infant from
changes in temperature.
- most comfortable position likely head-down posture at base of uterus, w/ limbs curled up
-stages of development through developing organism passes do not correspond to trimester stages used to
describe pregnant woman's experience
-developing organism passes through all three stages of prenatal development in pregnant
woman's first trimester.
Environmental Influences on Prenatal Development
-teratogens external agents ex viruses, drugs, chemicals, radiation can harm developing embryo or fetus
-causing physical deformities, severely retarded growth, blindness, brain damage, and even death
-sensitive period during which organism quite susceptible to certain environmental influences; outside period, same
environmental influences must stronger to produce comparable effects.
- Olli Heinonen : concluded many birth defects found among children in sample were anytime malformations-
problems could have been caused by teratogens at any point during prenatal period
-Some disease agents capable of crossing placental barrier , doing much more damage to a developing embryo or
fetus than pregnant woman herself
-embryo or fetus has immature immune system cannot produce enough antibodies to combat infections
-rubella (German measles) disease has little effect on mother but may cause number of serious birth defects in
unborn children who exposed in first 3 to 4 months of pregnancy.
-1941 McAllister Gregg, noticed many mothers who had rubella (German measles) early in pregnancy
delivered babies who were blind
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