Psychology 2040A/B Chapter Notes - Chapter 4: Embryonic Disc, Endometrium, Umbilical Cord

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18 Nov 2011
Psych 2040a
Chapter 4: Prenatal Development, Birth, and Newbornsʼ Readiness for Life
Prenatal Development: the development that occurs between the moment of
conception and the beginning of the birth process.
From Conception to Birth
prenatal development is divided into 3 major phases:
period of the zygote (germinal period)
period of the embryo - usually from the 3rd to 8th week
period of the fetus - usually from the 9th week to the pregnancy
The Period of the Zygote
zygote (ovum + sperm) moves down the fallopian tube towards the uterus - undergoes
through mitosis
a blastocyst is formed (a ball shaped structure) that will contain 60-80 cells within 4
days of conception
inner layer of the blastocyst contains the embryo (is called the embryonic disk
before it attaches to the uterus wall)
implantation: the burrowing of the blastocyst into the uterus lining; burrowing taps
into the motherʼs blood supply
there is a specific window of implantation - usually takes about 48 hours and
around 7-10 days after ovulation
Development of Support Systems
the blastocystʼs outer layer rapidly forms 4 major support structures for the embryo
amnion: watertight membrane that surrounds the embryo, regulating its
temperature and to cushion it against injuries (amniotic fluid)
chorion: membrane that surrounds the amnion and is attached to the uterine
later to gather nourishment
the lining of the chorion eventually becomes the lining of the placenta - a
multipurpose organ that provides respiration and nourishment of the unborn
child and elimination of its metabolic wastes
umbilical cord (allontois): soft tube containing blood vessels that connects the
embryo to the placenta
Purpose of the Placenta
purpose is to deliver nutrients such as oxygen, glucose, proteins, and carbon
dioxide to the embryo, coming from the mother
also transfers waste products from the embryo to be eliminated
The Period of the Embryo
usually from the 3rd to the 8th week of pregnancy
the embryonic disk in the blastocyst is rapidly differentiating into 3 layers:
ectoderm - becomes the nervous system, hair, and skin
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portion of the ectoderm folds into a neural tube: the primitive spinal cord that
eventually forms the CNS
mesoderm - muscles, bones, and circulatory system
endoderm - digestive system, lungs, urinary, and other vital organs
by the end of the 4th week, there is a heartbeat
The Second Month
becomes much more human in appearance
grows about 1mm per day
features such as hands, ears, eyes, and limbs develop by the end of the 2nd
brain develops during this period as well
during the 7th and 8th weeks, the embryoʼs sexual development begins with the
appearance of a genital ridge called the indifferent gonad
if the embryo is male, a gene on its Y chromosome triggers a biochemical
reaction that instructs the gonad to produce testes. if it is a girl, the gonad
receives no instructions and will produce ovaries
by the end of the 2nd month, the circulatory system is fully formed
The Period of the Fetus
period of rapid growth and refinement of the organ systems
The Third Month
organ systems become interconnected
by the end of the 3rd month, the sex of the fetus can be determined
systems work together to perform functions (ie. baby kicking)
The Second Trimester: The 4th - 6th Months
simple movements of the tongue, pharynx, and larynx increase in complexity
fetus begins to suck, hiccup, swallow, cough, and snort
hardening of the skeleton also takes place
by the end of the 16th week, the fetus has a human-like appearance, but still has
no chance of prematurely surviving
5th-6th months: nails harden, skin thickens, and eyebrows/lashes/scalp hair begins
to appear
20 weeks: sweat glands are functioning
fetus is covered with vernix (white cheesy substance that covers the fetus to
protect the skin from chapping) and lanugo (fine hair covering the fetusʼs body
to help the vernix stick to the skin)
by the end of the 6th month, the fetusʼs visual and auditory senses are fully intact
The Third Trimester: The 7th - 9th Months
somewhere in between 22-28 weeks after conception (usually in the 7th month),
the fetus reaches the age of viability (the point in which the fetus can start
surviving outside the uterus)
fetuses who are premature usually still need oxygen assistance since the
pulmonary alveoli in their lungs are too immature to inflate and exchange
oxygen for carbon dioxide on their own
fetuses are eventually positioned for labor in which it positions the head into the
gap between the pelvic bones to be ʻpushedʼ through
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Environmental Influences on Prenatal Development
Teratogens: external agents such as viruses, drugs, chemicals, and radiation that can
harm a developing embryo or fetus
can cause physical deformities, severely retarded growth, blindness, brain
damage, and even death
the effects of a teratogen on a body part or organ system are worst during the
period when that structure is forming and growing most rapidly
sensitive period: each system has a different period
3rd-5th week: most crucial period for gross physical defects of the head and
central nervous system
the heart is vulnerable from the middle of the 3rd through the 6th week
same defect can be caused by different teratogens
variety of defects can result from a single teratogen
long-term effects of a teratogen can depend on the postnatal environment
some teratogen cause “sleeper effects” that may not be apparent until later in life
teratogens can have subtle effects on babiesʼ behaviour that are not obvious at
birth but can influence their psychological development
Maternal Diseases
some disease agents can cross the placental barrier - can affect an embryo that
has an immature immune system
Rubella (German measles)
a disease that has little effect on the mother but may cause a number of serious
birth defects in unborn children in the first 3-4 months of pregnancy
can cause blindness, deafness, cardiac abnormalities, and mental retardation
can also increase the risk of developing psychotic disorders
most dangerous during the first trimester
eye and heart defects greatest in the first 8 weeks
deafness is greatest in the 6-13th week
Other Infectious Diseases
toxoplasmosis: disease caused by a parasite found in raw meat and cat
feces; can cause birth defects or miscarriage
even though it produces mild coldlike symptoms, it can cause severe eye and
brain injury
Sexually Transmitted Diseases/Infections
examples include syphilis, genital herpes, and AIDS - can cause birth defects
even mild drugs could have lasting effects on a pregnant womanʼs child
The Thalidomide Tragedy
thalidomide: a mild tranquilizer that, taken early in pregnancy, can product a
variety of malformations of the limbs, eyes, ears, and heart of the baby
a German drug company began selling it to alleviate nausea and vomiting for
pregnant women - morning sickness
babies had deformed eyes, ears, noses, and hearts
many displayed phocomelia - a structural abnormality in which all parts of the
limbs are missing and the feet or hands may be attached directly to the torso,
similar to flippers
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