896
UNIT SIX
Placenta
Blood flow from fetus, branch of umbilical artery
Blood flow to fetus, branch of umbilical vein
Chorionic
villus
Diffusion
Waste substances
into maternal blood
Diffusion
Oxygen and
nutrients into
fetal blood
Maternal blood
in lacuna
Fetal capillaries
Umbilical vein
Umbilical arteries
Uterine wall
the f
rst trimester leads to cataracts, deaFness, and
heart deFects, and later exposure causes learning
disabilities, speech and hearing problems, and
type 1 diabetes mellitus. Widespread vaccination
has slashed the incidence oF “congenital rubella
syndrome,” and today it occurs only where people
are not vaccinated.
Alcohol
A pregnant woman who has just one or two
alcoholic drinks a day, or perhaps many drinks
at a crucial time in prenatal development, risks
fetal alcohol syndrome
or the more prevalent
fetal alcohol effects
in her unborn child. The
ects oF small amounts oF alcohol at di±
erent
stages oF pregnancy are not yet well understood
and because each woman metabolizes alcohol
slightly diFFerently, it is best to avoid drinking
alcohol entirely when pregnant or when trying
to become pregnant.
A child with Fetal alcohol syndrome has a
characteristic small head, misshapen eyes, and
a Flat Face and nose (Fig. 23C). Growth is slow
beFore and aFter birth. Intellect is impaired,
Thalidomide
T
he idea that the placenta protects the
embryo and Fetus From harmFul sub-
stances was tragically disproven between
1957 and 1961, when 10,000 children in Europe
were born with ²
ippers in place oF limbs. Doctors
soon identif
ed a mild tranquilizer, thalidomide,
which all oF the mothers oF deFormed inFants had
taken early in pregnancy, during the time oF limb
Formation. Although some women in the United
States did use thalidomide and had a±
ected chil-
dren, the United States was spared a thalidomide
disaster because an astute government physician
noted adverse eFFects oF the drug on monkeys
in experiments, and she halted use oF the drug.
However, thalidomide is used today to treat lep-
rosy and certain blood disorders.
Rubella
The virus that causes rubella (German measles) is
a powerFul teratogen. Australian physicians f
rst
noted its e±
ects in 1941, and a rubella epidemic in
the United States in the early 1960s caused 20,000
birth deFects and 30,000 stillbirths. Exposure in
ranging From minor learning disabilities to men-
tal retardation. Teens and young adults with
Fetal alcohol syndrome are short and have small
heads. Many individuals remain at early grade-
school level. They oFten lack social and com-
munication skills, such as understanding the
consequences oF actions, Forming Friendships,
taking initiative, and interpreting social cues.
Problems in children oF alcoholic mothers
were noted by Aristotle more than twenty-three
centuries ago. Today, Fetal alcohol syndrome is
the third most common cause oF mental retar-
dation in newborns. One to 3 in every 1,000
inFants has the syndrome, and more than 40,000
ected children are born each year.
Cigarettes
Chemicals in cigarette smoke stress a Fetus.
Carbon monoxide crosses the placenta and plugs
up the sites on the Fetus’s hemoglobin molecules
that would normally bind oxygen. Other chemi-
cals in smoke prevent nutrients From reaching
the Fetus. Studies comparing placentas oF smok-
ers and nonsmokers show that smoke-exposed
23.1
CLINICAL APPLICATION
Some Causes of Birth Defects
FIGURE 23.24
³Oxygen³and³
nutrients di±
use into the Fetal
blood From the maternal blood.
Waste di±
uses into the maternal
blood From the Fetal blood.
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