Essentials of Anatomy and Physiology

difficult. This is called a breech birth and may

necessitate a cesarean section(C-section), which

is delivery of the fetus through a surgical incision in

the abdominal wall and uterus. For some women,

the central opening in the pelvic bone may be too

small to permit a vaginal delivery. Fetal distress, as

determined by fetal monitoring of heartbeat for

example, may also require a cesarean section.

484 Human Development and Genetics

Maternal

arteriole

Maternal

venule

Chorionic

villus

Maternal blood

sinus

Fetal arteriole

and venule

Umbilical vein

Umbilical cord

Umbilical

arteries

Chorion

(fetal part of

placenta)

(maternal

part of

placenta)

Myometrium

Endometrium

Figure 21–5. Placenta and umbilical cord. The fetal capillaries in chorionic villi are within

the maternal blood sinuses. Arrows indicate the direction of blood flow in maternal and

fetal vessels.

QUESTION:What substances move from maternal blood to fetal blood?

BOX21–4 FETAL ALCOHOL SYNDROME

defects, malformation of other organs, and irritabil-

ity and agitation. The infant often grows slowly,

both physically and mentally, and mental retarda-

tion is also a possible outcome.

Because there is no way to reverse the damage

done by intrauterine exposure to alcohol, the best

course is prevention. Education is very important;

women should be aware of the consequences their

consumption of alcohol may have for a fetus.

Fetal alcohol syndrome is the term for a group of

characteristics present in infants who were exposed

to alcohol during their fetal life. Alcohol is a toxin

for adults and even more so for fetal tissues that are

immature and growing rapidly. Either alcohol or its

toxic intermediate product (acetaldehyde) may

pass from maternal to fetal circulation and impair

fetal development.

Consequences for infants include low birth

weight, small head with facial abnormalities, heart