898
UNIT SIX
Aortic arch
Superior vena cava
Inferior vena cava
Hepatic portal vein
Foramen ovale
(becomes fossa ovalis)
Ductus venosus
(becomes ligamentum
venosum)
Umbilical vein
(becomes ligamentum
teres)
Ductus arteriosus
(becomes ligamentum
arteriosum)
Pulmonary artery
Left atrium
Pulmonary veins
Abdominal aorta
Pulmonary trunk
Left ventricle
Left renal artery
Common iliac artery
Internal iliac artery
Decreasing
blood
oxygen
level
Umbilical arteries
(become medial
umbilical ligaments)
Umbilical vein
Umbilical arteries
Placenta
FIGURE 23.25
The general pattern of fetal circulation is shown anatomically.
condition is often associated with other cardiovascular, uro-
genital, or gastrointestinal disorders. The vessels within the
severed cord are routinely counted following a birth because
of the possibility of these conditions.
Table 23.4
summarizes the major features of fetal cir-
culation. At the time of birth, important adjustments must
occur in the cardiovascular system when the placenta ceases
to function and the newborn begins to breathe. Clinical
Application 23.2 describes a case in which fetal ultrasound
revealed two hearts and bloodstreams, yet a single body.
PRACTICE
24
Which umbilical vessel carries oxygenated blood to the fetus?
25
What is the function of the ductus venosus?
26
What characteristic of fetal pulmonary circulation shunts blood
away from the lungs?
27
How does fetal circulation allow blood to bypass the lungs?
trunk to the descending portion of the aortic arch. As a result
of this connection, the blood with a relatively low oxygen
concentration, returning to the heart through the superior
vena cava, bypasses the lungs and does not enter the portion
of the aorta that branches to the heart and brain.
The more highly oxygenated blood that enters the
left atrium through the foramen ovale mixes with a small
amount of deoxygenated blood returning from the pulmo-
nary veins. This mixture moves into the left ventricle and is
pumped into the aorta. Some of it reaches the myocardium
through the coronary arteries, and some reaches the brain
tissues through the carotid arteries.
Blood carried by the descending aorta includes the less oxy-
genated blood from the ductus arteriosus. Some of the blood
is carried into the branches of the aorta that lead to the lower
regions of the body. The rest passes into the
umbilical arteries,
which branch from the internal iliac arteries and lead to the pla-
centa. There the blood is reoxygenated
(f gs. 23.25
and
23.26)
.
The umbilical cord usually contains two arteries and one
vein. Rarely, newborns have only one umbilical artery. This
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