Essentials of Anatomy and Physiology

Fig. 13–8). Because the fetal lungs are deflated and do
not provide for gas exchange, blood is shunted away
from the lungs and to the body. The foramen ovaleis
an opening in the interatrial septum that permits some
blood to flow from the right atrium to the left atrium,
not, as usual, to the right ventricle. The blood that
does enter the right ventricle is pumped into the pul-
monary artery. The ductus arteriosusis a short ves-
sel that diverts most of the blood in the pulmonary

artery to the aorta, to the body. Both the foramen

ovale and the ductus arteriosus permit blood to bypass

the fetal lungs.

Just after birth, the baby breathes and expands its

lungs, which pulls more blood into the pulmonary cir-

culation. More blood then returns to the left atrium,

and a flap on the left side of the foramen ovale is

closed. The ductus arteriosus constricts, probably in

response to the higher oxygen content of the blood,

The Vascular System 305

Aortic arch

Ductus arteriosus

Pulmonary artery

Left atrium

Foramen

ovale

Right

atrium

Inferior vena cava

Aorta

Ductus venosus

Umbilical cord

Navel of fetus

Umbilical arteries

Umbilical vein

Placenta

Internal

iliac arteries

Maternal

blood vessels

Figure 13–8. Fetal circulation. Fetal heart and blood vessels are shown on the left.

Arrows depict the direction of blood flow. The placenta and umbilical blood vessels are

shown on the right. See text for description.

QUESTION:Find the foramen ovale in the fetal heart. Which way does blood flow through

it, and why?