The document summarizes the fetal circulation system and how it differs from the newborn circulation. In the fetus, oxygen-rich blood from the placenta travels through the umbilical vein to the liver and mixes with venous blood before entering the heart. It then passes through the foramen ovale into the left side of the heart and mixes with pulmonary blood to be pumped throughout the body. After birth, the foramen ovale, ductus arteriosus, and umbilical vessels close as the lungs inflate and the placental circulation is lost. This allows the cardiovascular system to transition to adult circulation.

1. INTERNATIONAL UNIVERSITY
Fetal circulation
Dr. Sam Nang

3. • All of the respiratory, excretory,
and nutritional needs of the fetus
are provided for by diffusion across
the placenta instead of by the fetal
lungs, kidneys, and
gastrointestinal tract.
• Fetal circulation is adaptive to these
conditions.

4. Objective :
• Describe the fetal circulation
to and from the placenta.
• Describe the structure and
function of the foramen
ovale, ductus venosus, and
ductus arteriosus.

5. • The circulation of blood through
a fetus is by necessity different
from blood circulation in a
newborn .
• Respiration, the procurement of
nutrients, and the elimination of
metabolic wastes occur through
the maternal blood instead of
through the organs of the fetus.

6. • The capillary exchange between
the maternal and fetal
circulation occurs within the
placenta .
• This remarkable structure, which
includes maternal and fetal
capillary beds, is discharged
following delivery as the
afterbirth.

7. • The umbilical cord is the
connection between the placenta
and the fetal umbilicus.
• It includes one umbilical vein and
two umbilical arteries,
surrounded by a gelatinous
substance.

9. • Oxygenated and nutrient
rich blood flows through the
umbilical vein toward the
inferior surface of the liver.
• At this point, the umbilical
vein divides into two
branches.

12. • One branch merges with the
portal vein, while the other
branch, called the ductus
venosus , enters the inferior
vena cava.

13. • Thus, oxygenated blood is
mixed with venous blood
returning from the lower
extremities of the fetus before it
enters the heart.
• The umbilical vein is the only
vessel of the fetus that carries
fully oxygenated blood.

14. • The inferior vena cava
empties into the right atrium
of the fetal heart.
• Most of the blood passes from
the right atrium into the left
atrium through the foramen
ovale, an opening between
the two atria.

16. • Here, it mixes with a small
quantity of blood returning
through the pulmonary
circulation.
• The blood then passes in to
the left ventricle, from which
it is pumped into the aorta and
through the body of the fetus.

18. • Some blood entering the right
atrium passes into the right
ventricle and out of the heart via
the pulmonary trunk.
• Since the lungs of the fetus are
not functional, only a small portion
of blood continues through the
pulmonary circulation (the
resistance to blood flow is very
high in the collapsed fetal lungs).

19. • Most of the blood in the pulmonary
trunk passes through the ductus
arteriosus into the aortic arch,
where it mixes with blood coming from
the left ventricle.
• Blood is returned to the placenta by
the two umbilical arteries that arise
from the internal iliac arteries.

21. • Notice that, in the fetus,
oxygen-rich blood is
transported by the inferior
vena cava to the heart, and
via the foramen ovale and
ductus arteriosus to the
systemic circulation.

22. • Important changes occur in
the cardiovascular system at
birth.
• The foramen ovale, ductus
arteriosus, ductus venosus,
and the umbilical vessels are
no longer necessary.

24. • The foramen ovale abruptly
close with the first breath of
air because the reduced
pressure in the right side of
the heart causes a flap to
cover the opening.

25. • This reduction in pressure occurs
because the vascular resistance to
blood flow in the pulmonary
circulation falls far below that of the
systemic circulation when the lungs
fill with air.
• The pressure in the inferior vena
cava and right atrium falls as a result
of the loss of the placental
circulation.

27. • The constriction of the
ductus arteriosus occurs
gradually over a period of
about 6 weeks after birth as
the vascular smooth muscle
fibers constrict in response to
the higher oxygen
concentration in the
postnatal blood.

28. • The remaining structure of the
ductus arteriosus gradually
atrophies and becomes
nonfunctional as a blood vessel.
• Transformation of the unique fetal
cardiovascular system is
summarized in table 16.6.

31. THE END