The fetal circulation allows the developing fetus to exchange materials with its mother through structures like the umbilical cord and placenta. There are three major shunts in the fetal circulatory system - the ductus venosus, ductus arteriosus, and foramen ovale - that direct highly-oxygenated blood from the placenta away from the lungs and toward vital organs like the brain and heart. At birth, the loss of placental blood flow and beginning of breathing cause pressure changes and closure of the shunts, redirecting blood flow to the lungs for oxygenation and establishing the postnatal circulatory pattern.

1. FETAL CIRCULATION
PREPARED BY
MRS.RESHMA AJAY
ASSOCIATE PROFESSOR
MURLIDHAR COLLEGE OF NURSING

2. MEANING
• The circulatory system of fetus, called the fetal
circulation, exists only in the fetus & contains
special structure that allows the developing fetus
to exchange material with its mother.
• Umbilical cord:
• 2 umbilical arteries(carries non-o2 blood from
fetus to placenta).
• 1 umbilical vein arteries(carries o2 blood from
placenta to fetus).

3. COMPARISION
REVIEW OF ADULT BLOOD
CIRCULATION
3 shunts in fetal circulation
• Ductus venosus: connects
umbilical vein to inferior
venacava.
• Ductus arteriosus:
connects pulmonary artery
to aorta.
• Foramen ovale: opening
between right and left
aterium.

7. FETAL CIRCULATION
• Before birth, blood from the placenta, about
80% saturated with oxygen, returns to the
fetus by way of the umbilical vein.
• On approaching the liver, most of this blood
flows through the ductus venosus directly
into the inferior vena cava, bypassing the
liver.
• After a short course in the inferior vena
cava, where placental blood mixes with
deoxygenated blood returning from the
lower limbs, it enters the right atrium.

8. FETAL CIRCULATION
• Here it is guided toward the oval foramen by
the valve of the inferior vena cava, and most
of the blood passes directly into the left
atrium.
• From the left atrium, where it mixes with a
small amount of desaturated blood
returning from the lungs, blood enters the
left ventricle and ascending aorta.
• Since the coronary and carotid arteries are
the first branches of the ascending aorta,
the heart musculature and the brain are
supplied with well-oxygenated blood.

9. FETAL CIRCULATION
• A small amount from the IVC is prevented
from entering the left atrium and remains in
the right atrium.
• It mixes with desaturated blood returning
from the head and arms by way of the
superior vena cava.
• Desaturated blood from the superior vena
cava flows by way of the right ventricle into
the pulmonary trunk.

10. FETAL CIRCULATION
• During fetal life, resistance in the pulmonary
vessels is high, such that most of this blood
passes directly through the ductus
arteriosus into the descending aorta, where
it mixes with blood from the proximal aorta.
• After coursing through the descending
aorta, blood flows toward the placenta by
way of the two umbilical arteries.
• The oxygen saturation in the umbilical
arteries is approximately 52-58%.

11. FETAL CIRCULATION
• Theoretically, mixing may occur in the following
places :
1)In the liver by mixture with a small amount of
blood returning from the portal system.
2)In the inferior vena cava which carries
deoxygenated blood returning from the lower
extremities, pelvis, and kidneys.
3)In the right atrium by mixture with blood returning
from the head and limbs.
4)In the left atrium by mixture with blood returning
from the lungs.
5)At the entrance of the ductus arteriosus into the
descending aorta.

12. CIRCULATORY CHANGES AT BIRTH
• Changes in the vascular system at birth are
caused by cessation of placental blood flow and
the beginning of respiration.
• Since the ductus arteriosus closes by muscular
contraction of its wall, the amount of blood
flowing through the lung vessels increases
rapidly.
• This, in turn, raises pressure in the left atrium.
• Simultaneously, pressure in the right atrium
decreases as a result of interruption of placental
blood flow.
• The septum primum is then apposed to the
septum secundum and functionally the oval

13. Foramen ovale Closes shortly after birth,
fuses completely in first year.
Ductus arteriousus Closes soon after birth,
becomes ligamentum
arteriousum in about 3
months.
Ductus venosus Ligamentum venosum
Umbilical arteries Medial umbilical ligaments
Umbilical vein Ligamentum teres

15. Loss of placenta also leads to:
1. First breath
2. Lungs expand and fluid
is expelled
3. Decreased pulmonary
resistance
4. Increased pressure in
left atrium
5. Closure of foramen
ovale
• Increased systemic
resistance
• Pressure in right atrium
decreased
• Change from right to left
shunting to left to right
blood flow
• Increased O2 levels in
pulmonary circulation
• Closure of the ductus
arteriosus
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