Fetal Circulation
Fetal
Circulation
Salient Features of Fetal
Growth
• Placenta is very active.
• Liver and lungs are passive.
• Head is growing faster.
Hemodynamics of Fetal
Circulation
•
•
•
•
Venous and arterial blood mix up in atria
The venacava carries mixed blood to the
right atrium bypassing liver and lungs.
Aorta carries mixed blood back to placenta
Blood circulation in the fetus is never as
saturated with oxygen as that blood
circulating through the adult. That is,
difference in oxygen tension between blood
of the umbilical arteries is much less than
that of adult venous and arterial blood.
Fetal
Circulation
Course of Fetal Circulation
Pre-delivery phase
• The arterial blood flows to the fetus through
•
•
•
•
the umbilical vein.
It passes to the undersurface of liver and
separates in to two branches.
Lager is joined by the portal vein and enters
the right lobe of the liver.
The other continued upwards as ductus
venosus and joins the inferior venacava.
In the inferior venacava blood carried by the
ductus venosus and hepatic veins becomes
mixed with blood returning from the lower
extremities, so it is a mixture of oxygenated
and de oxygenated blood
Continued
•
It enters the right atrium and is directed
through the foramen ovale into the left atrium.
In the left atrium, it mixes with a small quantity
of blood returning from the lungs through the
pulmonary veins.
• From the left atrium, blood passes into the left
ventricle, and from the left ventricle into the
aorta. From the aortal it is distributed almost
entirely to the head and upper extremities – a
small quantity of blood continuing into the
descending aorta.
Continued
• After circulation in the head and upper
extremities, blood is returned by the superior
vena cava to the right atrium, where it mixes
with a small portion of that blood entering from
the inferior vena cava.
• From the right atrium it descends into the right
ventricle and passes into the main pulmonary
artery.
• From the pulmonary artery, most of the blood
passes trough the ductus arterioss into the
aorta, where it mixes with blood from the left
ventricle.
Continued
•
Some of the blood with main pulmonary artery is
distributed to the lungs by the right and left
pulmonary arteries. The pulmonary veins returns
this blood the the left atrium.
• The blood passing from the main pulmonary
artery through the ductus arteries descends
through the aorta and is in part distributed to the
lower extremities and viscera of the abdomen and
pelvis. The greater amount is conveyed by the
hypogastric arteries to the umbilical arteries The
umbilical arteries return the blood to the
placenta.
Intermediate Phase
• Immediately after delivery , the baby begins to
breathe, and pulmonary circulation changes, An
increased quantity of blood is pumped into the
pulmonary arteries by the right ventricle, and a
smaller quantity passes through the ductus arteriosus.
The ductus arteriosus begins to atrophy, eventually
becoming the ligamentum arteriosum.
•
Pulmonary circulation increases, and more blood is
returned from the lungs to the left atrium. Pressure
rises in the left atrium, causing the foramen ovale to
close. Placental circulation ceases to function as soon
as the umbilical cord is tied. The ends of the
hypogastric arteries atrophy, and these vessels
become the hypo-gastric ligaments.
Adult Phase
• Closure of ductus arterosus in early postnatal
period due to reflex action secondary to increased
oxygen tension and the interaction of prosta
glandin
PDA
•
machinery murmur
Obliteration of foramen ovale – 6 to 8 weeks
Patent foramen ovale with few or no symptoms
• Occluded umblical vein – ligamentum teres
• Obliterated ductus venosus – ligamentum
venosum
Hemodynamics of Normal
Adult
•
•
•
Venous and arterial blood no longer mix in the
atria
The venacava carries only deoxygenated blood
into the right atrium and right ventricle which
is pumped to the pulmonary arteries and
finally to the pulmonary capillaries
Aorta carries only oxygenated blood from the
left heart via the pulmonary veins for
distribution to the rest of the body.
Thank You