Transcript Fetal Circulation

Fetal Circulation
By : Sanjeev
Anatomy and Physiology
Fetal Circulation
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Umbilical cord
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umbilical arteries: return
non-oxygenated blood, fecal
waste, CO2 to placenta
 1umbilical vein: brings
oxygenated blood and
nutrients to the fetus
Anatomy and Physiology
Fetus depends on placenta to meet O2
needs while organs continue formation
 Oxygenated blood flows from the
placenta to the fetus via the umbilical
vein
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After reaching
fetus the blood
flows through
the inferior
vena cava
A/P Fetal Circulation
Blood continues to travel to the inferior
vena cava from the ductus venosus
 Ductus Venosus
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 Small
amount of blood routed to growing liver
 Increased blood flow leads to large liver in
newborns
A/P Fetal Circulation
Blood continues to travel up the inferior
vena cava
 Empties into the right atrium of the
heart
 The blood then passes to the left atrium
through the foramen ovale
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A/P Fetal Circulation
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Foramen ovale
 Small
opening in the septum of the heart
 Completely bypasses the non-functioning lungs
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Blood continues journey to the left ventricle
blood is then pumped into the aorta
Blood is circulated to the upper extremities
Blood then returns to the right atrium
A/P Fetal Circulation
From the right atrium, the blood goes to
the right ventricle then to the pulmonary
arteries
 Pulmonary arteries
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 Small
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amount goes to the maturing lungs
Rest of blood is shunted away from lungs
by ductous ateriosus back to aorta
A/P Fetal Circulation
Blood travels back from aorta to the two
umbilical arteries to the placenta
 The placenta will re-supply the blood with
oxygen
 Fetal circulation is a low-pressure system
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Why more blood flow directly to the
Lt. atrium?
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Due to the higher pressure of the blood in the
inferior vena cava, more blood flows from it directly
into the left atrium via the foramen ovale.
foramen ovale opens like a valve and can direct
the blood stream that comes from below directly
into the left atrium.
the diameters of the inferior and superior vena cava
are larger than that of the foramen ovale and
therefore a small portion of the blood seeps into the
right ventricle via the tricuspid valve.
The heart is filled only with a mixed blood.
A/P Fetal Circulation
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Low pressure system
 Lungs
are closed
 Most oxygenated blood flows between the
atria of the heart through the foramen ovale
Conversion of Fetal to Infant
Circulation
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At birth
 Clamping
the cord shuts down low-pressure
system
 Increased atmospheric pressure(increased
systemic vascular resistance) causes lungs to
inflate with oxygen
 Lungs now become a low-pressure system
 Pressure from increased blood flow
Conversion: Fetal to Infant
Circulation
 In
the left side of the heart causes the
foramen ovale to close
 More heavily oxygenated blood passing by
the ductus arteriosus causes it constrict
 Functional closure of the foramen ovale and
ductus arteriosus occurs soon after birth
 Overall anatomic changes are not complete
for weeks
Conversion (cont)
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What happens to these special structures
after birth?
 Umbilical
arteries atrophy
 Umbilical vein becomes part of the fibrous
support ligament for the liver
 The foramen ovale, ductus arteriosus, ductus
venosus atrophy and become fibrous
ligaments
Overview of Conversion
Umbilical cord is clamped
 Loose placenta
 Closure of ductus venosus
 Blood is transported to liver and portal
system
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Overview of Conversion
Loss of placenta also leads to :
 First breath
 Lungs expand and fluid is expelled
 Decreased pulmonary resistance
 Increased pressure in left atrium
 Closure of foramen ovale
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Overview of Conversion
Loss of placenta
 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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Fetal vs. Infant Circulation
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Fetal
Low pressure system
Right to left shunting
Lungs non-functional
Increased pulmonary
resistance
Decreased systemic
resistance
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Infant
High pressure system
Left to right blood flow
Lungs functional
Decreased pulmonary
resistance
Increased systemic
resistance
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Oxygenated blood enters the umbilical
vein from the placenta
Enters ductus venosus
Passes through inferior venacava
Enters the right atrium
Enters the foramen ovale
Goes to the left atrium
Passes through left ventricle
Flows to ascending aorta to supply
nourishment to the brain and upper
extremeties
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Enters superior vena cava
Goes to right atrium
Enters the right ventricle
Enters pulmonary artery with some blood
going to the lungs to supply oxygen and
nourishment
Flows to ductus arteriosus
Enters descending aorta ( some blood going
to the lower extremeties)
Enters hypogastric arteries
Goes back to the placenta
Special Structures in Fetal Circulation
 Placenta – Where gas exchange takes place
. during fetal life
 Umbilical Arteries – Carry deoxygenated blood
from the fetus to placenta
 Umbilical Vein – Brings oxygenated blood coming
from the placenta to the fetus
 Foramen Ovale – Connects the left and right
atrium. It pushes blood from the right atrium to the
left atrium.
 Ductus Venosus - Carry oxygenated blood from
umbilical vein to inferior venacava, bypassing fetal
liver
 Ductus Arteriosus - Carry oxygenated blood from
pulmonary artery to aorta, bypassing fetal lungs.
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