fetal heart circulation.pdf for gnm b.sc post basic b.sc students

Diagram, introduction, after birth changes

1.  The umbilical vein carrying the oxygenated blood (80% saturated) from
placenta.
FETAL CIRCULATION

2.  Enters the fetus at the umbilicus and runs along the free margin of the
falciform ligament of the liver.
 In the liver, it gives off branches to the left lobe of the liver and receives
the deoxygenated blood from the portal vein.
 The greater portion of the oxygenated blood, mixed with some portal
venous blood, short circuits the liver through the ductus venous to enter
the inferior venacava and thence to right atrium of the heart.
 The o2 content of this mixed blood is thus reduced although both the
ductus venous and hepatic portal trunk bloods enter the right atrium
through the ivc.
 In the right atrium most of the well oxygenated ductus venous in to the
foramen oval by the valve of the IVC pass in to left atrium.
 Here it is mixed with small amount of venous blood returning from the lungs
through the pulmonary veins.
 This left atrial blood is passed on through the mitral opening in to left
ventricle.
 Lesser amount of blood 25% after reaching the right atrium via the
superior and inferior vana cava passes through the tricuspid opening in to
right ventricle.
 The left ventricular blood is pumped in to the ascending and arch of aorta
and distributed by their branches to the heart, head, neck, brain and arms.
 The right ventricular blood with low o2 content is discharge in to the
pulmonary trunk.
 The main portion of the blood passes directly through the ductus arterious
in to descending aorta by passing the lungs where it mix with the blood
from the aorta.
 About 70% of the cardiac output (60% from right and 10% from left
ventricle) is carried by the ductus arterious to the descending aorta.
 About 40%of the combined output goes to the placenta through umbilical
arteries.
 The deoxygenated blood leaves the body by way of two umbilical arteries to
reach the placenta.

3.  Changes in the fetal circulation at birth.
 After birth changes in fetal circulation two main reasons.
1. Stop the placental blood flow
2. Initiation of respispiration
The following changes occur in the vascular system.
1. Closure of the umbilical arteries.
2. Closure of the umbilical vein
3. Closure of the ductus arterious
4. Closure of the foramen ovale

1. Closure of the umbilical arteries:- function closure is almost instantaneous
preventing even slight amount of the fetal blood drain out. Anatomically
closure 2 to 3 months.
2. Closure of the umbilical vein: - the obliteration occurs a little later than
arteries, allowing few extra volume of blood received by the fetus from
the placenta. The ductus venous collapse and the venous pressure of the
IVC falls and so also the right arterial pressure .after obliteration the

4. umbilical vein forms the ligaments teres and the ductus venous becomes
ligamentum venoum.
3. Closure of ductus arterious:-
o In a full-term neonate, oxygen is the most important factor
Controlling ductal closure.
o When the PO2 of the blood passing through the ductus reaches about
50 mm Hg, the ductal wall constricts.
o The effects of oxygen on ductal smooth muscle may be direct or
mediated by its effects on prostaglandin synthesis.
o Gestational age also appears to play an important role; the ductus of a
premature infant is less responsive to oxygen, even though its
musculature is developed.
4. Closure of the foramen ovale:-
o This is caused by an increased pressure of the atrium combined with
a decreased pressure on the right atrium
o Functional closure occurs soon after birth but anatomical closure in
about 1 year time
o During the first few days the closure may be reversible.
o This is evidenced clinically by the cyanotic look of the baby during
crying when there is shunting of the blood from right or left.
o Within 1 or 2 hours following birth the cardiac output is estimated
to be about 500ml/min and the heart rate varies from 120 to
140/min.