foetal & neonatal circulation and respirationfoetal & neonatal circulation and respiration ....
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FOETAL &
NEONATAL
CIRCULATION AND
RESPIRATION
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FETAL AND NEONATAL CIRCULATION
• The human fetal heart begins beating
during the fourth week after fertilization,
contracting at a rate of about 65 beats/min
and increases steadily to about 140
beats/min immediately before birth.
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• Fetal blood passes to placenta through
umbilical vessels and the maternal blood
runs through uterine vessels.
• These two sets of blood vessels lie in
close proximity in the placenta through
which exchange of substances takes
place between mother’s blood and fetal
blood.
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• Blood returning from the placenta through
the umbilical vein passes through the
ductus venosus, mainly bypassing the
liver.
• Most of the blood entering the right
atrium from the inferior vena cava is
directed in a straight pathway across the
posterior aspect of the right atrium and
through the foramen ovale directly into
the left atrium
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• Thus, the well-oxygenated blood from the
placenta enters mainly the left side of the
heart, rather than the right side, and is
pumped by the left ventricle mainly into
the arteries of the head and forelimbs.
• The blood entering the right atrium from
the superior vena cava is directed
downward through the tricuspid valve into
the right ventricle.
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• This blood is mainly deoxygenated blood
from the head region of the fetus, and it is
pumped by the right ventricle into the
pulmonary artery and then mainly through
the ductus arteriosus into the descending
aorta, then through the two umbilical
arteries into the placenta, where the
deoxygenated blood becomes oxygenated.
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• In fetal circulation, 55 per cent of all the
blood goes through the placenta, leaving
only 45 per cent to pass through all the
tissues of the fetus and only 12 per cent
of the blood flows through the lungs;
immediately after birth, virtually all the
blood flows through the lungs.
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FETAL CIRCULATION.
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The changes that takes place in fetal
circulation at birth includes;
• Loss of the tremendous blood flow
through the placenta, which
approximately doubles the systemic
vascular resistance at birth which causes
an increase in aortic pressure, left
ventricular pressure and left atrial
pressure
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• The pulmonary vascular resistance
greatly decreases as a result of expansion
of the lungs.
• Closure of the Foramen Ovale (as a
result of backward flow of blood from
the left atrium into the right atrium)
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• Functional closure of the ductus
arteriosus( due to backward flow from the
aorta into the pulmonary artery through
the ductus arteriosus).
• Closure of the Ductus Venosus ( due to
ceasation of blood flow through the
umbilical veins)
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FETAL AND NEONATAL RESPIRATION
• Respiration cannot occur during fetal life because there is no air to breathe in the amniotic cavity.
• However, attempted respiratory movements do take place beginning at the end of the first trimester of pregnancy caused by tactile stimuli and fetal asphyxia.
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• One of the most important immediate
adjustments required of the infant is to
begin breathing.
• After normal delivery, the child
ordinarily begins to breathe within
seconds and has a normal respiratory
rhythm within less than 1 minute after
birth.
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This promptness in breathing is initiated
by sudden exposure to the external world
resulting from;
• a slightly asphyxiated state incident to
the birth process
• sensory impulses that originate in the
suddenly cooled skin.
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• At birth, the walls of the alveoli are at
first collapsed because of the surface
tension of the viscid fluid that fills them.
• About 25 mm Hg (or more)of negative
inspiratory pressure in the lungs is
usually required to oppose the effects of
this surface tension and to open the
alveoli for the first time.
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• Luckily, the first inspirations of the
normal neonate are extremely powerful
(about 60 mm Hg)