HEART AND FETAL CIRCULATION
Fetal
circulation
During embryological life gas exchange is not support by lungs but by
placenta (lungs starting to work at birth), then it is not necessary
to have high blood flow to the lungs. This and other fetal circulatory
requirements are obtained through some communication between the right
and the left heart side, typical of the fetal heart. These are foramen
ovale the communication between the atria, Aransius ductus venosus the
communication between umbilical artery and the inferior vena cava, ductus
arteriosus the communication between aorta and pulmonary artery.
-Fig.
2.2
schematic representation of fetal circulation: the oxygenated blood
coming from the placenta flow from the umbilical vena (UV) through the
ductus venosus of Aransius, in the inferior vena cava and from this
, principally through the foramen ovale, to the left atrium, to the
left ventricle and ascending aorta. Blood with low content of oxygen
flow preferentially through the tricuspid valve in right ventricle,
in pulmonary artery and through ductus arteriosus (DA) in the descending
aorta. Part of this blood flows back to the placenta through umbilical
arteries to be reoxygenated. PO2 indicates the oxygen level of the blood
in the different sectors of circulation (see the text for more details)-.
The oxygenated blood coming from the placenta through the umbilical
vein arrives in the inferior vena cava and then in the right atrium;
from here it drives essentially through the foramen ovale, in the left
atrium and then left ventricle and aorta. This oxygenated blood goes
principally to the brain. The non-oxygenated blood coming from the superior
vena cava enters the right atrium and goes to the right ventricle and
then in pulmonary artery. Only a little part of this blood goes to the
lung whereas the most part, through the ductus arteriosus, goes down
the descending aorta, in the umbilical arteries and then the placenta.
