2. โข Normally, oxygen-poor
(blue) blood returns to the
right atrium from the body,
travels to the right ventricle,
then is pumped into the
lungs where it receives
oxygen. Oxygen-rich (red)
blood returns to the left
atrium from the lungs,
passes into the left
ventricle, and then is
pumped out to the body
through the aorta.
3. โข An atrial septal defect
allows oxygen-rich (red)
blood to pass from the
left atrium, through the
opening in the septum,
and then mix with
oxygen-poor (blue)
blood in the right
atrium.
4. DEFINITION
โข An atrial septal defect is
an opening in the atrial
septum, or dividing wall
between the two upper
chambers of the heart
known as the right and
left atria..
6. EMBRYOLOGY
โข The heart is forming during the first 8 weeks
of fetal development. It begins as a hollow
tube, then partitions within the tube develop
that eventually become the septa (or walls)
dividing the right side of the heart from the
left. Atrial septal defects occur when the
partitioning process does not occur
completely, leaving an opening in the atrial
septum.
