4.3. Cardiovascular shunts
During the internal pipping stage of hatching, blood leaving
the right atria can pass through one of three routes: 1. a right-toleft
shunt through the interatrial foramina to the left side of the
heart and the systemic tissues; 2. a right-to-left shunt through
the ductus arteriosi to the dorsal aorta, the CAM and posterior
tissues of the embryo; or 3. through the pulmonary arteries to
the lungs (White, 1974). Internally pipped embryos have a
right-to-left shunt in which 60% of the right atrial output flows
through the interatrial foramina and the ductus arteriosi (Rahn
et al., 1985). The pulmonary arteries and lungs receive the
remaining 40% of the right atrial output. Thus, the internally
pipped embryo has a functional right-to-left shunt that it could
exploit when altering the perfusion of the lungs relative to the
rest of the embryo and the CAM.