During the first day of hatching, the developing chicken embryo internally pips the air cell and relies on both the lungs and chorioallantoic
membrane (CAM) for gas exchange. Our objective in this study was to examine respiratory and cardiovascular responses to acute changes in
oxygen at the air cell or the rest of the egg during internal pipping. We measured lung (V · O2lung) and CAM (V · O2CAM) oxygen consumption
independently before and after 60 min exposure to combinations of hypoxia, hyperoxia, and normoxia to the air cell and the remaining egg.
Significant changes in V ·
O2total were only observed with combined egg and air cell hypoxia (decreased V ·
O2total) or egg hyperoxia and air cell
hypoxia (increased V ·
O2total). In response to the different O2 treatments, a change in V ·
O2lung was compensated by an inverse change in V ·
O2CAM of
similar magnitude. To test for the underlying mechanism, we focused on ventilation and cardiovascular responses during hypoxic and hyperoxic
air cell exposure. Ventilation frequency and minute ventilation (VE) were unaffected by changes in air cell O2, but tidal volume (VT) increased
during hypoxia. Both VT and VE decreased significantly in response to decreased PCO2. The right-to-left shunt of blood away from the lungs
increased significantly during hypoxic air cell exposure and decreased significantly during hyperoxic exposure. These results demonstrate the
internally pipped embryo's ability to control the site of gas exchange by means of altering blood flow between the lungs and CAM.
© 2007 Elsevier Inc. All rights reserved.