title: The initiation of pulmonary respiration in a bird embryo: blood and air cell gas tensions.
abstract: The gaseous stimuli for pipping and the initiation of pulmonary respiration were examined in th Wedge-tailed Shearwater (Puffinus pacificus) by measuring blood gas tensions in the chorioallantoic vein and air cell gas tensions (Pao2 and Paco2) prior to and during the pipping process. External pipping (shell fracture) was the first observed pipping event and preceded internal pipping (penetration of air cell and initiation of pulmonary ventilation). This sequence of cracking the eggshell prior to the initiation of pulmonary respiration resulted in higher Pao2 and lower Paco2 values than the pre-pip air cell gas tensions. Pip-cracks in the shell allow greater diffusion than could normally be obtained across the intact eggshell. This also favors the establishment of large partial pressure gradients of O2 and CO2 across the chorioallantois, thereby improving gas exchange across the inner resistance barrier. The gaseous stimuli for pipping may be attenuated and thus favor the 5-6 day pip-to-hatch interval in this species.
mesh_terms: D000482:Allantois / Q000098:blood supply; D000818:Animals; D001717:Birds / Q000196:embryology / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood*; D004528:Egg Shell; D006863:Hydrogen-Ion Concentration; D008168:Lung / Q000196:embryology / Q000502:physiology*; D008566:Membranes / Q000033:anatomy & histology; D010100:Oxygen / Q000097:blood*; D010313:Partial Pressure; D012119:Respiration; D014680:Veins
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen