Cardiopulmonary Gas Exchange in the Turtle: A Model Analysis

• Published in: American zoologist 1987-01, Vol.27 (1), p.31-39
• Main Authors: WHITE, FRED N., BICKLER, PHILIP E.
• Format: Article
• Language: English
• Subjects: Air breathing; Biological and medical sciences; Blood; Body temperature; Cardiovascular Adaptation in Reptiles; Fundamental and applied biological sciences. Psychology; Gases; Lungs; Modeling; Perfusion; Pulmonary gas exchange; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Turtles; Ventilation systems; Vertebrates; Vertebrates: respiratory system
• ISSN: 1540-7063; 0003-1569; 1557-7023; 2162-4445
• DOI: 10.1093/icb/27.1.31

The performance of the cardiorespiratory gas exchange system of the turtle, Pseudemys scripla, at rest and at three body temperatures (15, 25, 35°C), was assessed in reference to theory and experimental data. The primary processes governing gas exchange(ventilation, perfusion, diffusion) were found to be uniformly balanced in regard to CO2 exchange. This was not true for O2 transport where, at higher body temperature, the systemis characterized by underventilation and overperfusion in conjunction with declining O2 saturation levels. Adjustments in convection of air or blood, which favor improvement in arterial O2 saturation levels, are incompatible with stability of the CO2stores and acid-base state. The latter were preserved across the temperature range. Comparisons between bird, mammal, and turtle illustrate close similarity in the relative roles of the primary processes governing CO2 exchange. This persists in the face of wide differences inmetabolic intensity, cardiopulmonary architecture and complexity, and body temperatures characterizing the species which were compared. The close control of carbon dioxide transport may reflect a fundamental adjustment to air breathing by lungs as primitive vertebrates emerged from water to the terrestrial domain. From a regulatory point of view the study emphasizes the importance of both structural and functional control of CO2 homeostasis. It does not rule out regulatory features which may insure more effective O2 transport; however, the latter are not evident within the context of the steady state assumptions underlying this analysis.