Functional anatomy of the hearts of lungfishes and amphibians

Abstract

Lungfishes and amphibians have bimodal gas exchange, but various species employ airbreathing with lungs to different degrees. An increased use of pulmonary breathing is correlated with progressive structural and functional separation of the pulmonary and systemic vascular circuits. Representatives from all genera of lungfishes and several anurans and urodeles utilizing pulmonary breathing, show a preferential distribution of blood tending to minimize recirculation to the systemic and pulmonary circuits. The degree of shunting between the two circuits is variable and may express normal shifts in regional blood flow.The most important structural and functional features influencing the preferential circulation through dipnoan and amphibian hearts include: (a) Dynamics of inflow in the pulmonary and systemic veins; (b) The extent and localization of atrial septation; (c) The partial ventricular septum in lungfishes and the massive ventricular trabeculation in both amphibians and lungfishes; (d) A laminar ventricular outflow pattern; (e) Structural guidance of flow in the partially separated bulbus segment of the heart; (f) Vasomotor reactions in the various outflow vessels from the heart. © 1968 by the American Society of Zoologists.