Mechanisms of ventilation in lower vertebrates: adaptations to respiratory and nonrespiratory constraints

Abstract

The design of vertebrate respiratory systems has been subject to two major sets of constraints. The first is the need to satisfy the primary function of the respiratory surface as an organ of gas exchange. These constraints include the need to reduce the diffusion gradient between air and blood while providing adequate ventilation and perfusion of the exchange surface. The second set of constraints arises from the need to satisfy other physiological, environmental, and behavioral demands. The constraints imposed by the low oxygen content and high density of water as a respiratory medium, the rigid shell of turtles, and the long thin body of snakes, as well as the life-style and habitat of diving animals, are all used to illustrate the unique features of several experiments in the design and performance of respiratory pumps. It is shown, however, that despite the tremendous diversity that exists among species, all mechanisms allow ventilation to be powered by surprisingly similar changes in pulmonary pressure.