The Regulation of Cutaneous Gas Exchange

Abstract

Although physiological studies usually focus on the human or mammalian lung to understand respiratory gas exchange, the laws of physics suggest that any permeable membrane can serve as a gas exchange organ and the phenomenology of natural history suggests that practically every suitable structure has done so in the past. Thus, the integument, limbs, head, pharynx, tail, gut, and even the cloaca have been specialized as gas exchange organs; air lungs, water lungs, external and internal gills, tracheae, and book lungs have evolved as organs primarily dedicated to gas exchange; the jelly coat, chorioallantois, eggshell, and placenta function similarly in a developmental sense; and medical technology has exploited the peritoneal membrane and developed the extracorporeal membrane oxygenator. The broad perspective occasioned by this diversity transforms the analysis of respiratory gas exchange from a case-by-case study of particular taxa into a general study in biological design, constraint and regulation: What are the general rules governing the function of gas exchange organs? Along what axes has the evolutionary diversification of gas exchange organs been permitted or constrained? (Indeed, the development of general models of gas exchange and its diversity has been a premier accomplishment of Johannes Piiper and his colleagues.) According to this perspective, each particular gas exchange organ, including the human lung and metazoan integument inter alia, constitutes a test of the robustness of hypothesized general patterns and predictions.KeywordsRespiratory MediumCapillary RecruitmentPlethodontid SalamanderRespiratory Surface AreaPerfusion LimitationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.