Comparative Aspects of Extracellular Acid-Base Balance

Interest in comparative acid-base physiology has considerably grown during last decades even in the absence of major technical or conceptual advances. This is firstly because it has become clear that the extracellular acid-base state reflects the performance of many exchange functions at the organism level: respiration and ventilation of the gas exchange surfaces, metab olism, iono-and osmoregulation. Such functions are much in fluenced by ambient conditions, and the measurement of acid base parameters thus provides useful information about the organism's responses to environmental challenges. Secondly, many processes at the molecular level are now known to be pH sensitive, and acid-base regulation thus appears to be a major requirement for the functional integrity of cells and organisms. How extracellular acid-base balance can be maintained in a wide variety of animals living in different conditions is the sub ject of this book. The approach is comparative and environ mental throughout. All body fluids share similar buffer proper ties, and common physicochemical principles apply to any acid base system. However, in accord with differing designs and con straints along animal evolution, varying effector organs and mechanisms are at work to maintain an appropriate acid-base state in the organism. Particular emphasis is placed on the fun damental differences between water and air breathers and on the acid-base and respiratory problems arising at the transition from an aquatic to a terrestrial life. Also the complex array of factors influencing the acid-base state in water-dwelling animals is thoroughly discussed.