Comparative Aspects of Extracellular Acid-Base Balance
by J.P. Truchot
Series: Zoophysiology (Volume 20)
Edition: 1st ed., 1987
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.
1. General Properties of Water and Body Fluids as Acid-Base Systems.- 1.1 Definition of an Acid-Base System.- 1.2 Components of Physiological Acid-Base Systems.- 1.2.1 Water, Hydrogen, and Hydroxyl Ions, and the Concepts of Neutrality, Acidity, and Alkalinity.- 1.2.2 Strong Ions.- 1.2.3 Weak Acids, Conjugate Bases, and Buffering.- 1.3 Physicochemical Constraints in Acid-Base Systems.- 1.3.1 Conservation of Mass.- 1.3.2 Law of Mass Action.- 1.3.3 Electrical Neutrality and the Concept of “Strong Ion Difference”.- 1.4 Dependent and Independent Variables in Physiological Acid-Base Systems.- 1.5 Titration Behavior of Acid-Base Systems.- 1.5.1 Titration by Changes of PCO2 at Constant [SID].- 1.5.2 Titration Involving [SID] Changes.- 1.5.3 Other Types of Titrations.- 18.104.22.168 Changes of Concentration of Noncarbonic Buffers.- 22.214.171.124 Changes of Dissociation Constants in a Multicomponent Buffer System.- 2. Methodological Approaches and Problems.- 2.1 Data Acquisition: The Description of the Acid-Base State.- 2.1.1 General Principles.- 2.1.2 Measurements.- 2.1.3 Calculations.- 2.2 Interpretation of the Data: “Normal” State, Disturbances, Compensations.- 2.2.1 Problems of Definition of a “Normal” Acid-Base State.- 2.2.2 Distinguishing Passive Disturbances and Physiologically Controlled Adjustments.- 2.3 Specific Methods to be Used in Aquatic Animals.- 2.3.1 Control of Water PCO2 and Acid-Base Balance.- 2.3.2 Methods for Studying Intercompartmental Acid-Base Movements.- 2.4 Some Other Specific Problems and Limitations.- 2.4.1 Compartimentalization of Extracellular Acid-Base Systems.- 2.4.2 Equilibrium and Disequilibrium Values.- 3. Extracellular Acid-Base Status and the Nature of the Respiratory Medium.- 3.1 Extracellular pH, PCO2, and [HCO?3] in Water Breathers and Air Breathers.- 3.2 Extracellular Acid-Base Balance in Bimodal Breathers.- 3.3 Extracellular Acid-Base Balance During the Transition from Water to Air Breathing.- 3.3.1 Increased Air Breathing at High Ambient Temperature.- 3.3.2 Increased Air Breathing in Hypoxic Water.- 3.3.3 Complete Transition to Air Breathing: Lungfishes.- 3.3.4 Complete Transition to Air Breathing: Intertidal Animals.- 3.3.5 Ontogenetic Transition to Air Breathing.- 4. Acid-Base Balance and Respiratory Gases in the Ambient Medium.- 4.1 Natural Variations of O2 and CO2 in Ambient Media.- 4.1.1 Air.- 4.1.2 Water.- 4.2 Extracellular Acid-Base Balance and the Oxygenation of the Ambient Medium.- 4.2.1 Water Breathers.- 4.2.2 Air Breathers.- 4.3 Extracellular Acid-Base Balance as a Function of Ambient PCO2.- 4.3.1 Air Breathers.- 4.3.2 Water Breathers.- 4.4 Extracellular Acid-Base Balance During Combined Changes of Ambient PO2 and PCO2.- 5. Extracellular Acid-Base Balance in Aquatic Animals as a Function of the Ionic Composition and the Acid-Base Balance of the Ambient Water.- 5.1 Extracellular Acid-Base State and the Salinity of the Ambient Water.- 5.2 Extracellular Acid-Base Balance and the Concentration of Certain Ions in Freshwater.- 5.3 Extracellular Acid-Base Balance and the Acid-Base State of Ambient Water.- 5.4 Extracellular Acid-Base Disturbances in Acid Waters.- 5.5 An Overview of Ambient Factors Affecting Extracellular Acid-Base Balance in Aquatic Animals.- 6. Extracellular Acid-Base Balance and Body Temperature.- 6.1 Temperature and the Acid-Base State of Buffer Systems in Vitro.- 6.1.1 Physical Effect of Temperature on Weak Acid Dissociation.- 6.1.2 Extracellular Fluids in Vitro at Variable Temperature.- 6.1.3 Binary Buffer Models.- 6.1.4 Application to Peripheral Blood in Homeotherms.- 6.2 Normal Extracellular pH at Variable Body Temperature in Poikilotherms.- 6.2.1 Historical Account.- 6.2.2 In Vivo pH vs. Body Temperature.- 6.2.3 What Extracellular Acid-Base Variable is Under Physiological Control in Ectotherms?.- 6.3 In Vivo Variations of the Carbonic System with Body Temperature.- 6.3.1 General Considerations.- 6.3.2 Air-Breathing Ectotherms.- 6.3.3 Water Breathers.- 6.4 Significance of the Extracellular pH-Body Temperature Relationship: a Critical Evaluation.- 7. Comparative Physiology and Evolution of Acid-Base Regulatory Mechanisms.- 7.1 Buffering of ECF Acid and Base Loads.- 7.1.1 Physicochemical Buffering Capacity of Extracellular Fluids.- 7.1.2 Buffering by Mineralized Tissues.- 7.1.3 Buffering of ECF by Cellular Buffers.- 7.2 Mechanisms and Organ Systems Involved in Excretion of Acid or Base Loads.- 7.2.1 Branchial Mechanisms.- 126.96.36.199 Branchial Acid-Base Fluxes.- 188.8.131.52 The Ammonia Mechanism.- 184.108.40.206 Ionic Mechanisms.- 220.127.116.11 The Role of Carbonic Anhydrase.- 7.2.2 The Amphibian Skin.- 7.2.3 Renal Mechanisms.- 18.104.22.168 Basic Mechanisms of Renal Acid Excretion.- 22.214.171.124 Renal Responses to Acid-Base Disturbances.- 7.2.4 Respiratory Mechanisms.- 126.96.36.199 Terrestrial Vertebrates.- 188.8.131.52 Aquatic Animals.- 184.108.40.206 Respiratory Regulation of Acid-Base Balance During Temperature Changes.- 7.3 Comparative Physiology of Acid-Base Regulation: An Evolutionary Overview.- 8. Extracellular Acid-Base Balance in Some Specific Physiological Situations.- 8.1 Muscular Activity.- 8.2 Panting.- 8.3 Diving.- 8.4 Hibernation.- 8.5 Miscellaneous.- 8.5.1 Acid-Base Balance of the Avian Embryo.- 8.5.2 The Laying Hen.- 8.5.3 The Crustacean Molting Cycle.- References.- Notes Added in Proof.- References Added in Proof.- Subject and Species Index.