G VITAL LIFE SUPPORT SYSTEMS The concept of homeostasis was introduced in Chapter 19, in relation to control systems that operate to preserve the internal environment. The following eight chapters describe the major vital systems that cooperate with each other in complex animals to support life. Their function can be described as being integrative, in that they are continually adjusted according to need and because changes in one system are usually accompanied by changes in the others. Three key physiologic systems - cardiovascular, respiratory, and renalsystems - play a dominant role in the preservation of the internal environment in face of external influences. They function cooperatively to maintain critical physiologic variables within acceptable comfort ranges. All three systems are primarily controlled by the autonomic nervous system, with additional significant input from endocrine mechanisms. The vital physiologic systems yield endless examples of the application of the control systems, introduced and described in earlier chapters. Furthermore, the operation of these vital systems is intimately related to the structure of the component tissues and organs. The adequacy of the function of the vital support systems is best assessed by a few key variables, the magnitude of which can readily be determined in the blood. Physiologists, clinicians, and animal scientists measure blood parameters and related variables such as heart rate, respiration rate, ease of respiration, and the like, as vital signs in the animals (or humans) with which they work. The circulation of blood provides linkage between the three vital systems, as is obvious in the example of gas exchange between the environment at large and the deep tissues. Indeed, Chapter 32 is devoted to a description of the integrative nature of blood and Chapter 35 will describe the important features of gas transport mechanisms. 2007 version – page 268
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