ABSTRACT
Physiological processes ultimately provide for the survival of organisms in a continuously varying world. It was Claude Bernard who first recognised that multicellular organisms might attain relative independence from the variability of the external environment by achieving constancy in the composition of the fluids bathing their cells. Thus, the concerted operation of such physiological processes as respiration, thermoregulation, fluid balance, muscular activity, and others produce a dynamic internal stability in the face of changing external conditions. As represented schematically in Fig. 1, this ideal state of homeostasis is embodied in the coordinated activities of three major integrative systems: the nervous, endocrine, and immune systems. Each of these systems has its own components and characteristics, yet homeostasis surely results from the harmony of these three.
