Homeostasis in dynamic self-regulatory physiological systems

Understanding the general principles of homeostasis and its regulation in health and disease is key to managing patients in intensive care units and operating theatres. In these environments, it is crucial to realize that physiological control is a dynamic process aimed at achieving a balance between two opposing sets of factors. Whereas one set of factors (e.g. the sympathetic nervous system) attempt to increase a physiological variable of interest at any given time, opposing forces acting almost concurrently, (e.g. the parasympathetic nervous system) will result in the reduction in the value of this variable. The human body is a self-adapting system and as a result of its ability to adapt, new physiological 'steady states' will be reached and maintained even in diseases. This review will explore some of the concepts and pathways involved in the regulation of homeostasis in the immediate, intermediate and delayed time scales following an initial perturbation, emphasizing the dynamic nature of this regulation.