Three Basic Levels of Homeostatic Regulation

The original concept of homeostasis focused primarily on the mechanisms responsible for maintaining the physical and chemical parameters of the extracellular fluid, especially blood (e.g., plasma pH and osmolality, blood pressure), within their physiological ranges. As blood forms the link between organ systems, the original concept of homeostasis focused on maintaining stability at the systemic level. However, the current concept of homeostasis is based on the premise that homeostatic regulation takes place at three levels, namely, the cellular, tissue, and systemic levels. These three levels of homeostatic regulation do not function autonomously, but are intimately connected and interact with each other. At each of these levels, the nervous system is involved in homeostatic regulation or its coordination.