Homeostasis

Homeostasis is the physiological regulation that keeps important features of an organism's internal environment within ranges compatible with normal function despite internal or external disturbances. Regulated variables can include body temperature, blood pressure, blood glucose, blood gases, ion concentrations, and extracellular fluid osmolality. Homeostasis does not mean that these variables remain perfectly constant. Instead, they fluctuate within ranges that regulatory systems act to maintain .^1,2

Many homeostatic systems operate through negative feedback. Sensors detect changes related to a regulated variable, and coordinating mechanisms activate effectors that oppose the disturbance. If a regulated variable moves too far in one direction, physiological or behavioral responses can act to return it toward its regulated range. Homeostatic control can also include anticipatory, or feedforward, responses that begin before a disturbance has fully developed .^1,2

Homeostasis is a dynamic process rather than a motionless equilibrium. Maintaining relative stability often requires continuous changes in processes such as hormone secretion, nervous-system activity, metabolism, circulation, or behavior. These responses may therefore vary considerably even while the regulated variable remains comparatively stable .²

Homeostasis is related to, but distinct from, allostasis. Homeostasis emphasizes the regulation of important physiological variables, whereas allostasis is commonly used to describe stability achieved through adaptive changes in physiological regulation, particularly in anticipation of or response to changing demands. The concepts overlap, and their precise distinction remains a subject of scientific discussion .²