Homeostasis is the tendency of the body to maintain a stable internal environment despite external changes. Temperature, blood sugar, fluid balance, and many other variables are kept within narrow limits by continuous regulatory processes.

Negative feedback is the basic mechanism. When a variable drifts from its set point, sensors detect the change and effectors act to restore the set point. If body temperature rises, sweating and increased blood flow to the skin release heat; if it falls, shivering and constriction of peripheral vessels conserve heat. The hypothalamus contains many of the control centers that orchestrate these responses.

Drive states such as hunger and thirst arise when homeostatic systems detect deficits and motivate corrective behavior. The concept has been extended, with caution, to psychological regulation—maintaining optimal arousal or emotional equilibrium. Chronic stressors can push regulatory systems beyond their capacity, producing the wear and tear described as allostatic load.

Life requires a stable internal milieu. Homeostasis is the set of processes that defend it.