Your body holds its temperature at 37°C, its blood sugar, its pH — all against a world constantly knocking them off. That’s homeostasis: sense the deviation, and push back toward the setpoint. Sweat when hot, shiver when cold; release insulin when sugar spikes. It’s the same negative-feedback loop as a thermostat, run in flesh. Slide a shock to the system and watch it recover.
Homeostasis is biological negative feedback maintaining an internal variable near a SETPOINT despite external disturbance: sensors detect deviation, and effectors act to reduce it (thermoregulation by sweating/shivering, glucose by insulin/glucagon, blood pH by buffering and breathing). Modelled as dx/dt = −k(x − setpoint), any perturbation decays back exponentially with time constant 1/k — the larger the corrective gain, the faster the return. Walter Cannon named it (1926); it is the control loop of life, and the reason a body is a self-governing system. A fail-loud self-check throws unless a perturbed variable returns to its setpoint. ◆ real physiology / control theory, node-verified.
A linear first-order return-to-setpoint (the exact exponential recovery); real homeostasis has multiple setpoints, delays and can be overwhelmed (fever, diabetes) — the sense-deviation, push-back-to-setpoint loop is exact.