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Maintenance of a stable internal state (body temperature, blood sugar levels) Dynamic process requiring constant physiological adjustments Coordinated in all levels of organisation Essential for the survival of the organism Claude Bernard (19th C): appreciated the importance of constant internal sta...

Maintenance of a stable internal state (body temperature, blood sugar levels) Dynamic process requiring constant physiological adjustments Coordinated in all levels of organisation Essential for the survival of the organism Claude Bernard (19th C): appreciated the importance of constant internal state Walter Cannon (20th C): coined term: homeo (similar) stasis (state) Negative Feedback: To keep the internal state constant, organisms need to detect internal or external changes to environment and responsibilities accordingly Physiological response in opposite direction to detected change cool environment induces shivering, which generates heat Very important mechanism for maintaining homeostasis Occurs due to change from a set point narrow range of a variable (body temperature in mammals/birds Negative feedback system: Sensor: detects the change in external environment Integrator: compares the detected change with set-point of system Effector: induces response to restore system back to set point Antagonistic Control of Negative Feedback: Controls change in a variable in both directions Body temperature: too hot: sweat too cold: shiver Behaviour: NF controlled by automatic physiological responses and voluntary behaviour, acts as an effector Eg. Panting vs seeking shade on a hot sunny day Disadvantages: Delay between change is detected and response is initiated (by the time response kicks in, already change from set point) Delay in stopping response once set point is re-established (overshoot beyond set point) May not function properly in extreme environments (pressure: high altitude/under water) Several mechanisms have evolved to improve negative feedback: Anticipation: predict external change before it occurs: skin detects change in room temp before body temp changes turn off compensatory response before it overshoots set point: boiler shuts off just before reaching set temp) Acclimatisation: