Homeostasis is the tendency for an organism or cell to maintain a constant internal environment within tolerance limits

Internal equilibrium is maintained by adjusting physiological processes, including:

  • Body temperature (normally between 36 – 38ºC)
  • Carbon dioxide concentration (normally 35 – 45 mmHg)
  • Blood pH (normally between 7.35 – 7.45)
  • Blood glucose levels (normally 75 – 95 mg/dL)
  • Water balance (varies depending on individual body size)

Homeostatic mechanisms operate via a feedback loop that may involve either the nervous or endocrine systems (or both)

  • When specialised receptors detect an internal change to conditions, a response is generated to correct the change
  • Most homeostatic responses involve an effect that is antagonistic to the detected stimulus (negative feedback)
  • When levels return to equilibrium, the effector ceases to generate a response and an internal balance is therefore maintained
  • If a physiological condition moves outside of tolerance limits, disease will occur as a consequence