Homeostasis describes all of the processes that happen in a cell or organism to maintain (keep) conditions optimal. This is needed to respond to changes in the internal and external environment.

Enzyme functioning

Because humans are organisms that live in a changing environment, we must regulate our body’s internal conditions to make sure our enzymes and cells function well.


If conditions are not optimal, then our enzymes can denature (change shape). This reduces their ability to catalyse (speed-up) metabolic reactions (chemical reactions in organisms).

Regulating Internal Conditions

Humans must regulate their body’s internal conditions to make sure that enzymes and cells function well. The conditions that need to be regulated are:
  • Internal body temperature
  • Urea concentration (in urine)
  • Water levels
  • Blood sugar levels
  • Carbon dioxide levels

Control Systems

Control systems use both nervous and chemical responses. Control systems are made up of three parts:

  1. Receptors - Receptor cells detect changes in the environment.
  2. Coordination centres - Coordination centres receive and process information arriving from receptor cells.
  3. Effectors (muscles or glands) - Effectors (muscles or glands) carry out responses to stimuli (events or things) that help to restore optimum levels.

The Body's Negative Feedback Loop

When our internal conditions are optimal, the body does not need to respond. If an internal condition changes and is no longer optimal, this stimulus is detected and the body works to counteract (reverse) the change and return conditions to the optimum. This process is called negative feedback and needs all of the components of the nervous system to work together.

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