As human beings, our bodies are very complicated and all of the mechanisms in action need to be carefully monitored to make sure that they do what they are supposed to do. We may know for example that enzymes in the human body function best at body temperature, but that if the temperature starts to exceed that they start to become damaged (you may recall the word "denatured") or even destroyed.


As an analogy, think about your central heating system at home, if it gets too hot in your living room you turn the temperature down, but if it starts to get too cold you turn it back up. Why do you do this? Well of course you don't want to be too hot or too cold, and central heating systems nowadays have a thermostat which takes control of this function. The thermostat ensures that the conditions are kept just right for you, that is they act as a regulator.


The conditions inside your body, particularly temperature need similar regulation, so if you get too hot you start to sweat (because sweating is one way that your body can dispose of excess heat) and if you become too cold, you will shiver which is the body's way of utilising energy (from respiration) to warm you back up again. 


These processes are governed by a nervous system function known as "Homeostasis".



"Homeostasis is the regulation of the conditions inside your body (and cells) to maintain a 
stable internal environment, in response to changes in both internal and external conditions"


Perhaps the three most well-known systems, or bodily functions, that are automatically controlled in this way are:


  • Body Temperature
  • Blood Glucose Content/Levels
  • Water Content of the Body


These, and other systems are controlled by three main components which work together to maintain an equilibrium:


  1. Receptors.
  2. Coordination Centres.
  3. Effectors.


The analogy above, of the central heating system control is quite a good one. The receptors of an automatic control system will detect a stimulus when something changes. A message is sent to the coordination centre which processes the message and organises a response.


A "stimulus" (plural stimuli) can be light, sound, physical contact, pressure, pain et cetera and the response organised by the coordination centre will depend on the type of stimulus and the type of response required.


Just like in your central heating system, if the heating is too low the system will detect this via the thermostat, a signal will be sent to the electrical system controlling the boiler which will activate the boiler and bring it back online. Heat will be produced and passed to the radiators, and when the thermostat detects that the temperature is becoming too high, a similar signal will be sent to shut the boiler down. When the temperature cools down, the process will be repeated and this way the room temperature will be kept at an optimum level.



The mechanism which restores the optimum level is known as "negative feedback" and it may help for you to think of the word negative being pronounced "neh-GAY-tive" as opposed to the usual "nega-TIV" as you could say that the process negates the unwanted changes to restore the balance.


The homeostasis process relies on the participation of the central nervous system in an organism to be able to detect and respond to stimulus/stimuli.



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