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Inside all living things, a balance is needed to survive. This balance is needed in a large number of areas including temperature, chemicals, bodily fluids and the concentrations of water found in the body. The process of keeping a fine balance in the body is known as homeostasis. The word homeostasis literally means ‘steady state’ and refers to keeping conditions in the body constant.
If you drank a litre of water in 30 minutes, your body would even this out by producing urine and making you need the toilet. A litre is a lot of water to consume in such a short period of time, so it is not necessary for the body to have this much. As you are likely not very dehydrated when drinking this water, the water that is put into your body will cause the concentrations of water within you to exceed the optimum levels. Your body will then react to this by releasing the liquid so that you are back to the levels needed. This is a good example of your body reacting to external changes (the drinking of water) to keep your body in balance.
It is not only water that must be kept constant within the body. There are many areas that the body constantly monitors and adapts in order to ensure that everything is at the right level. Some examples of these are the amount of glucose in the blood, the pH levels in various areas and body temperature. For the many different areas that need to be kept in balance to remain working at optimum levels, homeostasis is key.
Receptors, effectors and stimuli
For homeostasis to be able to work and keep things in perfect balance, your body must be able to pick up on any changes that are made and respond to these. The first part of this process is completed by receptors. A receptor is designed to detect a change in the body (such as temperature) and send this message to the brain where it can be processed and a response organised. The change in situation is caused by something called a stimulus (with the plural being stimuli). The stimulus is a change in surroundings that the receptor notices. Examples of a stimulus include a change in temperature, a noise or an increase in a certain chemical. Once the receptor has detected a stimulus, it sends a message to the central nervous system (CNS). The CNS then sends a signal to an effector which produces a response. An effector is a muscle or organ which acts in a certain way to maintain homeostasis despite the effects of the stimulus.
An example of a change to a stimulus is when your eyes are exposed to a strong light. In this situation the light is the stimulus as it is the external influence that has an impact on your body. The eyes are the receptors (in fact they are one of the most used receptor organs in the body) as they detect the stimulus. A message is then sent to your central nervous system which will react by sending out a message to your pupils telling them to contract and let less light in. The muscles in the pupils are the effectors as they produce the effect which stops the stimulus (the light) from damaging your eyes.
