Introduction to Biological Negative Feedback Systems

In the biological world everything works as a complex web of interactions between many different systems. One of the key types of system is that of the negative feedback systems. In systems theory a negative feedback system is one in which the output of the system is fed back into the input of the system to achieve a stabilising effect in response to a perturbation away from an equilibrium state. A positive feedback system, in contrast, goes with the perturbation, amplifying the original signal. But what form do negative feedback systems take in the biological world?

Whereas in mechanics negative feedback is typically known as equilibrium (as in a thermostat, for example) in the biological world it is often called homeostasis. Such mechanisms are to be found throughout nature and at many different levels of complexity. They are to be found in the physiology and behaviour of all species. They are to be found in the interactions between species in the same ecosystems. So now let’s look at a few examples of negative feedback at work in the natural world.

At the heart of homeostasis is the idea of the regulation of the internal environment of an organism. It is about maintaining stable states in the face of perturbations. This is clearly vital in the survival of any creature. This can be seen in the regulation of blood pressure, for example. In this case the resistance to blood flow through the blood vessels can be registered and the information sent to the brain. If this is outside the normal range then the brain signals the heart to increase or decrease its rate, and this is accompanied by a signal to the blood vessels to decrease or increase in diameter, respectively, thus bringing the blood pressure back into the acceptable range.

Negative feedback is also at work extensively at the biochemical level with the levels of pretty much everything having to be regulated to maintain them within levels that are not harmful, whether because they are too high or too low. Insulin, for example, regulates the levels of blood sugar, removing glucose from the blood and into body cells. Diabetes involves a lack of insulin and thus a faulty negative feedback mechanism that is incapable of removing enough glucose from the blood.

But negative feedback may also appear at a higher level of complexity than the organism as well, at the ecological level. Ecological homeostasis is hypothesised to occur when biodiversity in a particular environment has reached a maximum. There is said to be a so-called climax community of plants and animals which represent a steady state and that will tend to resist any perturbation to that steady state.