Mechanisms of disease

Homeostasis is the process which maintains the stability of the human body's internal environment in response to changes in external conditions. Besides ‘whole body’ homeostasis, the term is also used to describe particular processes or systems like the regulation of body temperature.

An analogy is the knots in a fishing net. See Figure 1.

Figure 1: Illustration of the fishing net analogy

What can we learn from this analogy?

• Pulling locally on one of the knots changes the position but does not destroy the overall net structure. This reflects the whole body and the individual systems within it.
• Local changes (e.g. by lifting one of the knots) in a fishing net will not only give rise to the change of the position of the knot in question but also of some of the neighbouring knots. This shows that it is not possible to change a single parameter without influencing the surrounding system, just as in the body.
• Releasing the knot of the net brings the net back to its original position. You could think of this like pharmacotherapy, where treatments and medicines help to restore the balance in the body.

A medical doctor studies the groups of symptoms that characterise a disease (called a ‘symptom complex’) of all types of diseases. They do this in a similar way to that described in Example 2 for anaemia, but in much more detail. The space given in this section is too limited to go through all diseases. Instead we will focus in a systematic way on the principles behind disease mechanisms and how these mechanisms can be controlled through intervention in the form of pharmacotherapy.