Mechanisms of disease


1. Basic Concepts

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A disease is an abnormal physiological condition that affects part or all of an organism. It means that something has gone wrong with the normal body functions and/or processes. Diseases are linked with ‘symptoms’ and ‘signs’ – where a symptom is a manifestation of disease apparent to the patient himself, while a sign is a manifestation of disease that the physician perceives. The sign is objective evidence of disease; a symptom, subjective..

To determine the use of medicines for the treatment of diseases (pharmacotherapy), four concepts are important:

  • Symptoms
  • Diagnosis
  • Mechanism described at a physiological and a molecular level
  • Target responsible for the medicine’s action (in this context: organ, part, tissue that is to be affected by the medicine).

These are described in more detail below.


These are what the patient experiences as not being normal or worrisome (e.g. pain, bleeding, a lump felt somewhere, sweating a lot, dizziness, hearing problems etc.). The patient then presents these to the doctor. The doctor looks at these symptoms and tries to link them to a disease or a syndrome (where a collection of symptoms appear together). This allows the doctor to reach a diagnosis.


The doctor forms a diagnosis (i.e. the disease or syndrome) on the basis of:

  • the patient’s disease history and symptoms presented
  • physical examination
  • blood samples
  • viewing of internal structures of the body with X-ray, Computer Tomography (CT) or Magnetic Resonance (MR) scans.


Centuries of research have decoded many of the mechanisms that lead to the symptoms of disease and thereby to the diagnosis. These can be observed by:

  • the naked eye
  • physical and/or electrical measurements (e.g. of blood pressure, muscle strength, urine flow, size of a tumour, heart activity, etc.)
  • physicochemical measurements on blood samples or tissue samples (‘biopsies’).


Identifying the mechanism of the disease helps us to understand what has gone wrong. It is important to then understand exactly which molecules (often proteins) are involved - this forms the ‘target’ for the primary action of the medicine. When medicines act on the target, they change the molecular processes, which in turn change the physiological processes. This therefore corrects the imbalance, which has led to the symptoms of the disease. The medicines do this through various interactions with molecules.

Knowing the mechanisms behind the observed symptoms of a disease is crucial to be able to initiate the right treatment.

What does the right treatment mean? Simply it means re-establishing the correct balance in body function. This balance or equilibrium is also called ‘homeostasis’. This describes the balance that exists among all the components of the body. An adequate homeostasis means that you are healthy and feeling vital (e.g. being full of energy when you wake up in the morning) and you will not sense anything wrong with your body (i.e. nothing aches or shows problems).