Introduction to the study of illness

Study of illness: There are many distinct ailments, syndromes, and diseases that range in severity from very mild to extremely serious. Adopting a methodical strategy can make studying anomalies much simpler. When there are unmistakable connections between the causes (aetiology) and the effects of the abnormality (pathogenesis), the causes are described first.


The disease is usually caused by one or more of a limited number of factors including:

  • genetic abnormalities, either inherited or acquired
  • infection by microbes or parasites, e.g. viruses, bacteria or worms
  • chemicals
  • ionising radiation
  • physical trauma
  • degeneration, e.g. excessive use or ageing.

Some illnesses have more than one of the aetiological elements mentioned above at play, while others have no known origin and can be classified as essential, idiopathic, or spontaneous. Links with risk factors or predisposing variables may have been discovered for several diseases for which the exact aetiology is unknown. Latrogenic conditions are those that are the result of injury brought on by caregivers.

  • Acute: a disease with a sudden onset often requiring urgent treatment (compare with chronic).
  • Acquired: a disorder which develops any time after birth (compare with congenital).
  • Chronic: a long-standing disorder which cannot usually be cured (compare with acute).
  • Congenital: a disorder which one is born with (compare with acquired).
  • Sign: an abnormality seen or measured by people other than the patient
  • Symptom: an abnormality described by the patient.
  • Syndrome: a collection of signs and symptoms which tend to occur together


The main processes causing illness or disease are as follows.

Inflammation: This is a tissue response to damage by, e.g. trauma, invasion of microbes*. Inflammatory conditions are recognised by the suffix -itis, e.g. appendicitis.

Tumours: these arise when the rate of cell production exceeds that of normal cell destruction causing a mass to develop. Tumours are recognised by the suffix -oma, e.g. carcinoma.

Also read: Intake of raw materials and elimination of waste

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