Study of illness

Knowledge of anatomy and physiology is necessary for understating diseases. There are many different illnesses, disorders and diseases. A systematic approach is crucial in the study of abnormalities.


Aetiology is the study of the various factors that cause an illness. Diseases are caused by one or more mechanisms that may include:

  • Micro-organisms such as bacteria, microbes, viruses, parasites, etc.
  • Chemicals
  • Genetic abnormalities
  • Ionizing radiations
  • Injuries
  • Degeneration due to ageing

In most diseases, one or more of the factors mentioned above may be involved. However, for many diseases and disorders no specific causative factors have identified. Such diseases are known as essential, idiopathic or spontaneous diseases. Even though causative factors may not be known, risk factors or predisposing factors may be identifiable.

Aetiology Cause of the disease
Pathogenesis Nature of the disease process and its effect on body functions
Complications Consequences that arise if the disease progresses
Prognosis Likely outcome


Pathogenesis of a disease is the biological mechanism that leads to the diseased state. The word is derived from Greek: pathos (“disease”) and genesis (“creation”).

The main processes causing diseases are:

  • Inflammation: Inflammation is a protective tissue response involving immune cells, blood vessels, and molecular mediators to infection or trauma. The purpose of inflammation is to eliminate the initial cause of cell injury, clear out damaged cells and tissues and initiate tissue repair. Inflammatory conditions are recognised by the suffix –itis. e.g. pancreatitis.
  • Tumours: A tumour is a lump or growth in a part of the body. It is formed when cells proliferate abnormally. The rate of cell production exceeds that of normal cell death leading to formation of the tumour. Tumours are recognized by the suffix –oma. e.g. melanoma.
  • Abnormal immune responses: The immune system protects the body from infections but sometimes it can cause undesirable effects.
  • Metabolic abnormalities: These result in disorders related to metabolism. e.g. diabetes mellitus.
  • Thrombosis, embolism, infarction: These result from abnormal changes in blood and blood vessels.
  • Degeneration: Degeneration is associated with normal ageing. However, it may also arise prematurely leading to impaired functions.
  • Genetic abnormalities: Genetic defects may be either inherited or caused due to factors such exposure to ionizing radiations.