International Classification of Disease (ICD) (cont.)
ICD is a combination of specific bodily systems (e.g. nervous system), aetiologies (e.g. infections & parasites) and life-stage. A distinction is made between communicable diseases, non-communicable diseases and external causes – accidents, violence etc.
Most classification start with a particular area or system of the body. This breaks down into broad causes and these in turn break down into specific variants. There may be several layers of complexity.
The best way to understand this is to follow the links below to the WHO sites and explore!
To get to the actual classification of ICD-10 the link is:
http://apps.who.int/classifications/icd10/browse/2010/en#/I 
The slides below illustrate the hierarchical nature of the ICD classification:
To get to an online training package the link is:
NB The training package operates at different levels of involvement. One level is very basic and using this “short-track” adequate understanding of the classification process can be followed through in about 1 hour. The “How to get started” page explains how to follow the short-track explanation.