INTRODUCTION
Disease can be
defined as any abnormality or failure of the body to function properly and this
may require medical treatment (Figure 1.1).
The scientific study of diseases is called pathology.
Every disease
has a distinct set of features that include a cause, associated clinical
symptoms and a characteristic progression, with associated morphological and
functional changes in the patient. The presence of an abnormality on its own,
however, does not necessarily indicate disease since the affected individual
must also suffer from ill health. Health
can be defined as an absence of signs and symptoms associated with any disease.
This definition has limitations in that there are circumstances where individuals
believe they are ill even though detectable indications of disease are not
present. Conversely, there are individuals who believe they are healthy but on
detailed examination are found to suffer from a serious disease. For this
reason, the World Health Organization (WHO) devised the more appropriate
definition of health as a state of
physical, mental and social well-being and not merelythe absence of disease.
Currently there is considerable interest, particularly indeveloped countries,
in promoting health by improving lifestyle and reducing mental and social
factors associated with ill health.
Individuals
differ in their physical appearance and also internally in the composition of
the biological materials of which they are made. Differences between
individuals are due to biological variation. Variation in values for measurable
body features or biological substances (analytes)
occurs for a number of reasons. Differences in the genotypes of individuals
ensure that no two individuals are the same (other than identical twins).
Biological variation arises due to differences in lifestyle, experiences,
dietary and other factors as well as genes. There are also differences in
physiological processes arising from bodily control mechanisms. For example,
the concentration of blood glucose varies between individuals with diet, time
of day and physical activity.
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