What do you mean by disease? Describe the various causes of diseases



What do you mean by disease? Describe the various causes of diseases.
Disease is defined as a condition of the body or a part of it in which its normal functioning gets disturbed. The main causes of diseases are:
Biological agents which are disease-causing microorganisms or pathogens like viruses, bacteria, fungi, protozoans , etc.
Physical agents like heat, cold, radiation, humidity, pressure, electricity, sound, etc. Mechanical agents such as chronic friction as well as other mechanical forces that cause injuries, trauma and fractures, etc.
Chemical agents which are of two types:

Endogenous chemical agents which are formed in the body, like urea, uric acid, etc.
Exogenous chemical agents which enter the body of the individual from outside, like metals, spores and pollens, etc.
Inherited diseases: Some diseases are because of the hereditary reasons, disturbance in chromosomes or genes.
Social agents which may cause mental disorders.
Deficiency diseases are caused by insufficiency, absence or excess of a nutrient necessary for health.