Biology (NTSE/Olympiad)  

5. Human Disease

Sources (causes) of Disease

(B) Extrinsic or External Factor :
The factors causing diseases and existing outside the human body are called extrinsic or external factors.
The important extrinsic factors which upset human health are the following -
Unbalanced diet
Diseases causing micro-organism such as viruses, bacteria, fungi etc.
Environmental pollutants.
Tobacco, alcohol and narcotic drugs.
Extrinsic factors affect the health of our body by interfering with normal fuctioning of the body system.
Some of diseases caused by extrinsic factors are–
Night blindness
Beri Beri etc.

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