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Why Do We Fall ill?

Tutormate > CBSE Syllabus-Class 9th Biology > Why Do We Fall ill?

2 Diseases

A disease is the uncomfortable condition or discomfort that may be felt by us at times. Being healthy does not only mean being disease-free but the terms are correlated. A disease is diagnosed by certain symptoms and signs. Health is the state of physical, mental and social well-being that is affected by a factor called disease. It can be either due to structural disorder or functional abnormality in the body. Diseases can be classified based on certain criteria like the duration of occurrence, communicability, type of causative agent and source of transmission.

Sources of Disease:

Disease may either be caused by internal factors or external factors

1. Internal Factors include:

  • Malfunctioning or improper functioning of various body parts like heart, kidney, liver, etc;
  • Hormonal imbalances
  • Genetic disorder
  • Malfunctioning of immune system of body, e.g, allergy.

2. External Factors include:

  • Inadequate or unbalanced diet
  • Disease causing microorganisms such as viruses, bacteria, fungi, protozoans, helminthes, worms, etc.
  • Environmental pollutants;
  • Tobacco, alcohol and narcotic drugs.

Types of Diseases

Diseases can be classified into the following:

  • Diseases are of two types based on duration:
    • Acute diseases: When symptoms of diseases are quickly visible in the body, they are said to be acute diseases. They are of short term e.g, common cold. An acute disease if not treated properly can eventually become a chronic disease.
    • Chronic diseases. When symptoms of diseases last for months or years, they are said to be chronic diseases. They are of long time. e.g, elephantiasis, tuberculosis.

Differences between acute and chronic disease

Acute disease Chronic disease
Acute diseases last for only short period of time. Chronic diseases last for a long time, even as much as a life time.
They do not cause long term bad effects on human health.

They cause drastic long term effects on human health.

Examples include cold, cough, typhoid, cholera, etc. Examples include elephantiasis, cardiovascular disease, tuberculosis, diabetes, arthritis, cancer etc.
  • Diseases are of two types based on time of development:
    • Congenital disease: Congenital diseases are diseases that are present since birth. They are caused due to genetic abnormalities or due to metabolic disorders or malfunctioning of any organ in the body.
    • Acquired diseases: These are the diseases which develop after birth.
  • Diseases are of two types based on ways of spreading:
    • Infectious diseases or communicable diseases 
      Infectious diseases are caused by some biological agents or pathogens such as viruses, bacteria, protozoans, helminthes, nematodes and fungi. These diseases can spread rapidly from one person to another by various means like physical contact, water, air, food and insects (vectors). Since these disease are communicated from a diseased person to a healthy person they are known as infectious diseases.
    • Non –infectious diseases or non-communicable diseases 
      Non-infectious diseases may be caused by:

      • Lack of certain essential substances in our diet, e.g, proteins, vitamins, minerals (deficiency disease);
      • General wearing out or degeneration of tissues as in old age (degenerative diseases);
      • Uncontrolled growth of tissues in any part of body (cancer);
      • Defects in the metabolic reactions (metabolic disorders); and
      • Injury and damage to any part of the body by accidents.
      • Genetics
      • Age and sex

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