Why Do We Fall Ill? Revision Notes

Health and Disease

  • Health is defined as the state of complete physical, mental and social well-being. 
  • The health of an individual is affected by changing internal and external factors including personal, economic, environmental and social factors.
  • Disease is the departure from normal health through a structural or functional disorder of the body.

Causes of Diseases

Intrinsic/Internal FactorsThese are disease-causing factors that exist within the human body. Genetic disorders. Example: Haemophilia
Extrinsic/External FactorsThese are disease-causing factors that enter the human body from outside and cause disease. 
 Disease-causing microorganisms. Example: Malaria
Levels of Immediate CausesFirst-level cause: Primary cause/causative agent: Bacteria, virus Second-level cause: Secondary cause: Lack of good nourishment
 Third-level cause: Tertiary cause: Poverty

Types of Diseases

Types of Diseases
  • Diseases in which the symptoms are quickly visible in the body and last for a shorter duration are called acute diseases. Examples: Common cold, malaria
  • Diseases which are long-term, with their symptoms lasting for months or years, are called chronic diseases. Examples: Elephantiasis, tuberculosis
  • Diseases which develop after birth are called acquired diseases. 
  • Diseases caused by infectious agents or pathogens are called communicable or infectious diseases. Examples: Tuberculosis, chickenpox, measles 
  • Diseases which do not spread from one person to another are called non-communicable or noninfectious diseases. Examples: Beriberi, scurvy, arthritis

Differences between Infectious and Non-infectious Diseases

1. Caused by attack of pathogens1. Caused by factors other than pathogens
2. Caused by extrinsic factors2. Caused by intrinsic factors
3. Transmitted            from    one      person       to another3. Do not get transmitted from one person to another
4. Transmission of diseases occurs through direct contact or some medium 4. Transmission in hereditary diseases is from parent to offspring
5. Examples: Cholera, malaria5. Examples: Diabetes, goitre

Infectious Diseases 

Infectious Agents

Infectious Agents

Means of Spread of Infectious Diseases

Air-borne diseases  Spread through air when droplets of pathogens are expelled into the air because of coughing, sneezing or talking.  Examples: Influenza, meningitis
Water-borne diseases  Caused by consumption of contaminated water.  Examples: Typhoid fever, cholera, hepatitis A
Food-borne diseases  Caused by consumption of food contaminated with chemical toxins or pathogens.  Examples: Taeniasis, trichinosis
Vector-borne diseases  Caused by pathogens transmitted by vectors such as insects and ticks. Examples: Malaria, elephantiasis
Sexually             transmitted diseasesCaused by pathogens transmitted by sexual contact.  Examples: AIDS, syphilis
Fomite-borne diseases  Caused by pathogens present on inanimate objects such as clothing and bedding used by infected people.  Examples: Scabies, ringworm

Organ-specific and Tissue-specific Manifestations of Diseases

  • The signs and symptoms of a disease depend on the tissue or organ which the microbe targets. 
  • The severity of disease manifestation depends on the number of microbes within the body. 
  • During infection, the immune system gets activated. It sends many soldier cells to the affected tissue to kill the microbes. This causes inflammation. 
  • Inflammation is due to the escape of some chemicals which cause allergic reactions in our body. They attract blood supply because of which the amount of blood and the temperature of the surrounding area increase. The consequent swelling of the area is called oedema
  • Plasma and white blood cells (WBCs) of the immune system of the body are discharged at the affected site. Plasma contains products such as antibodies and macrophages which kill or inhibit the growth of pathogens. 
  • Doctors carry out confirmatory tests such as laboratory tests of blood, urine and stool or even perform an X-ray to confirm the presence of a disease.

Principles of Treatment of Diseases

Principles of Treatment of Diseases

Principles of Prevention of Diseases

  • Prevention of diseases follows three basic principles:
Principles of Prevention of Diseases

General Ways of Prevention of Infectious Diseases

  • We can prevent exposure to air-borne microbes by providing living conditions which are not overcrowded. 
  • We can prevent exposure to water-borne microbes by providing safe, filtered and boiled drinking water. 
  • We can provide clean environments to prevent exposure to vector-borne microbes. This would not allow their multiplication.

Specific Ways of Prevention of Infectious Diseases

  • Immunisation is the process by which an individual’s immune system is equipped to fight off infectious agents. 
  • Vaccination provides active immunity. 
  • Vaccines against some common diseases such as BCG vaccine, DPT vaccine, polio vaccine, vaccines for tetanus, diphtheria, whooping cough, measles and many others have been administered in India.