a physical or mental disorder of malfunction with signs or symptoms. Diseases may be caused by a single factor or be multi factorial which may depend on lifestyle

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  • bacteria, viruses, fungi
  • disease causing microorganisms

For a microorganism to become a pathogen it must:

  • Gain entry to host
  • Colonise host tissue
  • Resist host defences
  • Cause harm to host tissue
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Methods of Transmission

  • Airbourne
  • Waterbourne
  • Direct contact
  • Contaminated food
  • Animals
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Common interfaces of the body

Interface = a surface or boundary between two systems

  • Gas exchange system: Through the mouth and noce (TB, influenza, bronchitus)
  • Digestive system: Through food and water (Cholera, typhoid, dysentery)
  • Skin: Through open cuts or wounds into the bloodstream (HIV, AIDS)
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The body's natural defences


  • The skin flora keeps the pH levels down
  • Sweat and oil is antiseptic
  • White blood cells attracted to open wounds to prevent infection

Gas exchange system:

  • Mucus lines the passageways trapping invading pathogens
  • These are then moved to the top of the system by cilla, to be removed
  • Macrophages remove any pathogens that get beyond the mucus

Digestive system:

  • Mucus is an antiseptic to kill bacteria
  • Gastric juice - HCL - lowers pH - denatures pathogen enzymes, killing bacteria
  • Friendly bacteria helps remove harmful bacteria

Enzymes such as lysosomes in the tears and saliva help to destroy any bacteria

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How pathogens cause disease

  • Damage host tissue - inhibit the synthesis of DNA, RNA and proteins, which may break down the membrane of the host cell
  • Produce toxins - have various effects such as increased water loss from cholera bacteria
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Data and disease

  • Epidemiology - the study of incidence and pattern of a disease, with regards to risk factors
  • Correlation occurs when a change in one of the two variables is reflected by change in the other two variables (when one variable changes, so does the other)
  • Casual relationship - when a correlation can be reflected with evidence to show a direct link between them
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Risk is a measure of the probability that damage to health will occur as a result of a hazard

  • The probability that a hazardous event will occur
  • The consequences of the hazardous event

Risk ia measured on a % scale, 0% = no risk, 100% = harm will occur

Risk always needs a time scale

Risk is relative compared to those who are not exposed to the hazard (e.g. 10 times more likely)

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Coronary Heart Disease

The artery taking blood to the heart gets partially or fully blocked causing cholesteral to be deposited beneath the endothelium, which then causes atheroma, meaning that the artery is less flexible, as it pushes into the lumen restricting the blood flow

Risk factors:

  • Genetics: Genes, age, sex
  • Lifestyle: Smoking (2-6x more likely), Cholesterol, High blood pressure, Obesity (increases BMI), Diet, Alcohol, Stress, Physical activity
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Where uncontrolled cell division occurs, creating a tumour which is caused by a mutation in the oncogene, responsible for normal cell division.

Risk factors:

  • Genetics: Genes, age, sex
  • Lifestyle: Smoking (tar carcinogen), Diet, UV light, Physical activity
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