Causes of Disease - AQA - Unit 1

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  • Created by: Eleanor
  • Created on: 21-03-13 08:42
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  • Causes of Disease
    • Disease can be described as certain symptoms: either mental, physical or both
      • Disease suggests a malfunction of body or mind which does not lead to good health
    • For a microorganism to be considered a pathogen it must:
      • 1) gain entry to the host
      • 2) Colonise the hosts tissues
      • 3) Resist the defences of the host
      • 4) Cause damage to the hosts tissues
    • Pathogens include bacteria, viruses and fungi
      • When a pathogen is transferred from one host to another then it is called transmission
    • Most commonly pathogens penetrate one of the bodies links to the external environment
      • An example of an interface is the skin, which acts as a barrier and forms a continuous layer
        • When the skin is broken though (e.g. a cut) it allows an area for a pathogen to enter.
      • At areas with contact to the environment, it is often thin, moist, with a large surface area and well supplied with blood vessels
        • Although this leads to efficient exchange of materials, it is perfect entry for a pathogen
      • Most common points of entry are:
        • Gas-exchange system
          • These types of pathogens can be inhaled and spread through air
          • Pathogens that cause influenza, bronchitis and tuberculosis infect this way
        • Digestive System
          • Food and water may carry pathogens into the stomach and small intestine
          • Cholera and typhoid causing pathogens enter the body this way
    • Natural defences against pathogens are present in the body
      • A mucous layer that covers exchange surfaces and forms a thick sticky barrier
      • The production of enzymes that break down the pathogens
      • The production of stomach acid, with a pH to kill pathogens
    • Pathogens affect the body in two main ways
      • Damaging host tissues
        • Viruses prevent the synthesis of DNA, RNA and proteins by the host cells
        • Many pathogens break down the membranes of host cells
      • Producing toxins
        • Most pathogens do this, whether in the blood stream or inside the host cells


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