Edexcel A (SNAB) A Level Biology

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6.2.2 Entry Routes of Pathogens

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Entry Routes of Pathogens

  • In order for pathogens to cause disease they need to enter the body
  • There are four main ways in which pathogens can enter
    • Broken skin
      • This provides direct access to the tissues and bloodstream
    • The digestive system
      • When we consume contaminated food and drink
    • The respiratory system
      • Every time we inhale
    • Mucosal surfaces
      • The lining of body cavities e.g. inside of nose, mouth, genitals

Barriers to infection

  • Skin
    • This provides a physical barrier against infection
    • If the skin is damaged it leaves the exposed tissue beneath vulnerable to pathogens
    • The blood clotting mechanism of the body plays an important role in preventing pathogen entry in the case of damage to the skin
    • Blood clotting takes time, however, so a few pathogens may still enter before a clot forms
  • Microorganisms of the gut and skin
    • Collectively these harmless microorganisms are known as the gut or skin flora
    • They compete with pathogens for resources, thereby limiting their numbers and therefore their ability to infect the body
  • Stomach acid
    • The hydrochloric acid that makes up a large part of the gastric juices in the stomach creates an acidic environment that is unfavourable to many pathogens present on food and drink
    • Sometimes a few of these pathogens may survive and make their way to the intestines where they infect the gut wall cells and cause disease
  • Lysozyme
    • Secretions of the mucosal surfaces, e.g. tears, saliva, and mucus, contains an enzyme called lysozyme
    • This enzyme will damage bacterial cell walls, causing them to burst, or lyse

Chemical and physical barriers 1Chemical and physical barriers 2

The body has physical defences that prevent the entry of pathogens

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Marlene

Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.