10. Diseases And Immunity

    Cards (15)

    • Pathogen
      A disease-causing organism
    • Pathogens
      • They are passed on from one host to another and therefore the diseases they cause are known as transmissible diseases
    • Ways pathogens can be passed on from host to host
      • Direct contact
      • Indirect contact
    • Direct contact
      The pathogen is passed directly from one host to another by transfer of body fluids such as blood or semen (eg HIV, gonorrhoea, hepatitis B & C)
    • Indirect contact
      The pathogen leaves the host and is carried in some way to another, uninfected individual
    • Main ways the body defends itself against disease
      • Mechanical barriers
      • Chemical barriers
      • Cells
    • Mechanical barriers

      • Structures that make it difficult for pathogens to get past them and into the body
    • Mechanical barriers

      • Skin
      • Hairs in the nose
    • Skin
      Covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab
    • Hairs in the nose

      These make it difficult for pathogens to get past them further up the nose so they are not inhaled into the lungs
    • Chemical barriers
      • Substances produced by the body cells that trap / kill pathogens before they can get further into the body and cause disease
    • Chemical barriers

      • Mucus
      • Stomach acid
    • Mucus
      Made in various places in the body, pathogens get trapped in the mucus and can then be removed from the body (by coughing, blowing the nose, swallowing etc)
    • Stomach acid
      Contains hydrochloric acid which is strong enough to kill any pathogens that have been caught in mucus in the airways and then swallowed or have been consumed in food or water
    • Cells
      • Different types of white blood cell work to prevent pathogens reaching areas of the body they can replicate in
      • By phagocytosis - engulfing and digesting pathogenic cells
      • By producing antibodies - which clump pathogenic cells together so they can't move as easily (known as agglutination) and releasing chemicals that signal to other cells that they must be destroyed
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