Disease & Immunity

  • Created by: ernily
  • Created on: 22-03-15 18:43


  • pathogen is any organism that causes disease.
  • Pathogens cause disease by producing toxins and damaging cells.
  • Pathogens can physically damage host cells by:
    • Rupturing them to release nutrients.
    • Breaking down nutrients, which starves and kills the cell.
    • Replicating inside the cell, causing them to burst.

Pathogens can enter the body in 3 ways:

  • Respiratory System: Breathing in air containing pathogens causes them to be trapped in the mucus that lines the lugs. However, some will still reach alveoli in the lungs and cause damage.
  • Digestive System: Pathogens wich survive stomach acid can pass into the intestines and invade cells and the gut wall.
  • Skin: Pathogens enter the bloodstream through cuts and scratches.
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Risk Factors:

  • Coronary Heart Disease
    • Poor diet (high in salt or saturated fat),
    • Smoking (can lead to high blood pressure),
    • Lack of Exercise (can lead to high blood pressure).
  • Cancer:
    • Smoking (can lead to high blood pressure),
    • Excessive sun exposure (can lead to skin cancer).
    • Excessive alcohol intake (can lead to liver cancer).
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The Immune System

  • A phagocyte is a type of white blood cell (WBC) that carries out phagocytosis.
    • A phagocyte recognises the antigens on a pathogen.
    • The cytoplasm on the phagocyte engulfs the pathogen.
    • The pathogen is now contained in a phagocytic vacuole in the cytoplasm.
    • A lysosome fuses with the vacuole. The lysosomal enzymes digest the pathogen.
    • The phagocyte presents the pathogen's antigens; it sticks the antigens on it's surface to activate the immune system.
  • Phagocytes activate T Cells:
    • A T Cell is another type of WBC with proteins on it's surface that bind to antigens.
    • Some release substances to activate B Cells.
    • Some attach to antigens on a pathogen and kill the cell.
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The Immune System

  • T Cells activate B Cells, which divide into plasma cells.
    • B Cells are also a type of WBC covered in antibodies.
    • Antibodies are proteins that bind to antigens to form antigen-antibody complexes.
      • When the antibody on a B Cell meets a complementary shaped antigen, it binds to it.
      • This activates the B Cell.
      • The activated B Cell divides into plasma cells.
  • Plasma cells make more antibodies to a specific antigen.
    • Plasma cells are clones of B Cells. They secrete lots of antibodies.
    • Antibody functions:
      • Coating the pathogen so phagocytes can easily engulf it.
      • Coating the pathogen to prevent it entering host cells.
      • Binding to, and neutralising, toxins produces by the pathogen.
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The Immune System

  • Cellular Immune Response: T Cells and other cells they interact with.
  • Humoral Immune Response: B Cells and antibody production.
  • Primary Immune Response:
    • When an antigen first enters the body, it activates the immune system.
    • The primary response is slow due to the lack of B Cells.
    • Eventually, the body produces enough antibodies. The infected person shows symptoms.
    • T&B Cells produce memory cells which remain in the body
      • T Cells remember the antigen.
      • B Cells remember the antibody.
    • The person is now immune.
  • Secondary Immune Response:
    • Memory B Cells divide into plasma cells.
    • Memory T Cells divide to kill the antigen.
    • The secondary response is quicker and stronger.
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Vaccines & Antibodies In Medicine

  • Vaccines contain antigens, causing your body to produce memory cells without getting the disease.
  • Herd  Immunity: Vaccines reduce the occurence of the diease, so those not vaccinated are less likely to get the disease.
  • Vaccines contain free or dead/weakened pathogens.
  • Vaccines may be injected or taken orally.
    • If taken orally, the vaccine could be broken down by enzymes, or the molecules could be too large to be absorbed into the blood.
  • Booster vaccines are given later on to ensure that memory cells are produced.
  • Antigens on the surface of pathogens activate the primary response.
  • The second time of infection, the secondary response is activated.
  • Antigenic variability: Pathogens can change their surace antigens. 
  • So the second time of infection, the memory cells won't recognise the different antigens; the primary response starts again.
  • The primary respose takes time, so you will get ill again.
  • Antigenic variation makes it difficult to develop vaccines.
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Vaccines & Immunity In Medicine

  • Monoclonal Antibodies are produced from a single group of genetically identical B Cells. They're all identical in structure.
  • Monoclonal antibodies can be made to bind to anything.
  • Example: Cancer.
    • Cancer cells have antigens called tumour markers, which aren't found on normal body cells.
    • Monoclonal antibodies are made to bind to tumour markers.
    • You can attach anti-cancer drugs to antibodies.
    • So drugs will only accumulate where there are cancer cells.
    • Side effects of this are loer because they accumulate near specific cells.
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