Pathogens and Disease

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  • Disease and Immunity
    • Disease
      • Diseases can be infectious, or non-infectious.
      • Anything that increases the chance of getting a disease is called a risk factor.
    • Pathogens
      • Pathogens are organisms that cause disease. There are three main pathogens.
        • Virus
          • All viruses are pathogens.
        • Fungi
        • Bacteria
      • Pathogens enter the body through three main interfaces.
        • The gas exchange system.
          • Cilia in the trachea waft up pathogens.
          • Most pathogens get caught in the mucus lining of the trachea.
        • The Skin
          • Platelets in the blood clot to prevent pathogens entering the blood stream.
        • The Digestive System
          • Most pathogens are killed by the hydrochloric acid in the stomach.
          • Pathogens not killed in the stomach will enter the blood stream through the intestinal lining.
      • Pathogens are covered in proteins called antigens which  stimulate an immune response.
    • The Immune Response
      • There are 4 main stages of the immune response.
        • Phagocytosis
          • A phagocyte recognises antigens on pathogens, engulfs pathogens and releases enzymes that destroy the pathogen.
        • T-Cell Activation
          • Phagocytes activate T-Cells. The T-cells then either activate B-cells or kill pathogens.
        • B-Cell Acitvation
          • B-Cells bind with pathogens and then produce more B-Cells and plasma cells.
          • Plasma cells (memory cells) produce antibodies during the second immune response.
        • Antibody Production
          • Antibodies coat pathogens to make them easier to engulf and to prevent them from entering host cells.
          • Antibodies bind to toxins released by pathogens and neutralise them.
    • Vaccines
      • Vaccine contain inactive pathogens/antigens which stimulate an immune response.
      • During the primary immune response, plasma cells are produced so during the secondary immune response antibodies can be produced immediately before symptoms are shown.
      • Herd Immunity can occur.
        • If a large amount of the population are vaccinated, those who are not vaccinated are also less likely to get infected as there are less carriers of the disease.
    • Antigenic Variation
      • Some pathogens have antigenic variation meaning not all pathogens of the species present the same antigens.
      • As antigens are used in vaccines to stimulate an immune response, pathogens with a wide amount of genetic variation are difficult to vaccinate against.
    • Monoclonal Antibodies
      • Monoclonal antibodies are antibodies produced form a single group of genetically identical B-cells.
      • They are often used to ensure that the antibodies all have the correct variable regions to bind to the antigens of the pathogens.


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