4.1 - Non Specific Defences

4.1 - Non Specific Defences

1. Physical and Chemical Defences

   • Epithelial Cells
     • Form a physical barrier to prevent entry of pathogens
       • Skin
     • Produce secretions against infection
       • Mucus in trachea
       • Lysozyme in tears
       • Acid in the stomach
   • The immune system protects the body against pathogens, some toxins and cancer cells

2. Inflammatory Response

   • Caused by release of histamine by mast cells
     • Causes vasodilation of arterioles
       • Increases blood flow
     • Increased capillary permeability
   • Increased blood flow and secretion of cytokines
     • An accumulation of phagocytes
     • Delivery of antimicrobial proteins
       • Kill bacteria
     • Delivery of clotting elements
       • Form a clot to prevent microbes entering the bloodstream

3. Phagocytes and Natural Killer Cells

   • Phagocytes
     • Phagocytes and NK cells secrete cytokines
       • Stimulate the specific immune response
     • Phagocytes recognise surface antigen molecules on pathogens
       • Destroy the pathogen by phagocytosis
   • Natural Killer Cells
     • NK cells cause virally infected cells to destroy themselves by apoptosis
       • Cause the production of self-destructive/digestive enzymes within the virally infected cell