Immune System

OCR AS BIOLOGY

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Primary Defences

  • Skin acts as a physical barrier blocking pathogens from entering the body. Also acts as a chemical barrier by producing chemicals that are antimicrobial and can lower pH inhibiting growth of pathogens
  • Mucous Membranes they protect body openings that are exposed to the environment. Some membranes secrete mucous which traps pathogens and contains antimicrobial enzymes
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Immune systems responds

  • if a pathogen gets past the primary defences and enters the body the immune system will respond
  • an immune response is the body's reaction to a foreign antigen
  • antigens are molecules on the surface of cells
  • when a pathogen invades the body the antigen on its surface is identified as foreign activati ng the immune system
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Stage 1 - Phagocytes engulf pathogens

  • A phagocyte (e.g a macrophage) is a type of white blood cell that carried out phagocytosis. They are found in the blood and in tissues and are the first cells to respond to a pathogen`

1) Phagocyte recognises antigens on pathogen

2) Cytoplasm of phagocyte engulfs pathogen

3) Pathogen is contained in a phagocytic vacuole in the cytoplasm of the phagocyte

4) Lysosome fuses with phagocytic vacuole breaking down the pathogen

5) Phagocyte presents the pathogen's antigens on its surface to activate other immune system cells

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