The Immune System

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  • The Immune System
    • Primary Responses
      • SKIN-  Acts has a physical barrier, blocking pathogens from entering the body. Also acts as a chemical barrier, producing chemicals that are antimicrobial and can lower the pH.
      • MUCUS MEMBRANES- Protect the body openings that are exposed to the environment. Some membranes secrete mucus which traps pathogens.
    • Immune System Response
      • PRIMARY RESPONSE- (Happens when an antigen enters the body for the first time)   It's a slow process. Shows symptoms.  Leads to immunity through memory cells
        • STEP 1. PHAGOCYTES ENGULF THE PATHOGEN...1. Phagocyte recognises the antigens on a pathogen.     2. The cytoplasm of the phagocyte moves round the pathogen to engulf it.    3. Pathogen contained in the phagocytic vacuole in the cytoplasm.   4. A lysosome fuses with the phagocytic vacuole. The lysosomal enzyme breaks down the pathogen.     5. The phagocyte then presents the pathogen's antigens to activate other immune system cells.
        • STEP 2. PHAGOCYTES ACTIVATE T-CELLS.           A t-cell (white blood cell) has proteins on it's surface the bind to antigens. This activates the T-cell. It can respond in different ways:           1. Some release substances to activate B-cells.              2. Some attach to antigens on a pathogen and kill the cell.
        • STEP 3. T-CELLS ACTIVATE B-CELLS, WHICH DIVIDE INTO PLASMA CELLS.           B-cells (WBC) are covered with antibodies which bind to the antigens to form an antigen-antibody complex. Antibodies= unique.            1. When the antibody meets a complementary shape antigen, it binds to it.       2. This with substances releases by T-cells, activates the B-cell.             3. The activated B-cell divides into plasma cells.
        • PLASMA CELLS MAKE MORE ANTIBODIES TO A SPECIFIC ANTIGEN.      Plasma cells are identical to the B-cell (they're clones)     They secrete loads of the antibody specific to the antigen.     Antibody functions include:        1. Coating the pathogen to make it easier for the phagocyte to engulf it.       2. Coating the pathogen to prevent it from entering host cells.     3. Binding to and neutralising toxins produced by the pathogen.
      • Secondary Response.    If the same pathogen enters the body again, the immune system will produce a quicker and


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