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  • The Immune System
    • phagocytis
      • 1. antigens are recognised by the phagocyte as foreign
        • 2. the cytoplasm of the phagocyte moves around the pathogen engulfing it. this ay be helped by opsonins
          • 3. the pathogen is now contained in a phagosome in the cytoplasm of the phagocyte
            • 4. a lysosome fuses with the phagosome. the enzymes break down the pathogen.
              • 5. the phagocyte the presents the pathogens antigens on its surface to activate other immune system cells. becomes and antigen presenting cell (APC)
      • T lymphocytes
        • T lymphocytes are a type of white blood cell
          • their surface is covered in unique  receptors
            • when a receptor meets a  complementary antigen it binds to it.
            • this is called colonal selection. it then under goes colonal expansion where it divides to produce clones of itself. produces different types.
              • types of T lymphocyte.
                • T helper- these release substances to activate B lymphocytes and T killer cells
                  • T killer cells- these attach to and kill cells that are infected with a virus.
                    • T regulatory cells- these suppress the immune response from other white blood cells. this stops the immune cells from attacking the hosts body cells.
      • B lymphocytes
        • another type of white blood cell, covered with antibodies
          • antibodies bind to antigens to form an antigen-antibody on its surface
            • antibody binds to a complementary antigen
              • this together with substances from T helper cells activates the b lymphocyte. this process is called clonal selection
                • this activated b lymphocyte divids by mitosis into plasma cells and memory cells, clonal expansion
                  • they produce plasma cells which are clones of B lymphocytes. they secrete loads of antibodies.
                    • Structure of anti bodies
                      • variable regions- form the antigen binding sites. variable region is complementary to particular antigen.
                        • hinge region- allows flexibility when antibody binds to antigen.
                          • constant region- allows binding to receptors on immune system cells. (phagocytes). same in all antibodies.
                            • Didulphide bridges- hold the polypeptide chains of the protein together.
    • The primary response
      • the primary response is slow because there aren't many B lymphocytes that can make to antibody needed to bind to it.
        • eventually there will be enough of the right antibodies to overcome the infection meanwhile the host will show symptoms of the disease.
          • T and B hen produce memory cells these cells remain in the body for a long time.
            • memory T lymphocytes remember the specific antigen and memory B lymphocytes record the specific antibodies needed to bind to the antigen.
              • the person is now immune
    • The secondary response
      • if the same pathogen enters the body the immune system will produce a quicker faster response.
        • clonal selection happens faster. memory B lymphocytes activated and divide into plasma cells that produce right antibody to antigen. memory T lymphocytes activated and divide inot correct type of T lymphocytes to kill the cell carrying the antigen
          • secondary response gets rid of the pathogen before you experience any of the symptoms.


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