Immunity

• Defence mechanisms split into specific and non-specific
• non-specific defence mechanisms are immediate and the same for all pathogens
• specific defence mechanisms are slower and specific to each pathogen
• Non-specific defence mechanisms include physical/chemical barriers and phagocytosis
• Physical/ chemical barriers are the first line of defence
• Phagocytosis is the second line of defence
• specific defences include cell-mediated responses and humoral responses
• cell mediated responses involve T lymphocytes
• humoral responses involve B lymphocytes
• cell mediated and humoral responses are part of the third line of defence
• Ear's defence: cerumen inhibits bacteria growth
• eye's defence: cleansed by tears which contain a chemical that inhibits bacteria growth
• stomach's defence: stomach acid kills most pathogens
• mouth's defence: saliva contains lysozymes (enzyme) that breaks down bacterial cell walls
• skin's defence: keratinised outer layer prevents water loss, dead skin cells shed regularly, melanin pigment protects from UV radiation, sweat glands produce antimicrobial chemicals
• urinary system's defence: urine is sterile due to urethra being short and narrow, kidneys have immune cells called macrophages that destroy pathogens
• trachea and bronchi's defence: mucous layer traps microorganisms
• vagina's defence: acidic secretion inhibits growth of pathogens
• Phagocytosis is a non-specific immune response where white blood cells engulf and digest foreign particles
• Steps of phagocytosis:

  1. adherence of microbe to phagocyte
  2. Phagocyte ingests microbe
  3. Formation of phagosome
  4. Phagosome fuses with lysosome
  5. Enzymes digest microbe
  6. Indigestible material forms a residual body
  7. Waste is discharged
• Once a phagocyte has engulfed and digested an antigen, it can become an antigen presenting cell
• Cells involved in the specific immune response are smaller white blood cells called T and B lymphocytes
• Lymphocytes have a specific mode of action against infection and the response is specific to the pathogen
• The specific immune response is triggered by the recognition of an antigen via specific, complimentary cell surface receptors
• Antibodies are proteins produced by activated B cells
• The specificity of an antibody depends on the antigen binding sites which have a unique tertiary structure
• All antibodies have the same constant regions
• Plasma cells are 'clones' of B cells
• B cells bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes
• B cells secrete antibodies specific to antigens that are also known as 'monoclonal antibodies'
• The antigen-binding site matches the epitopes of antigens on the surface of the pathogen
• Antibodies are made up of 4 long polypeptide chains
• 2 of the polypeptide chains that make up an antibody are long and called 'heavy chains'. 2 are short and are called 'light chains'
• The hinge region of an antibody allows movement so that the antigen binding site can be placed at different angles in order to bind to the antigens
• Agglutination- clumping of antibodies to form a mass
• An antibody has two binding sites and so can actually bind to 2 pathogens simultaneously
• Phagocytes bind to the antibodies that are binded to the pathogens to engulf them
• T helper cells stimulate cytotoxin T cells, B cells and phagocytes
• T helper cells are essential in immunity and allow the activation of specific immune cells
• Without T helper cells a person is immunodeficient