Disease

Disease

1. Defence against pathogens

   • Skin
     • physical barrier to prevent pathogen entry
     • produces anti-microbial chemicals that can lower pH, inhibiting growth of pathogens
   • inflammation
     • blood vessel permeability increases. more fluid leaks into tissue fluid
       • causes swelling and helps isolate any pathogens that may have entered the damaged tissue
     • signs= swelling, pain, heat and redness
     • inflammation triggered by tissue damage- damaged tissue released molecules which increases permeability of blood vessels
       • molecules also cause vasodilation which increases blood flow to the affected area. makes area hot and brings white blood cells to the area to fight off any pathogens that may be present
   • wound repair
     • surface repaired by outer layer of skin cells dividing and migrating to the edges of the wound. tissue below the wound then contracts to bring the edges of the wound closer together. repaired using collagen fibre- too many collagen fibres and you will end up with a scar
     • skin is able to repair itself in the event of an injury and reform a barrier against pathogen entry
   • mucous membranes
     • goblet cells excrete mucus which traps dirt and pathogens
       • mucus contains anti-microbial enzymes
     • cilia waft mucus with trapped dirt and pathogens out of the body
     • prevent pathogens entering the body
     • protect body openings exposed to the environment such as mouth and ears
   • expulsive reflexes
     • sneezing is a reaction to irritation in the nose
       • mucous membranes irritated
     • coughing is reaction to irritation in the respiratory tract
     • expels foreign object
   • blood clotting
     • formed by a series of chemical reactions that take place when platelets (fragments of cells in the blood) are exposed to damaged blood vessels
     • network of protein fibres forms around the wound to plug wound, prevent blood loss and pathogen entry
     • a blood clot is a mesh of protein (fibrin) fibres

2. immune system

   • phagocytes
     • non specific defence
     • recognise antigen on pathogen as foreign
     • engulf pathogens
       • pathogen becomes encased in a phagosome inside the phagocyte
         • phagocyte fuses with a lysosome in the phagocyte cytoplasm
           • enzymes in the lysosome break down the pathogen
             • the phagocyte presents the pathogen's antigens on it's cell surface membrane, becoming an antigen presenting cell
               • this activates other immune system cells
       • membrane and cytoplasm of the phagocyte move around the pathogen
         • made easier by presence of opsonins- molecules in the blood that bind to pathogens and increase phagocytosis
     • neutrophils are a type of phagocyte. they are the first WBC to respond to a pathogen inside the body. Neutrophils move towards a wound in response to signals from cytokines. the cytokines are released by cells at the site of the wound
   • B lymphocytes
     • contain specific antibodies complementary to antigen
     • activates by substances produced by T helper cells such as cytokines
     • binds to complementary antigen and undergoes clonal selection and expansion by mitosis
       • divides into plasma cells which produce antibodies
         • Actions of anibodies
           • agglutinins
             • each antibody has two binding sites meaning it can bind to two pathogens at once. this causes the pathogens to clump together, making them easier to phagocytose
           • antitoxins
             • antitoxins bind to toxins produced by pathogens, forming toxin-antitoxin complexes. these complexes are then phagocytosed
             • prevents toxins from affecting human cells, so the toxins are neutralised
           • prevent pathogen from binding to body cells
             • when antibodies bind to the antigens on pathogens, they may block the cell surface receptors that the pathogens need to bind to the host cells. this means the pathogen can't attach to or infect the host cells
       • forms antigen-antibody complex
   • T lymphocytes
     • contains receptors on cell surface that are complementary to a specific antigen. when T lymphocyte binds to complementary antigen, is activated and it undergoes clonal expansion
       • bind to antigens presented by APCs
     • T helper cells release interleukins which activates B lymphocytes and stimulates B cell clonal expansion
     • T killer cells attach to and kill cells infected by a virus
     • T-regulatory cells suppress the immune system from other WBC. helps to stop immune system cells from mistakenly attacking the host's body cells

Images and files in the map