Health and Disease Part One - Unit 2 OCR

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  • Health and Disease - Part One
    • Defining Health and Disease
      • What is Health? - state of physical mental and social well being which includes the absence of disease and infirmity, you need to eat nutritious food so you're not malnourished and have shelter : these things help maintain health as they help avoid disease
      • What is Disease? - condition that impairs the normal functioning of an organism, can be infectious non-infectious acute or chronic
        • Infectious - passed between individuals and caused by pathogens or parasites
          • Pathogen - an organism that can cause disease : HIV, Mycobacterium tuberculosis, Trichophyton rubrum
          • Parasite - an organism that lives on or in another organism and causes damage to it, some cause disease so are also pathogens : Plasmodium (malaria) also pathogen, Tapeworms, Fleas
        • Non-Infectious - caused by genetic defects, nutritional deficiencies, lifestyle and environmental factors : Coronary Heart Disease, Emphysema
        • Acute - usually only cause a problem for short period of time and symptoms usually appear rapidly : a cold
        • Chronic - more persistant so can have them your whole life, symptoms often appear slowly but get progressively worse over time : diabetes, chronic bronchitis
    • The Immune System
      • Primary Defences - body has a number of these to prevent pathogens and parasites entering
        • Skin - acts as physical barrier blocking pathogens from entering, acts as chemical barrier by producing anrimicrobial chemicals and can lower pH to inhibit pathogen growth
        • Mucous Membranes - protect body openings exposed to the environment, some secrete mucus (a sticky substance that traps pathogens and contains antimicrobial enzymes
      • The Immune Response - if pathogen or parasite gets past primary and enters the body the immune system responds, it is the body's reaction to a foreign antigen, antigens are molecules found on cell surfaces and when pathogen invades body its antigens are identified as foreign which activates cells in the immune system
      • Main Stages of the Immune Response
        • 1. Phagocytosis - a phagocyte is a type of white blood cell that carries out this process, found in blood and in tissues, first cell to respond to pathogen inside body
          • Phagocyte recognises the antigens on pathogen, cytoplasm of phagocyte moves round the pathogen to engulf it, pathogen is now contained in a phagocytic vacuole in cytoplasm, a lysosome fuses with phagocytic vacuole and enzymes break down the pathogen and it is absorbed into cytoplasm
            • Phagocyte then presents pathogen's antigens and sticks the antigens to its surface activating other immune system calls
        • 2. T Lymphocyte Activation - another type of white blood cell, surface is covered in receptors which bind to antigens present of phagocyte, each has a different receptor on its surface so much be complimentary to antigen to bind to it, this is known as clonal selection
          • The activated T cells undergo clonal  expansion (divide to produce clones that differentiate into different types of T cells), different cells have different functions
            • Some activate T helper cells which release substances to activate B lymphocytes
              • Some attach to antigens on pathogens and kill the cell
                • Some become memory cells
        • 3. B Lymphocyte Activation and Plasma Production - also a type of white blood cell, covered with antibodies (proteins that bind to antigens), each B lymphocyte has different shape antibody on membrane so needs complimentary shape to bind
          • When antibody meets complimentary it binds to it, this together with substances released from T helper cells activates B lymphocyte, process is another example of clonal expansion, the activated B then divides by mitosis into plasma cells and memory cells
        • 4. Antibody Production - plasma cells are clones of B lymphocyte and secrete lots of antibodies specific to antigens into the blood, these bind to antigens to form lots os antigen-antibody complexes, this signals immune response to attack and destroy pathogen
      • Cell Signalling - how cells communicate, cell may release or present substance that binds to receptor on another which causes a response of some kind in other cells
        • Really important in immune response as it helps activate all different types of white blood cell needed
    • Antibodies
      • Structure - proteins made up of chains of amino acid monomers linked with peptide bonds
        • Variable Region - form the antigen binding site, shape of it is complimentary to particular antigen and differs between antibodies
        • Hinge Region - allows flexibility when binding to the antigen
        • Constant Region - allows binding to receptors on immune system cells and is the same in all antobodies
        • Disulphide Bridges - hold polypeptide chains together
      • Role in Clearing Infections
        • 1. Agglutinating Pathogens - each antibody has two binding sites so it can bind to two pathogens at the same time so they become clumped together, phagocytes then bind to antibodies and phagocytose a lot of pathogens at once
        • 2. Neutralising Toxins - antibodies can bind to toxins produced by pathogens to prevent them from affecting human cells so toxins become neutralised, toxin-antibody complexes are phagocytosed
        • 3. Preventing Pathogen from Binding to Human Cells - when antibody binds to antigen on pathogen it may block cell surface receptors that pathogens need to bind to host cell meaning pathogen can't attach to or interact with host cell
    • Primary and Secondary Immune Responses
      • Primary Immune Response - when antigen enters body for the first time it activates immune system, this response is slow as there aren't many B lymphocytes that can make antibody needed to bind to it, eventually the body produces enough of right antibody to overcome infection meanwhile the infected person will show symptoms
        • After being exposed to antigen both T and B lymphocytes produce memory cells which remain in body for a long time, memory T remember specific antigen and recognise it a second time round, memory B record specific antibody needed to bind to antigen, person is not immune as immune system has ability to respond quickly to second infection
      • Secondary Immune Response - if same pathogen enters the immune system will produce a quicker stronger response, memory B divide into plasma cells that produce the right antibody while memory T divide into correct type of T lymphocyte to kill cell carrying antigen,  often gets rid of pathogen before symptoms start to show
      • Maintaining Immunity - memory B and T have limited life span meaning someone who is immune to particular pathogen won't be immune forever
        • Once all B and T have died the person may be susceptible to attack by pathogen again, immunity can be maintained by being continually exposed to pathogen so you continue to make more memory T and B
      • Comparing Two Responses
        • Pathogen - Primary enters first time, Secondary enters second time
        • Speed - Primary is slow, Secondary is fast
        • Cell Activation - Primary B and T lymphocytes, Secondary memory cells
        • Symptoms - Primary yes, Secondary no


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