FreeScienceLessons

• Blood clotting


  Process that prevents or reduces the entry of pathogens when the skin is damaged
• Platelets


  • Tiny short-lived fragments of cells with no nucleus
  • Formed continuously in the bone marrow
  • Released into the bloodstream
• Blood clotting


  1. Platelets exposed to proteins outside the endothelium

  2. Platelets activated

  3. Platelets form a plug over the damaged area

  4. Platelets release clotting factors

  5. Clotting factors convert prothrombin to thrombin

  6. Thrombin converts fibrinogen to insoluble fibrin

  7. Fibrin forms a mesh trapping red blood cells
• Activated platelets


  • Release serotonin
  • Serotonin causes smooth muscle cells to contract
  • Blood vessel narrows, reducing blood flow
• Inflammation


  Body's response to tissue damage
• Inflammation


  1. Tissue damage activates mast cells

  2. Mast cells release histamine

  3. Histamine causes vasodilation

  4. Histamine increases blood vessel permeability

  5. Tissue fluid forms, causing swelling

  6. Mast cells release cytokines

  7. Cytokines attract phagocytes

  8. Cytokines trigger fever
• Inflammation and blood clotting protect the body against pathogens
• T lymphocytes


  Cells involved in cell-mediated immunity
• T lymphocytes are produced in the bone marrow and migrate to the thymus gland to mature
• T Cell receptor


  Attaches to antigens on the surface of cells
• Each unique T lymphocyte has a unique T Cell receptor
• Situations where T lymphocytes can recognize antigens

  • Cell infected with a virus
  • Cell is a mutated cancer cell
  • Transplanted cell or tissue
  • Macrophage engulfs a pathogen
• Antigen presenting cells


  • Cells that display antigens on their surface for T lymphocytes to recognize
• T helper cells


  T lymphocytes that carry out a range of functions
• T helper cell activation

  1. Attaches to antigen presented on cell surface

  2. Undergoes mitosis to produce clones

  3. Produces cytokines (interleukins)

  4. Can activate cytotoxic T cells
• Cytotoxic T cells (T killer cells)


  Identify and destroy abnormal or infected cells
• T memory cells


  Long-lived T cells that can rapidly differentiate into cytotoxic T cells if the same pathogen is encountered again
• T regulator cells


  Down-regulate the immune system once a pathogen has been destroyed, and help prevent autoimmune disorders
• Antibodies


  Play a critical role in the specific immune system, called humoral immunity
• Antibody production


  1. Pathogen enters body

  2. Pathogen engulfed by macrophage

  3. Macrophage digests pathogen and displays antigen

  4. Macrophage interacts with T helper cell

  5. T helper cell activated

  6. Activated T helper cell undergoes mitosis

  7. Activated T helper cell produces interleukins

  8. Interleukins stimulate B lymphocyte

  9. B lymphocyte undergoes mitosis to form plasma cells and memory cells

  10. Plasma cells release antibodies
• T helper cells


  • Formed in bone marrow, mature in thymus
  • Each has unique T cell receptor specific for an individual antigen
  • Activated by binding to antigen on macrophage surface
  • Produce interleukins to stimulate B lymphocytes
• B lymphocytes


  • Formed in bone marrow, mature before release
  • Have membrane-bound antibodies as antigen receptors
  • Each has antibodies that bind to a different antigen
  • Activated by T helper cell, undergo mitosis to form plasma cells and memory cells
• Primary immune response


  Takes days or weeks to develop, pathogen can reproduce causing symptoms
• Secondary immune response


  B memory cells rapidly turn into plasma cells, release high levels of antibodies, can destroy pathogen before symptoms develop
• Antigen


  Molecules on the surface of cells, such as proteins and polysaccharides, that carry out normal cellular functions
• Antibody


  Also called immunoglobulins, produced by B lymphocytes to bind to antigens
• Specific immune system


  • Responds to each pathogen in an individual way
  • Produces a more effective response if it encounters the same pathogen again
  • Can recognize individual pathogens
• Self-antigens


  Antigens on the surface of your body cells that do not trigger an immune response, as the immune system identifies them as normal parts of your body
• Antibody structure


  • Glycoproteins consisting of 4 polypeptide chains: 2 long heavy chains and 2 shorter light chains
  • Held together by disulfide bridges
  • Has 2 antigen binding sites
  • Tertiary structure of antigen binding site is complementary to the antigen
  • Hinge region is flexible
• Constant region


  Same structure for every antibody, no matter which B lymphocyte produced it
• Variable regions


  Different for the antibodies produced by different B lymphocytes, allowing them to bind to different antigens
• The human body contains millions of different B lymphocytes, so there are millions of different antibodies targeting a vast range of antigens
• Functions of antibodies


  • Act as opsonins, tagging foreign bodies for phagocytosis
  • Agglutinate (stick) pathogens together, preventing them from spreading
  • Bind to pathogens like viruses, preventing them from invading host cells
  • Bind to bacterial toxins, preventing them from harming body cells (antitoxins)
• Neutrophils


  Phagocytes that can rapidly engulf and destroy pathogens at the site of an infection
• Macrophages


  Phagocytes that can destroy pathogens by phagocytosis and also have the additional function of antigen presentation
• Phagocytosis


  1. Pathogen tagged by opsonins

  2. Phagocyte attaches to opsonins

  3. Phagocyte engulfs pathogen

  4. Phagosome forms

  5. Lysosome fuses with phagosome

  6. Lysosomal enzymes digest pathogen
• Opsonins


  Molecules that recognize foreign chemicals on pathogens and tag them as foreign
• Cytokines


  Chemicals released by phagocytes that signal to other immune cells to move to the site of infection and can trigger inflammation and fever
• Macrophages function as antigen presenting cells (APCs) by presenting antigens to lymphocytes
• Phagocytes are part of the non-specific immune defenses, while lymphocytes form the specific immune system