The Immunological System

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The Immunological System
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Objectives

• List and describe the major functions of the
  lymphatic and immunological system
• Describe the structure of a lymph node
• Describe the types of formed elements of the
  blood which are involved with an immune response
• Compare and contrast a cell mediated and humoral
  immune response
• Define, describe compare and contrast the various
  types of immunity (passive, active, acquired,
  artificial)
• List and describe various disorders and diseases
  of the immunological system

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Lymphatic System

• Consists of two semi-independent parts
• Lymphatic vessels
• Lymphoid tissues and organs
• Lymphatic system functions
• Transport fluids back to the blood
• Play essential roles in body defense and
  resistance to disease
• Lymph excess tissue fluid produced when plasma
  fluid leaves the capillaries and enters the
  surrounding tissues carrying materials the
  tissues need it then enters lymphatic vessels, is
  filtered and re-enters the blood stream.
• Harmful materials that enter lymph vessels
• Bacteria
• Viruses
• Cancer cells
• Cell debris
• Materials returned to the blood
• Water
• Blood cells
• Proteins
• Properties of lymphatic vessels
• One way system toward the heart
• No pump

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Lymphatic System Lymph Nodes

• Filter lymph before it is returned to the blood
• Defense cells within lymph nodes
• Macrophages engulf and destroy foreign
  substances
• Lymphocytes provide immune response to antigens
  
• Most are kidney-shaped, less than 1 inch long
• Cortex
• Outer part
• Contains follicles collections of lymphocytes
  (B and T cells)
• Medulla
• Inner part
• Contains phagocytic macrophages

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Lymphatic System Lymph Node Structure
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Major Lymphatic Organs
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Lymphatic Organs Spleen

• Spleen
• Located on the left side of the abdomen
• Filters blood
• Destroys worn out blood cells
• Forms blood cells in the fetus
• Acts as a blood reservoir

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Lymphatic Organs Thymus Gland

• Thymus
• Located low in the throat, overlying the heart
• Functions at peak levels only during childhood
• Produces hormones (like thymosin) to program
  lymphocytes

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Lymphatic Organs Tonsils

• Tonsils
• Small masses of lymphoid tissue around the
  pharynx
• Trap and remove bacteria and other foreign
  materials
• Tonsillitis is caused by congestion with bacteria

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Lymphatic Organs Peyers Patches

• Peyers Patches
• Found in the wall of the small intestine
• Resemble tonsils in structure
• Capture and destroy bacteria in the intestine

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(MALT) Mucosal Associated Lymphatic Tissues

• Mucosal tissues are epithelial tissues which
  produce mucus and are moist associated with the
  digestive tract and the upper respiratory tract.
• Includes
• Peyers patches
• Tonsils
• Other small accumulations of lymphoid tissue
• Acts as a sentinal to protect respiratory and
  digestive tracts

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Immunological System

• Pathogen any disease causing agent which
  interferes with the normal homeostatic state of
  the body. Viruses, bacteria, fungi, and animal
  parasitic organisms all are pathogens. An
  antigen is a foreign molecule, usually protein,
  which stimulates an immune response by the body.

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Immunological System

• The body is constantly in contact with bacteria,
  fungi, and viruses
• The body has two defense systems for foreign
  materials
• Nonspecific defense system
• Mechanisms protect against a variety of invaders
• Responds immediately to protect body from foreign
  materials
• Specific defense system
• Specific defense is required for each type of
  invader
• Also known as the immune system

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Nonspecific Body Defenses

• Body surface coverings
• Intact skin
• Mucous membranes
• Specialized human cells
• Chemicals produced by the body
• These are the bodys primary means of warding off
  pathogenic invaders.

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First Line Defense Skin and External Surface
Membranes

• The skin
• Physical barrier to foreign materials
• pH of the skin is acidic to inhibit bacterial
  growth
• Sebum is toxic to bacteria
• Vaginal secretions are very acidic
• Stomach mucosa
• Secretes hydrochloric acid kills bacteria
• Has protein-digesting enzymes
• Saliva and lacrimal fluid (tears) contain
  lysozyme
• Mucus traps microogranisms in digestive and
  respiratory pathways

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First Line of Defense Non-specific Cells

• Phagocytes (neutrophils and macrophages)
• Engulfs foreign material into a vacuole
• Enzymes from lysosomes digest the material
• Natural killer cells
• Can lyse (rupture) and kill cancer cells
• Can destroy virus- infected cells

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Secondary Line of Defense Inflammatory Response

• Triggered when body tissues are injured in the
  affected area or tissues
• Carried out in part by leukocytes ( basophils,
  mast cells, neutrophils, monocytes, and
  lymphocytes)
• Produces four cardinal signs
• Redness
• Heat
• Swelling
• Pain
• Results in a chain of events leading to
  protection and healing
• Prevents spread of damaging agents
• Disposes of cell debris and pathogens
• Sets the stage for repair

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Inflammatory Response
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Chemical Anti-microbial Agents

• Complement
• A group of at least 20 plasma proteins
• Activated when they encounter and attach to cells
  (complement fixation)
• Damage foreign cell surfaces
• Has vasodilators, chemotaxis, and opsonization
  (marks pathogen for phagocytosis by monocytes and
  macrophages)
• Interferon
• Secreted proteins of virus-infected cells
• Bind to healthy cell surfaces to inhibit viruses
  binding

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What is Fever?

• Abnormally high body temperature
• Hypothalmus heat regulation can be reset by
  pyrogens (secreted by white blood cells)
• High temperatures inhibit the release of iron and
  zinc from liver and spleen needed by bacteria for
  growth
• Denatures enzymes produced by bacteria that are
  necessary for their growth
• Fever also increases the speed of tissue repair

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Third Line DefenseThe Specific Immune Response

• Antigen specific recognizes and acts against
  particular foreign substances
• Systemic not restricted to the initial
  infection site
• Has memory recognizes and mounts a stronger
  attack on previously encountered pathogens

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Specific Immunity Two Forms

• Humoral immunity
• Antibody-mediated immunity
• Cells produce chemicals for defense (antibodies)
• Primary cells are B-lymphocytes
• Cellular immunity
• Cell-mediated immunity
• Cells target virus infected cells
• Primary cells are T-lymphocytes

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Cells of the Immune System

• Lymphocytes
• Originate from hemocytoblasts in the red bone
  marrow
• B lymphocytes become immunocompetent in the bone
  marrow
• T lymphocytes become immunocompetent in the
  thymus
• Macrophages
• Arise from monocytes
• Become widely distributed in lymphoid organs

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Lymphocyte Development
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Humoral Response

• B lymphocytes with specific receptors bind to a
  specific antigen which is on the surface of a
  macrophage which has phagocytized the pathogen,
  destroyed it, and placed some of the part of the
  pathogen on it surface. This can also be carried
  of by T-helper cells. (Presentation)
• The binding event activates the lymphocyte to
  undergo clonal selection
• A large number of clones are produced (primary
  humoral response)
• Most B cells become plasma cells
• Produce antibodies to destroy antigens
• Activity lasts for four or five days
• Some B cells become long-lived memory cells
  (secondary humoral response) and provide long
  term immunity against the pathogen

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Humoral Response
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Humoral Response Antibodies

• Soluble proteins secreted by B cells (plasma
  cells)
• Carried in blood plasma
• Capable of binding specifically to an antigen
• Antibodies of each class have slightly different
  roles
• Five major immunoglobulin classes
• IgM can fix complement
• IgA found mainly in mucus
• IgD important in activation of B cell
• IgG can cross the placental barrier
• IgE involved in allergies
• Antibodies inactivate antigens in a number of
  ways
• Complement fixation
• Neutralization
• Agglutination
• Precipitation

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Humoral Response Antibody Action
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Cell Mediated Response

• Antigens must be presented by macrophages to an
  immunocompetent T cell (antigen presentation)
• T cells must recognize nonself and self (double
  recognition)
• After antigen binding, clones form as with B
  cells, but different classes of cells are
  produced
• Cytotoxic T cells
• Specialize in killing infected cells
• Insert a toxic chemical (perforin)
• Helper T cells
• Recruit other cells to fight the invaders
• Interact directly with B cells
• Suppressor T cells
• Release chemicals to suppress the activity of T
  and B cells
• Stop the immune response to prevent uncontrolled
  activity
• A few members of each clone are memory cells

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Cell Mediated Response
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Specific Immune Response
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Immunity Against Pathogens

• Acquired Immunity is how your body protects
  itself against pathogens.
• Active immunity (natural or artificial) is long
  lived because you undergo an immune response and
  produce B and T memory cells.
• Passive immunity (natural or artificial) is
  short lived because you receive antibodies from
  another source and do not produce them yourself,
  therefore there are no memory cells.

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Comparison of a Primary and Secondary Immune
Response

• Memory cells are long-lived
• A second exposure causes a rapid response
• The secondary response is stronger and longer
  lasting

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Diseases and Disorders of the Immune System
Allergies

• Many small molecules (called haptens or
  incomplete antigens) are not antigenic, but link
  up with our own proteins. Pollen, pet dander,
  mold spores, dust mite feces, and certain types
  of foods can form hapten-protein complexes.
• The immune system may recognize and respond to a
  protein-hapten combination
• The immune response is harmful rather than
  protective because it attacks our own cells
• Abnormal, vigorous immune responses
• Types of allergies
• Immediate hypersensitivity (Most serious)
• Triggered by release of histamine from IgE
  binding to mast cells
• Reactions begin within seconds of contact with
  allergen
• Anaphylactic shock dangerous, systemic response
• Delayed hypersensitivity
• Triggered by the release of lymphokines from
  activated helper T cells
• Symptoms usually appear 13 days after contact
  with antigen

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Diseases and Disorders of the Immunological
System Allergic Response
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Diseases and Disorders of the Immunological
System Auto Immune Diseases

• The immune system does not distinguish between
  self and nonself
• The body produces antibodies and sensitized T
  lymphocytes that attack its own tissues
• Multiple sclerosis white matter of brain and
  spinal cord are destroyed
• Myasthenia gravis impairs communication between
  nerves and skeletal muscles
• Juvenile diabetes destroys pancreatic beta
  cells that produce insulin
• Rheumatoid arthritis destroys joints
• Systemic lupus erythematosus (SLE) affects
  kidney, heart, lung and skin
• Glomerulonephritis impairment of renal function

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Diseases and Disorders of the Immunological
System Self Tolerance Breakdown

• Appearance of self-proteins in the circulation
  that have not been exposed to the immune system
  bodys immune system becomes sensitized to these
  proteins and responds
• Eggs
• Sperm
• Eye lens
• Cross-reaction of antibodies produced against
  foreign antigens with self-antigens
• Rheumatic fever antibodies that destroy
  Streptococci pyogenes bacteria also attach to
  and destroy the valve tissues of the heart.

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Diseases and Disorders of the Immunological
System Immunodeficiency

• Production or function of immune cells or
  complement is abnormal
• May be congenital or acquired
• Includes AIDS Acquired Immune Deficiency
  Syndrome

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Diseases and Disorders of the Immunological
System HIV and AIDS

• HIV (Human Immunodeficiency Virus) is a
  retro-virus which is transmitted through
  contaminated body fluids. It infects ,
  replicates within, and destroys the T- helper
  cells of the immune system. The virus originated
  in Africa and has become a pandemic infecting
  people all over the world. It can be transmitted
  by sexual intercourse, sharing of needles by IV
  drug users, blood transfusions or use of blood
  products, through pregnancy or nursing by a
  mother which is infected to her child.

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Diseases and Disorders of the Immunological
System HIV and AIDS

• Acquired Immune Deficiency Syndrome (AIDS) is the
  result of HIV infection. Since the bodys immune
  system is compromised, pathogenic and
  opportunistic organisms now infect the body and
  grow rampantly. Not only pathogenic organisms
  but certain types of cancer kept in check by the
  immune system, now commonly appear. It is the
  opportunistic infections which cause the death of
  individuals suffering from AIDS.

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Immunological System HIV and AIDS