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Defenses Against Disease Infection
The presence of a pathogen in or on the body
Pathogen A disease-causing agent
Innate immunity Nonspecific defenses to
protect against pathogens
Nonspecific defenses Species resistance
Mechanical barriers
Chemical barriers
Phagocytosis
Fever
Inflammation
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Defenses Against Disease: Specific Defenses
Immunities Protect against very
specific pathogens Antigens
Foreign substances in the body
Haptens Foreign substances too
small to start an immune response by themselves
Other substances Proteins – antibodies and
complements WBCs – lymphocytes and
macrophages Lymph system
Cytokines – assist in immune response regulation
Monokines – increase B cell production and stimulate WBC production
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Defenses Against Disease (cont.)
Two major types of lymphocytes
B Cells and T Cells
Recognize antigens in the body
T Cells Cell-mediated response Bind to antigens on cells
and attack them directly Secrete lymphokines that increase T cell production and directly kill cells with antigens
T Cells Cell-mediated response Bind to antigens on cells
and attack them directly Secrete lymphokines that increase T cell production and directly kill cells with antigens
B cells Respond to antigens by becoming plasma cells Plasma cells make antibodies Memory B cells produce stronger response with next exposure to antigen
B cells Respond to antigens by becoming plasma cells Plasma cells make antibodies Memory B cells produce stronger response with next exposure to antigen
Response
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Defenses Against Disease (cont.)
T cell activation Begins when macrophage ingests and digests
pathogen with antigen on it Antigens are placed on cell membrane of
macrophage T cell recognizes and binds to antigen and the
major histocompatibility complex (MHC) on the surface of the macrophage
Now can divide to form other types of T cells
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Defenses Against Disease (cont.)
Types Cytotoxic T cells
Protect body against viruses and cancer cells Helper T cells
Increase antibody formation, memory cell formation, B cell formation, and phagocytosis
Memory T cells Remember the pathogen that activated original T cell Later exposures trigger an immune response more
effective than initial response
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Defenses Against Disease (cont.)
Natural killer (NK) cells
Type of lymphocyte
Primarily target cancer cells
Kill on contact
Do not recognize a specific antigen
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Antibodies
Also called immunoglobulins IgA
Prevents pathogens from entering body IgD
Found on B cell membranes Thought to control B cell activity
IgE Found with IgA Involved in triggering allergic reactions
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Antibodies (cont.)
IgG Recognizes bacteria, viruses, and toxins Activates complements
IgM Large and binds to antigens on food, bacteria, or
incompatible blood cells Activates compliments
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Antibodies (cont.)
Actions that occur when antibodies bind to antigens Allow phagocytes to recognize and destroy antigens
Cause antigens to clump together, causing them to be destroyed by macrophages
Cover the toxic portions of antigens, making them harmless
Activate complement Group of proteins in serum that attack pathogens by forming holes
in them
Attract macrophages to pathogens and can stimulate inflammation
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Immune Responses and Acquired Immunity
Primary immune response occurs with first exposure to antigen Slow process Memory cells are formed
Secondary immune response with next exposure to same antigen Quick and carried out by memory cells Usually prevents person from developing disease from
the antigen
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Immune Responses and Acquired Immunity (cont.)
Naturally acquired active immunity Natural exposure to antigen – having an illness Makes antibodies and memory cells Long-lasting
Artificially acquired active immunity Injected with pathogen – immunizations Makes antibodies and memory cells Long-lasting
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Immune Responses and Acquired Immunity (cont.)
Naturally acquired passive immunity Acquired from mother
Breast milk Placenta
Short-lived
Artificially acquired passive immunity Injected with antibodies (such as antivenom) Short-lived
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Major Immune System Disorders Cancer
Uncontrolled growth of abnormal cells form malignant tumors
200 known types Treatment based on stage
0 – very early; cancer cells localizedI – spread to deeper layers or some in surrounding tissuesII – spread to surrounding tissues but contained in primary siteIII – spread beyond primary site into nearby areasIV – spread to other organsRecurrent – reappeared after treatment
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Major Immune System Disorders (cont.)
Allergies Immune response to an allergen
Can be excessive IgE antibodies bind to allergens and stimulate mast cells
to release histamine and heparin Triggers allergic response
Allergy shots Small amounts of allergen stimulates production of IgG to
prevent IgE from binding to antigen IgG antibodies do not stimulate mast cells, so immune response
is not generated
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Signs/symptoms Inhaled allergens – runny nose, sneezing, coughing, wheezing Ingested allergens – nausea, vomiting, diarrhea Skin allergens – rashes Allergens in blood – most life-threatening; can affect many
organs
Treatment Antihistamines, decongestants – OTC or prescription Epinephrine for anaphylaxis – vasoconstriction, increasing BP
Anaphylaxis – life-threatening response
Major Immune System Disorders (cont.)
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Common Immune System Disorders Autoimmune disease
Body attacks its own antigens Examples
Scleroderma Rheumatoid arthritis Multiple sclerosis Glomerulonephritis Chron’s disease Diabetes mellitus, type I
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Common Immune System Disorders (cont.)
Disorder Description AIDS Development of severe signs and symptoms
caused by HIV as it destroys lymphocytes; leaves immune system weakened and susceptible to other diseases
Chronic fatigue syndrome (CFS)
Condition of severe tiredness not relieved by rest and not related to other illnesses
Lymphedema Blockage of lymphatic vessels results in tissue swelling that increases over time
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Common IS Disorders (cont.)
Disorder Description Mononucleosis “Mono”; highly contagious viral infection
spread through saliva of infected person
Systemic lupus erythematous (SLE)
Autoimmune disorder; antibodies produces that target own cells and tissues; affects women more often than men
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In Summary Immune system is the body’s major line of defense
Primary function – protect against infection, toxins, and cancer
Specific or nonspecific defenses Lymphocytes are major cells of immune system
Immune response may be primary or secondary Medical assistant must understand immune system
Aseptic technique Infection control Educate patients