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immunity
type of resistance that involves activation of specific lymphocytes that combat a foreign substance
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resistance
the ability to ward off the pathogens that produce disease
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susceptibility
lack of resistance
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DEF'N: lymphatic system
body system that carries out immune responses
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non-specific (innate) immunity
general defense mechanisms effective on a wide range of pathogens
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specific (adaptive) immunity
ability to fight a specific pathogen
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2 types of specific immunity
- 1) cell-mediated immunity
- 2) antibody-mediated immunity
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lymph
fluid flowing within lymphatic vessels
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Where are lymphocytes produced?
bone marrow
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3 functions of the lymphatic system
- 1) draining excess interstitial fluid/plasma proteins from tissue spaces
- 2) transporting dietary lipids/vitamins from GI tract to blood
- 3) facilitating immune responses (recognize foreign substances)
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4 primary lymphatic organs
- 1) red bone marrow
- 2) thymus
- 3) spleen
- 4) lymph nodes
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3 secondary lymphatic organs
- 1) tonsils
- 2) adenoids
- 3) MALT
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how lymphatic vessels differ from blood vessels
- 1) larger in diameter
- 2) one-way structure (interstitial fluid can flow in, but not out)
- 3) overlapping endothelial cells
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lacteals
- lymphatic capillary in the villus of the small intestine;
- functions to transport fats from small intestine into blood
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2 major lymphatic ducts
- 1) thoracic duct
- 2) right lymphatic duct
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3 parts of the body the thoracic duct drains
- 1) left side of the head, neck, and chest
- 2) left upper extremity
- 3) entire body below ribs
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parts of the body the right lymphatic duct drains
upper right side of the body
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Where is the thymus gland located?
mediastinum
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2 types of cells found in the thymic cortex
- 1) T lymphocytes
- 2) macrophages
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2 types of cells found in the thymic medulla
- 1) reticular epithelial cells (produce thymic hormones)
- 2) Hassall's corpuscles (T cell death site)
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Hassall's corpuscles
clusters of concentric layers of epithelial cells in the thymic medulla that are the possible site of T cell death
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Major function of thymus
location of T cell maturation
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Difference in size and function of a thymus in a newborn vs. an adult
- larger in infants (70g vs. 3g)
- before atrophy, populates secondary lymphatic organs/tissues with T cells
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lymph node structure
- bean shaped
- dense connective tissue capsule extends into node
- supporting network of reticular fibers & fibroblasts internal to capsule
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function of lymph nodes
- filters lymph
- foreign substances trapped by reticular fibers
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parenchyma of lymph node
functioning part of lymph node
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What is found in the white pulp?
lymphatic tissue (lymphocytes, macrophages) around branches of splenic artery
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What is found in the red pulp?
venous sinuses filled with blood and splenic cords (RBCs, macrophages, lymphocytes, plasma cells, granulocytes)
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2 components of splenic parenchyma
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What role does the spleen play in pregnancy?
red pulp is involved in the production of blood cells during this time
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trabeculae
capsular extensions that divide the lymph nodes into compartments, and provide support and a route for blood vessels into the interior of a node
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Where is MALT found?
throughout connective tissue of mucous membranes (no capsule)
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Where are the tonsils?
ring at top of throat
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Where is the appendix?
cecum
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metastasis
spread of disease from one part of the body to another
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How does a tumor metastasize?
cancer cells travel via blood/lymphatic system and establish new tumors where they lodge
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methods of mechanical innate immunity
- 1) skin closely packed
- 2) mucous membranes trap/move microbes
- 3) washing action of tears, urine, saliva
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methods of chemical innate immunity
- 1) sebum inhibits growth
- 2) perspiration lysozymes
- 3) acidic pH of gastric juice, vaginal secretions
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3 antimicrobial proteins
- 1) interferons
- 2) complement
- 3) defensins
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IFNs
- interferons;
- induce synthesis of antiviral proteins that interfere with viral replication
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complement
- enhance certain immune reactions
- cause cytolysis of microbes, promotes phagocytosis, and contributes to inflammation
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natural killer cells
- kill microbes and tumor cells
- attack cells displaying abnormal MHC antigens
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2 phagocytic cells
- 1) neutrophils
- 2) macrophages
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5 phases of phagocytosis
- 1) chemotaxis
- 2) adherence
- 3) ingestion
- 4) digestion
- 5) killing
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4 methods of evasion of phagocytes by microbes
- 1) capsule formation
- 2) toxin production
- 3) interference with lysozyme secretion
- 4) ability to counter oxidants produced by phagocytes
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2 functions of inflammation
- 1) trap foreign material
- 2) begin tissue repair
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5 clinical signs of inflammation
- 1) redness
- 2) heat
- 3) swelling
- 4) pain
- (5) loss of function
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3 stages of inflammation
- 1) vasodilation/increased permeability of blood vessels
- 2) phagocyte migration
- 3) tissue repair
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abscess
accumulation of pus in a confined space
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fever
- abnormally high T that occurs because the hypothalamic thermostat is reset
- intensifies effects of interferons, inhibits bacterial growth, speeds up tissue repair
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cytokine that is major inducer of fever
IL-1 (interleukin 1)
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specificity
recognition of self & non-self
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memory
2nd encounter produces more vigorous response
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antigen
substances recognized as foreign by the immune responses
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Where are pre-T cells formed?
stem cells in bone marrow
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Where do T cells mature?
thymus
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types of invaders are T cells most able to combat
- fungi
- viruses
- parasites
- cancer
- tissue transplants
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Where do B cells develop?
bone marrow
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type of invader B cells are most able to combat
bacteria
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epitope
small part of the antigen that triggers an immune response
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hapten
- smaller than antigen
- can't trigger immune response unless attached to body protein
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2 major characteristics of antigens
- 1) immunogenicity (ability to provoke immune response)
- 2) reactivity (ability to react to cells/Ab's it caused to be formed)
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Why can the immune system recognize and respond to so many different epitopes?
cells have a great diversity of receptors due to genetic recombination
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MHC antigen
- major histocompatibility complex
- molecules that are unique surface markers on all nucleated cells
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MHC-I molecules
built into cell membrane of all cells except RBCs
endogenous antigen by an infected body cell
viruses
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MHC-II molecules
only on membrane of APCs (macrophages, B cells, thymus cells)
exogenous antigen by an APC
microbes
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function of MHC antigens
help a T cell recognize whether something is foreign
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histocompatibility testing
tests similarity of MHC antigens on body cells of different individuals
for tissue typing and IDing biological parents
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3 cells types of APCs
- 1) macrophages
- 2) B cells
- 3) dendritic cells
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cytokine
small local mediator proteins involved in immune response
mostly secreted by lymphocytes and APCs
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interleukin
costimulates proliferation of T and B cells
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interferon
activates macrophages, NK cells
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IL-2
cytokine most important in costimulation of proliferation of helper T cells, cytotoxic T cells, and B cells
activates NK cells
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-interferon
strongly stimulates phagocytosis by neutrophils and macrophages
activates NK cells
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lymphocyte important in cell-mediated immunity
T cell
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cytotoxic T cell
- from CD8+ T cells
- recognize foreign antigens combined with MHC-I molecules on surface of infected body cells, some tumor cells, cells of tissue transplant
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helper T cell
- from CD4+ T cells
- recognize exogenous antigens associated with MHC-II molecules on the surface of APCs
- costimulates lymphocytes (secretes IL-2)
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memory T cell
- don't attack infected body cells
- can quickly proliferate/differentiate into active T cells and more memory T cells if the same ag enters in the future
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3 steps in activation, proliferation, differentiation of CD8 (cytotoxic) T cells
- 1) receptor binds to foreign part of MHC-I complex (on infected cell)
- 2) costimulation by IL-2 from helper T cell results in proliferation of CD8 cells
- 3) CD8 T cells proliferate/differentiate into Tc cells and memory Tc cells
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3 steps in activation, proliferation, differentiation of CD4 (helper) T cells
- 1) inactive helper T cell receptor binds to foreign part of MHC-II (on APC) & becomes activated
- 2) activated cells produce IL-2 (costimulator)
- 3) Th cell proliferates/differentiates into Th cells and memory Th cells
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3 methods of cytotoxic (CD8+) T cell attack
- 1) secretion of granules containing perforin and granulysin
- 2) secretion of lymphotoxin that activates enzymes in the target cell resulting in DNA fragmentation
- 3) secretion of (gamma)interferon stimulates macrophages to phagocytose
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immunological surveillance
immune system finds, recognizes, & destroys cells with tumor antigens
not effective in destroying types of tumors caused by viruses
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lymphocyte responsible for antibody-mediated immunity
B cells
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Where in the lymphatic system does antigen come in contact with B cells?
in lymph nodes, spleen, Peyer's patches
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plasma cells
B cells after they have differentiated into antibody-secreting cells
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steps in activation, proliferation, differentiation of B cells
- 1) antigen on microbe binds to B cell receptors
- 2) antigen is taken into B cell, broken down, and moved to cell membrane
- 3) helper T cells recognize Ag-MHC-II complex & secretes IL-2 to costimulate B cell
- 4) B cell proliferates/differentiates into plasma cells and memory B cells
- 5) plasma cells enter circulation
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IgG antibody structure
- 4 polypeptide chains
- -heavy and light chains
- -variable (tips of H&L) and constant portions
- monomer
- Y shaped
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5 different classes of antibodies
IgG, IgA, IgM, IgD, IgE
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IgG function
protects against viruses and bacteria
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IgA function
localized protection of mucous membranes against viruses/bacteria
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IgM function
- activates complement
- causes agglutination and lysis of microbes
- antigen receptors on B cells
ABO antibodies
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IgD function
activation of B cells
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IgE function
- allergic/hypersensitivity reactions
- protection against parasitic worms
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monoclonal antibody
clone of plasma cells that recognize just 1 epitope
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How are monoclonal antibodies produced?
fusing B cells with tumor cells (hybridoma) and culturing them
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4 types of hypersensitivity
- I) anaphylaxis
- II) cytotoxic
- III) immune complex
- IV) cell-mediated
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Type I hypersensitivity
- anaphylaxis
- most common
- interaction of allergens with IgE Abs of mast cells&basophils
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Type II hypersensitivity
- cytotoxic
- reactions by IgG or IgM against blood/tissue cells
- results in complement activation
- incompatible blood
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Type III hypersensitivity
- immune complex
- involve antigens, IgA or IgM, and complement
- most autoimmune diseases
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Type IV hypersensitivity
- cell mediated/delayed hypersensitivity
- allergens are taken up by APCs that migrate to lymph and present allergen to T cells
- intracellular bacteria, some allergens (poison ivy)
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