The Lymphatic and Immune System

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    Innate Immunity

    defenses that are present at birth that do not involve specific recognition of a microbe but acts against all microbes in the same way - includes the external physical and chemical barriers provided by the skin and mucous membranes. It also includes various internal defenses, such as antimicrobial substances, natural killer cells, phagocytes, inflammation, and fever.

    Adaptive Immunity

    defenses that involve specific recognition of a microbe and memory to handle the microbe during subsequent exposures. Involves T lymphocytes (T cells) and B lymphocytes (B cells).

    Pathogens

    disease-producing microbes such as bacteria and viruses

    Lymph

    interstitial fluid that has passed into lymphatic vessels.

    Functions of the Lymphatic System

    drain excess interstitial fluid, transport dietary lipids, and carry out immune responses.

    Lacteals

    specialized lymphatic capillaries in the small intestine that carry dietary lipids into lymphatic vessels and ultimately into the blood.

    Thoracic duct

    the largest lymph vessel that forms the main duct for return of lymph to the blood.

    Cisterna chyli

    the large dilated region of the thoracic duct that acts as a reservoir by receiving lymph from the right and left lumbar trunks.

    Subclavian veins

    location where lymph finally drains into the bloodstream.

    Primary lymphatic organs

    locations (bone marrow and thymus) where stem cells divide and become immunocompetent.

    Secondary lymphatic organs

    locations where most immune responses occur.

    Thymus

    bilobed organ located in the mediastinum between the sternum and the aorta - site of T cell maturation.

    Red bone marrow

    site where pluripotent stem cells give rise to mature, immunocompetent B cells and to pre-T cells.

    Lymph nodes

    small, bean-shaped organs present throughout the body, usually clustered in groups - act to filter lymph by trapping foreign substances.

    Spleen

    largest single mass of lymphatic tissue located in the in the left hypochondriac region between the stomach and diaphragm - functions include (1) removal by macrophages of ruptured, worn out, or defective blood cells and platelets; (2) storage of platelets, up to one-third of the body's supply; and (3) production of blood cells (hemopoiesis) during fetal life.

    Lymphatic nodules

    masses of lymphatic tissue that are not surrounded by a capsule - include mucosa-associated lymphatic tissue (MALT), tonsils, Peyer's patches and the appendix.

    Skin and mucous membranes

    first line of defense against pathogens.

    Cilia

    microscopic hairlike projections on the surface of the epithelial cells along the respiratory tract -waving action propels inhaled dust and microbes that have become trapped in mucus toward the throat.

    Lysozyme

    enzyme found in tears, saliva, perspiration and nasal secretions capable of breaking down the cell walls of certain bacteria.

    Sebum

    oily substance with antimicrobial properties that forms a protective film over the surface of the skin.

    Interferons

    proteins released by virus-infected cells that diffuse to uninfected neighboring cells, where they induce synthesis of antiviral proteins that interfere with viral replication.

    Complement

    proteins that enhance certain immune reactions like cytolysis (bursting) of microbes, phagocytosis, and inflammation.

    Neutrophils and Macrophages

    The two major types of phagocytes.

    Inflammation

    a nonspecific, defensive response of the body to tissue damage - sign/symptoms include PRISH: pain, redness, immobility, swelling and heat.

    3 states of Inflammation

    vasodilation and increase permeability of blood vessels, phagocyte emigration, and tissue repair.

    Histamine

    molecule produced by basophils and mast cells that causes vasodilation and increased permeability of blood vessels in the area of inflammation.

    Prostaglandins

    molecules released by damaged cells that intensify inflammation

    Leukotrienes

    molecules that increase permeability; they also function in adherence of phagocytes to pathogens and as chemotactic agents that attract phagocytes.

    Emigration

    process by which cells such as neutrophils squeeze through the wall of the blood vessel to reach the damaged area.

    Fever

    Elevated body temperature that intensifies the effects of interferons, inhibits the growth of some microbes, and speeds up body reactions that aid repair. Many bacterial toxins (such as LPS) elevate body temperature, sometimes by triggering release of fever-causing cytokines such as interleukin-1 from macrophages.

    Antigens

    foreign substances that provoke immune responses.

    Cell-mediated immunity

    type of adaptive immunity where cytotoxic T cells directly attack invading antigens.

    Antibody-mediated immunity

    type of adaptive immunity where B cells transform into plasma cells, which synthesize and secrete specific proteins called antibodies - also referred to as humoral immunity.

    Antigen-presenting cell (APC)

    cells such as macrophages that phagocytose exogenous antigens, digest the antigen into fragments and present those fragments on the surface of their plasma membrane.

    Major histocompatibility complex II (MHC-II)

    proteins used by antigen-presenting cells to present exogenous antigens on the surface of their plasma membrane.

    Major histocompatibility complex I (MHC-I)

    proteins used by infected body cells to present endogenous antigens on the surface of their plasma membrane.

    Cytokines

    group of small protein hormones that stimulate or inhibit many normal cell functions, such as cell growth and differentiation.

    Interleukin-1

    cytokine produced by macrophages; promotes proliferation of helper T cells; acts on hypothalamus to cause fever.

    Interleukin-2

    cytokine secreted by helper T cells; costimulates proliferation of helper T cells, cytotoxic T cells, and B cells; activates NK cells.

    CD4

    protein used by helper T cells to "recognize" the MHC-II on the surface of APCs.

    CD8

    protein used by cytotoxic T cells to "recognize" the MHC-I on the surface of infected body cells.

    T-cell receptor (TCR)

    protein on T cells that recognize and bind to specific foreign antigen fragments that are presented in antigen-MHC complexes.

    Memory cytotoxic T cell

    T cells that do not attack infected body cells. Instead, they can quickly proliferate and differentiate into more active cytotoxic T cells and more memory cytotoxic T cells if the same antigen enters the body at a future time.

    Cytotoxic T cell

    cells that release granzymes that trigger apoptosis and perforin that triggers cytolysis of infected target cells.

    Helper T cell

    cells that release interleukin-2 which stimulates proliferation of T cells and B cells.

    Plasma cell

    cells that secrete antibodies.

    Memory B cell

    cells that can quickly proliferate and differentiate into more plasma cells and more memory B cells should the same antigen reappear at a future time.

    Opsonization

    process by which antibodies and the C3b protein of the complement system enhances phagocytosis by promoting attachment of a phagocyte to a microbe.

    IgG

    most abundant class of immunoglobulin that protects against bacteria and viruses by enhancing phagocytosis, neutralizing toxins, and triggering complement system. Is the only class of antibody to cross placenta from mother to fetus, conferring considerable immune protection in newborns.

    IgA

    class of immunoglobulin found mainly in sweat, tears, saliva, mucus, breast milk, and gastrointestinal secretions. Levels decrease during stress, lowering resistance to infection.

    IgM

    first antibody class to be secreted by plasma cells after initial exposure to any antigen. Anti-A and anti-B antibodies of ABO blood group are this class of immunoglobulin.

    IgD

    class of immunoglobulin mainly found on surfaces of B cells as antigen receptors.

    IgE

    class of immunoglobulin located on mast cells and basophils. Involved in allergic and hypersensitivity reactions; provides protection against parasitic worms.

    Naturally acquired active immunity

    type of immunity following exposure to a microbe, antigen recognition by B cells and T cells and costimulation lead to formation of antibody-secreting plasma cells, cytotoxic T cells, and B and T memory cells.

    Naturally acquired passive immunity

    type of immunity when IgG antibodies are transferred from mother to fetus across placenta, or IgA antibodies are transferred from mother to baby in milk during breast-feeding.

    Artificially acquired active immunity

    type of immunity when antigens introduced during vaccination stimulate cell-mediated and antibody-mediated immune responses, leading to production of memory cells. Antigens are pretreated to be immunogenic but not pathogenic (they will trigger an immune response but not cause significant illness).

    Artificially acquired passive immunity

    type of immunity following Intravenous injection of immunoglobulins (antibodies).

    Self-recognition

    lymphocytes ability to recognize your own major histocompatibility complex (MHC) proteins.

    Immunological tolerance

    lymphocytes lack of reactivity to peptide fragments from your own proteins.