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Chapter 22 - Lymphatic System and Immunity


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Lymphatic system
body system that includes lymph, lymphatic vessels, lymphatic tissue,lymphatic nodules, lymph nodes, tonsils, the spleen, and the thymus
List three functions of the lymphatic system
1) fluid balance
2) fat absorption
3) defense
excess fluid passed from the bloodstream into bodily tissues accumulates and drains into lymphatic capillaries where it passes back into the circulatory system, this fluid is called lymph;
contains water, substances normally found in plasma, and substances derived from cells (hormones, enzymes, and waste)
special lymphatic vessels that are located in the lining of the small intestine;
fats enter these vessels and pass through lymphatic vessels to the venous circulation
lymph passing through lacteals;
has a milky appearance due to its fat content
Lymphatic capillaries
small dead-end tubes into which extra fluids from the body tissues enter into and becomes lymph;
differ from blood capillaries in that they lack a basement membrane and that cells of the simple squamous epithelium ovelap and are loosely connected
Lymphatic vessels
formed by the merging of lymphatic capillaries;
resemble small veins;
consists of three layers and contains one-way valves that keep lymph flowing in a single direciton
What are three factors that are responsible for the movement of lymph through lymphatic vessels?
1) contraction of surrounding skeletal muscles during activity
2) periodic contraction of the smooth muscles in the lymphatic vessel walls
3) pressure changes in the thorax during respiration
Lymph nodes
small, round structures located along the course of the lymphatic vessels;
filter lymph;
sight of lymphocyte congregation, function, and proliferation
Lymphatic trunks
lymphatic vessels converge to form lymphatic trunks, which drain major portions of the body;
juglar, subclavian, bronchomediastinal, intestinal, lumbar trunks
Lymphatic ducts
larger vessels which connect lymphatic trunks to large veins
Right lymphatic duct
drains the right side of the head, right-upper limb, and right thorax
Thoracic duct
drains the right side of the body inferior to the thorax and the entire left side of the body
Lymphatic tissue
tissue that consists of primarily lymphocytes, but also includes macrophages, dendritic cells, reticular cells, and other cell types
a type of white blood cell that originates from red bone marrow and carried by blood to lymphatic organs and other tissues;
divide in response to microorganisms and foreign pathogens
Reticular fibers
very fine collagen fibers contained within lymphatic tissue;
produced by reticular cells;
lmphocytes and other cells attach to these fibers and forms a network that traps microorganisms and other particles in the lymph
Mucosa-associated lymphoid tissue (MALT)
aggregates of nonencapsulated (no connective tissue layering) lymphatic tissue found in and beneath the mucous membranes lining the digestive, respiratory, urinary, and reproductive tracts
Diffuse lymphatic tissue
contains dispersed lymphocytes, macrophages, and other cells;
has no clear boundary and blends with surrounding tissues;
located deep to mucous membranes, around lymphatic nodules and within lymph nodes and spleen
Lymphatic nodules
denser arrangements of lymphoid tissue organized into compact, somewhat spherical structures;
numerous in loose connective tissue of the digestive, respiratory, urinary, and reproductive systems
Peyer's patches
aggregations of lymphatic nodules found in the distal half of the small intestine and the appendix
large groups of lymphatic nodules and diffuse lymphatic tissue located deep to the mucous membranes with the pharynx;
provide protection against bacteria and other potentially harmful material entering the pharynx from the nasal or oral cavities;
decrease in size in adults
Germinal centers
areas of rapid lymphocyte division found in lymph nodes and especially in the lymphatic nodules of the cortex
Afferent lymphatic vessels
vessels that carry lymph to the lymph nodes
Efferent lymphatic vessels
vessels that carry lymph away from the nodes
a lymphatic organ that is roughly the size of a clenched fist and is located on the left side in the extreme, superior part of the abdominal cavity;
destroys defective red blood cells, detects and responds to foreign substances in the blood, and acts as a blood reservoir
White pulp
lymphatic tissue surrounding the arteries within the spleen
Red pulp
lymphatic tissue associated with the veins in the spleen;
consists of a fibrous network, filled with macrophages and red blood cells, and enlarged capillaries that connect to the veins
Periarterial lymphatic sheath
diffuse lymphatic tissue surrounding arteries and arterioles extending to lymphatic nodules
Splenic cords
a network of reticular cells within the spleen which produce reticular fibers
Venous sinuses
enlarged capillaries between the splenic cords
a bilobed gland located in the superior mediastinum;
thought to increase in size until the first year of life;
site of maturation of T lymphocytes
the ability to resist damage from foreign substances such as microorganisms and harmful chemicals;
categorizes as either innate immunity and adaptive immunity
Innate (non-specific) immunity
immune response in which the body recognizes and destroys certain foreign substances, but the responses to them is the same each time the body is exposed to them
Adaptive (specific) immunity
immune response in which the body recognizes and destroys foreign substances, but the response to them improves each time the foreign substance is encountered
the ability of adaptive immunity to recognize a particular substance
the ability of adaptive immunity to "remember" previous encounters with a particular substance, resulting in a faster, stronger, and longer lasting response
Mechanical mechanisms
barriers that form the first line of defense against pathogens;
skin, mucous membranes;
either form barrier to prevent entry into body, or secrete chemicals that impede organisms from getting in
Chemical mediators
molecules responsible for many aspects of innate immunity;
found on the surface of cells, in chemicals secreted by cells, etc.; lysozyme, sebum, mucus, histamine, complement
a group of about 20 proteins that make up approximately 10% of the globulin part of serum;
include proetins named C1-C9 and factors B, D, and P;
aid in innate immune response
Complement cascade
a series of reactions in which each component of the series activates the next component;
complement normally circulates in the bloodstream inactivated
Alternative pathway
part of innate immunity and is initiated when complement protein C3 becomes spontaneously active;
activated C3 can combine with some foreign substances, become stabilized, and activate the complement cascade
Classical pathway
part of the adaptive immune system;
initiated by the constant region of antibodies;
stimulates inflammation; attracts neutrophils, monocytes, macrophages, and eosinophils to sites of infection; and kills bacteria by lysis
Membrane attack complex (MAC)
can be formed by activated complement proteins;
produces a channel through the plasma membrane of pathogen cell, causing the cell to lyse
proteins that protect the body against viral infection and perhaps some forms of cancer
Chemotactic factors
parts of microbes or chemicals released by tissue cells that act as chemical signals to attract white blood cells;
i.e., complement, leukotrienes, kinins, histamine
the ability of some cells to detect and move from areas of low chemical concentration to areas of higher chemical conc.;
move toward the source of a chemotactic factor
the endocytosis and destruction of particles by cells
small phagocytic cells produced in large numbers in red bone marrow that are released into the blood;
usually the first cells to enter infected tissues in large number and often die after a single phagocytic event;
release lysosomal enzymes that kill microorganisms and cause tissue damage and inflammation
an accumulation of dead neutrophils, dead microorganisms, debris from dead tissue, and fluid
large phagocytic cells that are called monocytes when found in blood;
outlive neutrophils and ingest more and larger particles;
accumulate in tissues after neutrophils and are responsible for most phagocytic activity late in an infection;
produce interferons, prostaglandins, and complement
motile white blood cells that are derived from red bone marrow and can leave the blood and enter infected tissues;
can be activated through specific or non-specific immunity;
release inflammatory chemicals, histamine, leukotrienes
Mast cells
nonmotile cells in connective tissue, located at potential points of entry of microorganisms into the body;
can be activated through specific or non-specific immunity;
release inflammatory chemicals, histamine, leukotrienes
white blood cells produced in red bone marrow, leave bloodstream within a few minutes;
releases enzymes that break down chemicals released by basophils and mast cells;
contain and reduce the inflammatory response
Natural killer (NK) cells
a type of lymphocyte produced in red bone marrow, account for 15% of lymphocytes;
recognize general classes of cells and release chemicals that cause the cells to lyse
Inflammatory resposne
a complex sequence of events involving many of the chemical mediators and cells of innate immunity;
caused by tissue injury
Local inflammation
an inflammatory response confined to a specific area of the body;
symptoms include redness, heat, swelling, pain, and loss of function
Systemic inflammation
an inflammatory response that occurs in many parts of the body;
symptoms include redness, heat, swelling, pain, and loss of function, as well as the release of large numbers of neutrophils by red bone marrow, the release of pyrogens that stimulate fever production, and in severe cases, vaso-permeability increases dramatically
chemicals released by microorganisms, macrophages, neutrophils, and other cells, that stimulate fever production
substances that stimulate adaptive or specific immunity;
usually large molecules
small molecules capable of combining with larger molecules like blood proteins to stimulate an adaptive immune system response
Foreign antigens
antigens that are not produced by one's one body, but are introduced from outside of it
Allergic reaction
an overreaction of the immune system that can be stimulated by pollen, animal dander, foods, drugs, etc.
molecules produced by the body that stimulate an adaptive immune system response;
can be beneficial or harmful
Autoimmune disease
a condition that can result when self-antigens stimulate unwanted tissue destruction
Humoral immunity (antibody-mediated immunity)
immunity due to antibodies in serum;
effective against extracellular antigens such as bacteria, viruses, protozoans, fungi, parasites, and toxins when they are outside cells
Cell-mediated immunity
immunity due to the actions of T cells and null cells
B cells
lymphocytes that give rise to cells that produce antibodies
T cells
lymphocytes that are responsible for cell-mediated immunity
Effector T cells
T cells that are responsible for producing the effects of cell-mediated immunity;
i.e., cytotoxic T cells and delayed hypersensitivity T cells
Regulatory T cells
T cells that promote or inhibit the activites of both antibody-medaited immunity and cell-mediated immunity
i.e., helper T cells, suppressor T cells
Positive selection
a process that results in the survival of pre-B and pre-T cells that are capable of an immune response
Negative selection
a process that eliminates or suppresses clones acting against self-antigens, thereby preventing the destruction of self-cells;
occurs mostly during prenatal development, but continues throughout life
Primary lymphatic organs
the sites where lymphocytes mature into functional cells;
red bone marrow and thymus
Secondary lymphatic tissues
the sites where lymphocytes interact with each other, antigen-presenting cells, and antigens to produce an immune response;
diffuse lymphatic tissue, lymphatic nodules, tonsils, lymph nodes, spleen
Antigenic determinants (Epitopes)
specific regions of a given antigen recognized by a lymphocyte;
each antigen has many different antigenic determinants
Antigen receptors
surface proteins found on lymphocyte clones that combines with antigenic determinant;
specific to each antigen;
result is similar to the lock-and-key model for enzymes
T-cell receptor
consists of two polypeptide chains, which are subdivided into a variable and a constant region;
variable region can bind to an antigen, different T cells have receptors with different variable regions
B-cell receptor
consists of four polypeptide chains with two identical variable regions, a type of antibody
Major histocompatibility complex (MHC) molecules
glycoproteins located on the surface of cells that are responsible for most lymphocyte activation;
attached to plamsa membranes and have a variable region that can attach to foreign and self-antigens
MHC class I molecules
MHC molecules found on nucleated cells and function to display antigens produced inside the cells on their surfaces;
allow a way for the immune system to respond to problems within a cell, such as viruses;
viral proteins attach to these molecules and they migrate to cell surface form MHC class I/antigen complex, activating T cells;
stimulates destruction of the cell
a process that requires both the antigen, and the organism's own MHC to be functional
MHC class II molecules
found on antigen-presenting cells;
vesicles containing MHC class II molecule combine with endocytotic vesicles containing antigen, forming a complex which is transported to the cell's surface;
can bind to T-cell receptors on the surface of T-cells;
does not stimulate the destruction of the cell, but rather stimulates an immune resposne against the antigen
Antigen-presenting cells
include macrophages, B cells, monocytes, and dendritic cells;
can take in foreign antigens by endocytosis
Dendritic cells
large, motile cells with long cytoplasmic extensions;
scattered throughout most tissues with their highest conc. in lymphatic tissue and skin (Langerhans' cells)
additional stimulus that is often needed to cause an immune response, in addition to MHC class II/antigen complexes;
accomplished by molecules released from cells and by molecules attached to the surface of cells
proteins or peptides secreted by one cell as a regulator of neighboring cell;
promote costimulation;
involved in the regulation of immunity, inflammation, tissue repari, cell growth, etc.
cytokines produced by lymphocytes
a state of unresponsiveness of lymphocytes to a specific antigen;
most important funciton of tolerance is to prevent the immune system from responding to self-antigens;
can be induced by deletion of self-reactive lymphocytes, preventing activation of lymphocytes, or by activation of suppressor T cells
"without working";
a condition of inactivity in which a B or T cell does not respond to an antigen
Suppressor T cells
cells with the ability to suppress immune responses;
currently not well understood;
likely that they are subpopulations of helper T cells and cytotoxic T cells
Gamma globulins
Immunoglobulins (Ig)
other names for antibodies
Variable region
the portion of the antibody that combines with the antigenic determinant of the antigen; different antibodies have different variable regions that are specific for different antigens
Constant region
portion of an antibody that is responsible for activities of antibodies like ability to activat complement or to attach the antibody to such cells as macrophages, basophils, mast cells, and eosinophils
substances that make an antigen more susceptible to phagocytosis; IgG can act as an opsonin
Primary response
results from the first exposure of a B cell to an antigen for which it is specific and includes a series of cell divisions, cell differentiation, and antibody production;
normally takes 3-14 days to produce enough antibodies to be effective against the antigen
Plasma cells
large lymphocytes produced by the mitotic division of B cells;
produces antibodies
Memory B cells
small lymphocytes that are produced when B cells undergo mitosis;
Secondary (memory) response
occurs when the immune system is exposed to an antigen against which it has already produced a primary response;
results from memory B cells, which rapidly divide to form plasma cells and large amounts of the antibody;
requires only a few hours to days to produce sufficient numbers of antibodies and produces a much larger number of antibodies than primary response
Cytotoxic T cells
T cells that lyse cells and produce cytokines
a protein which is similar to the complement protein C9 and is used by cytotoxic T cells to cause cell lysis;
forms a channel in the plasma membrane of the target cell through which water enters the cell
Delayed hypersensitivity T cells
T cells that respond to antigens by releasing cytokines;
promote phagocytosis and inflammation, especially in allergic reactions
treats disease by altering immune system function or by directly attacking harmful cells
a process in which monoclonal antibodies are modified to resemble human antibodies;
allows monoclonal antibodies to sneak past the immune system
a deliberate introduction of an antigen or antibody into the body
Active immunity
occurs when an individual is naturally or artificially exposed to an antigen and an adaptive immune system response can occur that produces antibodies
Passive immunity
occurs when another person or animal develops antibodies and the antibodies are transferred to a nonimmune individual
Active natural immunity
achieved when a natural exposure to an antigen can cause an individual's immune system to mount an adaptive immune system response against the antigen
Active artificial immunity
an antigen is deliberately introduced into an individual to stimulate the immune system (vaccination)
Passive natural immunity
results from the tranfer of antibodies from a mother to her child across the placenta before birth or through breastfeeding
Passive artifical immunity
a process by which an animal is injected with an antigen (vaccine) and once its immune system produces a response, antibodies are removed and injected into the individual requiring immunity
the general term used for serum, which is plasma minus the clotting factors;
contains antibodies responsible for passive artifical immunity

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