Chapter 21 Lymphatic System

Immune System

a body system consisting of organs, cells, and chemical substances that protects the body against infection by pathogenic organisms, by destroying the invading organisms and preventing their proliferation.

Lymphatic System

a body system consisting of lymphatic vessels, cells, lymph nodes, and other organs; transports fluid from the interstitial spaces back to the bloodstream.

Lymph

the fluid flowing through the lymphatic system; derived from interstitial fluid that has entered a lymphatic capillary.

Lymphatic Capillaries

the smallest vessels of the lymphatic system; pick up interstitial fluid from the tissue spaces and transport it through the lymphatic system, to eventually return it to the bloodstream.

Lacteals

lymphatic capillaries in the villi of the small intestine that absorb and transport dietary lipids and lipid-soluble vitamins to the bloodstream.

Lymphatic Trunks

large lymphatic vessels that receive lymph from smaller lymphatic vessels and empty it into lymphatic ducts.

Cisterna Chyli

a saclike vessel that forms the beginning of the thoracic duct; formed from the merging of the two lumbar trunks and the intestinal trunk.

Right Lymphatic Duct

the smaller of the two lymphatic collecting ducts; drains lymph from the right side of the head, upper limb, and chest into the right subclavian vein.

Thoracic duct

the larger of the two lymphatic collecting ducts; drains lymph from the lower limbs, abdomen, left upper limb, and the left side of the head and chest, and empties it into the left subclavian vein.

Lymph nodes

a small, bean-shaped organ of the lymphatic system, which lies along a lymphatic vessel; filters lymph, removing pathogenic organisms and engaging in antigen recognition and attack.

Afferent Lymphatic Vessels

lymphatic vessels that drain lymph into a lymph node to be filtered.

Efferent Lymphatic Vessels

lymphatic vessels that transport filtered lymph out of a lymph node.

subcapsular sinus

the region of a lymph node through which lymph enters; lies just inside of the capsule; filters the lymph, bringing pathogens and debris into contact with phagocytic cells that can engulf and destroy them.

Lymphoid nodules

unencapsulated masses of lymphoid tissue found mainly in the walls of organs of the respiratory and digestive tracts; protect the body from infection by pathogens entering the body in the air or food.

Tonsils

masses of lymphoid nodules associated with the pharynx; consist of the pharyngeal tonsil (adenoid), the palatine tonsils, and the lingual tonsil

Tonsillar crypts

deep indentations of the epithelium of a tonsil, which accumulate materials entering the body through eating and breathing; contain macrophages and leukocytes, which interact with incoming materials to destroy pathogens.

Mucosa-associated lymphoid tissue (MALT)

lymphoid nodules found in the mucosa of the digestive, respiratory, genital, and urinary tracts, as well as the breast, eye, and skin, which protect against infection by pathogenic organisms entering the body from the external environment.

Bronchus-associated lymphoid tissue (BALT)

lymphoid nodules found in the mucosa of the respiratory tract, especially the bronchi; a type of MALT (mucosa-associated lymphoid tissue), which protects against infection by pathogenic microorganisms entering the body in inhaled air.

Spleen

one of the secondary lymphoid organs, and the largest lymphatic organ in the body; removes pathogenic organisms from the blood, produces B lymphocytes (white pulp) for the adaptive immune response, and removes worn-out or damaged red blood cells and platelets from the bloodstream (red pulp)

Red pulp

an area in the spleen that consists mainly of red blood cells; removes damaged or worn-out red blood cells from the circulation.

White pulp

the portion of the spleen that contains B cells and T cells, and macrophages; filter pathogens from the blood and engage in antigen recognition and attack.

Innate immune response

the rapid, nonspecific immune response against foreign antigens associated with pathogenic organisms; examples include barriers such as the skin, inflammation, phagocytosis, and the action of neutrophils and natural killer (NK) cells and various chemical substances, such as enzymes and interferon.

Adaptive Immune Response

the relatively slow, specific immune response, directed against a particular type of pathogenic organism; performed by B and T lymphocytes and antigen-presenting cells.

White Blood Cells

cells that defend the body against infection; consist of phagocytic cells (such as monocytes), lymphocytes, and granular cells (such as neutrophils, eosinophils, and basophils).

Phagocytic cells

cells that can engulf pathogens or other cellular debris and digest them with their lysosomal enzymes.

Lymphocytes

agranular leukocytes (white blood cells), which function in adaptive (specific) immunity; types of lymphocytes include B-lymphocytes, T-lymphocytes, and NK (natural killer) cells; comprise approximately 25 to 33 percent of the leukocyte population.

Granular cells

cells such as neutrophils, eosinophils, basophils, and mast cells, which contain granules consisting of chemicals that are toxic to pathogens.

Lysozyme

an enzyme found in saliva, mucus, tears, and milk, which destroys bacteria by digesting their cell walls

Macrophage

large phagocytic cell, found in various tissues of the body, which arises from the differentiation of monocytes after they leave the bloodstream.

Dendritic Cells

phagocytic cells similar to macrophages in function, which transport antigens to lymph nodes and function as antigen-presenting cells for T cells.

Neutrophils

granulocytes that are especially effective in the phagocytosis of bacteria, make up the largest percentage of the leukocytes, and are stained by neutral dyes.

Mast cell

a cell found near blood and lymphatic vessels, under the skin, and in various connective tissues, that secretes heparin (which prevents blood clotting), histamine (which promotes the inflammatory response), and prostaglandins; also participates in certain allergic responses.

Pattern Recognition Receptor (PRR)

a protein receptor found in the cell membranes of certain cells, such as macrophages and dendritic cells, that recognizes and binds to specific foreign molecules commonly found on the surface of bacteria and viruses; utilized in the innate immune response.

Cytokine

a chemical messenger, secreted by a macrophage, lymphocyte (such as a helper T cell), neutrophil, mast cell, or other cell, that delivers information to nearby cells; used in various immune responses, such as inflammation, and cell differentiation.

Chemokine

a chemical messenger, secreted by a damaged cell, that attracts leukocytes to infection or injury sites.

Interferons

a type of cytokine, secreted by virus-infected cells, which travels to nearby cells and causes them to produce antiviral proteins; this prevents viral replication in these cells.

Opsonization

the binding of a pathogenic organism to a phagocyte by an antibody or complement protein; this aids in the process of phagocytosis

Complement system

a group of several proteins that circulate in the blood plasma, which can be activated either by antibodies or an innate immune response; once activated, it works in a cascade of reactions, with each reaction product activating the next protein in the sequence; the various proteins function in opsonization, enhancement of phagocytosis, or lysis (rupture) of the antigenic cell.

Fever

an increase of more than 1°C (1.8°F) above the set point for body temperature; a mechanism used by the immune system to create a hostile environment for the replication of pathogens and to increase the reaction rate of the immune response.

Antigens

molecules that evoke an immune response in the body, since they are recognized as being foreign by B and T lymphocytes.

Cellular Response

a set of actions of the adaptive immune response that involves T cells traveling to an infection site and directing an attack on infected body cells, cancerous cells, or donor graft cells.

Antibody-mediated responses

a set of actions of the adaptive immune response that involves antibodies traveling to an infection site and organizing an immune attack on pathogenic organisms.

Primary Response

the immune response of the body during the first exposure to a pathogen.

Secondary Adaptive Response

an immune response that occurs upon the second or subsequent exposures to a pathogen, which occurs more quickly and produces a higher concentration of antibodies than the primary response

Immunological memory

the ability of the immune system to remember and recognize previously encountered antigens, so it can launch a strong, rapid immune response upon subsequent exposure.

Autoimmune disease

diseases that result from a person producing antibodies against self-antigens and attacking their own cells or tissues.

Antigen-binding site

the portion of a receptor on the cell membrane of a T cell, B cell, or antibody, which is specific for binding to a particular antigen.

Antigenic determinant

the portion of an antigen that an antibody or lymphocyte receptor recognizes and binds to; forms a complex with a major histocompatibility complex (MHC) protein for antigen presentation to T lymphocytes.

Antigen-presenting cells (APCs)

cells that display antigens on their own cell membranes, bound to major histocompatibility complex proteins, to help T cells to recognize their antigens.

Major Histocompatibility Complex (MHC)

a group of genes that codes for MHC proteins, which form complexes with antigenic determinants for antigen presentation to T cells.

MHC class I

proteins found on all cells of the body except erythrocytes, which form complexes with antigenic determinants to present the antigens to the CD8 molecules on cytotoxic T cells.

MHC class II

proteins found only on macrophages, dendritic cells, and B cells, which form complexes with antigenic determinants to present the antigens to the CD4 molecules on helper T cells.

T cell tolerance

a lack of responsiveness of T cells against self-antigens, due to the destruction of T cells that recognize these antigens.

Clonal expansion

the reproduction of a particular type of lymphocytes, which results from the binding of an antigen to a specific lymphocyte receptor.

Clonal selection

the binding of an antigen only to lymphocytes that contain specific receptors for that antigen.

Memory T cells

T lymphocytes (T cells) that remain dormant after their first exposure to an antigen, but remember the antigen and remain in the body fluids for a long period of time to respond to subsequent exposure to that antigen.

Helper T cells ( CD4+ T cells)

T lymphocytes (T cells) that activate B cells, cytotoxic T cells, macrophages, and other immune cells, and regulate the immune response, by secreting cytokines.

Cytotoxic T cells (CD 8 T cells)

T lymphocytes (T cells) that destroy cells that contain foreign antigens, such as virus-infected and tumor cells.

Regulatory T cells

a special group of helper T cells that reduces the immune response by secreting inhibitory cytokines to lessen the activity of other T cells.

B cell receptors

receptors on the cell membrane of B cells that are specific for a particular type of antigen; when a B cell encounters an antigen that matches its receptors, the B cell binds to the antigen.

Plasma cells

a group of differentiated B cells that secretes antibodies against specific antigens.

Heavy Chains

the larger chain of proteins found in an antibody molecule; antibodies contain two heavy chains and two light chains.

Light cells

the smaller chain of proteins found in an antibody molecule; antibodies contain two heavy chains and two light chains.

Fc region

the “tail” portion of a Y-shaped antibody molecule; called the “fragment crystallizable” region, it is the area in which the two heavy chains of the antibody lie side by side; binds to some complement proteins and some plasma membrane proteins of various cells of the immune system.

IgM

the first class of antibodies to be secreted during the initial response to an antigen; circulates mainly in the blood plasma and lymph for a short time, and levels decline as IgG antibodies increase.

Class switching

the process by which an activated B cell shifts its production of IgM antibodies to a different class (IgA, IgE, or IgG) while retaining antigen specificity.

IgG

the most abundant class of antibodies, comprising about 80 percent of all antibodies; found in blood plasma and interstitial fluid, and can cross the placenta.

IgA

a class of antibodies found in the secretions of exocrine glands, such as milk, saliva, sweat, and gastric and intestinal fluid; very effective against pathogens of the digestive and respiratory systems.

IgE

a class of antibodies found in the secretions of exocrine glands; binds to mast cells and and basophils to promote inflammatory and allergic responses in the body.

IgD

a class of antibodies found mainly on the cell membranes of B cells, but also found in small quantities in the blood plasma; functions as an antigen receptor for B cells.

Neutralization

the binding of an antibody to a virus or bacterial toxin, rendering the pathogen unable to bind to body cell receptors and therefore harmless.

Active immunity

immunity obtained via antigen exposure, which evokes an immune response by the person’s own immune system; this results in the production of antibodies and immunological memory against the antigen.

Passive Immunity

temporary immunity obtained by the transfer of antibodies to a person, either via the injection of antibodies (gammaglobulins) or passed through the placenta to a fetus or through the milk to a baby.