Chapter 15 The Lymphatic System And Immunity

Chapter 15The Lymphatic Systemand Immunity

Objectives Describe general functions of thelymphatic system and list the mainlymphatic structures Compare nonspecific and specificimmunity Name the major disorders associatedwith the lymphatic system2

Objectives Discuss the major types of immunesystem molecules Discuss and contrast the developmentand functions of B and T cells3

Objectives Describe the mechanisms of allergy,autoimmunity, and isoimmunity List the major types of immunedeficiencies and explain their causes4

The Lymphatic System Lymph—fluid in the tissue spaces thatcarries protein molecules and othersubstances back to the blood5

Lymph Road Map1. Blood plasma filters out2. Liquid enters as interstitial fluid3. Enters lymphatic capillaries4. VenulesLymph is filtered along way by organs andglands5.Veins6.Right lymphatic duct and thoracic duct7.Blood veins in neck6

The Lymphatic System Lymphatic vessels—permit only one-waymovement of lymph– Lymphatic capillaries—tiny blind-ended tubesdistributed in tissue spaces Microscopic in size Sheets consisting of one cell layer of simple squamousepithelium Poor ―fit‖ between adjacent cells results in porous walls Called lacteals in the intestinal wall (for fattransportation)7

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The Lymphatic System Lymphatic vessels– Right lymphatic duct Drains lymph from the right upper extremity andright side of head, neck, and upper torso– Thoracic duct Largest lymphatic vessel Has an enlarged pouch along its course, calledcisterna chyli Drains lymph from about three fourths of thebody10

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The Lymphatic System Lymphedema—swelling (edema) oftissues caused by blockage of lymphaticvessels– Lymphangitis—inflammation of lymphaticvessels, may progress to septicemia (bloodinfection)– Elephantiasis—severe lymphedema oflimbs resulting from parasite infestation oflymphatic vessels12

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The Lymphatic System Lymph nodes– Filter lymph– Located in clusters along the pathway of lymphaticvessels– Lymphoid tissue—mass of lymphocytes andrelated cells inside a lymphoid organ; providesimmune function and development of immunecells– Lymph nodes and other lymphoid organs havefunctions that include defense and WBC formation15

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The Lymphatic System Lymph nodes– Flow of lymph: to node via several afferentlymphatic vessels and drained from nodeby a single efferent lymphatic vessel– Lymphadenitis—swelling and tendernessof lymph nodes– Cancer cells can easily move throughlymphatic vessels to other parts of thebody in a process called metastasis19

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The Lymphatic System Lymphoma—malignant tumor of lymphnodes– Two types: Hodgkin disease and nonHodgkin lymphoma Thymus– Lymphoid tissue organ located inmediastinum– Total weight of about 35–40 g—a littlemore than an ounce21

The Lymphatic System Thymus– Plays a vital and central role in immunity– Produces T lymphocytes or T cells– Secretes hormone called thymosin– Lymphoid tissue is largely replaced by fatin the process called involution22

The Lymphatic System Tonsils– Composed of three masses of lymphoid tissuearound the openings of the mouth and throat Palatine tonsils (―the tonsils‖) Pharyngeal tonsils (adenoids) Lingual tonsils– Subject to chronic infection– Enlargement of pharyngeal tonsils may impairbreathing23

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The Lymphatic System Spleen– Largest lymphoid organ in body– Located in upper left quadrant of abdomen– Often injured by trauma to abdomen– Surgical removal called splenectomy– Functions include phagocytosis of bacteriaand old RBCs; acts as a blood reservoir– Splenomegaly—enlargement of the spleen25

The Immune System Protects body from pathologicalbacteria, foreign tissue cells, andcancerous cells Made up of defensive cells andmolecules Nonspecific immunity– Skin—mechanical barrier to bacteria andother harmful agents26

The Immune System Nonspecific immunity– Tears and mucus—wash eyes and trapand kill bacteria– Inflammation attracts immune cells to siteof injury, increases local blood flow,increases vascular permeability; promotesmovement of WBCs to site of injury orinfection27

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The Immune System Specific immunity—ability of body torecognize, respond to, and rememberharmful substances or bacteria Inherited or inborn immunity—inheritedimmunity to certain diseases from timeof birth29

The Immune System Acquired immunity– Natural immunity—exposure to causativeagent is not deliberate Active—active disease produces immunitymeasles Passive—immunity passes from mother tofetus through placenta or from mother to childthrough mother’s milk30

The Immune System Acquired immunity– Artificial immunity—exposure to causativeagent is deliberate Active—vaccination results in immunity Passive—protective material developed inanother individual’s immune system and givento previously nonimmune individual- i.e.antibodies in mother’s milk31

Immune System Molecules Antibodies– Protein compounds with specific combining sites– Combining sites attach antibodies to specificantigens (foreign proteins), forming antigenantibody complex—called humoral or antibodymediated immunity– Antigen-antibody complexes may: Neutralize toxins Clump or agglutinate enemy cells Promote phagocytosis32

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Immune System Molecules Complement proteins– Group of proteins normally present in bloodin inactive state– Complement cascade Important mechanism of action for antibodies– Complement-binding sites on antibody are exposedafter attaching to antigen– Complement triggers a series (cascade) of reactionsthat produce tiny protein rings that create holes in thesurface of a foreign cell34

Immune System Molecules Complement proteins– Complement cascade Ultimately causes cell lysis by permitting entryof water through a defect created in the plasmamembrane of the foreign cell– Complement proteins play many otherroles in immunity, including theinflammatory response35

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Immune System Cells Phagocytes– Types Neutrophils—short-lived phagocytic cells Monocytes—develop into phagocyticmacrophages and migrate to tissues (Figure15-15) Dendritic cells (DCs)—often found at or nearexternal surfaces37

Phagocytosis38

Immune System Cells Phagocytes– Ingest and destroy foreign cells or otherharmful substances via phagocytosis– Macrophages and DCs act as antigenpresenting cells (APCs) by displayingingested antigens on their outer surface totrigger specific immune cells39

Immune System Cells Lymphocytes– Most numerous of immune system cells– Development of B cells—primitive stemcells migrate from bone marrow and gothrough two stages of development40

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Immune System Cells Lymphocytes– Development of B cells First stage—stem cells develop into immatureB cells– Takes place in the liver and bone marrow beforebirth and in the bone marrow only in adults– B cells are small lymphocytes with antibodymolecules (which they have synthesized) in theirplasma membranes– After they mature, inactive B cells migrate chiefly tolymph nodes42

Immune System Cells– Development of B cells Second stage—inactive B cell develops into activated Bcell– Initiated by inactive B cell’s contact with antigens, whichbind to its surface antibodies, plus signal chemicals from Tcells– Activated B cell, by dividing repeatedly, forms two clonesof cells—plasma (effector) cells and memory cells– Plasma cells secrete antibodies into blood; memory cellsare stored in lymph nodes– If subsequent exposure to antigen that activated B celloccurs, memory cells become plasma cells and secreteantibodies43

Immune System Cells– Function of B cells—indirectly, B cellsproduce humoral immunity Activated B cells develop into plasma cells Plasma cells secrete antibodies into the blood Circulating antibodies produce humoralimmunity44

Immune System Cells– Development of T cells—stem cells from bonemarrow migrate to thymus gland First stage—stem cells develop into T cells– Occurs in thymus during few months before and after birth– T cells migrate chiefly to lymph nodes Second stage—T cells develop into activated T cells– Occurs when, and if, antigen binds to T cell’s surfaceproteins and chemical signal received from another T cell– As with B cells, clones made up of effector cells andmemory cells are formed45

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Immune System Cells– Functions of T cells—produce cell-mediatedimmunity Cytotoxic T cells—kill infected or tumor cells byreleasing a substance that poisons infected ortumor cells Helper T cells—release chemicals that attract andactivate macrophages to kill cells byphagocytosis; produce chemicals that helpactivate B cells Regulatory T cells—release chemicals tosuppress immune responses47

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Hypersensitivity ofthe Immune System Inappropriate or excessive immuneresponse Allergy—hypersensitivity to harmlessenvironmental antigens (allergens)– Immediate allergic responses usuallyinvolve humoral immunity– Delayed allergic responses usually involvecell-mediated immunity50

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Hypersensitivity ofthe Immune System Autoimmunity—inappropriate, excessiveresponse to self-antigens– Causes autoimmune diseases– Systemic lupus erythematosus (SLE)—chronic inflammatory disease caused bynumerous antibodies attacking a variety oftissues52

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Hypersensitivity ofthe Immune System Isoimmunity—excessive reaction toantigens from another human– May occur between mother and fetusduring pregnancy– May occur in tissue transplants (causingrejection syndrome)54

Immune System Deficiency Congenital immune deficiency orimmunodeficiency (rare)– Results from improper lymphocytedevelopment before birth– Severe combined immune deficiency(SCID)—caused by disruption of stem celldevelopment55

Immune System Deficiency Acquired immune deficiency– Develops after birth– Acquired immunodeficiency syndrome(AIDS)—caused by HIV infection of T cells56

Chapter 15 The Lymphatic System and Immunity. 2 Objectives Describe general functions of the lymphatic system and list the main lymphatic structures Compare nonspecific and specific immunity . 22 The Lymphatic System Thymus –Plays a vital and central role in immunity