Introduction



IntroductionThe lymphatic system consists of:LymphLymphatic vesselsLymphoid organsAn Overview of the Lymphatic SystemLymph consists of:Interstitial fluidLymphocytesMacrophagesLymphatic vessels:Pass through lymphoid tissuePass through lymphoid organsAn Overview of the Lymphatic SystemLymphoid Organs or TissuePrimary organs or tissueThymusBone marrowSecondary organs or tissueTonsilsNodesAxillary, lumbar, pelvic, inguinalSpleenMucosa-associated lymphoid tissueAn Overview of the Lymphatic SystemFunctions of the Lymphatic SystemProduce, maintain, and distribute lymphocytesMaintain normal blood volume and the normal composition of the interstitial fluidProvide an alternative route for the transport ofHormonesNutrientsWaste An Overview of the Lymphatic SystemFunctions of the Lymphatic SystemPrimary lymphoid structures (central structures) Causes differentiation of lymphocytes resulting in T cells, B cells, and NK cellsSecondary lymphoid structures (peripheral structures)Considered to be the “front line” of defense Consist of lymphocytes and more B cells to battle infectious agentsAn Overview of the Lymphatic SystemFunctions of the Lymphatic SystemThe maintenance of normal blood volume and chemical composition of the interstitial fluidThe blood pressure in capillaries is about 35 mm HgThis pressure forces solutes and waste out of the plasma into the interstitial fluid areaSome interstitial fluid enters the lymphatic systemThe lymphatic system eventually connects with the venous systemAn Overview of the Lymphatic SystemFunctions of the Lymphatic SystemProvides an alternative route for the transport of:HormonesNutrientsFor example: some lipids are absorbed by the digestive tract and carried to the bloodstream via the lymphatic vesselsWaste productsStructure of Lymphatic VesselsSmall lymphatic vessels are called:Lymphatic capillariesLarge-diameter lymphatic vessels are called:Lymphatic ductsStructure of Lymphatic VesselsLymphatic CapillariesComparisons to the vascular capillariesLymphatic capillaries are larger in diameterLymphatic capillaries have thinner wallsLymphatic capillaries have an irregular outlineLymphatic capillaries have anchoring filaments that connect to the surrounding connective tissue to keep the capillaries openLymphatic capillaries have greater permeabilityStructure of Lymphatic VesselsValves of Lymphatic VesselsComparing larger lymphatics to veinsLymphatic vessels have thinner wallsLymphatic vessels have larger lumensLymphatic vessels do not have easily identifiable tunicsLarger lymphatic vessels have valves just like most veins haveStructure of Lymphatic VesselsValves of Lymphatic VesselsPressure in the lymphatic vessels is lower than the pressure in the veinsValves prevent the backflow of lymphSkeletal muscles contract to help propel lymphInhalation decreases thoracic pressure, which helps to move lymph toward the venous system (subclavians)Major Lymph-Collecting VesselsTwo Sets of Lymphatic VesselsSuperficial lymphaticsFound in the subcutaneous layerFound in the mucous lining of the digestive, respiratory, urinary, and reproductive tractsFound in the serous lining of the pleural, pericardial, and peritoneal cavitiesDeep lymphatics Collect lymph from skeletal muscles and tissues of the neck, limbs, trunk, and visceral organsMajor Lymph-Collecting VesselsThe superficial and deep lymphatic vessels converge to form lymphatic trunksThere are five major lymphatic trunksLumbar trunksIntestinal trunksBronchomediastinal trunksSubclavian trunksJugular trunksMajor Lymph-Collecting VesselsThe Thoracic DuctDrains into the left subclavian veinDrains lymph inferior to the diaphragmDrains lymph from Left armLeft side of the torsoLeft side of the neckLeft side of the headAbdomenBoth legsMajor Lymph-Collecting VesselsThe Thoracic DuctBegins with a saclike structure called the cisterna chyliCollects lymph fromLeft and right lumbar trunksIntestinal trunksLeft bronchomediastinal trunkLeft subclavian trunkLeft jugular trunkMajor Lymph-Collecting VesselsThe Right Lymphatic DuctDrains into the right subclavian veinDrains lymph fromRight armRight side of the torsoRight side of the neckRight side of the headMajor Lymph-Collecting VesselsRight Lymphatic DuctCollects lymph fromThe right bronchomediastinal trunkThe right subclavian trunkThe right jugular trunkLymphocytesLymphocytes are the primary cells of the lymphatic systemThey respond to: Invading bacteria and virusesAbnormal body cells such as cancer cellsForeign proteins such as toxins released by some bacteriaLymphocytesTypes of LymphocytesT cells (Thymus-dependent cells)B cells (bone marrow–derived cells)NK cells (natural killer cells)LymphocytesT CellsOriginate in the bone marrow but travel to the thymus gland and become activated (immunocompetent) by thymosinDifferent types of T cellsCytotoxic T cellsHelper T cellsSuppressor T cellsMemory T cells LymphocytesT CellsDifferent types of T cellsCytotoxic T cellsAttack foreign cells and virusesHelper T cellsEnhance antibody productionSuppressor T cellsInhibit antibody productionMemory T cellsBecome activated if the same antigen appears in the body at a later dateLymphocytesB CellsOriginate and become immunocompetent in the bone marrowCan differentiate to form PlasmocytesProduce antibodies that react with antigensAntibodies are also called immunoglobulinsMemory B cellsBecome activated if the same antigen appears at a later dateLymphocytesNK CellsAttack foreign cellsAttack normal cells that are infected with virusesAttack cancer cellsNK cells are often called immunological surveillance cellsLymphocytes Lymphocytes and the Immune ResponseThere are two response mechanismsCell-mediated immunityT cells directly attach the pathogenAntibody-mediated immunityPathogen is attacked by antibodies produced by B cellsLymphocytesLymphocytes and the Immune ResponseThe following is a sequence of events involved in the immune response to a bacterial antigen (for example)Macrophages will phagocytize the foreign substanceMacrophages will present the antigen to specific T cellsThis is called antigen presentationT cells begin to divide to produce cytotoxic T cells, helper T cells, and memory T cellsLymphocytesLymphocytes and the Immune Response (continued)The cytotoxic T cells will kill the bacterial agent directlyThe helper T cells will activate the B cellsB cells will begin producing antibodies against the bacterial antigensAntibodies will bind to the bacterial antigensThis antigen–antibody combination will attract an “army” of leukocytesThese leukocytes will kill the bacteriaLymphocytesDistribution and Life Span of LymphocytesRatio of T cells to B cellsIn the blood = 8:1In the spleen = 1:1In the bone marrow = 1:3Life spanMost live 4 to 20 yearsLymphocytesLymphopoiesis: Lymphocyte ProductionThe pluripotential stem cells produce two sets of lymphoid stem cells each with a different fateOne set of lymphoid stem cells will:Migrate to the thymus glandUpon exposure to thymosin, the lymphocytes will mature to form T cellsMature T cells will reside in peripheral tissue or circulate throughout the bodyLymphocytesLymphopoiesis: Lymphocyte Production (continued)The other set of lymphoid stem cells willstay in the bone and differentiate to form B cells and NK cellsB cells produce antibodiesNK cells act as immunological surveillance cellsBoth will reside in peripheral tissues or circulate throughout the bodyLymphoid TissuesLymphoid Tissue CharacteristicsTissue dominated by lymphocytesLymphocytes are loosely aggregated within connective tissueLymphoid Nodule CharacteristicsLymphocytes aggregated within a supporting framework of reticular fibersNodules have a germinal center, which contains the lymphocytesLymphoid TissuesTypes of NodulesMucosa-associated lymphoid tissue (MALT)TonsilsPharyngeal tonsilPalatine tonsilsLingual tonsilsAggregated lymphoid nodules (Peyer’s patches and appendix)Lymphoid TissuesMucosa-associated lymphoid tissue (MALT)Lymphoid nodules associated with the digestive tractTonsilsThere are five sets of tonsilsOne pharyngeal tonsilTwo palatine tonsilsTwo lingual tonsilsAggregated lymphoid nodules (Peyer’s patches and appendix)Lymphoid nodules associated with the small intestineLymphoid OrgansLymphoid organs include:Lymph nodesThymus glandSpleenLymphoid OrgansLymph Nodes1 to 25 mm in diameterScattered throughout the body but high concentrations can be found in the following areas:Cervical regionAxillary regionBreastsAbdominal regionInguinal regionLymphoid OrgansStructure of a Lymph NodeLymph nodes consist ofCapsule with afferent vesselsSubcapsular spaceOuter cortexGerminal centerMedullaMedullary cordsHilum with efferent vesselsLymphoid OrgansDistribution of Lymphoid Tissues and Lymph NodesLymphoid tissue and lymph nodes are in high concentrations where the body is more susceptible to injury or invasionLymphoid OrgansDistribution of Lymphoid Tissues and Lymph NodesCervical lymph nodesFound in the head and neck regionAxillary lymph nodesFound in the axillary regionFilter lymph from the trunk and armsIn women, filters lymph from the mammary glandsPopliteal lymph nodesFilter lymph from the legsLymphoid OrgansDistribution of Lymphoid Tissues and Lymph NodesInguinal lymph nodesFilter lymph from the lower limbs and trunkThoracic lymph nodesFilter lymph from the lungs, respiratory passageways, and mediastinal structuresAbdominal lymph nodesFilter lymph from the urinary and reproductive systemsLymphoid OrgansDistribution of Lymphoid Tissues and Lymph NodesIntestinal lymph nodesFilter lymph from the digestive tractMesenterial lymph nodesFilter lymph from the digestive tractLymphoid OrgansThe ThymusLies posterior to the manubrium of the sternumReaches its greatest size by age 1 or 2Reaches maximum size by pubertyDiminishes in size after pubertyConsists of two thymic lobes (left and right)Consists of numerous lobules (about 2 mm in width) separated by septaConsists of a cortex and a medullaLymphoid OrgansThe Thymus (continued)The cortex consists of:Stem cells that differentiate to form T cellsMature T cells migrate to the medullaThe medulla consists of:T cells that remain inactive until they enter circulationThymic corpuscles (function is unknown)Lymphoid OrgansThe SpleenLargest lymphoid organ (12 cm in length)Located on the left edge of the stomachAttached to the stomach via the gastrosplenic ligamentLymphoid OrgansThe SpleenConsists of the following areas or regionsDiaphragmatic surfaceVisceral surface The visceral surface contains the hilumLymphoid OrgansHistology of the SpleenThe spleen consists of:CapsuleRed pulp Contains large quantities of red blood cellsWhite pulpForms lymphoid nodulesAging and the Lymphatic SystemAs we age:T cells become less responsive to antigensB cells then become less responsive as wellThymus gland diminishes in size ................
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