2 Chapter 24 Outline Functions of the Lymphatic System Lymph and Lymph VesselsLymphatic CellsLymphatic StructuresAging and the Lymphatic SystemDevelopment of the Lymphatic System
3 Functions Return interstitial fluid back to the bloodstream Transport lipids and lipid-soluble vitamins into the bloodstream3. Production and maturation of lymphocytesGenerate an immune response againstantigens in the interstitial fluid
7 Lymphatic Capillaries Lymphatic capillaries are closed-ended tubes that are found interspersed among most blood capillary beds.They resemble blood capillaries but they have overlapping endothelial cells that act as one-way valves allowing interstitial fluid a one-way entrance into lymphatic capillaries.
9 Lymphatic Capillaries The gastrointestinal tract contains specialized lymph capillaries called lacteals that collect not only interstitial fluid, but also lipids and lipid-soluble vitamins.The lymph collected from the gastrointestinal system has a milky color due to the lipid absorption and is called chyle.
10 Lymphatic VesselsLymphatic capillaries merge to form lymphatic vessels.They resemble venules, in that they have components of all three vascular tunics and possess valves similar to veins.Afferent lymphatic vessels bring lymph to a lymph node.Efferent lymphatic vessels transport filtered lymph away from the lymph node.
12 Lymphatic TrunksLeft and right lymphatic trunks form from merging lymphatic vessels. Each trunk drains lymph from a specific region of the body, as follows:Jugular trunks—head and neckSubclavian trunks—upper limbs, breasts andsuperficial thoracic wall3. Bronchiomediastinal trunks—deep thoracicstructures4. Intestinal trunks—most abdominal structuresLumbar trunks—lower limbs, abdominopelvicwall and pelvic organs
14 Lymphatic DuctsLymphatic ducts are formed from the fusion of lymphatic trunks.The right lymphatic duct is located deep to the right clavicle and returns lymph at the junction of the right subclavian and internal jugular veins.The right lymphatic duct returns lymph from the right side of the head and neck, right upper limb and the right side of the thorax.
15 Lymphatic Ducts The thoracic duct is the largest lymphatic vessel. It begins just inferior to the diaphragm as a rounded saclike structure called the cisterna chyli.The thoracic duct collects lymph from most of the body (excluding the right lymphatic duct drainage).The thoracic duct passes through the aortic opening of the diaphragm and returns lymph into the junction between the left subclavian and internal jugular veins.
18 Lymphatic CellsThere are several types of lymphatic cells that are located in the lymphatic and circulatory systems:Macrophages=Monocytes (leukocytes)Nurse cells=Epithelial at ThymusDendritic cells=Epithelial at L. NodulesLymphocytes=Most abundant
19 Types of Lymphocytes The body contains three types of lymphocytes: T-lymphocytes (T-cells)B-lymphocytes (B-cells)Natural killer (NK cells)All three cell types migrate through the lymphatic system and search for the presence of antigens.
20 T-Lymphocytes Make up about 70–85% of body lymphocytes They express a plasma membrane coreceptor (CD) that can recognize a particular antigenThere are several types of T-lymphocytes; two main groups are:helper T-lymphocytescytotoxic T-lymphocytes
21 Helper T-LymphocytesPrimarily contain the CD4 coreceptor and are referred to as CD4+ cells or T4 cellsMany types of T4 cells, each one responds to a different antigenT4 cells initiate and oversee the immune response in two ways:present the antigen to other lymphocytessecrete cytokines, which are hormones that activate other lymphatic cells
22 Cytotoxic T-Lymphocytes Also called CD8+ cells or T8 cells, they contain the CD8 coreceptorCome in direct contact with infected or foreign cells and kill themAct only after activated by a helper T-lymphocyte that presents an antigen to it
24 B-Lymphocytes Make up about 15–30% of body lymphocytes Contain antigen receptors to only one antigen and produce immunoglobulins or antibodies to that single antigenB-lymphocytes become activated when presented with an antigen from a helper T-lymphocyte
25 B-LymphocytesMost of the activated B-lymphocytes become plasma cells that produce and secrete large amounts of antibodies.Plasma cells may be either short-lived (less than a week) or long-lived (months or years).The long-lived B-lymphocytes are called memory B-lymphocytes and confer years or lifetime immunity to certain antigens.
26 B-Lymphocytes and Their Role in the Immune Response Figure 24.6
27 NK (Natural Killer) Cells Also called large granular lymphocytesRelatively small percentage of all lymphocytesTend to express the CD16 receptorsUnlike T-cells and B-cells that respond to one antigen, NK cells can kill a wide variety of infected cells and some cancerous cells
29 Lymphopoiesis Lymphopoiesis is the process of lymphocyte development. The final result of lymphopoiesis is that the lymphocyte becomes immunocompetent, meaning the cell can participate in the immune response.All lymphocytes originate in the red bone marrow but their maturation sites differ.
31 Lymphatic NodulesOval clusters of lymphatic cells with some extracellular matrix but not surrounded by a connective tissue capsuleCenter of nodule is called the germinal center; contains proliferating B-lymphocytes and macrophagesT-lymphocytes located outside the germinal centerLymphatic nodules filter and attack antigens
32 MALT(Mucosa-Associated Lymphatic Tissue) Lymphatic nodules located in the mucosa of the gastrointestinal, respiratory, genital, and urinary tractsThese nodules monitor and respond to antigens that may enter these tractsMALT is very prominent in the ileum; these nodules are called Peyer patches
34 Tonsils Located mainly in the pharynx Large clusters of lymphatic cells and extracellular matrix that do not have a completed surrounding capsuleOuter edges are invaginated to form crypts, which allow for trapping of antigens to be presented to the lymphocytes
36 Tonsils There are three types of tonsils: Pharyngeal tonsils (adenoids)—located in the posterosuperior wall of the nasopharynxPalatine tonsils—located in the posterolateral wall of the oral cavityLingual tonsils—located along the posterior one-third of the tongue
37 Lymphatic OrgansConsists of lymphatic cells and extracellular matrix and is completely surrounded by a connective tissue capsuleThe main lymphatic organs are:thymuslymph nodesspleen
38 Thymus Bilobed organ located superficial to the heart Consists of two fused thymic lobes, which are divided into lobulesEach lobule has an outer cortex and an inner medullaContinues to grow until puberty and then begins to regress in size and function and, in adults, it becomes replaced mostly by adipose connective tissue
40 Function of Thymus Site of T-lymphocyte differentiation and maturation Cortex contains immature T-lymphocytesMedulla contains mature T-lymphocytesIn adulthood, T-lymphocytes can only be produced by cell division and not by the maturation of new cells in the thymus
41 Lymph NodesSmall, round or oval structures located along the pathway of lymph vesselsTypically found in clusters ranging from 1–25 mm in diameterThe primary function of a lymph node is to filter antigens from the lymph and initiate an immune response
44 Structure of Lymph Nodes Surrounded by a tough connective tissue capsuleInternal extensions of the capsule, trabeculae, project into the nodeLymphatic cells surround the trabeculae and lymphatic sinuses provide a pathway for lymph flow
45 Structure of Lymph Nodes Lymph node is divided into outer cortex and inner medullaCortex consists of nodules and sinuses called cortical sinusesThe medulla contains medullary cords and medullary sinusesAfferent vessels deliver lymph to the nodeLymph exits nodes via efferent vessels at an indentation of the node called the hilum
47 Spleen There are several functions of the spleen: Initiates an immune response when antigens are found in blood (white pulp function)Serves as a reservoir for erythrocytes and platelets (red pulp function)Phagocytizes old, defective erythrocytes and platelets (red pulp function)Phagocytizes bacteria and other foreign materials
48 Spleen Largest lymphatic organ in body just lateral to left kidney A splenic artery/vein enter/leave the spleen via a hilum or indentation on its medial surfaceSpleen surrounded by a dense irregular connective tissue capsule, which sends extensions called trabeculae into the organ
50 SpleenTrabecular vessels (branches of splenic arteries and veins) extend within the trabeculae.Cells around the trabeculae are subdivided into white pulp and red pulp.Red pulp surrounds each cluster of white pulp.
52 Red and White Pulp of Spleen The white pulp is associated with the arterial supply and consists of T- and B-lymphocytes and macrophages.In the center of each cluster is a central artery.The red pulp is associated with the venous supply.Red pulp consists of splenic cords and splenic sinusoids that contain erythrocytes, platelets, macrophages, and some plasma cells.Blood cells can easily enter and leave the blood stream in the spleen because of the discontinuous basal lamina of the capillaries in the splenic sinusoids.