9/29/2014 Lymphatic System Lymphoid Organs and Tissues • Returns fluids that leaked from blood • Provide structural basis of immune system vessels back to blood • House phagocytic cells and lymphocytes • Consists of three parts • Structures include spleen, thymus, tonsils, 1. Network of lymphatic vessels (lymphatics) lymph nodes, other lymphoid tissues 2. Lymph – fluid in vessels 3. Lymph nodes – cleanse lymph © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Figure 20.1 Distribution and special features of lymphatic capillaries. Venous system Arterial system Lymphatic System: Functions Heart Lymphatic system: Lymph duct Lymph trunk Lymph node Collecting lymphatic • Lymphatic vessels (lymphatics) vessels, with valves Lymphatic capillary Blood capillaries – Return interstitial fluid and leaked plasma proteins back to blood – ~ 3L / day – Once interstitial fluid enters lymphatics, called Tissue fluid Tissue cell Blood Lymphatic lymph capillaries capillaries Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries. Filaments anchored to connective tissue Endothelial cell Flaplike minivalve Fibroblast in loose connective tissue Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. forming flaplike minivalves. Lymphatic Vessels: Distribution and Lymphatic Capillaries Structure • One-way system; lymph flows toward • Similar to blood capillaries, except heart – Very permeable (take up proteins, cell debris, • Lymph vessels (lymphatics) include: pathogens, and cancer cells) • Endothelial cells overlap loosely to form one-way – Lymphatic capillaries minivalves – Collecting lymphatic vessels • Anchored by collagen filaments, preventing – Lymphatic trunks and ducts collapse of capillaries; increased ECF volume opens minivalves – Pathogens travel throughout body via lymphatics © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. 1 9/29/2014 Lymphatic Capillaries Figure 20.1b Distribution and special features of lymphatic capillaries. Filaments anchored • Absent from bones, teeth, bone marrow, to connective tissue and CNS • Lacteals: specialized lymph capillaries Endothelial cell present in intestinal mucosa – Absorb digested fat and deliver fatty lymph Flaplike minivalve (chyle) to the blood Fibroblast in loose connective tissue Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves. © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Lymphatic Collecting Vessels Lymphatic Trunks • Similar to veins, except • Formed by union of largest collecting – Have thinner walls, with more internal valves ducts – Anastomose more frequently – Paired lumbar • Collecting vessels in skin travel with – Paired bronchomediastinal superficial veins – Paired subclavian • Deep vessels travel with arteries – Paired jugular trunks • Nutrients supplied from branching vasa – Single intestinal trunk vasorum © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Figure 20.2a The lymphatic system. Lymphatic Ducts Regional Internal lymph jugular vein nodes: Entrance of Cervical • Lymph delivered into one of two large right lymphatic nodes duct into vein ducts Entrance of thoracic duct – Right lymphatic duct drains right upper arm into vein Axillary nodes and right side of head and thorax Thoracic duct – Thoracic duct arises as cisterna chyli; Cisterna Aorta drains rest of body chyli Inguinal Collecting nodes • Each empties lymph into venous lymphatic vessels circulation at junction of internal jugular and subclavian veins on its own side of Drained by the right lymphatic duct body Drained by the thoracic duct General distribution of collecting lymphatic vessels and regional lymph nodes. © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. 2 9/29/2014 Figure 20.2b The lymphatic system. Right jugular trunk Internal Lymph Transport jugular veins Right lymphatic Esophagus duct Trachea Right subclavian Left jugular trunk trunk Right subclavian Left subclavian vein trunk • Lymph propelled by Left subclavian Right broncho- vein mediastinal trunk Entrance of – Milking action of skeletal muscle Brachiocephalic thoracic duct veins into vein – Pressure changes in thorax during breathing Superior Left broncho- vena cava mediastinal Azygos vein trunk – Valves to prevent backflow Ribs – Pulsations of nearby arteries Thoracic duct Hemiazygos – Contractions of smooth muscle in walls of Cisterna chyli vein lymphatics Right lumbar trunk Left lumbar trunk Inferior vena cava Intestinal trunk Major lymphatic trunks and ducts in relation to veins and surrounding structures. Anterior view of thoracic and abdominal wall. © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Lymphoid Cells Lymphocytes • Lymphocytes main warriors of immune • T cells and B cells protect against system antigens – Arise in red bone marrow – Anything body perceives as foreign • Mature into one of two main varieties • Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells – T cells (T lymphocytes) – B cells (B lymphocytes) © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Lymphocytes Other Lymphoid Cells • T cells • Macrophages phagocytize foreign – Manage immune response substances; help activate T cells – Attack and destroy infected cells • Dendritic cells capture antigens and • B cells deliver them to lymph nodes; activate – Produce plasma cells, which secrete T cells antibodies • Reticular cells produce reticular fiber • Antibodies mark antigens for destruction by stroma that supports other cells in phagocytosis or other means lymphoid organs © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. 3 9/29/2014 Figure 20.3 Reticular connective tissue in a human lymph node. Lymphoid Tissue Macrophage • Houses, and provides proliferation site for, Reticular cells on lymphocytes reticular fibers • Surveillance vantage point for Lymphocytes lymphocytes and macrophages • Largely reticular connective tissue – Medullary sinus type of loose connective tissue Reticular fiber • Two main types – Diffuse lymphoid tissue; Lymphoid follicles © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Lymphoid Tissue Lymphoid Tissue • Diffuse lymphoid tissue of lymphoid cells • Lymphoid follicles (nodules) are solid, and reticular fibers in ~ every body organ spherical bodies of tightly packed – Larger collections in lamina propria of mucous lymphoid cells and reticular fibers membranes – Germinal centers of proliferating B cells – May form part of larger lymphoid organs – Isolated aggregations of Peyer's patches and in appendix © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Figure 20.5 Lymphoid organs. Lymph Nodes Tonsils (in pharyngeal region) Thymus (in thorax; most • Principal lymphoid organs of body active during youth) • Embedded in connective tissue, in clusters along lymphatic vessels • Near body surface in inguinal, axillary, and Spleen (curves around cervical regions of body left side of stomach) Peyer’s patches (aggregated lymphoid nodules in small intestine) Appendix © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. 4 9/29/2014 Figure 20.2a The lymphatic system. Regional Lymph Nodes Internal lymph jugular vein nodes: Entrance of Cervical right lymphatic nodes • Functions duct into vein Entrance of 1. Filter lymph—macrophages destroy thoracic duct into vein Axillary microorganisms and debris nodes Thoracic duct 2. Immune system activation—lymphocytes activated and mount attack against antigens Cisterna Aorta chyli Inguinal Collecting nodes lymphatic vessels Drained by the right lymphatic duct Drained by the thoracic duct General distribution of collecting lymphatic vessels and regional lymph nodes. © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Structure of a Lymph Node Structure of a Lymph Node • Vary in shape and size but most bean • Cortex contains follicles with germinal shaped centers, heavy with dividing B cells • External fibrous capsule • Dendritic cells nearly encapsulate follicles • Trabeculae extend inward and divide • Deep cortex houses T cells in transit node into compartments • T cells circulate continuously among • Two histologically distinct regions blood, lymph nodes, and lymph – Cortex – Medulla © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Figure 20.4a Lymph node. Afferent Cortex Structure of a Lymph Node lymphatic vessels • Lymphoid follicle • Germinal center • Subcapsular sinus • Medullary cords extend inward from cortex Efferent lymphatic vessels and contain B cells, T cells, and plasma cells • Lymph sinuses contain macrophages Hilum Medulla • Medullary cord • Medullary sinus Trabeculae Capsule Longitudinal view of the internal structure of a lymph node and associated lymphatics © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. 5 9/29/2014 Figure 20.4b Lymph node. Circulation in the Lymph Nodes Follicles • Lymph Trabecula – Enters convex side via afferent lymphatic Subcapsular vessels; travels through large subcapsular sinus sinus and smaller sinuses to medullary sinuses; exits concave side at hilum via Capsule efferent vessels • Fewer efferent vessels so flow somewhat Medullary stagnate; allows lymphocytes and cords macrophages time to function Medullary sinuses Photomicrograph of part of a lymph node (72x) © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. Figure 20.4 Lymph node. Spleen Afferent