1. Lymphatic System Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th ed. Portions copyright Pearson Education

2. Functions Lymphatic System Solves a plumbing problem: leaky pipes Returns fluids that leaked from blood vessels (capillaries) back to blood Solves a security problem Monitors for presence of foreign material and initiates defensive countermeasures when necessary

3. Functions Lymphatic System Components 1.Lymphatic vessels (lymphatics) 2.Lymphoid organs and tissues Monitor lymph and initiate immune response if pathogens or abnormal cells are detected; provide a home for immune cells 3.Lymph – fluid in vessels

4. Dept. of K.A.A.P. Lymphatic Vessels (lymphatics) Return interstitial fluid and leaked plasma proteins back to blood Approximately 3L / day Once interstitial fluid enters lymphatics, it is called lymph

5. Lymphatic Vessels One-way system; lymph flows toward heart Lymph vessels (lymphatics) include: Lymphatic capillaries Collecting lymphatic vessels Lymphatic trunks and ducts

6. Dept. of K.A.A.P. Marieb & Hoehn 9 th ed. Fig 20.01a

7. © 2013 Pearson Education, Inc. Lymphatic Capillaries Similar to blood capillaries, except –Very permeable (take up proteins, cell debris, pathogens, and cancer cells) Endothelial cells overlap loosely to form one-way minivalves Anchored by collagen filaments, preventing collapse of capillaries; increased ECF volume opens minivalves –Pathogens travel throughout body via lymphatics

8. © 2013 Pearson Education, Inc. Lymphatic Capillaries Absent from bones, teeth, bone marrow, and CNS Lacteals: specialized lymph capillaries present in intestinal mucosa –Absorb digested fat and deliver fatty lymph (chyle) to the blood

9. © 2013 Pearson Education, Inc. Figure 20.1b Distribution and special features of 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, forming flaplike minivalves.

10. © 2013 Pearson Education, Inc. Lymphatic Collecting Vessels Similar to veins, except –Have thinner walls, with more internal valves –Anastomose more frequently Collecting vessels in skin travel with superficial veins Deep vessels travel with arteries Nutrients supplied from branching vasa vasorum

11. © 2013 Pearson Education, Inc. Lymphatic Trunks Formed by union of largest collecting ducts –Paired lumbar –Paired bronchomediastinal –Paired subclavian –Paired jugular trunks –Single intestinal trunk

12. © 2013 Pearson Education, Inc. Lymphatic Ducts Lymph delivered into one of two large ducts –Right lymphatic duct drains right upper arm and right side of head and thorax –Thoracic duct arises as cisterna chyli; drains rest of body Each empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body

13. © 2013 Pearson Education, Inc. Internal jugular vein Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Thoracic duct Cisterna chyli Collecting lymphatic vessels Regional lymph nodes: Cervical nodes Axillary nodes Inguinal nodes Aorta Drained by the right lymphatic duct Drained by the thoracic duct Lymphatic vessels and ducts

14. © 2013 Pearson Education, Inc. Right jugular trunk Right lymphatic duct Right subclavian trunk Right subclavian vein Right broncho- mediastinal trunk Brachiocephalic veins Superior vena cava Azygos vein Cisterna chyli Right lumbar trunk Lymphatic Vessels Anterior view of thoracic and abdominal wall. Internal jugular veins Esophagus Trachea Left jugular trunk Left subclavian trunk Left subclavian vein Entrance of thoracic duct into vein Left broncho- mediastinal trunk Ribs Thoracic duct Hemiazygos vein Left lumbar trunk Inferior vena cava Intestinal trunk

15. © 2013 Pearson Education, Inc. Lymph Transport Lymph propelled by –Milking action of skeletal muscle –Pressure changes in thorax during breathing –Valves to prevent backflow –Pulsations of nearby arteries –Contractions of smooth muscle in walls of lymphatics

16. Dept. of K.A.A.P. Lymphoid Organs and Tissues Structural basis of immune system House phagocytic cells and lymphocytes Structures Lymph nodes Spleen Thymus “MALT”: mucosa-associated lymphoid tissue Tonsils, Peyer’s patches, appendix

17. © 2013 Pearson Education, Inc. Lymphoid Cells Lymphocytes main warriors of immune system –Arise in red bone marrow Mature into one of two main varieties –T cells (T lymphocytes) –B cells (B lymphocytes)

18. © 2013 Pearson Education, Inc. Lymphocytes T cells and B cells protect against antigens –Anything body perceives as foreign Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells

19. © 2013 Pearson Education, Inc. Lymphocytes T cells –Manage immune response –Attack and destroy infected cells B cells –Produce plasma cells, which secrete antibodies Antibodies mark antigens for destruction by phagocytosis or other means

20. © 2013 Pearson Education, Inc. Other Lymphoid Cells Macrophages phagocytize foreign substances; help activate T cells Dendritic cells capture antigens and deliver them to lymph nodes; activate T cells Reticular cells produce reticular fiber stroma that supports other cells in lymphoid organs

21. © 2013 Pearson Education, Inc. Figure 20.3 Reticular connective tissue in a human lymph node. Macrophage Reticular cells on reticular fibers Lymphocytes Medullary sinus Reticular fiber

22. © 2013 Pearson Education, Inc. Lymphoid Tissue Home and proliferation site for lymphocytes Surveillance vantage point for lymphocytes and macrophages Largely reticular connective tissue Two main types Diffuse lymphoid tissue Lymphoid follicles

23. © 2013 Pearson Education, Inc. Diffuse Lymphoid Tissue Lymphoid cells and reticular fibers in almost all body organs Larger collections are found in lamina propria of mucous membranes: MALT

24. © 2013 Pearson Education, Inc. Lymphoid Follicles (Nodules) Solid, spherical bodies of tightly packed lymphoid cells and reticular fibers – Germinal centers of proliferating B cells – May form part of larger lymphoid organs – Isolated aggregations of Peyer's patches and in appendix

25. © 2013 Pearson Education, Inc. Lymphoid Organs Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (aggregated lymphoid nodules in small intestine) Appendix

26. © 2013 Pearson Education, Inc. Lymph Nodes Principal lymphoid organs of body Embedded in connective tissue, in clusters along lymphatic vessels Near body surface in inguinal, axillary, and cervical regions of body

27. © 2013 Pearson Education, Inc. Internal jugular vein Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Thoracic duct Cisterna chyli Collecting lymphatic vessels Regional lymph nodes: Cervical nodes Axillary nodes Inguinal nodes Aorta Drained by the right lymphatic duct Drained by the thoracic duct Lymph node distribution

28. © 2013 Pearson Education, Inc. Lymph Nodes Functions 1.Filter lymph—macrophages destroy microorganisms and debris 2.Immune system activation—lymphocytes activated and mount attack against antigens

29. © 2013 Pearson Education, Inc. Structure of a Lymph Node Vary in shape and size but most bean shaped External fibrous capsule Trabeculae extend inward and divide node into compartments Two histologically distinct regions –Cortex –Medulla

30. © 2013 Pearson Education, Inc. Structure of a Lymph Node Cortex contains follicles with germinal centers, heavy with dividing B cells Dendritic cells nearly encapsulate follicles Deep cortex houses T cells in transit T cells circulate continuously among blood, lymph nodes, and lymph

31. © 2013 Pearson Education, Inc. Figure 20.4a Lymph node. Afferent lymphatic vessels Cortex Lymphoid follicle Germinal center Subcapsular sinus Efferent lymphatic vessels Trabeculae Medullary sinus Medullary cord Medulla Hilum Longitudinal view of the internal structure of a lymph node and associated lymphatics Capsule

32. © 2013 Pearson Education, Inc. Structure of a Lymph Node Medullary cords extend inward from cortex and contain B cells, T cells, and plasma cells Lymph sinuses contain macrophages

33. © 2013 Pearson Education, Inc. Figure 20.4b Lymph node. Follicles Trabecula Subcapsular sinus Capsule Medullary cords Medullary sinuses Photomicrograph of part of a lymph node (72 x )

34. © 2013 Pearson Education, Inc. Circulation in the Lymph Nodes Lymph –Enters convex side via afferent lymphatic vessels; travels through large subcapsular sinus and smaller sinuses to medullary sinuses; exits concave side at hilum via efferent vessels Fewer efferent vessels so flow somewhat stagnate; allows lymphocytes and macrophages time to function

35. © 2013 Pearson Education, Inc. Figure 20.4 Lymph node. Afferent lymphatic vessels Cortex Lymphoid follicle Germinal center Subcapsular sinus Efferent lymphatic vessels Follicles Trabecula Subcapsular sinus Capsule Medullary cords Medullary sinuses Trabeculae Medullary sinus Medullary cord Medulla Hilum Longitudinal view of the internal structure of a lymph node and associated lymphatics Photomicrograph of part of a lymph node (72 x ) Capsule

36. KAAP The procedure involves the injection of a dye (sometimes mildly radioactive) to pinpoint the lymph node which is closest to the cancer site. Sentinel node biopsy is used to stage many kinds of cancer, including lung and skin (melanoma). NYT ©2009. Sentinel node biopsy is a technique which helps determine if a cancer has spread (metastasized), or is contained locally. When a cancer has been detected, often the next step is to find the lymph node closest to the tumor site and retrieve it for analysis. The concept of the "sentinel" node, or the first node to drain the area of the cancer, allows a more accurate staging of the cancer, and leaves unaffected nodes behind to continue the important job of draining fluids. NYT ©2009.

37. © 2013 Pearson Education, Inc. Spleen Largest lymphoid organ Served by splenic artery and vein, which enter and exit at the hilum Functions –Site of lymphocyte proliferation and immune surveillance and response –Cleanses blood of aged cells and platelets, macrophages remove debris

38. © 2013 Pearson Education, Inc. Figure 20.6c The spleen. Diaphragm Spleen Adrenal gland Left kidney Splenic artery Pancreas Photograph of the spleen in its normal position in the abdominal cavity, anterior view.

39. © 2013 Pearson Education, Inc. Spleen: Additional Functions Stores breakdown products of RBCs (e.g., iron) for later reuse Stores blood platelets and monocytes May be site of fetal erythrocyte production (normally ceases before birth) Encased by fibrous capsule; has trabeculae Contains lymphocytes, macrophages, and huge numbers of erythrocytes

40. © 2013 Pearson Education, Inc. Structure of the Spleen Two distinct areas –White pulp around central arteries Mostly lymphocytes on reticular fibers; involved in immune functions –Red pulp in venous sinuses and splenic cords Rich in RBCs and macrophages for disposal of worn-out RBCs and bloodborne pathogens Composed of splenic cords and sinusoids

41. © 2013 Pearson Education, Inc. Figure 20.6a–b The spleen. Splenic artery Splenic vein Hilum Diagram of the spleen, anterior view Capsule Trabecula Splenic cords Splenic sinusoids Arterioles and capillaries Red pulp White pulp Central artery Splenic artery Splenic vein Diagram of spleen histology

42. © 2013 Pearson Education, Inc. Thymus Important functions early in life Found in inferior neck; extends into mediastinum; partially overlies heart Increases in size and most active during childhood Stops growing during adolescence, then gradually atrophies –Still produces immunocompetent cells, though slowly

43. © 2013 Pearson Education, Inc. Thymus Thymic lobules contain outer cortex and inner medulla Most thymic cells are lymphocytes –Cortex contains rapidly dividing lymphocytes and scattered macrophages Medulla contains fewer lymphocytes and thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)

44. © 2013 Pearson Education, Inc. Capsule Cortex Medulla Thymic corpuscles Figure 20.7 The thymus.

45. © 2013 Pearson Education, Inc. Thymus Differs from other lymphoid organs in important ways –Has no follicles because it lacks B cells –Does not directly fight antigens Functions strictly in T lymphocyte maturation –Keeps isolated via blood thymus barrier Stroma of epithelial cells (not reticular fibers) –Provide environment in which T lymphocytes become immunocompetent

46. © 2013 Pearson Education, Inc. Mucosa-associated Lymphoid Tissue (MALT) Lymphoid tissues in mucous membranes throughout body Protects from pathogens trying to enter body Largest collections of MALT in tonsils, Peyer's patches, appendix Also in mucosa of respiratory and genitourinary organs; rest of digestive tract

47. © 2013 Pearson Education, Inc. Tonsils Simplest lymphoid organs Form ring of lymphatic tissue around pharynx –Palatine tonsils—at posterior end of oral cavity –Lingual tonsil—grouped at base of tongue –Pharyngeal tonsil—in posterior wall of nasopharynx –Tubal tonsils—surrounding openings of auditory tubes into pharynx Gather and remove pathogens in food or air

48. © 2013 Pearson Education, Inc. Tonsils Contain follicles with germinal centers Are not fully encapsulated Overlying epithelium invaginates forming tonsillar crypts –Trap and destroy bacteria and particulate matter –Allow immune cells to build memory for pathogens

49. © 2013 Pearson Education, Inc. Figure 20.8 Histology of the palatine tonsil. Pharyngeal tonsil Palatine tonsil Lingual tonsil Germinal centers in lymphoid follicles Tonsillar crypt

50. © 2013 Pearson Education, Inc. Aggregates of Lymphoid Follicles Peyer's patches and appendix –Clusters of lymphoid follicles –In wall of distal portion of small intestine –Similar structures are also found in the appendix –Destroy bacteria, preventing them from breaching intestinal wall –Generate "memory" lymphocytes

51. © 2013 Pearson Education, Inc. Figure 20.9 Peyer’s patch (aggregated lymphoid nodules). Follicles of a Peyer’s patch (aggregated lymphoid nodules) Smooth muscle in the intestinal wall

52. College or Department name here Spleen images Splenic cyst: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJM200311273492222 http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJM200311273492222 Pelvic spleen: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMicm0802024 http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMicm0802024 Impaled rower: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMcpc079004 http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMcpc079004

53. Dept. of K.A.A.P. Figure 1. Computed Tomography of the Abdomen. Coronal (Panel A) and axial (Panel B) images show splenomegaly (30 cm in greatest length, Panel A) and scattered, slightly enlarged lymph nodes in the para-aortic and splenic hilar regions (arrows, Panel B). Abramson, Chatterji, Rahemtullah. “Case 39-2008 — A 51-Year-Old Woman with Splenomegaly and Anemia”. N Engl J Med 2008; 359:2707-2718 Dx: Splenic marginal-zone lymphoma (a lymphoma of B cells) Tx: Splenectomy, followed 15 mos later by chemotherapy when cancer symptoms returned.

54. College or Department name here Abramson, Chatterji, Rahemtullah. “Case 39-2008 — A 51-Year-Old Woman with Splenomegaly and Anemia”. N Engl J Med 2008; 359:2707-2718