The Lymphatic and Immune Systems

1. The Lymphatic and Immune Systems Chapter 21

2. The Lymphatic and Immune Systems • Lymphatic system • Main function is to return excess tissue fluid to blood vascular system • Lymphatic vessels collect tissue fluid • Immune system • Protects our bodies from foreign organisms • Confers immunity to disease • Main components • Lymphocytes, lymphoid tissue, and lymphoid organs

3. The Lymphatic System • Lymphatic vessels collect tissue fluid from loose connective tissue • Carry fluid to great veins in the neck • Fluid flows only toward the heart • Once tissue fluid is within lymphatic vessels it is termed lymph • Functions of lymphatic vessels – collect excess tissue fluid and blood proteins • Return tissue fluid and blood proteins to bloodstream

4. Venous system Arterial system Heart Lymphatic system Lymph duct Lymph trunk Lymph node Lymphatic collecting vessels, with valves Blood capillaries Lymphatic capillary (a) Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries Orders of Lymphatic Vessels • Lymph capillaries – smallest lymph vessels • First to receive lymph • Lymphatic collecting vessels – collect from lymph capillaries • Lymph nodes are scattered along collection vessels

5. Orders of Lymphatic Vessels • Lymph nodes • Scattered along collecting vessels • Lymph trunks • Collect lymph from collecting vessels • Lymph ducts • Empty into veins of the neck

6. Lymphatic Capillaries • Located near blood capillaries • Receive tissue fluid from CT • Increased volume of tissue fluid • Minivalve flaps open and allow fluid to enter • High permeability allows entrance of • Tissue fluid and protein molecules • Bacteria, viruses, and cancer cells

7. Lymphatic Capillaries • Lacteals—specialized lymphatic capillaries • Located in the villi of the small intestines • Receive digested fats • Fatty lymph—chyle

8. Venous system Arterial system Heart Lymphatic system Lymph duct Lymph trunk Tissue fluid Lymph node Lymphatic collecting vessels, with valves Tissue cell Blood capillaries Lymphatic capillaries Blood capillaries Lymphatic capillary Filaments anchored to connective tissue (a) Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries Endothelial cell Flaplike minivalve Fibroblast in loose connective tissue (b) Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves. Distribution and Features of Lymphatic Capillaries Figure 21.1

9. Lymphatic Collecting Vessels • Accompany blood vessels • Composed of the same three tunics as blood vessels • Contain more valves than veins do • Helps direct the flow of blood • Lymph propelled by • Skeletal muscles bulging • Nearby arteries pulsing • Tunica media of the lymph vessels • Lymph flow is unaided by heartbeat

10. Lymph Nodes • Cleanse the lymph of pathogens • Human body contains around 500 • Superficial lymph nodes located in • Cervical, axillary, and inguinal regions • Deep nodes are • Tracheobronchial, aortic, and iliac lymph nodes

11. Regional lymph nodes Internal jugular vein Cervical nodes Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Axillary nodes Thoracic duct Cisterna chyli Aorta Inguinal nodes Lymphatic collecting vessels Drained by the right lymphatic duct Drained by the thoracic duct General Distribution of Lymphatic Collecting Vessels and Regional Lymph Nodes Figure 21.2

12. Microscopic Anatomy of a Lymph Node • Fibrous capsule—surrounds lymph nodes • Trabeculae—connective tissue strands • Lymph vessels • Afferent lymphatic vessels • Efferent lymphatic vessels

13. Cortex Afferent lymphatic vessels Lymphoid follicle Germinal center Subcapsular sinus Efferent lymphatic vessels Hilum Medulla Medullary cord Medullary sinus Trabeculae Capsule (a) Longitudinal view of the internal structure of a lymph node and associated lymphatics Microscopic Anatomy of a Lymph Node Figure 21.3a

14. Follicles Trabecula Subcapsular sinus Capsule Medullary cords Medullary sinuses (b) Photomicrograph of part of a lymph node (14X) Microscopic Anatomy of a Lymph Node Figure 21.3b

15. Macrophage Reticular cells on reticular fibers Lymphocytes Medullary sinus Reticular fiber (c) Reticular tissue within the medullary sinus (540X) Microscopic Anatomy of a Lymph Node Figure 21.3c

16. Lymph Trunks • Lymphatic collecting vessels converge • Five major lymph trunks • Lumbar trunks • Receives lymph from lower limbs • Intestinal trunk • Receives chyle from digestive organs • Bronchomediastinal trunks • Collects lymph from thoracic viscera

17. Lymph Trunks • Five major lymph trunks (continued) • Subclavian trunks • Receive lymph from upper limbs and thoracic wall • Jugular trunks • Drain lymph from the head and neck

18. Right jugular trunk Internal jugular veins Esophagus Right lymphatic duct Trachea Right subclavian trunk Left jugular trunk Left subclavian trunk Right subclavian vein Right broncho- mediastinal trunk Left subclavian vein Entrance of thoracic duct into vein Brachiocephalic veins Superior vena cava Left broncho- mediastinal trunk Azygos vein Ribs Thoracic duct Hemiazygos vein Cisterna chyli Right lumbar trunk Left lumbar trunk Inferior vena cava Intestinal trunk (a) Major lymphatic trunks and ducts in relation to veins and surrounding structures, anterior view The Lymphatic Trunks Figure 21.4a

19. Aorta Thoracic duct Azygos vein on vertebral bodies (b) Thoracic duct (colored green) along the posterior thoracic wall The Lymphatic Trunks Figure 21.4b

20. Lymph Ducts • Cisterna chyli • Located at the union of lumbar and intestinal trunks • Thoracic duct • Ascends along vertebral bodies • Empties into venous circulation • Junction of left internal jugular and left subclavian veins • Drains three quarters of the body

21. Right jugular trunk Internal jugular veins 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 Right Lymphatic Duct • Empties into right internal jugular and subclavian veins

22. The Immune System • Recognizes specific foreign molecules • Destroys pathogens effectively • Key cells—lymphocytes • Also includes lymphoid tissue and lymphoid organs • Lymphoid organs • Lymph nodes, spleen, thymus, tonsils, aggregated lymphoid nodules, and appendix

23. Lymphocytes • Infectious organisms attacked by inflammatory response • Macrophages, then lymphocytes • Are effective fighters of infectious organisms • Each lymphocyte recognizes a specific foreign molecule • Antigens are any molecules inducing a response from a lymphocyte

24. Lymphocytes • B lymphocytes and T lymphocytes are the two main classes of lymphocytes • Cytotoxic T lymphocytes • Attack foreign cells directly • Binds to antigen-bearing cells • Perforates cell membrane • Signals cell to undergo apoptosis • Destroy virus infected cells and some cancer cells

25. Lymphocytes • B lymphocytes • Become plasma cells • Secrete antibodies • Mark cells for destruction by macrophages • Respond primarily to bacteria and bacterial toxins

26. Target cell, bearing antigen T lymphocyte Dead target cell Antigen 1 3 2 T lymphocyte binds to target cell, secretes proteins that lyse the cell’s membrane, and signals the cell to die. T lymphocyte detaches from target cell. Target cell dies by apoptosis. (a) Action of cytotoxic T lymphocyte Antibodies B lymphocyte Plasma cell Bacterium Surface antigen Macrophage 3 2 1 B lymphocyte gives rise to plasma cell, which secretes antibodies. Antibodies bind to antigens on bacteria, marking the bacteria for destruction. Antibody-coated bacteria are avidly phagocytized. (b) Differentiation and activity of B lymphocyte Lymphocyte Function Figure 21.5

27. Lymphocyte Activation • Lymphocytes originate in bone marrow • Some travel to the thymus gland • T lymphocytes • Some stay in bone marrow • B lymphocytes • Able to recognize a unique antigen • Gain immunocompetence • Travels through blood stream • Meets and binds to a specific antigen

28. Lymphocyte Activation • During activation • Lymphocyte is presented its antigen by • A macrophage • Or a dendritic cell

29. Lymphocyte Activation • Both T and B lymphocytes produce clones of • Effector lymphocytes • Respond immediately, then die • Memory cells • Wait until the body encounters the antigen again • Basis of acquired immunity • Prevent subsequent infections of the same illness

30. Immature lymphocytes 1 Lymphocytes destined to become T cells migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. Red bone marrow: site of lymphocyte origin Red bone marrow Primary lymphoid organs: site of development of immuno- competence as B or T cells Thymus Bone marrow Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells 2 Immunocompetent but still naive lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues where they encounter their antigen. Lymph nodes, spleen, and other lymphoid tissues 3 Antigen-activated immuno- competent lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body. Lymphocyte Activation Figure 21.6

31. Lymphoid Tissue • Most important tissue of the immune system • Two general locations • Mucous membranes of • Digestive, urinary, respiratory, and reproductive tracts • Mucosa-associated lymphoid tissue (MALT) • Lymphoid organs (except thymus)

32. Intestine Lymphoid follicle Lumen Muscle layers Mucous membrane lining small intestine Lumen of intestine Germinal center Lymphoid tissue from mucosa of small intestine (14) Lymphoid Tissue Figure 21.7

33. Lymphoid Organs • Primary lymphoid organs • Bone marrow • Thymus • Secondary lymphoid organs • Lymph nodes, spleen, tonsils • Aggregated lymphoid nodules • Appendix

34. Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Aggregated lymphoid nodule (in intestine) Appendix Lymphoid Organs • Designed to gather and destroy infectious microorganisms and to store lymphocytes Figure 21.8

35. Thymus • Immature lymphocytes develop into T lymphocytes • Secretes thymic hormones • Most active in childhood • Functional tissue atrophies with age • Composed of cortex and medulla • Medulla contains Hassall’s corpuscles (thymic corpuseles) • Differs from other lymphoid organs • Functions strictly in lymphocyte maturation • Arises from epithelial tissue

36. Cortex Thymus Medulla Thymic corpuscle (a)Thymus located in the superior mediastinum (b) Micrograph of thymic tissue showing part of a lobule Thymus Figure 21.9

37. Lymph Nodes • Function • Lymph percolates through lymph sinuses • Most antigenic challenges occur in lymph nodes • Antigens destroyed and activate B and T lymphocytes

38. Spleen • Largest lymphoid organ • Two main blood-cleansing functions • Removal of blood-borne antigens • Removal and destruction of old or defective blood cells • Site of hematopoiesis in the fetus

39. Spleen • Destruction of antigens • Site of B cell maturation into plasma cells • Phagocytosis of bacteria and worn-out RBCs, WBCs and platelets • Storage of platelets

40. Spleen • White pulp • Thick sleeves of lymphoid tissue • Blood-borne antigens are destroyed as they activate the immune response • Provides the immune function of the spleen • Red pulp • Surrounds white pulp • Composed of • Venous sinuses • Splenic cords • Responsible for disposing of worn out RBCs

41. Capsule Trabecula Splenic cords Venous sinuses Arterioles and capillaries Red pulp White pulp Splenic artery Splenic vein Central artery Hilum (a) Diagram of the spleen, anterior view Splenic artery Splenic vein (b) Diagram of spleen histology Spleen Figure 21.10a, b

42. Capsule Diaphragm Spleen Adrenal gland White pulp Left kidney Red pulp Splenic artery Pancreas (d) Photomicrograph of spleen tissue (7). The white pulp, a lymphoid tissue with many lymphocytes, is surrounded by red pulp containing abundant erythrocytes. (c) Photograph of the spleen in its normal position in the abdominal cavity, anterior view Spleen Figure 21.10c, d

43. Tonsils • Simplest lymphoid organs • Four groups of tonsils • Palatine, lingual, pharyngeal, and tubal tonsils • Arranged in a ring to gather and remove pathogens • Underlying lamina propria consists of MALT

44. Pharyngeal tonsil Palatine tonsil Lingual tonsil Tonsil Germinal centers in lymphoid follicles Tonsillar crypt Palatine Tonsil Figure 21.11

45. Aggregated Lymphoid Nodules & Appendix • MALT—abundant in walls of intestines • Fight invading bacteria • Generate a wide variety of memory lymphocytes • Aggregated lymphoid nodules (Peyer’s patches) • Located in the distal part of the small intestine • Appendix—tubular offshoot of the cecum

46. Aggregated lymphoid nodules (Peyer’s patch) Smooth muscle in the intestinal wall Aggregated Lymphoid Nodule Figure 21.12

47. Disorders of the Lymphatic and Immune Systems • Chylothorax • Leakage of fatty lymph into the thorax • Lymphangitis • Inflammation of a lymph vessel • Mononucleosis • Viral disease caused by Epstein-Barr virus • Attacks B lymphocytes

48. Disorders of the Lymphatic and Immune Systems • Hodgkin’s disease • Malignancy of lymph nodes • Non-Hodgkin’s lymphoma • Uncontrolled multiplication and metastasis of undifferentiated lymphocytes

49. The Lymphatic and Immune Systems Throughout Life • Lymphatic vessels and lymph nodes • Develop from lymphatic sacs • Thymus originates as an outgrowth of the endoderm • Spleen, lymph nodes, and MALT • Arise from mesodermal mesenchyme