Lymphatic System: Structure, Function, and Immune Role

. What is the main function of the lymphatic system

— Returns leaked fluid and plasma proteins from tissues back to the blood.

2. What are the three parts of the lymphatic system

— Lymphatic vessels, lymph, and lymph nodes.

3. What is lymph

— Interstitial fluid after it enters lymphatic vessels.

4. How does lymph flow through the body

— One-way, toward the heart.

5. How much fluid does the lymphatic system return to the blood each day

— About 3 L per day.

6. What are the three types of lymphatic vessels

— Lymphatic capillaries, collecting lymphatic vessels, and lymphatic trunks/ducts.

7. What is the function of lymphatic vessels

— Return interstitial fluid and leaked plasma proteins to the blood.

8. What are lymphatic capillaries

— Blind-ended tubes that collect excess tissue fluid.

9. How are lymphatic capillaries different from blood capillaries

— They are much more permeable and have overlapping endothelial cells.

10. What do overlapping endothelial cells of lymphatic capillaries form

— Flaplike minivalves.

11. What is the function of lymphatic minivalves

— Allow fluid to enter but prevent it from flowing backward.

12. What anchors lymphatic capillaries to connective tissue

— Collagen filaments.

13. Why are lymphatic capillaries anchored by collagen filaments

— To prevent the capillaries from collapsing.

14. What happens to lymphatic minivalves when extracellular fluid volume increases

— They open.

15. What can lymphatic capillaries take up

— Proteins, cell debris, pathogens, and cancer cells.

16. Where are lymphatic capillaries absent

— Bones, teeth, bone marrow, cartilage, and the CNS.

17. What are lacteals

— Specialized lymphatic capillaries in the intestinal mucosa.

18. What is the function of lacteals

— Absorb digested fats and deliver fatty lymph to the blood.

19. What is fatty lymph called

— Chyle.

20. How are lymphatic collecting vessels similar to veins

— Both have valves and carry fluid toward the heart.

21. How are lymphatic collecting vessels different from veins

— They have thinner walls, more internal valves, and more frequent anastomoses.

22. Where do collecting lymphatic vessels in the skin travel

— With superficial veins.

23. Where do deep lymphatic vessels travel

— With arteries.

24. What supplies nutrients to lymphatic collecting vessels

— Branching vasa vasorum.

25. What are lymphatic trunks

— Large vessels formed by the union of the largest collecting lymphatic vessels.

26. What are the paired lymphatic trunks

— Lumbar, bronchomediastinal, subclavian, and jugular trunks.

27. What is the single unpaired lymphatic trunk

— The intestinal trunk.

28. How many major lymphatic ducts are there

— Two: the right lymphatic duct and thoracic duct.

29. What does the right lymphatic duct drain

— The right upper arm and right side of the head and thorax.

30. What does the thoracic duct drain

— The rest of the body.

31. Where does the thoracic duct arise

— From the cisterna chyli.

32. Where do the lymphatic ducts empty lymph

— Into the venous circulation at the junction of the internal jugular and subclavian veins.

33. What mechanisms propel lymph through lymphatic vessels

— Skeletal muscle, breathing, valves, arterial pulsations, and smooth muscle contractions.

34. How does skeletal muscle help move lymph

— Its milking action compresses lymphatic vessels.

35. How does breathing help move lymph

— Pressure changes in the thorax help propel lymph.

36. How do valves help move lymph

— They prevent backflow.

37. How do nearby arteries help move lymph

— Their pulsations help compress lymphatic vessels.

38. How does smooth muscle help move lymph

— Contractions in lymphatic vessel walls propel lymph.

39. What are lymphoid organs and tissues

— Structures that provide the structural basis of the immune system.

40. What types of cells are housed in lymphoid organs and tissues

— Phagocytic cells and lymphocytes.

41. What are the major lymphoid organs and tissues

— Spleen, thymus, tonsils, and other lymphoid tissues.

42. What are lymphocytes

— The main warriors of the immune system.

43. Where do lymphocytes originate

— Red bone marrow.

44. What are the two main types of lymphocytes

— T cells and B cells.

45. What do T cells and B cells protect against

— Antigens.

46. What is an antigen

— Anything the body perceives as foreign.

47. What are examples of antigens

— Bacteria, bacterial toxins, viruses, mismatched RBCs, and cancer cells.

48. What do T cells do

— Manage immune responses and attack and destroy infected cells.

49. What do B cells do

— Produce plasma cells that secrete antibodies.

50. What do antibodies do

— Mark antigens for destruction by phagocytosis or other means.

51. What do macrophages do

— Phagocytize foreign substances and help activate T cells.

52. What do dendritic cells do

— Capture antigens and deliver them to lymph nodes.

53. What do reticular cells do

— Produce reticular fiber stroma that supports other cells in lymphoid organs.

54. What is lymphoid tissue

— Tissue that houses and provides a site for lymphocyte proliferation.

55. What is the main connective tissue found in lymphoid tissue

— Reticular connective tissue.

56. What are the two main types of lymphoid tissue

— Diffuse lymphoid tissue and lymphoid follicles.

57. What is diffuse lymphoid tissue

— Lymphoid cells and reticular fibers found throughout body organs.

58. What are lymphoid follicles

— Solid, spherical bodies of tightly packed lymphoid cells and reticular fibers.

59. What is found in the germinal centers of lymphoid follicles

— Proliferating B cells.

60. Where can isolated lymphoid follicles be found

— In structures such as the appendix and Peyer's patches.

61. What are lymph nodes

— Principal lymphoid organs that are embedded in connective tissue along lymphatic vessels.

62. Where are lymph nodes commonly located near the body surface

— Inguinal, axillary, and cervical regions.

63. What are the two major functions of lymph nodes

— Filter lymph and activate the immune system.

64. How do lymph nodes filter lymph

— Macrophages destroy microorganisms and debris.

65. How do lymph nodes activate the immune system

— Lymphocytes become activated and mount an attack against antigens.

66. What is the typical shape of a lymph node

— Most are bean-shaped.

67. What surrounds a lymph node

— An external fibrous capsule.

68. What are trabeculae

— Extensions of the capsule that divide the lymph node into compartments.

69. What are the two main regions of a lymph node

— Cortex and medulla.

70. What is found in the cortex of a lymph node

— Lymphoid follicles with germinal centers containing dividing B cells.

71. What cells are found near lymph node follicles

— Dendritic cells.

72. What is found in the deep cortex of a lymph node

— T cells in transit.

73. How do T cells circulate

— Continuously among the blood, lymph nodes, and lymph.

74. What are medullary cords

— Structures extending inward from the cortex that contain B cells, T cells, and plasma cells.

75. What is found in lymph node sinuses

— Macrophages.

76. What are afferent lymphatic vessels

— Vessels that bring lymph into a lymph node.

77. What are efferent lymphatic vessels

— Vessels that carry lymph away from a lymph node.

78. What is the hilum of a lymph node

— The region where vessels enter and leave the lymph node.

79. What is the spleen

— The largest lymphoid organ.

80. What vessels enter and leave the spleen at the hilum

— The splenic artery and splenic vein.

81. What are the immune functions of the spleen

— Lymphocyte proliferation, immune surveillance, and immune response.

82. What does the spleen cleanse from the blood

— Aged cells, platelets, debris, and bloodborne pathogens.

83. What does the spleen store for later reuse

— Breakdown products of RBCs, such as iron.

84. What else does the spleen store

— Blood platelets and monocytes.

85. What can the spleen do during fetal development

— Produce erythrocytes.

86. What are the two distinct areas of the spleen

— White pulp and red pulp.

87. Where is white pulp located

— Around central arteries.

88. What is white pulp mostly composed of

— Lymphocytes on reticular fibers.

89. What is the function of white pulp

— Immune functions.

90. What is red pulp composed of

— Splenic cords and sinusoids.

91. What is red pulp rich in

— RBCs and macrophages.

92. What is the function of red pulp

— Disposal of worn-out RBCs and bloodborne pathogens.

93. What is the main function of the thymus

— T-lymphocyte maturation and development of central tolerance.

94. What does the thymus teach T lymphocytes

— To differentiate self from non-self.

95. Where is the thymus located

— In the inferior neck, extending into the mediastinum and partially overlying the heart.

96. When is the thymus most active

— During the neonatal and pre-adolescent periods.

97. What happens to the thymus during adolescence

— It stops growing and gradually atrophies.

98. What are the two regions of thymic lobules

— Outer cortex and inner medulla.

99. What is found in the thymic cortex

— Rapidly dividing lymphocytes and scattered macrophages.

100. What is found in the thymic medulla

— Fewer lymphocytes and thymic corpuscles involved in regulatory T-cell development.