The Lymphatic System and Immunity

1. The Lymphatic System and Immunity

2. Functions Draining excess interstitial fluid Transporting dietary lipids

3. Lymphatic vessels: • In spaces between cells • Closed at one end, • converge to form larger • vessels (like veins) to trunks • to right and left duct to • venous blood • Contain valves to ensure one • way movement • Flow through lymph nodes • (masses of B and T cells) • Lymphatic capillaries: • Anchored by elastic • filaments • Open and close with • pressure differences

5. Lymphatic Organs & Tissues • Divided into 2 groups • Primary lymphatic organs • Sites where stem cells divide & become immunocompetent • Red bone marrow, thymus • Secondary lymphatic organs • Sites where immune response occurs • Lymph nodes, spleen, lymphatic nodules, etc.

6. Thymus: • Located between sternum and aorta (mediastinum) • Two lobes divided into lobules • Cortex (outer layer) of immature cells • -T cells: antigenic activity: • -dendritic cells: assist maturation • -epithelial cells: “educate” pre-T cells by positive selection • -macrophages: clear debris and dead cells • Medulla (inner layer) of mature T cells, epithelial cells, dendritic cells, and macrophages

7. Lymph nodes: • Lymph flows in • through afferent • vessels and out • through efferent • vessels • Made up of nodules • -Primary nodules: B cells • -Secondary nodules: plasma cell and memory B cell formation

8. Spleen: • Located between stomach and • diaphragm • Contains white and red pulp • -White pulp: lymphocytes and macrophages around central arteries • -Red pulp: red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes • Removes worn out or defective • RBCs • Stores platelet • Produces blood cells in fetus

9. Lymphatic nodules: no capsule • Throughout mucus membranes (MALT= mucosa-associated lymphatic tissue) • Tonsils MALT

10. Figure 12.6

11. Nonspecific Resistance/ • Innate Defenses: born with and offer immediate protection • First line of defense- • skin and mucous • membranes • Physical and chemical • barrier

12. Nonspecific Resistance Barriers

13. Phagocyte Inflammation NK

15. Figure 12.7

16. Adaptive Defense System: Third Line of Defense • Three aspects of adaptive defense • Antigen specific—recognizes and acts against particular foreign substances • Systemic—not restricted to the initial infection site • Memory—recognizes and mounts a stronger attack on previously encountered pathogens

17. Adaptive Defense System: Third Line of Defense • Cells of the adaptive defense system • Lymphocytes respond to specific antigens • B lymphocytes (B cells) • T lymphocytes (T cells) • Macrophages help lymphocytes

18. Adaptive Defense System: Third Line of Defense • Immunocompetent—cell becomes capable of responding to a specific antigen by binding to it • Cells of the adaptive defense system • Lymphocytes • Originate from hemocytoblasts in the red bone marrow • B lymphocytes become immunocompetent in the bone marrow (remember B for Bone marrow) • T lymphocytes become immunocompetent in the thymus (remember T for Thymus)

20. KEY: Red bone marrow: site of lymphocyte origin Primary lymphoid organs: site of development of immunocompetence as B or T cells Red bone marrow Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells Immature (naive) lymphocytes Figure 12.11, step 1a

21. KEY: Red bone marrow: site of lymphocyte origin Primary lymphoid organs: site of development of immunocompetence as B or T cells Red bone marrow Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells Immature (naive) lymphocytes Lymphocytes destined to become T cells migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. 1 Thymus Bone marrow Figure 12.11, step 1b

22. KEY: Red bone marrow: site of lymphocyte origin Primary lymphoid organs: site of development of immunocompetence as B or T cells Red bone marrow Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells Immature (naive) lymphocytes Lymphocytes destined to become T cells migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. 1 Thymus Bone marrow 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 and become activated. 2 Lymph nodes, spleen, and other lymphoid tissues Figure 12.11, step 2

23. KEY: Red bone marrow: site of lymphocyte origin Primary lymphoid organs: site of development of immunocompetence as B or T cells Red bone marrow Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells Immature (naive) lymphocytes Lymphocytes destined to become T cells migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. 1 Thymus Bone marrow 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 and become activated. 2 Lymph nodes, spleen, and other lymphoid tissues Antigen-activated (mature) immunocompetent lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body. 3 Figure 12.11, step 3

24. Helper T Cell Cytotoxic T Cell

26. Hapten

32. Active immunity

33. Artificially-acquired active immunity Passive immunity