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Lymphoid System I & II

Lymphoid System I & II. Dr. Jack L. Haar Department of Anatomy and Neurobiology. Overview of Immune System. Functions Provides immune surveillance and defense Provides immune tolerance (distinguishes self from non-self) Absorbs lipids

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Lymphoid System I & II

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  1. Lymphoid System I & II Dr. Jack L. Haar Department of Anatomy and Neurobiology

  2. Overview of Immune System • Functions • Provides immune surveillance and defense • Provides immune tolerance (distinguishes self from non-self) • Absorbs lipids • Maintains fluid balance by returning tissue fluid and lymphocytes to the blood

  3. Overview continued • Concept of immunity • Immune system provides a way to recognize “self” from “non-self” • An individual mounts an immune response to foreign material • If person survives an attack by foreign material (infection), immunity may result, meaning the foreign material is “remembered” • Thus immunity has specificity and memory

  4. Overview continued • Terminology • Antigen: a foreign (non-self) substance. Could be bacterial, tumor cells, transplanted cells or virus-infected cells • Antibody: circulating protein in blood plasma (immunoglobulin) that interacts with a specific antigen • Humoral immunity: antibodies against antigen circulating in blood stream; produced by plasma cells derived from B lymphocytes • Cellular (cell-mediated) immunity: Immunocompetent cells contact, react against, and destroy antigen; mediated by T lymphocytes

  5. Major lymphoid organs and tissues

  6. Cells of the Immune response20 – 50% WBC’s are lymphocytes

  7. A. 35% of circulating lymphocytes are B lymphocytes or B cells Become Plasma cells or B memory cellsB. 65% of circulating lymphocytes are T lymphocytes or T cells Become Helper, Killer, or T memory cells

  8. ImmunoblastsForm from T or B lymphocytes when stimulated by Antigen • Antigen -presenting cellsMonocyte-macrophage derived. Process antigen to present to lymphocytes • Includes macrophages, epidermal Langerhans cells, dendritic cells of lymphoid organs, and epithelial cells of thymus

  9. Lines of Defense

  10. IV. ThymusLocated in mediastinum

  11. Thymus undergoes involution with age • Is influenced by adrenal cortical steroids and radiation • Thymus is a bilobed organ

  12. Stroma formed from thymic epithelial cells with bundles of tonofibrils and linked by desmosomes • Thymocytes develop from HSC from yolk sac (mesoblastic), fetal liver (hepatic), and bone marrow (myeloid) phases of development • Thymus is not exposed to external environment

  13. Histology • Dense irregular CT capsule • Septa form lobules • Cortex and medulla • Stroma formed from thymic epithelial cells

  14. Cortex • Thymic epithelial cells • Large numbers of thymocytes (lymphocytes) • Macrophages

  15. Medulla • Thymocytes are larger and fewer in number than in cortex Only 5% of thymocytes are in the medulla • Hassall’s corpuscles form from the stromal cells Keratohyaline granules

  16. Vessels enter and leave through the capsule and follow the septa • Blood thymus barrier

  17. Function of the thymus • Thymus is seeded with HSC’s • Thymocytes proliferate in cortex • Self-reactive thymocytes are eliminated • Non-self reactive cells migrate to medulla • Cells enter blood stream and migrate to secondary lymphoid organs • They occupy T-dependant areas of lymphoid organs where they nest, divide, and mature • The thymus is an endocrine organ and responds to many hormones, viz. ACTH, GH, and sex hormones • Thymectomy at birth impairs immune function

  18. Bursa of Fabricius • Functions in birds as primary lymphoid organ giving rise to B-lymphocytes

  19. Bone marrow • Functions in mammals as primary lymphoid organ giving rise to B-lymphocytes

  20. Lines of Defense

  21. Outer Line of Defense - MALT

  22. MALT • GI tract • Respiratory tract • Genito-urinary tract • Diffuse lymphatic tissue • Lamina propria • Reticular fibers • Lymphocytes • Primary lymphatic nodule

  23. Secondary Lymphatic nodule • Germinal center • B-dependant spherical area • Cap of tightly packed small lymphocytes • Not encapsulated by C.T.

  24. Germinal center • Oval pale-staining area • Contains dividing cells and macrophages

  25. Solitary nodules • Not encapsulated by C.T. • May be primary or secondary

  26. High endothelial venules • Associated with diffuse lymphatic tissue • Allow lymphocytes to escape from vessel

  27. Locations of aggregates of nodules • Peyer’s patches • Typhoid nodules • Appendix

  28. Typhoid Fever - a bacterial illness caused by Salmonella typhi

  29. Appendix

  30. Tonsils1. Palatine 2. Lingual 3. Pharyngeal

  31. Lymphoid System II Dr. Jack L. Haar Department of Anatomy and Neurobiology

  32. Lines of Defense

  33. Inner Line of Defense

  34. Lymphatic Vessels • Lymphatic capillaries • Lacteals for lipid • Valves direct flow • Asymmetrical system • Edema

  35. Lymphatic filariasis, also known as elephantiasis, is best known from dramatic photos of people with grossly enlarged or swollen arms and legs. The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million of these people have serious disease.

  36. Lymph node Histology • Distributed along vessels • Filter lymph • Produce lymphocytes • Dense CT capsule • Afferent lymphatics on convex surface • Reticular fiber framework Subcapsular sinus Lymphoid nodule in cortex

  37. Hilus • Blood vessels enter and leave • Efferent lymphatics leave node

  38. Cortex of lymph node • Lymphoid nodules and diffuse lymphatic tissue • Lymphatic sinuses • Subcapsular • Cortical

  39. Medulla of lymph node • Medullary cords • Medullary sinuses

  40. Blood vessels follow trabeculae into nodeHEV with cuboidal endothelium Lymphocytes pass from blood into lymph node

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