Chapter 8 Lymphoid system

1. Chapter 8 Lymphoid system

2. General organization of lymphoid organ: largely consist of lymphoid tissue Reticular tissue:stellate-shaped with processes to form network Diffuse lymphoid tissue Lymphoid nodules Cells: Lymphocyte (chiefly) Plasma cell antigen presenting cell other cells

3. a. Diffuse lymphoid tissue: • no clear boundary • mainly consists of T-lymphocyte • postcapillary venules: -high endothelial venules, lining of tall cuboidal cells -opening for lymphocyte enter lymphoid tissue from blood Lymphoid nodule Diffuse LT

4. b. Lymphoid nodule: • spherical or ovoid • have clear boundaries • mainly composed of B-lymphocyte • germinal center: lighter-stained central zone, these cells produce antibody-synthesizing plasma cells

5. Cells of lymphatic tissue

6. 1) Lymphocyte: a. T-lymphocytes: • cytotoxic T cell: Tc C- kill the tumor cell, virus infective cell and foreign cell • helper T cell: Th C- stimulate the B-lymphocyte differentiate into plasma cell • suppressor T cell: Ts C – regulate the function of B-lymphocyte and T-lymphocyte b. B-lymphocytes: become into plasma cell c. NK cell: attack virus infective cell and tumor cell without previous stimulation

7. 2) Plasma cell 3) Antigen presenting cell: a. dendritic cell b.macrophage Antigen processing is a necessary preliminary step for activation of T cell.

8. 4) other cells: • granulated cell • mast cell • blood platelet • blood-bone stem cell Function: i.      immunologic defense ii.     immune surveillance iii.    immune homeostasis

9. Lymphatic organs:central lymphatic organs: produce the lymphocyte antigen-independent proliferation contain: thymus---T-lymphocyte bone marrow---B-lymphocyteperipheral lymphatic organs: receive the lymphocyte and perform the immune response antigen-dependent proliferation contain: lymph node spleen tonsils

10. The immune system: • consists of the lymphatic organs, lymphocytes of the blood and lymph, and collections of different types of lymphocytes dispersed throughout the connective tissue. • is essential to the body’s immunological defense against bacteria, viruses and other foreign bodies. • Immune response: • Cellular immunity: involving mainly T-lymphocytes • Humoral immunity: involving mainly B-lymphocytes • Mast cells, macrophages and other white blood cells are also involved in the immune response.

11. thymus • A flattened, bi-lobed structure lying in the superior mediastinum • In the new-born child it is at its greatest size relative to body size • Thymus continue to grow until puberty when it is replaced by fibrofatty tissue

12. Structure: • Capsule ( C.T.) interlobular septa (trabecula) Endothelial reticular cell (ERC) Lymphocyte: thymocyte Macrophage: secrete IL-1 • Cortex: ERC Lymphocyte: few Macrophage: secrete IL-1 Thymic corpuscles • Medulla:

13. Thymus

14. Cortex medulla

15. The cortex of thymus A very active site of lymphocyte production More than 90% of the thymocyte degenerate in this area, only less than 10% of thymocyte will mature and leave the thymus as T-lymphocytes through the postcapillary venules. Endothelial reticular cell (ERC)

17. The medulla of thymus • Hassall’s ( thymic) corpuscles • a characteristic feature of the thymus • their significance is as yet unknown

18. Hassall’s ( thymic) corpuscles spherical or ovoid body, 20-150um in diameter, composed of concentrically-arranged epithelial reticular cells, the central cells often show degeneration

19. Blood-thymus barrier: provide a stable environment for lymphocytes developing in the cortex---prevents circular antigens from reaching the thymic cortex where T cells are being formed Consists of : • endothelial cell of continuous capillary • very thick basement membrane • perivascular space with macrophage in it • basement membrane of ERC • ERC or their processes with desmosome

20. Thymus function: • the thymic epithelial reticular cells can secrete thymic hormones (thymosin, thymolin, thymopoietin) • induce the stem cell to differentiate into T-lymphocyte

21. Adult thymus has high infiltration of adipose tissue (A)

22. Older adult thymus has large amounts of adipose tissue

23. Lymph node • A mass of lymphatic tissue enclosed in a capsule of connective tissue • Widely scattered along the course of lymph vessels • Concentrated in area in neck, axilla (arm pits), and groin.

24. Structure ---capsule: CT, trabeculae or septa ---cortex: outer densely-stained part ---medulla: inner paler-stained part hilum

25. Structure: • capsule trabecula several afferent lymph vessels, • cortex lymphoid nodule (B-LC) internodule zone out cortex: (superficial cortex) inner cortex: diffuse lymphoid tissue (T-LC) (paracortical zone) subcapsular sinus: peritrabecular sinus macrophage cortical lymphatic sinuses

26. capsule outer cortex inner cortex

27. SS: subcapsular sinus T: trabecular

28. Capsule Subcapsular sinuses Trabeculae

29. Afferent lymph vessels GC

30. Postcapillary venules in inner cortex

31. Medulla • ---medullary cord: • LT cord: • B-lymphocyte, plasma cell, macrophage, mast cell • ---medullary sinus: • similar to cortical sinus and connect with them • more macrophage

32. capsule outer cortex inner cortex

33. Passage of lymph in lymph node Afferent lymph vessels Subcapsular sinus Cortical sinuses Medullary sinuses Efferent lymph vessels

34. Lymph enters afferent lymph vessels passes through subcapsular sinuses and down through trabecular sinuses around trabeculae.

35. Efferent lymph vessels in hilum

36. Recirculation of lymphocytes: Lymphoid tissue Efferent lymphatic vessel Postcapillary venules Blood circulation

37. Functions of lymph node • Filter the lymph • Place to perform the immune response • Involve in the recirculation of lymphocyte

38. Spleen • located in the passages of blood capsule white pulp red pulp marginal zone • structure parenchyma

39. Structure: • capsule: D.C.T. containing smooth muscle----trabecular; capsule is covered by mesothelium The splenic artery branch into trabecular arteries

40. White pulp: • gray-white spots • periarterial lymphatic sheath: - diffuse lymphoid tissue : T-lymphocyte, macrophage - central artery • splenic corpuscle: -lymphoid nodules: B-lymphocyte, macrophage

41. splenic corpuscle Marginal zone: • between White pulp and Red pulp • T-, B-lymphocyte, macrophage, less erythrocyte • marginal sinus: central artery’s branch- channel for antigen and lymphocyte enter lymphoid tissue • function: first capture, recognize antigen and induce immune reaction

42. Red pulp: splenic cord: • Lymph tissue cord • B-,T-lymphocyte, macrophage, erythrocytes • function: filter blood splenic cord splenic sinus

43. splenic sinus: Blood sinus; 12-14um endothelial cell: rod-liked, gap Reticular fiber basal lamina: incomplete Abundant macrophage splenic sinus splenic cord endothelial cell

45. Blood supply of spleen Study by yourself splenic A→trabecular A→central A branches → marginal sinuses → penicillar arterioles (including: pulp arteriole→ sheathed capillary→ arterial capillary) → splenic sinus→ pulp venule→ trabecular vein→ splenic vein

47. Function: a. filter the blood b. immunological defence c. production of blood cells in fetus d. blood storage: 40 ml

48. Tonsil(Study by yourself) ---palatine tonsil ---pharyngeal tonsil ---lingual tonsil

49. structure • Mucosa stratified squamous epithelium Epithelium form crypts lymphocyte infiltration lymphatic nodules diffuse lymphatic tissue Lamina propria • Capsule: C.T.

50. Tonsil