The Lymphatic & Immune Systems

1. The Lymphatic & Immune Systems

2. Consists of two semi-independent parts • A meandering network of lymphatic vessels • Lymphoid tissues and organs scattered throughout the body • Returns interstitial fluid and leaked plasma proteins back to the blood • Lymph – interstitial fluid once it has entered lymphatic vessels Lymphatic System: Overview

3. Lymphatic System: Overview

4. Lymphatic System: Overview

5. A one-way system in which lymph flows toward the heart • Lymph vessels include: • Microscopic, permeable, blind-ended capillaries • Lymphatic collecting vessels • Trunks and ducts Lymphatic Vessels

6. Similar to blood capillaries, with modifications • Remarkably permeable • Loosely joined endothelial minivalves • Withstand interstitial pressure and remain open • The minivalves function as one-way gates that: • Allow interstitial fluid to enter lymph capillaries • Do not allow lymph to escape from the capillaries Lymphatic Capillaries

7. Lymphatic Capillaries

8. Lymphatic Vessels and Valves Figure 22–3

9. Lymphatic Trunks & Ducts

10. The lymphatic system lacks an organ that acts as a pump • Vessels are low-pressure conduits • Uses the same methods as veins to propel lymph • Pulsations of nearby arteries • Contractions of smooth muscle in the walls of the lymphatics Lymph Transport

11. General circulation of lymph

12. Lymphocytes are the main cells involved in the immune response • The two main varieties are T cells and B cells Lymphoid Cells

13. T cells and B cells protect the body against antigens • Antigen – anything the body perceives as foreign • Bacteria and their toxins; viruses • Mismatched RBCs or cancer cells Lymphocytes

14. T cells • Manage the immune response • Attack and destroy foreign cells • B cells • Produce plasma cells, which secrete antibodies • Antibodies immobilize antigens Lymphocytes

15. Macrophages – phagocytize foreign substances and help activate T cells • Dendritic cells – spiny-looking cells with functions similar to macrophages • Reticular cells – fibroblastlike cells that produce a stroma, or network, that supports other cell types in lymphoid organs Other Lymphoid Cells

16. Lymphoid Nodules Figure 22–6

17. Lymph nodes are the principal lymphoid organs of the body • Nodes are imbedded in connective tissue and clustered along lymphatic vessels • Aggregations of these nodes occur near the body surface in inguinal, axillary, and cervical regions of the body Lymph Nodes

18. Their two basic functions are: • Filtration – macrophages destroy microorganisms and debris • Immune system activation – monitor for antigens and mount an attack against them Lymph Nodes

19. Range from 1–25 mm diameter Lymph Nodes Figure 22–7

20. Lymph nodeStructure

21. Structure of a Lymph Node

22. The spleen, thymus gland, and tonsils • Peyer’s patches and bits of lymphatic tissue scattered in connective tissue • All are composed of reticular connective tissue and all help protect the body • Only lymph nodes filter lymph Other Lymphoid Organs

23. The Thymus

24. Structure of the Spleen

25. Innate (nonspecific) system responds quickly and consists of: • First line of defense – intact skin and mucosae prevent entry of microorganisms • Second line of defense – antimicrobial proteins, phagocytes, and other cells • Inhibit spread of invaders throughout the body • Inflammation is its hallmark and most important mechanism Immunity: Two Intrinsic Defense Systems

26. Adaptive (specific) defense system • Third line of defense – mounts attack against particular foreign substances • Takes longer to react than the innate system • Works in conjunction with the innate system Immunity: Two Intrinsic Defense Systems

27. The 7 Nonspecific Defenses Figure 22–10

28. Skin, mucous membranes, and their secretions make up the first line of defense • Keratin in the skin: • Presents a formidable physical barrier to most microorganisms • Is resistant to weak acids and bases, bacterial enzymes, and toxins • Mucosae provide similar mechanical barriers Surface Barriers

29. Mucus-coated hairs in the nose trap inhaled particles • Mucosa of the upper respiratory tract is ciliated • Cilia sweep dust- and bacteria-laden mucus away from lower respiratory passages Respiratory Tract Mucosae

30. The body uses nonspecific cellular and chemical devices to protect itself • Phagocytes and natural killer (NK) cells • Antimicrobial proteins in blood and tissue fluid • Inflammatory response enlists macrophages, mast cells, WBCs, and chemicals • Harmful substances are identified by surface carbohydrates unique to infectious organisms Internal Defenses: Cells and Chemicals

31. Natural Killer Cell Function Figure 22–11

32. Macrophages are the chief phagocytic cells • Free macrophages wander throughout a region in search of cellular debris • Kupffer cells (liver) and microglia (brain) are fixed macrophages • Neutrophils become phagocytic when encountering infectious material • Eosinophils are weakly phagocytic against parasitic worms • Mast cells bind and ingest a wide range of bacteria Phagocytes

33. Mechanism of Phagocytosis

34. Inflammation is caused by: • Pathogens • Mechanical irritation or damage • Chemical irritants • Extreme temperatures • Marked by four “cardinal signs” • Redness • Pain • Swelling • Heat Inflammation

35. Vasodilation & increased capillary permeability • Release of: • Histamine – attract leukocytes (chemotaxis), cause further vasodilation and increased permeability • Kinnins – Similar to histamine • Prostaglandins – synergistic with the above. Trigger pain. • Leukotrienes – allow adherence of phagocytes to pathogens • Complement – more histamine, and a bunch of other stuff (about which more later) Overview of inflammatory response

36. Neutrophils and Monocytes respond to “Chemotaxis”

37. Caused by resetting of hypothalamic thermostat • Bacterial toxins • Triggers release of cytokines & interleukin-1 (endogenous pyrogens) • Increases interferon effects • Increases metabolic rate to enhance tissue repair and increase immune response • Makes environment hostile to microbes Fever

38. The adaptive immune system is a functional system that: • Recognizes specific foreign substances • Acts to immobilize, neutralize, or destroy foreign substances • Amplifies inflammatory response and activates complement Adaptive (Specific) Defenses

39. The Immune Response Figure 22–15 (Navigator)

40. Substances that can mobilize the immune system and provoke an immune response • The ultimate targets of all immune responses are mostly large, complex molecules not normally found in the body (nonself) Antigens

41. Antigens & Antigenic Determinants (epitopes)

42. Immature lymphocytes released from bone marrow are essentially identical • Whether a lymphocyte matures into a B cell or a T cell depends on where in the body it becomes immunocompetent • B cells mature in the bone marrow • T cells mature in the thymus Lymphocytes

43. Cell-mediated and Antibody mediated defenses

44. The MHC is a group of genes that code for proteins that act as an ID badge for your cells • The “self antigens” are glycoproteins that are also called human leukocyte antigens (HLA) • There are two classes, MHC-I & MHC-II • MHC-I is on all cells (except erythrocytes) • MHC-II is found on antigen-presenting cells (APCs) Major Histocompatability Complex and recognition of “self”

45. Antigen processing

46. Antigen Presentation Figure 22–16b

47. Helper T Cells (CD4) • Secrete interleukin-2 (IL-2) • Helps activate cytotoxic T Cells, B Cells and/or NK cells • Involved in both cell and antibody mediated responses Types of T Cells

48. Cytotoxic T Cells (CD8) a.k.a. “killer T Cells” • Attack virally or bacterial infected cells and cancerous cells directly • Memory T Cells provide for a prolonged protection against specific antigens (immunity in the true sense) Types of T Lymphocytes

49. T lymphocyte activity:The cell mediated response

50. Pathways of T Cell Activation Figure 22–19