Exploring the Lymphatic System and Immunity Pathways

1. Chapter 14Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

2. Chapter 14 Lymphatic System and Immunity 2

3. 14.1 Introduction 3

4. The lymphatic system is comprised of a network of vessels that assist in the circulation of body fluids. • Lymphatic vessels collect and carry away excess fluid from interstitial spaces and special vessels called lacteals transport fats to the circulatory system. C. The organs, cells, and biochemicals of the lymphatic system help defend against disease. 4

5. 14.2 Lymphatic Pathways 5

6. Lymphatic pathways start as lymphatic capillaries that merge to form larger vessels that empty into the veins in the thoracic cavity. • Lymphatic Capillaries • Lymphatic capillaries are tiny, closed-ended tubes that extend into interstitial spaces, paralleling the blood capillaries. • They receive tissue fluid through their thin walls and slits between cells; once inside, tissue fluid is called lymph. 6

7. Fig 14.2 7

8. Lymphatic Vessels • The walls of lymphatic vessels are thinner than those of veins but are constructed with the same three layers with semilunar valves on the inside. • Larger lymphatic vessels pass through lymph nodes and merge to form lymphatic trunks. 8

9. Fig 14.1 9

10. Lymphatic Trunks and Collecting Ducts • The lymphatic trunks drain lymph from the body and are named for the regions they drain. • These trunks join one of two collecting ducts-either the thoracic duct or right lymphatic duct. • The right lymphatic duct drains the right side of the head and neck, the right arm, and right thorax into the right subclavian vein. • The thoracic duct drains the rest of the body into the left subclavian vein. 10

11. Fig 14.4a & 14.5 11

12. 14.3 Tissue Fluid and Lymph 12

13. Tissue fluid becomes lymph once it has entered a lymphatic capillary; lymph formation depends on tissue fluid formation. • Tissue Fluid Formation • Tissue fluid is made up of water and dissolved substances that leave blood capillaries by filtration and diffusion. • Plasma proteins create plasma osmotic pressure that draws fluids back into the capillaries, but it is not 100%. • Fluid that does not return to the capillaries becomes tissue fluid. 13

14. Lymph Formation and Function • Rising osmotic pressure in tissues interferes with the return of fluids to the bloodstream. • Increasing tissue fluid hydrostatic pressure forces some of the fluid into lymphatic capillaries. 14

15. 14.4 Lymph Movement 15

16. The hydrostatic pressure of tissue fluid drives the entry of lymph into lymphatic capillaries. • Forces that move blood in veins (skeletal muscle contraction, breathing movements), and contraction of smooth muscle in the walls of lymphatic trunks are the forces that propel lymph through lymphatic vessels. • A condition that interferes with the flow in lymph will result in edema. • During surgery, lymphatic vessels or tissues may be removed or disturbed, resulting in edema. 16

17. Fig 14.4b 17

18. 14.5 Lymphatic Tissue and Organs 18

19. Introduction • Lymphatic tissue contains lymphocytes, macrophages, and other cells. • Lymphatic tissue associated with the digestive, respiratory, urinary, and reproductive systems is called MALT (mucosa-associated lymphatic tissue) and is diffuse and unencapsulated. • Tonsils, appendix, and Peyer’s patches are compact masses of lymphatic tissue called lymph nodules. • Lymphatic organs include lymph nodes, the thymus, and spleen. 19

20. Lymph Nodes • Lymph nodes, which contain lymphocytes and macrophages, are located along lymphatic vessels. • Structure of a Lymph node • Lymph nodes are bean-shaped, with blood vessels, nerves, and efferent lymphatic vessels attached o the indented hilum, and with afferent lymphatic vessels entering on the convex surface. 20

21. Structure of a lymph node, cont. • Lymph nodes are covered with connective tissue that extends inside the node and divides it into nodules and spaces called sinuses. • These contain both lymphocytes and macrophages which clean the lymph as it flows through the node. 21

22. Fig 14.6 22

23. Locations of Lymph Nodes • The lymph nodes generally occur in chains along the parts of the larger lymphatic vessels. • Major areas – cervical, thoracic, axillary, supratrochlear, abdominal, pelvic, and inguinal. 23

24. Fig 14.8 24

25. Functions of Lymph Nodes The macrophages and lymphocytes within lymph nodes filter lymph and remove bacteria and cellular debris before lymph is returned to the blood. Lymph nodes are also centers of lymphocyte production; these cells function in immune surveillance. 25

26. Thymus • The thymus is a soft, bi-lobed organ located behind the sternum, above the heart; it shrinks in size during the lifetime (large in children, microscopic in the elderly). • The thymus is surrounded by a connective tissue capsule that extends inside it and divides it into lobules. 26

27. Thymus, cont. • Lobules contain lymphocytes, some of which mature into T lymphocytes (T cells) that leave the thymus to provide immunity. • The thymus secretes hormones called thymosins, which influences the maturation of T lymphocytes. 27

28. Fig 14.9a 28

29. Spleen • The spleen lies in the upper left abdominal cavity and is the body’s largest lymphatic organ. • The spleen resembles a large lymph node except that it contains blood instead of lymph. • It is composed of white pulp (containing many lymphocytes) and red pulp (containing red blood cells, macrophages, and lymphocytes). • The spleen filters the blood and removes damaged blood cells and bacteria. 29

30. Fig 14.10 30

31. 14.6 Body Defenses Against Infection 31

32. Diseases-causing agents, also called pathogens, can produce infections within the body. • The body has two lines of defense against pathogens:innate (nonspecific) defenses that guard against any pathogen, and adaptive (specific)defenses(immunity) that mount a response against a very specific target. • Innate defenses, that respond rapidly, include species resistance, mechanical barriers, chemical barriers, natural killer cells, inflammation, phagocytosis, and fever. 32

33. Specific defenses, that develop slowly, are carried out by lymphocytes that recognize a specific invader. • Nonspecific and specific defenses work together to protect the body against infection. 33

34. 14.7 Innate (nonspecific) Defenses 34

35. Species Resistance • A species is resistant to diseases that affect other species because it has a unique chemical environment or temperature that fails to provide the conditions required by the pathogens of another species. 35

36. Mechanical Barriers • The unbroken skin and mucous membranes of the body create mechanical barriers that prevent the entry of certain pathogens. • Includes hair, mucus, and sweat. • Mechanical barriers represent the body’s first line of defense. • The rest of the innate defenses are part of the second line of defense. 36

37. Chemical Barriers • Chemical barriers, such as the highly acidic and caustic environment provided by gastric juice, or lyzozyme in tears, kill many pathogens. • Interferons, hormone-like peptides that serve as antiviral substances, are produced by cells when they are infected with viruses and induce nearby cells to produce antiviral enzymes that protect them from infection; they also stimulate phagocytosis. • Activation of complement stimulates inflammation, attracts phagocytes and enhances phagocytosis. 37

38. Natural Killer (NK ) cells • NK cells are a type of lymphocyte that defend the body against various viruses and cancer cells by secreting cytolytic substances called perforins. • NK cells also secrete chemicals that enhance inflammation. 38

39. Inflammation • Inflammation, a tissue response to a pathogen, is characterized by redness, swelling, heat, and pain. • Major actions that occur during an inflammatory response include: dilation of blood vessels; increase of blood volume in affected areas; invasion of white blood cells into the affected area; blood clotting; and appearance of fibroblasts and their production of a sac around the area. 39

40. Phagocytosis • The most active phagocytes are neutrophils and monocytes; these leave the bloodstream at areas of injury by diapedesis. • They are attracted to the injured area by chemotaxis. • Neutrophils engulf smaller particles; monocytes attack larger ones. • Monocytes give rise to macrophages, which become fixed in various tissues. 40

41. Phagocytosis, cont. • Monocytes, macrophages, and neutrophils constitute the mononuclear phagocytic system. • Phagocytosis also removes foreign particles from the lymph. 41

42. Fever • Fever offers powerful protection against infection by interfering with the proper conditions that promote bacterial growth. • During fever, the amount of iron in the blood is reduced, and thus fewer nutrients are available to support the growth of pathogens. • Phagocytic cells attack with greater vigor when the temperature rises. 42

43. 14.8 Adaptive (specific) Defenses, or Immunity 43

44. The body’s third line of defense, immunity refers to the response mounted by the body against specific, recognized foreign molecules. 44

45. Fig 14.11 45

46. Antigens • Antigens are proteins, polysaccharides, glycoproteins, or glycolipids that can elicit an immune response. • Before birth, the body makes an inventory of “self” proteins and other large molecules. • Antigens are generally larger and more complex molecules. • Sometimes small molecules called haptens combine with larger molecules and become antigenic. 46

47. Lymphocyte Origins • During fetal development, red bone marrow releases lymphocytes into circulation, 70-80% of which become T lymphocytes(T cells) and the remainder of which become B lymphocytes(B cells). • Undifferentiated lymphocytes that reach the thymus become T cells; B cells mature in the bone marrow. • Both B and T cells reside in lymphatic organs. 47

48. Fig 14.12 48

49. Table 14.1 49

50. Fig 14.13 50