Introduction

1. Introduction • The main components of the immune system (lymphocytes, lymphoid tissue, and lymphoid organs) fight infections and provides immunity to disease

2. The Lymphatic System • Lymphatic vessels runs throughout the body • Lymphatic vessels transport fluids that have escaped from the cardiovascular system • These vessels collect a fluid called lymph from the loose connective tissue around blood capillaries and carry this fluid to the great veins at the root of the neck

3. The Lymphatic System • Lymphatic vessels form a one-way system rather than a full circuit • Lymph only flows toward the heart

4. The Lymphatic System • All blood capillaries are surrounded by a loose connective tissue that contains interstitial fluid (I.F.) • I.F. arises from blood filtered through the capillary walls

5. The Lymphatic System • Interstitial Fluid consists of small molecules of blood plasma, water, various ions, nutrient molecules, and respiratory gases

6. The Lymphatic System Interstitial Fluid is continuously leaving and re-entering the blood capillaries

7. The Lymphatic System • Lymphatic vessels collect this excess fluid and return it to the bloodstream • Any blockage of the lymphatic vessels causes the affected body region to swell with excess interstitial fluid resulting in edema

8. The Lymphatic System • Lymphatic vessels also perform another related function • Blood proteins leak slowly from blood capillaries into the surrounding tissue fluid • Lymph vessels return leaked proteins to the bloodstream • This is important because proteins in blood generate osmotic forces that are essential for keeping water in the bloodstream

9. Lymph Capillaries • Once interstitial fluid enters the lymphatic ducts it is called lymph • Lymph capillaries allows bacteria, viruses, or cancer cells in the loose connective tissue to enter these capillaries with ease

10. Lymph Capillaries • These pathogenic agents can then travel throughout the body via the lymphatic vessels • Most pathogenic agents are destroyed in the lymph nodes by various antibodies before reaching the general circulation • Cancer cells can be the most problematic and can actually use lymph nodes as a site to metastasize further

11. Lymph Collecting Vessels • From the lymph capillaries, lymph enters lymphatic collecting vessels which accompany blood vessels

12. Lymph Collecting Vessels • Unaided by pressure from a pump, lymph is propelled through lymph vessels by a series of weaker mechanisms • The action of contracting skeletal muscle and the pulsation of nearby arteries push on lymph vessels, squeezing lymph through them

13. Lymph Collecting Vessels • The muscular middle layer of the lymph vessels also contacts to help propel the lymph • Additionally, the normal movements of the limbs and trunk keep the lymph flowing • Despite these mechanisms, the transport of lymph is slow • People who are inactive or who stand for long times often develop edema

14. EDEMA

15. Lymph Nodes • Lymph nodes, which cleanse the lymph of pathogens, are bean shaped organs situated along lymphatic collecting vessels • Approximately 500 Lymph nodes in the body

16. Right lymphatic Duct • Lymph is returned to the bloodstream when it is deposited into veins in the neck

17. Lymphatic Vessels • In summary, the lymphatic vessels…. • Return excess tissue fluid to the bloodstream • Return leaked proteins to the blood • Carry absorbed fat from the intestine to the blood through lacteals

18. THE END

19. Immune System • The immune system is central to the body’s fight against disease • Unlike the body’s other defense systems, it recognizes and attacks specific foreign molecules • It destroys pathogens more and more effectively with each new exposure

20. Immune System • The immune system centers around the key defense cells from lymphocytes • But it also includes lymphoid tissue, and the lymphoid organs these include… • Lymph nodes, spleen, thymus, tonsils, aggregated lymphoid nodules in the small intestine, and appendix

21. Lymphocytes • Infectious microorganisms that penetrate the epithelial barriers of the body enter the underlying loose connective tissues, where they are attacked by the inflammatory response, by macrophages and finally, by lymphocytes of the immune system • Lymphocytes are white blood cells and that each lymphocyte recognizes and attacks its own type of foreign molecule, called an antigen

22. Lymphocytes • B lymphocytes multiply to become plasma cells that secrete antibodies • Cytotoxic (CD8+) T lymphocytes destroy antigen bearing cells by penetrating their membranes and inducing programmed cell death

23. Lymphocytes • B and T cells continuously travel in the blood and lymph streams to reach infected connective tissues throughout the body, where they fight infection • They repeatedly enter and exit these connective tissues, including the often infected lymphoid tissue, by squeezing through the walls of capillaries and venules

24. Lymphocytes • This repeated movement of activated lymphocytes between the circulatory vessels and the connective tissues, called recirculation, ensures that lymphocytes reach all infection sites quickly

25. Lymphocyte Activation • Immature lymphocytes go through several stages before they are able to attack antigens • Most lymphocytes pass through these stages during infancy and childhood, by many do so in adulthood as well

26. Lymphocyte Activation • This illustration provides an overview of lymphocyte activation

27. Lymphocyte Activation • Lymphocytes originate in the bone marrow from lymphoid stem cells, some of which travel in the bloodstream to the thymus in the thorax and become T lymphocytes (T is for Thymus)

28. Lymphocyte Activation • Other lymphocytes stay in the bone marrow and become B lymphcytes

29. Lymphocyte Activation • These new T and B lymphocytes divide rapidly and generate many lymphocyte families (clones), each of which is able to recognize one unique type of antigen (this is called gaining immunocompetence)

30. Lymphocyte Activation • Young T or B lymphocytes travel through the bloodstream to an infected connective tissue, where it binds to its specific antigen, an encounter called antigen challenge

31. Lymphocyte Activation • As a consequence of the antigen challenge the lymphocyte becomes fully activated, gaining the ability to attack its antigen, proliferates rapidly, and produces mature lymphocytes that recirculate throughout the body seeking pathogens to attack

32. Lymphocyte Activation • During the antigen challenge, an activating lymphocyte interacts with several other cells types • The lymphocyte receives its antigen from an antigen presenting cell, such as a macrophage that has recently phagocytized the antigen, or a star shaped dendritic cell, a professional antigen gathered that patrols the body seeking antigens and carries them to places where lymphocytes gather

33. Lymphocyte Activation • A distinct type of lymphocyte, called a helper (CD4+) T lymphocyte, secretes chemical signals that greatly stimulate the proliferation of activating B and cytotoxic T lymphocytes • Helper T cells are important because their signals amplify and fine-tune the immune response

34. Lymphocyte Activation • The importance of helper T lymphocytes is illustrated by acquired immune deficiency syndrome (AIDS), a viral disease in which a drastic decline in the body’s helper T cells greatly weakens the immune system

35. Lymphocyte Activation • As more activating T or B cells proliferates within infected connective tissue, it produces two types of mature lymphocytes, effector and memory • Short lived effector lymphocytes attack the pathogen immediately and then die • Memory lymphocytes, by contrast, wait until the body encounters their antigen again - maybe decades later

36. Lymphocyte Activation • When a memory lymphocyte finally encounters its antigen, its proliferating response and its attack are most vigorous and rapid • Memory lymphocytes are the basis for acquired immunity • They guard against subsequent infections and prevent us from getting many diseases more than once • There are T and B varieties of memory lymphocytes

37. Lymph Nodes: Clinical • Inflammation of a node is caused by a large number of bacteria trapped in a node • Inflammation results in swelling and pain • Lymph nodes can become secondary cancer sites, particularly in metastasizing cancers that enter lymphatic vessels and become trapped • Cancer infiltrated nodes are swollen but not painful

38. Lymphoid Tissue • Lymphoid tissue is an important component of the immune system because it • Houses and provides a proliferation site for lymphocytes • Furnishes an ideal surveillance vantage point for both lymphocytes and macrophages

39. Lymphoid Tissue • Lymphoid tissue is the most important tissue of the immune system • The tissue is an often infected connective tissue in which vast quantities of lymphocytes gather to fight invading microorganisms • This tissue had two general locations • Mucous membranes • Lymphoid organs

40. Lymphoid Tissue • Mucous membranes • Found within the digestive, respiratory, urinary and reproductive tracks where it is called mucosa-assocaited lymphoid tissue (MALT) • Lymphoid Organs • Lymph nodes, spleen, thymus, tonsils, aggregated lymphoid nodules, and appendix

41. Lymphoid Tissue • This tissue is the main battleground in the fight against infection • Lymphoid tissue is where most lymphocytes become activated and most effector and memory lymphocytes are generated

42. Lymphoid Tissue • Lymphoid tissue, a type of loose connective tissue called reticular connective tissue, dominates all lymphoid organs except the thymus • The dark staining areas represent the connective tissue fibers

43. Lymphoid Tissue • The structural features of lymphoid tissue serves its infection fighting role • It is a reticular connective tissue whose basic framework is a network of reticular fibers secreted by reticular cells (fibroblasts)

44. Lymphoid Tissue • Within the spaces of this network reside the many T and B lymphocytes that arrive continuously from venules coursing through the tissue Macrophage Lymphocytes Reticular fiber

45. Lymphoid Tissue • Macrophages on the fiber network kill invading microorganisms by phagocytosis and along with dendritic cells, they activate nearby lymphocytes by presenting them with antigens Macrophage Lymphocytes Reticular fiber

46. Lymphoid Tissue • Evident within lymphoid tissues are scattered, spherical clusters of densely packed lymphocytes, called lymphoid nodules or follicles • These nodules often exhibit lighter staining germinal centers

47. Lymphoid Tissue • Nodules derive from the activation of a single B cell, whose rapid proliferation generates the thousands of lymphocytes in the nodule • Newly produced B cells migrate away from the nodule to become plasma cells

48. Lymphoid Organs • Lymphoid organs are the lymph nodes, spleen, thymus, aggregated lymphoid nodules in the small intestine, and appendix

49. Lymphoid Organs • Lymph nodes are more than filters • The regions of the node between the lymph sinuses are tadpole shaped masses of lymphoid tissue

50. Lymphoid Organs • As lymph moves through the sinuses, some of the contained antigens leak out through the sinus wall into the lymphatic tissue • Most antigen challenges in the human body occur in the lymph nodes