Immune System Part 1

1. Immune System Part 1 http://www.electroresponse.com

2. Much of the text material is from, “Principles of Anatomy and Physiology, 12th edition” by Gerald J. Tortora and Bryan Derrickson (2009). I don’t claim authorship. Other sources are noted when they are used.

3. Outline • Introduction • Lymphatic system • Innate immunity, external defenses • Innate immunity, internal defenses • Inflammation and fever

4. Introduction

5. Immunity • Most people remain healthy despite constant exposure to pathogens; that is, disease-producing bacteria and viruses. • The body is also susceptible to abrasions and cuts, exposure to ultra-violet (UV) radiation from sunlight, exposure to chemical toxins, and burns. • Immunity or resistance involves the body’s defenses that respond to diseases and other damage. • The two general types are called innate immunity and adaptive immu-nity. Chapter 22, page 831

6. Immunity (continued) http://www.rikenresearch.riken.jp

7. Innate Immunity • Innate or nonspecific immunity consists of defenses that are active as early as birth. • They can respond rapidly to provide protection against many dis-eases. • Innate immunity does not recognize specific microbes—its mech-anisms respond to all microbes in the same manner and with sim-ilar actions. Microbe = a very tiny form of life—microbes include bacteria, fungi, and protozoan parasites—best visualized under a microscope. (www.emedicinehealth.com) Also, another term for a microorganism. Chapter 22, page 831

8. Innate Immunity (continued) • The first line of defense includes physical and chemical barriers of the skin and mucous membranes. • The second line includes anti-microbial substances, natural killer cells, phagocytes, inflammation, and fever. • Both help prevent microbes from entering the body and eliminate those that gain access. • Second-line responses serve as an ‘early-warning system’ for the body. Natural killer (NK) cell = a type of white blood cell that can kill microbial or tumor cells. Phagocyte = a cell that engulfs and digests debris and invading microbes. Chapter 22, page 831

9. Adaptive Immunity • Adaptive or specific immunity are defenses involving the recognition of specific microbes if they have breached the nonspecific defenses. • Adaptive immunity is slower to respond than innate immunity, but it has ‘memory’ to facilitate the immune response if the microbe is ever encountered again. • The responses involve T lymphocytes (T cells) and B lymphocytes (B cells). Lymphocyte = type of white blood cell. Chapter 22, page 831

10. Lymphatic System

11. Lymphatic System • The lymphatic system mediates adaptive immunity and aspects of innate immunity. • It also works with the cardiovascular system, and with the digestive system in the absorption of lipids. Chapter 22, page 831

12. Lymphatic System (continued) • The lymphatic system consists of: • Fluid known as lymph, • Lymphatic vessels that transport the lymph, • Structures and organs containing lymphatic tissue, and • Red bone marrow where stem cells develop into blood cells. • The lymphatic system, like the cardiovascular system, circulates body fluids. Figure 22.1 Chapter 22, page 832

13. Lymphatic System (continued) http://www.clinic-clinic.com

14. Lymph • Most components of blood plasma filter through the blood capillary walls to form interstitial fluid. • Once interstitial fluid passes into lymphatic vessels, it is known as lymph. • The major differences between interstitial fluid and lymph are their locations. • Interstitial fluid is found between cells, and lymph in lymphatic ves-sels and lymphatic tissue. Chapter 22, page 832

15. Lymphatic Tissue and Lymphocytes • Lymphatic tissue is composed of reticular connective tissue that contains large numbers of lymphocytes. • Lymphocytes (T cells and B cells) are agranular white blood cells, as covered in the lecture on blood. Reticular connective tissue = a network of reticular fibers, made of type III collagen. Agranular = lacking granules when viewed under a light microscope. Chapter 22, page 832

16. Functions • The primary functions of the lymphatic system are to: • Drain excess fluid from the interstitial spaces and return it to the blood. • Transport lipid-soluble food molecules and lipid-soluble vitamins (A, D, E, and K) absorbed by the gastrointestinal tract. • Initiate immune responses against microbes and abnormal cells. • These functions are covered in subsequent slides and the textbook. Chapter 22, page 832

17. Lymphatic Vessels • Lymphatic vessels begin as lymphatic capillaries in the interstitial space. • Lymphatic capillaries are closed at the end terminating in the inter-stitial space. • These capillaries converge to form larger lymphatic vessels, just as blood capillaries converge to form venules and then veins. • Although lymphatic vessels resemble veins, they have thinner walls and a greater number of valves to permit one-way flow of lymphatic fluid. Figure 22.2 Chapter 22, page 832

18. Lymphatic Vessels (continued) • Lymph passes through lymph nodes found at intervals along lym-phatic vessels. • Lymph nodes are encapsulated, bean-shaped organs consisting of masses of B cells and T cells. Figure 22.2 Chapter 22, page 832

19. Lymphatic Vessels (continued) • Lymphatic vessels in the subcutaneous tissue generally follow the same routes as veins. • Lymphatic vessels in the viscera typically follow arteries and form plexuses or networks. Figure 22.2 Chapter 22, page 832

20. Lymphatic Vessels (continued) • Some tissues do not contain lymphatic capillaries—they include: • Avascular tissues including cartilage, epidermis, and cornea of the eye • Central nervous system • Portions of the spleen • Red bone marrow Avascular = without blood vessels. Figure 22.2 Chapter 22, page 832

21. Lymphatic Capillaries • Lymphatic capillaries have slightly larger diameters than blood capil-laries. • Their walls have a one-way structure to enable interstitial fluid to flow into, but not out of, the lumen. • The endothelial cells of the lymphatic capillary wall overlap to enable one-way flow. Figure 22.2 Chapter 22, page 832

22. Lymphatic Capillaries (continued) http://www.web-books.com/elibrary/medicine/hysiology

23. Lymphatic Capillaries (continued) • When the hydrostatic pressure is higher in the interstitial fluid than in the lymphatic capillary, the endothelial cells open slightly, as in a one-way swinging door. • Interstitial fluid enters the lymphatic capillary through the openings. • When the hydrostatic pressure is higher in the lymphatic capillary than in the interstitial fluid, the cells adhere more closely to ‘shut the door.’ • Therefore, lymph cannot re-enter the interstitial fluid since the open-ings are closed. Figure 22.2 Chapter 22, page 832

24. Lymphatic Capillaries (continued) • Further inflow of interstitial fluid occurs as the pressure is reduced when lymph flows down the lymphatic capillary. • Lymphatic capillaries are attached to elastic anchoring filaments that connect the lymphatic endothelial cells to surrounding tissues. • The filaments are pulled when excess interstitial fluid accumulates and causes tissue swelling. • The openings widen between endothelial cells to permit even more interstitial fluid to flow into the lymphatic capillary. Figure 22.2 Chapter 22, page 832

25. Lacteals • Lacteals—specialized lymphatic capillaries in the small intestine— transport dietary lipids into lymphatic vessels and into the blood. • The lipids make the lymphatic fluid, known as chyle juice, appear creamy-white. • Lymph is a clear, pale-yellow fluid in the other tissues of the body. Chapter 22, page 832

26. Digestive Tract Note the centrally-located lacteal in the enlarged villus to the right.

27. Lymph Production • Most components of the blood plasma can filter through the walls of blood capillary to produce interstitial fluid. • Formed elements (RBCs, WBCs, and platelets) usually cannot pass. • More fluid filters out of blood capillaries than is reabsorbed into the capillaries. • The excess fluid—about 3 liters per day—drains into the lymphatic vessels to produce lymph. Figure 21.7 Chapter 22, page 834

28. Lymph Production (continued) • Interstitial fluid has only a small amount of proteins since most protein molecules are too large to pass from the blood plasma through blood capillary walls. • The smaller amount of proteins in interstitial fluid is not reabsorbed through the blood capillary walls because of the opposing concentra-tion gradient. • These proteins,therefore, pass into the more readily-permeable lym-phatic capillaries. • The proteins are returned to the blood through the lymphatic system. Figure 22.4 Chapter 22, page 834

29. Lymphatic Flow • Lymph flows from lymphatic capillaries, into afferent lymphatic vessels, and then into lymph nodes. • Efferent lymphatic vessels exit the lymph nodes and converge to form lymph trunks. • Lymph then drains into the thoracic and right lymphatic ducts, and then into venous blood. • The anatomical relationships between the lymphatic system and cardio-vascular system are shown in Figure 22.4 in the textbook. Figure 22.4 Chapter 22, page 834

30. Skeletal Muscle Pump • Lymphatic vessels, like veins in the cardiovascular system, have valves that permit one-way flow. • Skeletal muscle and respiratory pumps assist in the flow of lymph, just as they aid in the return of venous blood to the right atrium of the heart. • Skeletal muscle contractions compress the lymphatic vessel walls. • The compressions force lymph toward the junction of the internal jugular and subclavian veins where it empties into blood circulation. Figure 21.9 Chapter 22, page 834

31. Respiratory Pump • During inhalation, lymph flows from the abdominal region where the pressure is higher to the thoracic region where the pressure is lower. • When a lymphatic vessel is distended, the smooth muscle in its wall contracts in response, which propels lymph from one segment of the vessel to the next. • Valves prevent the backflow of lymph when the pressure differential is reversed during exhalation. Chapter 22, page 834

32. Primary Lymphatic Organs • Lymphatic organs and tissues are either primary or secondary based on their functions. • Primary lymphatic organs are sites where stem cells can divide and become immunocompetent—that is, capable of an immune response. • The primary lymphatic organs are the red bone marrow and thymus. Chapter 22, page 834

33. Red Bone Marrow • Pluripotent stem cells in red bone marrow form mature, immunocom-petent B cells, and pre-T cells. • Pre-T cells migrate to the thymus where they mature into immunocom petent T cells. Chapter 22, page 834

34. Red Bone Marrow (continued) http://gardenrain.files.wordpress.com

35. Secondary Lymphatic Organs and Tissues • Most immune responses occur in the secondary lymphatic organs and tissues. • They include the spleen, lymph nodes, and lymphatic nodules (or follicles). • The thymus, spleen, and lymph nodes are organs since each one is surrounded by a capsule of connective tissue. • Lymphatic nodules lack this capsule, and are not considered to be organs. Chapter 22, page 836

36. Thymus • The thymus is a bilobed organ located in the mediastinum between the sternum and aorta. • A layer of connective tissue holds the two lobes closely together. • Each lobe is further divided by extensions of the connective tissue capsule to form smaller lobules. • A lobule has a darker-staining outer cortex and lighter-staining cen-tral medulla. Bilobed = divided into two lobes. Figure 22.5 Chapter 22, page 836

37. Thymus (continued) http://www.acm.uiuc.edu

38. Thymus—Cortex • The cortex is composed of large numbers of T cells, and dendritic cells, epithelial cells, and macrophages. • Immature pre-T cells migrate from red bone marrow to the cortex where they proliferate and begin maturation. • Dendritic cells, derived from monocytes, assist in this maturation process. Proliferate = to increase in number or spread rapidly. Monocyte = large phagocytic white blood cell which, when it enters tissue, develops into a macrophage. (http://thyroid.about.com) Figure 22.5 Chapter 22, page 836

39. Thymus—Cortex (continued) • The epithelial cells have long processes that surround and form a framework for as many as 50 T cells. • They also produce thymic hormones for the maturation of T cells. • About 2 percent of the T cells survive in the cortex—the others die by apoptosis. • The surviving T cells enter the medulla of the thymus, and macro-phages dispose of the dead and dying T cells in the thymic cortex. Process = a natural prolongation or projection from a part of an organism. (http://wordnetweb.princeton.edu) Apoptosis = normal cellular process involving a genetically programmed series of events leading to the death of a cell. (http://science.education.nih.gov) Figure 22.5 Chapter 22, page 836

40. Thymus—Medulla • The medulla contains more-mature T cells, epithelial cells, dendritic cells, and macrophages. • Epithelial cells form concentric layers of flat cells that serve as sites for T cell death. • The surviving T cells eventually exit the medulla via the blood, and migrate to lymph nodes, spleen, and other lymphatic tissues to colo-nize these tissues. Concentric = circles sharing the same center. Figure 22.5 Chapter 22, page 837

41. Thymus—Age Progression • The thymus is large in infants, weighing about 70 grams. • Adipose and areolar connective tissue begin replacing thymic tissue at puberty. • The thymus atrophies substantially by adulthood. • It can weigh as little as 3 grams later in life—a 96 percent decrease from infancy. Atrophy = wasting away of tissue or an organ due to the degeneration of cells. (http://medclinic.bli.uci.edu) Chapter 22, page 837

42. Thymus—Age Progression (continued) • The thymus populates the secondary lymphatic organs and tissues with T cells before it atrophies. • Small numbers of T cells, however, continue to proliferate in the thy-mus during an individual’s lifetime. Chapter 22, page 837

43. Lymph Nodes • About 600 lymph nodes are located among the lymphatic vessels. • Lymph nodes are found in both superficial and deep tissues of the body. • The nodes often form groups, including near the mammary glands and in the axillae and groin. Axillae = plural for axilla; the armpits. Figure 22.1 Chapter 22, page 837

44. Lymph Nodes (continued) http://www.acm.uiuc.edu

45. Lymph Nodes—Structure • Lymph nodes, ranging from 1-to-25 mm in length, are enclosed in capsules of dense connective tissue that extends into each node. • These trabeculae divide the node into compartments to provide structural support and a path for blood vessels into the node. • Collectively, the capsule, trabeculae, reticular fibers, and fibro-blasts form the stroma (supporting connective tissue) of a lymph node. Figure 22.6 Chapter 22, page 837

46. Lymph Nodes—Structure (continued) http://www.acm.uiuc.edu

47. Lymph Nodes—Outer Cortex • The functioning part of a lymph node is known as its parenchyma. • The parenchyma consist of an outer and inner cortex and a deeper medulla. • The outer region contains aggregates of B cells known as lymphatic nodules or follicles. Figure 22.6 Chapter 22, page 839

48. Outer Cortex (continued) • A nodule consisting mostly of B cells is known as a primary lym-phatic nodule. • Secondary lymphatic nodules—the more common type—form in response to antigens. • These nodules are sites of plasma cell and memory B cell forma-tion. Antigen = any substance (as a toxin or enzyme) that stimulates an immune response in the body (especially the production of antibodies). (http://wordnetweb.princeton.edu) Figure 22.6 Chapter 22, page 839

49. Germinal Center • The central region of a secondary lymphatic nodule has cells known as the germinal center. • The germinal center contains B cells, follicular dendritic cells, and macrophages. Chapter 22, page 839

50. B Cell Responses • B cells proliferate into antibody-producing plasma cells or memory B cells when follicular dendritic cells present an antigen. • Memory B cells persist after the immune response ends to ‘remember’ a specific antigen if it is encountered again. • B cells that fail to develop properly undergo apoptosis and destruction by macrophages. • The region surrounding the germinal center has dense accumulations of B cells that migrated from their site or origin within the nodule. Antibody = any of a large variety of proteins normally present in the body or produced in response to an antigen which it neutralizes, thus producing an immune response. (http://wordnetweb.princeton.edu) Chapter 22, page 839