ANPATH1-08-Lymphatic-and-Immune-System PDF

CHAPTER 08 LYMPHATIC AND IMMUNE SYSTEM I. Introduction This chapter presents the lymphatic and immune system. The environment in which we live is filled with microbes that have the ability to cause disease if given the right opportunity. If we did...

CHAPTER 08 LYMPHATIC AND IMMUNE SYSTEM I. Introduction This chapter presents the lymphatic and immune system. The environment in which we live is filled with microbes that have the ability to cause disease if given the right opportunity. If we did not resist these microbes, we would be ill constantly or even die. Fortunately, we have a number of defenses that keep microbes from either entering our bodies or combat them if they do gain entrance. The lymphatic system is one of the principal body systems that helps to defend us against disease- producing microbes. In this chapter you will learn about the organization and components of the lymphatic system and its role in keeping us healthy (Tortora & Derrickson, 2017). II. Objectives of the Lesson On completion of the module, the learner should be able to: 1. accurately locate the different organs of the lymphatic system; 2. distinguish fittingly nonspecific from specific immunity; 3. clearly appreciate the importance of the immune system in maintaining a healthy body; and 4. thoroughly point out the physiology of the lymphatic system. III. Lesson Proper INTRODUCTION A. The ability to ward off the pathogens that produce disease is called resistance. B. Lack of resistance is called susceptibility. C. Resistance to disease can be grouped into two broad areas. 1. Nonspecific resistance, or innate immunity, is present at birth and includes defense mechanisms that provide general protection against invasion by a wide range of pathogens. 2. Immunity involves activation of specific lymphocytes that combat a particular pathogen or other foreign substance. D. The body system that carries out immune responses is the lymphatic system. LYMPHATIC SYSTEM STRUCTURE AND FUNCTION A. The lymphatic system consists of a fluid called lymph flowing within lymphatic vessels, several structures and organs that contain lymphatic tissue (specialized reticular tissue containing large numbers of lymphocytes), and bone marrow, which is the site of lymphocyte production. 1. Interstitial fluid and lymph are basically the same. 2. Their major difference is location. B. Functions of the lymphatic system 1. Drain interstitial fluid and return leaked plasma proteins to the blood 2. Transport dietary fats 3. Protect against invasion by nonspecific defenses and specific immune responses. C. Lymphatic vessels and lymph circulation 1. Lymphatic vessels begin as blind-ended lymph capillaries in tissue spaces between cells. a. Interstitial fluid drains into lymphatic capillaries, thus forming lymph. b. Lymph capillaries merge to form larger vessels, called lymphatic vessels, which convey lymph into and out of structures called lymph nodes. 2. Lymphatic capillaries a. Lymphatic capillaries are found throughout the body except in avascular tissue, the CNS, portions of the spleen, and red bone marrow. b. Lymphatic capillaries have a slightly larger diameter than blood capillaries and have overlapping endothelial cells which work as one-way valves for fluid to enter the lymphatic capillary. A Self-regulated Learning Module  c. Anchoring filaments attach endothelial cells to surround tissue. d. A lymphatic capillary in the villus of the small intestine is the lacteal. It functions to transport digested fats from the small intestine into blood. 3. Lymph trunk and ducts a. The principal lymph trunks, formed from the exiting vessels of lymph nodes, are the lumbar, intestinal, bronchomediastinal, subclavian, and jugular trunks. b. The thoracic duct begins as a dilation called the cisterna chyli and is the main collecting duct of the lymphatic system. 1) The thoracic duct receives lymph from the left side of the head, neck, and chest, the left upper extremity, and the entire body below the ribs. 2) It drains lymph into venous blood via the left subclavian vein. c. Right lymphatic duct 1) The right lymphatic duct drains lymph from the upper right side of the body. 2) It drains lymph into venous blood via the right subclavian vein. D. Formation and flow of lymph 1. Interstitial fluid drains into lymph capillaries. 2. The passage of lymph is from arteries and blood capillaries (blood) to interstitial spaces (interstitial fluid) to lymph capillaries (lymph) to lymphatic vessels to lymph trunks to the thoracic duct or right lymphatic duct to the subclavian veins (blood). a. Lymph flows as a result of the milking action of skeletal muscle contractions and respiratory movements. b. It is also aided by lymphatic vessel valves that prevent backflow o lymph. E. Lymphatic organs and tissues 1. The primary lymphatic organs are those in which cells become immunocompetent (capable of mounting an immune response) the red bone marrow (B cells) and the Thymus gland (T cells). a. The secondary lymphatic organs are the lymph nodes and spleen. b. Included as secondary lymphatic tissues are lymphatic nodules. c. Most immune responses occur in secondary lymphatic organs and tissues. 2. Thymus gland a. The thymus gland lies between the sternum and the heart and functions in immunity as the site of T cell maturation. b. The thymus gland is large in the infant and after puberty is largely replaced by adipose and areolar connective tissue. 3. Lymph nodes a. Lymph nodes are encapsulated oval structures located along lymphatic vessels. b. They contain T cells, macrophages, follicular dendritic cells, and B cells. c. Lymph enters nodes through afferent lymphatic vessels, and exits through efferent lymphatic vessels. 1) Foreign substances filtered by the lymph nodes are trapped by nodal reticular fibers. 2) Macrophages then destroy some foreign substances and cells by phagocytosis. 3) Lymphocytes bring about the destruction of other cells by immune responses. a) Lymph nodes are the site of proliferation of plasma cells and T cells. b) Knowledge of the location of the lymph nodes and the direction of lymph flow is important in the diagnosis and prognosis of the spread of cancer by metastasis; many cancer cells are spread by way of the lymphatic system, producing clusters of tumor cells where they lodge (clinical connection). 4. Spleen a. The spleen is the largest mass of lymphatic tissue in the body and is found in the left hypochondriac region between the fundus of the stomach and the diaphragm. b. The spleen consists of white and red pulp. c. The white pulp is lymphatic tissue. d. Its T lymphocytes directly attack and destroy antigens in blood, primarily via cytolysis. e. Its B lymphocytes develop into antibody producing plasma cells, and the antibodies inactivate antigens in blood. A Self-regulated Learning Module  f. Macrophages destroy antigens in blood by phagocytosis. g. The red pulp consists of venous sinuses filled with blood and splenic cords consisting of RBCs, macrophages, lymphocytes, plasma cells, and granulocytes. h. Macrophages remove worn-out or defective RBCs, WBCs, and platelets by phagocytosis i. The spleen stores blood platelets in the red pulp. j. The red pulp is involved in the production of blood cells during the second trimester of pregnancy. k. The spleen is often damaged in abdominal trauma. A splenectomy may be required to prevent excessive bleeding (clinical connection). 5. Lymphatic nodules a. Lymphatic nodules are oval-shaped concentrations of lymphatic tissue. b. They are scattered throughout the lamina propria of mucous membranes lining the GI tract, respiratory airways, urinary tract, and reproductive tract. c. This is the mucosa-associated lymphatic tissue (MALT). d. Peyer’s patches are lymphatic nodules in the ileum of the small intestine. e. Tonsils are multiple aggregations of large lymphatic nodules embedded in a mucous membrane at the junction of the oral cavity and the pharynx. f. They include the pharyngeal (adenoid), palatine, and lingual tonsils. g. They are situated strategically to protect against invasion of foreign substances and participate in immune responses by producing lymphocytes and antibodies. INNATE IMMUNITY A. First line of defense: skin and mucous membranes 1. Innate immunity (nonselective resistance) refers to a wide variety of body responses against a wide range of pathogens (disease producing organisms) and their toxins and is present at birth. 2. Mechanical protection includes the intact epidermis layer of the skin, mucous membranes, the lacrimal apparatus, saliva, mucus, cilia, the epiglottis, and the flow of urine. Defecation and vomiting also may be considered mechanical processes that expel microbes. 3. Chemical protection is localized on the skin, in loose connective tissue, stomach, and vagina. a. The skin produces sebum, which has a low pH due to the presence of unsaturated fatty acids and lactic acid. b. Lysozyme is an enzyme component of sweat that also has antimicrobial properties. c. Gastric juice renders the stomach nearly sterile because its low pH (1.5-3.0) kills many bacteria and destroys most of their toxins; vaginal secretions also are slightly acidic. B. Second line of defense: internal defenses 1. The second line of defense involves internal antimicrobial proteins, phagocytic and natural killer cells, inflammation, and fever. 2. Antimicrobial proteins a. Lymphocyte and macrophage cells infected with viruses produce proteins called interferons (IFNs). Once produced and released from virus-infected cells, IFN diffuses to uninfected neighboring cells and binds to surface receptors, inducing uninfected cells to synthesize antiviral proteins that interfere with or inhibit viral replication. b. A group of about 20 proteins present in blood plasma and on cell membranes comprises the complement system; when activated, these proteins “complement” or enhance certain immune, allergic, and inflammatory reactions. c. Iron-binding proteins remove iron from the body fluids thereby inhibiting microbial growth. d. Anti-microbial substances are peptides that produce anti-microbial activity and attract dendritic and mast cells. 3. Natural killer cells and phagocytes a. Natural killer (NK) cells are lymphocytes that lack the membrane molecules that identify T and B cells. b. They have the ability to “kill” a wide variety of infectious microbes. c. NK cells sometimes release perforins that insert into the plasma membrane of a microbe A Self-regulated Learning Module  and make the membrane leaky so that cytolysis occurs d. Phagocytes are cells specialized to perform phagocytosis and include neutrophils and macrophages. e. The three phases of phagocytosis include chemotaxis, adherence, and ingestion. 4. Inflammation a. Inflammation occurs when cells are damaged by microbes, physical agents, or chemical agents. The injury may be viewed as a form of stress. b. Inflammation is usually characterized by four symptoms: redness, pain, heat, and swelling. Loss of function may be a fifth symptom, depending on the site and extent of the injury. c. The three basic stages of inflammation are 1) vasodilation and increased permeability of blood vessels, 2) phagocyte migration, and 3) tissue repair. d. Substances that contribute to inflammation are histamines, kinins, prostaglandins, leukotrienes, and complement. e. After phagocytes engulf damaged tissue and microbes, they eventually die, forming a pocket of dead phagocytes and damaged tissue and fluid called pus. Pus must drain out of the body or it accumulates in a confined space, causing an abscess. When tissue sloughs off then an ulcer is formed. 5. Fever is usually caused by infection from bacteria (and their toxins) and viruses. The high body temperature inhibits some microbial growth and speeds up body reactions that aid repair. ADAPTIVE IMMUNITY A. Immunity is the ability of the body to defend itself against specific invading agents. 1. Antigens are substances recognized as foreign by the immune responses. 2. The distinguishing properties of immunity are specificity and memory. 3. The branch of science that deals with the responses of the body when challenged by antigens is called immunology. B. Maturation of T cells and B cells 1. Both T cells and B cells derive from stem cells in bone marrow. 2. B cells complete their development, becoming immunocompetent, in bone marrow. 3. T cells develop from pre-T cells that migrate to the thymus, where they become immunocompetent under the influence of thymic hormones. 4. Before T cells leave the thymus or B cells leave bone marrow, they acquire several distinctive surface proteins; some function as antigen receptors, molecules capable of recognizing specific antigens. C. Clonal selection 1. Clonal selection is the process by which an immune cell proliferates and differentiates in response to a specific antigen. 2. Two major types of cells result from clonal selection: effector cells and memory cells. 3. Effector cells are the cells that actually do the work to destroy the antigen and include cytotoxic T cells, helper T cells, and plasma cells (a clone of B cells). 4. Memory cells, with long life spans, provide a faster second invasion response by proliferating and differentiating into effector cells. D. Antigens and antigen receptors 1. Antigens are chemical substances that are recognized as foreign by antigen receptors when introduced into the body. Antigens are both immunogenic and reactive. An antigen that gets past the nonspecific defenses can get into lymphatic tissue by entering an injured blood vessel and being carried to the spleen, penetrating the skin and entering lymph vessels leading to lymph nodes, or penetrating mucous membranes and lodging in mucosa- associated lymphoid tissue. 2. Major histocompatibility complex (MHC) antigens (also called human leucocyte associated, or HLA, antigens) are unique to each person’s body cells. These self-antigens aid in the detection of foreign invaders. All cells except red blood cells display MHC class I antigens. Some cells also display MHC class II antigens. A Self-regulated Learning Module CELL-MEDIATED IMMUNITY A. In a cell-mediated immune response, an antigen is recognized (bound), a small number of specific T cells proliferate and differentiate into a clone of effector cells (a population of identical cells that can recognize the same antigen and carry out some aspect of the immune attack), and the antigen (intruder) is eliminated. B. Activation of T cells 1. T cell receptors recognize antigen fragments associated with MHC molecules on the surface of a body cell. 2. Proliferation of T cells requires co-stimulation, by cytokines such as interleukin-1 (IL-1) and interleukin-2 (IL-2), or by pairs of plasma membrane molecules, one on the surface of the T cell and a second on the surface of an APC. C. Activation and clonal selection of helper T cells 1. Helper T (TH) cells, or CD4 T cells, display CD4 protein, recognize antigen fragments associated with MHC-II molecules, and secrete several cytokines, most important, interleukin-2, which acts as a co-stimulator for other helper T cells, cytotoxic T cells, and B cells. 2. Once a helper T cell is activated it creates clones of other helper T and memory T cells. D. Activation and clonal selection of helper T cells 1. Cytotoxic T (TC) cells, or CD8 T cells, develop from T cells that display CD8 protein and recognize antigen fragments associated with MHC-I molecules. 2. Once activated cytotoxic T cells undergo clonal selection to form more active cytotoxic T cells and memory cytotoxic T cells. E. Elimination of invaders 1. Cytotoxic T cells fight foreign invaders by killing the target cell (the cell that bears the same antigen that stimulated activation or proliferation of their progenitor cells) without damaging the cytotoxic T cell itself. 2. One killing mechanism uses perforin to cause cytolysis of the target cell. 3. The second mechanism uses lymphotoxin to activate damaging enzymes within the target cell. F. Immunological surveillance 1. Immunological surveillance is carried out by cytotoxic T cells. 2. They recognize tumor antigens and destroy the tumor cell. 3. The immune system can recognize proteins in transplanted organs as foreign and mount a graft rejection. ANTIBODY-MEDIATED IMMUNITY A. The body contains not only millions of different T cells but also millions of different B cells, each capable of responding to a specific antigen. B. Activation and clonal selection of B cells 1. During activation of a B cell, an antigen binds to antigen receptors on the cell surface. 2. B cell antigen receptors are chemically similar to the antibodies that will eventually be secreted by their progeny. 3. Some antigen is taken into the B cell, broken down into peptide fragments and combined with the MHC-II self-antigen, and moved to the B cell surface. 4. Helper T cells recognize the antigen-MHC-II combination and deliver the costimulation needed for B cell proliferation and differentiation. 5. Some activated B cells become antibody-secretion plasma cells. Others become memory B cells. C. An antibody is a protein that can combine specifically with the antigenic determinant on the antigen that triggered its production. D. Antibody structure 1. Antibodies consist of heavy and light chains and variable and constant portions. 2. Based on chemistry and structure, antibodies are grouped into five principal classes each with specific biological roles (IgG, IgA, IgM, IgD, and IgE. A Self-regulated Learning Module E. The functions of antibodies include neutralizing antigen, immobilization of bacteria, agglutination and precipitation of antigen, activation of complement and enhancing phagocytosis. F. Role of complement system in immunity – a group of about 20 proteins present in blood plasma and on cell membranes comprises the complement system; when activated, these proteins “complement” or enhance certain immune, allergic, and inflammatory reactions. G. Immunological memory 1. Immunological memory is due to the presence of long-lived antibodies and very long- lived lymphocytes that arise during proliferation and differentiation of antigen- stimulated B and T cells. 2. Immunization against certain microbes is possible because memory B cells and memory T cells remain after the primary response to an antigen. H. The secondary response (immunological memory) provides protection should the same microbe enter the body again. There is rapid proliferation of memory cells, resulting in a far greater antibody titer (amount of antibody in serum) than during a primary response. A Self-regulated Learning Module IV. Assessment LECTURE Critical Thinking Questions. Answer the following questions extensively. 1. How does the body increase the exposure of antigens to immune cells? _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ 2. What does fever indicate about the immune system? Explain. _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ Rubrics for Essay 10 8 6 4 2 Answers show Answers show Answers show Answers do not Answers do not mastery of some analysis. some show address the content and Student’s answer understanding of understanding of questions. Answer deeper shows mastery essential content, basic content. s are not on analysis/understa and facts, but is Answers are prompt or track. nding of the understanding of lacking in greater incomplete or content. Give content. analysis and inaccurate. specific evidence. Answers show characteristic of that mastery of each type of the general ecosystem. content is missing. A Self-regulated Learning Module  LABORATORY ACTIVITY 1. Using a Venn diagram, identify the similarities and differences of blood and lymph. 2. Using two (2) flow diagrams, trace the blood circulation and lymphatic circulation, respectively. 3. In a tabular form, illustrate the different blood cells and briefly outline the characteristics of each beside its illustration. Follow the table below for the format. Illustration Characteristics 4. Briefly describe the primary and secondary organs of the lymphatic system. 5. Briefly discuss the mechanism of action of each of the three lines of defenses. Provide two (2) examples for each. 6. Briefly compare the following: a. Innate and adaptive immunity b. Cell- and antibody-mediated immunity c. Active and passive immunity A Self-regulated Learning Module