Immune System Part 1 PDF

Immune System Part I © McGraw Hill 1 © McGraw Hill 2  Introduction The body harbors at least 10 times as many bacterial cells as human cells Some beneficial; some potentially disease-causing Immune system—not an organ system, but a cell population th...

Immune System Part I © McGraw Hill 1 © McGraw Hill 2  Introduction The body harbors at least 10 times as many bacterial cells as human cells Some beneficial; some potentially disease-causing Immune system—not an organ system, but a cell population that inhabits all organs and defends the body from agents of disease Especially concentrated in the true organ system: lymphatic system Network of organs and vein-like vessels that recover fluid Inspect it for disease agents Activate immune responses Return fluid to the bloodstream © McGraw Hill 3 © McGraw Hill 4  The Lymphatic System Fluid recovery Fluid continually filters from the blood capillaries into the tissue spaces Blood capillaries reabsorb 85% 15% (2 to 4 L/day) of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the blood © McGraw Hill 5  The Lymphatic System Immunity Excess filtered fluid picks up foreign cells and chemicals from the tissues Passes through lymph nodes where immune cells stand guard against foreign matter Activates a protective immune response Lipid absorption Lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries © McGraw Hill 6  The Lymphatic System Lymph Lymphatic vessels Transport the lymph Lymphatic tissues Composed of aggregates of lymphocytes and macrophages that populate many organs in the body Lymphatic organs Defense cells are especially concentrated in these organs Separated from surrounding organs by connective tissue capsules © McGraw Hill 7  Lymph and the Lymphatic Vessels 1  Lymph  Clear, colorless fluid, similar to plasma, but much less protein  Originates as extracellular fluid drawn into lymphatic capillaries  Chemical composition varies in different places (in intestines, after lymph nodes) © McGraw Hill 8  Lymph and the Lymphatic Vessels 2  Lymphatic capillaries (terminal lymphatics)  Penetrate nearly every tissue of the body  Absent from cartilage, cornea, bone, and bone marrow  Capillary wall is endothelial cells overlapping each other like roof shingles  Closed at one end  Cells tethered to surrounding tissue by anchoring filaments  Gaps between cells are large enough to allow bacteria and cells to enter lymphatic capillary  Endothelium creates valve-like flaps that open when interstitial fluid pressure is high, and close when it is low © McGraw Hill 9  Lymphatic Capillaries 2 Figure 21.2b © McGraw Hill 10  Lymphatic Capillaries 1 Figure 21.2a © McGraw Hill 11  Lymphatic Vessels 1 Larger ones composed of three layers Tunica interna: endothelium and valves Tunica media: elastic fibers, smooth muscle Tunica externa: thin outer layer Converge into larger and larger vessels Collecting vessels course through many lymph nodes © McGraw Hill 12 Two collecting ducts Right lymphatic duct: receives lymph from right arm, right side of head and thorax; empties into right subclavian vein Thoracic duct: larger and longer, begins as a sac in abdomen called the cisterna chyli; receives lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein Subclavian veins: Collect from thoracic duct © McGraw Hill 13  Fluid Exchange Figure 21.4 Figure 21.1 © McGraw Hill 14  Lymphatics of the Thoracic Region Figure 21.5b © McGraw Hill 15  Drainage of Thorax Figure 21.5a © McGraw Hill 16  Flow of Lymph 1 Lymph flows under forces similar to those that govern venous return, except no pump (heart) Lymph flows at low pressure and slower speed than venous blood Moved along by rhythmic contractions of lymphatic vessels Stretching of vessels stimulates contraction © McGraw Hill 17  Flow of Lymph 2 Flow aided by skeletal muscle pump Arterial pulsation rhythmically squeezes lymphatic vessels Thoracic pump aids flow from abdominal to thoracic cavity Valves prevent backward flow Rapidly flowing blood in subclavian veins, draws lymph into it Exercise significantly increases lymphatic return Does this sound familiar?? © McGraw Hill 18 © McGraw Hill 19  Lymphatic Cells 1 Neutrophils—antibacterial Natural killer (NK) cells—large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or that have turned cancerous T lymphocytes (T cells)—mature in thymus B lymphocytes (B cells)—activation causes proliferation and differentiation into plasma cells that produce antibodies © McGraw Hill 20  Lymphatic Cells 2 Macrophages Large, avidly phagocytic cells of connective tissue Develop from monocytes or other macrophages Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter Process foreign matter and display antigenic fragments to certain T cells alerting immune system to the presence of the enemy Antigen-presenting cells (APCs) © McGraw Hill 21  Macrophages Figure 21.6 © McGraw Hill David M. Phillips/Science Source 22  Lymphatic Cells 3 Dendritic cells Branched, mobile APCs found in epidermis, mucous membranes, and lymphatic organs Alert immune system to pathogens that have breached the body surface Reticular cells Branched stationary cells that contribute to the stroma of a lymphatic organ © McGraw Hill 23  Lymphatic Tissues 1 Lymphatic (lymphoid) tissue—aggregations of lymphocytes in the connective tissues of mucous membranes and various organs Diffuse lymphatic tissue—simplest form Lymphocytes are scattered (not clustered) Prevalent in body passages open to the exterior Respiratory, digestive, urinary, and reproductive tracts Mucosa-associated lymphatic tissue (MALT) © McGraw Hill 24  Lymphatic Tissues 2 Lymphatic nodules (follicles) Dense masses of lymphocytes and macrophages that congregate in response to pathogens Constant feature of the lymph nodes, tonsils, and appendix Aggregated lymphoid nodules: dense clusters in the ileum, the distal portion of the small intestine © McGraw Hill 25  Lymphatic Nodule Figure 21.7 © McGraw Hill Garry DeLong/Science Source 26  Lymphatic Organs Lymphatic organs are anatomically well-defined Have connective tissue capsule that separates lymphatic tissue from neighboring tissues Primary lymphatic organs Red bone marrow and thymus Site where T and B cells become immunocompetent: able to recognize and respond to antigens Secondary lymphatic organs Lymph nodes, tonsils, and spleen Immunocompetent cells populate these tissues © McGraw Hill 27  Red Bone Marrow Red bone marrow is involved in hematopoiesis (blood formation) and immunity Soft, loosely organized, highly vascular material Separated from osseous tissue by endosteum of bone As blood cells mature, they push their way through the reticular and endothelial cells to enter the sinus and flow away in the bloodstream © McGraw Hill 28  Histology of Red Bone Marrow © McGraw Hill 29  Thymus 1 Thymus—member of the endocrine, lymphatic, and immune systems Houses developing lymphocytes Secretes hormones regulating their activity Bilobed organ located in superior mediastinum between sternum and aortic arch Degeneration (involution) with age © McGraw Hill 30  Thymus 2 Fibrous capsule gives off trabeculae (septa) that divide the gland into several lobes Lobes have cortex and medulla populated by T lymphocytes Epithelial cells seal off cortex from medulla forming blood– thymus barrier Produce signaling molecules thymosin, thymopoietin, thymulin, interleukins, and interferon © McGraw Hill 31  Thymus 3 Figure 21.9a,c © McGraw Hill 32  Histology of the Thymus Figure 21.9b © McGraw Hill b: Dennis Strete/McGraw-Hill Education 33  Lymph Nodes 1 Lymph nodes—most numerous lymphatic organs About 450 in typical young adult Serve two functions Cleanse the lymph Act as a site of T and B cell activation Elongated, bean-shaped structure with hilum Enclosed with fibrous capsule with trabeculae that divide interior into compartments Stroma of reticular fibers and reticular cells © McGraw Hill 34 © McGraw Hill 35  Lymph Nodes 2 Parenchyma divided into cortex and medulla Germinal centers where B cells multiply and differentiate into plasma cells Several afferent lymphatic vessels lead into the node along its convex surface Lymph leaves the node through one to three efferent lymphatic vessels that leave the hilum © McGraw Hill 36  Anatomy of a Lymph Node Figure 21.10 © McGraw Hill c: Francis Leroy, Biocosmos/Science Source 37 © McGraw Hill 38  Lymph Nodes 3 Cervical lymph nodes Deep and superficial group in the neck Monitor lymph coming from head and neck Axillary lymph nodes Concentrated in armpit Receive lymph from upper limb and female breast Thoracic lymph nodes In thoracic cavity, especially embedded in mediastinum Receive lymph from mediastinum, lungs, and airway © McGraw Hill 39  Lymph Nodes 4 Abdominal lymph nodes Occur in posterior abdominopelvic wall Monitor lymph from the urinary and reproductive systems Intestinal and mesenteric lymph nodes Found in the mesenteries, adjacent to the appendix and intestines Monitor lymph from the digestive tract Inguinal lymph nodes In the groin and receive lymph from the entire lower limb Popliteal lymph nodes Occur on the back of the knee Receive lymph from the foot and leg proper © McGraw Hill 40  Areas of Lymph Node Concentration 1 Figure 21.11a © McGraw Hill b: Rebecca Gray/Don Kincaid/McGraw-Hill Education 41  Areas of Lymph Node Concentration 2 Figure 21.11b © McGraw Hill b: Rebecca Gray/Don Kincaid/McGraw-Hill Education 42  Lymph Nodes 5 When a lymph node is under challenge by an antigen Lymphadenitis: swollen, painful node responding to foreign antigen Lymphadenopathy: collective term for all lymph node diseases © McGraw Hill 43  Lymph Nodes and Metastatic Cancer Metastasis—cancerous cells break free from original tumor, travel to other sites in the body and establish new tumors Metastasizing cells easily enter lymphatic vessels Tend to lodge in the first lymph node they encounter Multiply there and eventually destroy the node Swollen, firm, and usually painless Tend to spread to the next node downstream Treatment of breast cancer is lumpectomy, mastectomy, along with removal of nearby axillary nodes © McGraw Hill 44 © McGraw Hill 45  Tonsils 1 Tonsils—patches of lymphatic tissue located at the entrance to the pharynx Guard against ingested or inhaled pathogens Covered with epithelium Have deep pits: tonsillar crypts lined with lymphatic nodules Tonsillitis and tonsillectomy © McGraw Hill 46 © McGraw Hill 47  Tonsils 2 Three main sets of tonsils: Palatine tonsils Pair at posterior margin of oral cavity Most often infected Lingual tonsils Pair at root of tongue Pharyngeal tonsil (adenoids) Single tonsil on wall of nasopharynx © McGraw Hill 48  Tonsils 3 Figure 21.12a © McGraw Hill b: Biophoto Associates/Science Source 49 © McGraw Hill 50  Spleen 1 Spleen—the body’s largest lymphatic organ Parenchyma exhibits two types of tissue Red pulp: sinuses filled with erythrocytes White pulp: lymphocytes, macrophages surrounding small branches of splenic artery © McGraw Hill 51  Spleen Spleen functions Healthy red blood cells (RBCs) come and go For old, fragile RBCs, spleen is “erythrocyte graveyard” Blood cell production in fetus (and very anemic adults) White pulp monitors blood for foreign antigens and keeps an army of monocytes for release when needed Stabilizes blood volume through plasma transfers to lymphatic system Spleen is highly vascular and vulnerable to trauma and infection Ruptured spleen requires splenectomy, but this leaves person susceptible to future infections, premature death © McGraw Hill 52  Spleen 3 Figure 21.13 © McGraw Hill a, c: Dennis Strete/McGraw-Hill Education 53  Immunity © McGraw Hill 54  Innate Immunity 1 Pathogens—agents capable of producing disease Include viruses, bacteria, and fungi Three lines of defenses against pathogens First line of defense: skin and mucous membranes Second line of defense: several innate defense mechanisms Leukocytes and macrophages, antimicrobial proteins, natural killer cells, inflammation, and fever Third line of defense: adaptive immunity Defeats a pathogen and leaves the body with a “memory” of it so it can defeat it faster in the future © McGraw Hill 55  Innate Immunity 2  Innate defenses—guard equally against a broad range of pathogens  Local, nonspecific, lacks memory  Three kinds of innate defenses:  Protective proteins  Protective cells  Protective processes  Adaptive immunity—body must develop separate immunity to each pathogen  Body adapts to a pathogen and wards it off more easily upon future exposure (memory) © McGraw Hill 56  External Barriers 1 Skin Makes it mechanically difficult for microorganisms to enter the body Toughness of keratin Too dry and nutrient-poor for microbial growth Acid mantle: thin film of lactic and fatty acids from sweat and sebum that inhibits bacterial growth Dermicidin, defensins, and cathelicidins: peptides in the skin that kill microbes © McGraw Hill 57  External Barriers 2 Mucous membranes Digestive, respiratory, urinary, and reproductive tracts are open to the exterior and protected by mucous membranes Mucus physically traps microbes Lysozyme: enzyme destroys bacterial cell walls Subepithelial areolar tissue Viscous barrier of hyaluronic acid Hyaluronidase—enzyme used by pathogens to make hyaluronic acid less viscous © McGraw Hill 58  Leukocytes and Macrophages Five types of leukocytes: Neutrophils Eosinophils Basophils Monocytes Lymphocytes © McGraw Hill 59  Neutrophils Neutrophils Wander in connective tissue killing bacteria Can kill using phagocytosis and digestion Can kill by producing a cloud of bactericidal chemicals Lysosomes degranulate—discharge enzymes into tissue fluid causing a respiratory burst Creates a killing zone around neutrophil, destroying several bacteria © McGraw Hill 60  Eosinophils Eosinophils Found especially in mucous membranes Guard against parasites, allergens (allergy-causing agents), and other pathogens Kill tapeworms and roundworms by producing superoxide, hydrogen peroxide, and toxic proteins Promote action of basophils and mast cells Phagocytize antigen–antibody complexes Limit action of histamine and other inflammatory chemicals © McGraw Hill 61  Basophils Basophils Secrete chemicals that aid mobility and action of other leukocytes Leukotrienes: activate and attract neutrophils and eosinophils Histamine: a vasodilator, which increases blood flow Speeds delivery of leukocytes to the area Heparin: inhibits clot formation that would impede leukocyte mobility Mast cells also secrete these substances Type of connective tissue cell very similar to basophils © McGraw Hill 62  Lymphocytes 1 Lymphocytes Three basic categories: T, B, and NK cells Circulating blood contains 80% T cells 15% B cells 5% NK cells Many diverse functions NK cells are part of innate immunity, all others are part of adaptive immunity; helper T cells function in both © McGraw Hill 63  Monocytes and Macrophages Monocytes—emigrate from the blood into connective tissues and transform into macrophages Macrophage system—all the body’s avidly phagocytic cells, except leukocytes Wandering macrophages: actively seek pathogens Widely distributed in loose connective tissue Fixed macrophages: phagocytize only pathogens that come to them Microglia—in central nervous system Alveolar macrophages—in lungs Stellate macrophages—in liver © McGraw Hill 64  Antimicrobial Proteins Proteins that inhibit microbial reproduction and provide short- term, innate immunity to pathogenic bacteria and viruses Two families of antimicrobial proteins Interferons Complement system © McGraw Hill 65  Interferons 1 Interferons—secreted by certain cells infected by viruses Of no benefit to the cell that secretes them Alert neighboring cells and protect them from becoming infected Bind to surface receptors on neighboring cells Activate second-messenger systems within © McGraw Hill 66  Interferons 2 The alerted cell synthesizes various proteins that defend it from infection Breaks down viral genes or prevents replication Also activates NK cells and macrophages Destroy infected cell before they can liberate a swarm of newly replicated viruses Activated NK cells destroy malignant cells © McGraw Hill 67  Complement System 1 Complement system—a group of 30 or more globular proteins that make powerful contributions to both innate immunity and adaptive immunity Synthesized mainly by liver Circulate in the blood in inactive form Activated by presence of a pathogen © McGraw Hill 68  Complement System 2 Activated complement brings about four methods of pathogen destruction Inflammation Immune clearance Phagocytosis Cytolysis Three routes of complement activation Classical pathway Alternative pathway Lectin pathway © McGraw Hill 69  Complement System 3 Classical pathway Requires antibody molecule (thus part of adaptive immunity) Antibody binds to antigen on surface of the pathogenic organism; forms antigen–antibody (Ag– Ab) complex Changes the antibody’s shape Exposing a pair of complement-binding sites Binding of the first complement (C1) sets off a reaction cascade called complement fixation Results in a chain of complement proteins attaching to the antibody © McGraw Hill 70  Complement System 4 Alternative pathway Nonspecific, does not require antibody Binds directly to targets such as human tumor cells, viruses, bacteria, and yeasts Triggers cascade reaction with autocatalytic effect. Lectin pathway Lectins: plasma proteins that bind to carbohydrates Bind to certain sugars of a microbial cell surface © McGraw Hill 71  Complement System 5 Mechanisms of action of complement proteins Inflammation C3a stimulates mast cells and basophils to secrete histamine and other inflammatory chemicals Activates and attracts neutrophils and macrophages Speeds pathogen destruction in inflammation Immune clearance C3b binds with antigen–antibody (Ag-Ab) complexes to red blood cells that circulate through liver and spleen Macrophages of those organs strip off and destroy the Ag–Ab complexes leaving RBCs unharmed Principal means of clearing foreign antigens from the bloodstream © McGraw Hill 72  Complement System 6 Mechanisms of action of complement proteins (continued) Phagocytosis Neutrophils and macrophages cannot phagocytize “naked” bacteria, viruses, or other pathogens C3b assists them by opsonization Coats microbial cells and serves as binding sites for phagocyte attachment Makes the foreign cell more appetizing © McGraw Hill 73  Complement System 7 Mechanisms of action of complement proteins (continued) Cytolysis C3b splits complement protein C5 into C5a and C5b; C5b binds to enemy cell Attracts more complement proteins—membrane attack complex forms Forms a hole in the target cell Electrolytes leak out, water flows in rapidly, cell ruptures © McGraw Hill 74  Complement Activation Figure 21.14 © McGraw Hill 75  The Membrane Attack Complex Figure 21.15 © McGraw Hill 76  Natural Killer Cells Natural killer (NK) cells continually patrol body looking for pathogens and diseased host cells NK cells attack and destroy bacteria, transplanted cells, cells infected with viruses, and cancer cells Recognize enemy cell and bind to it Release proteins called perforins Polymerize a ring and create a hole in its plasma membrane Secrete a group of protein-degrading enzymes— granzymes Enter through pore and degrade cellular enzymes and induce apoptosis (programmed cell death) © McGraw Hill 77  The Action of a Natural Killer Cell Figure 21.16 © McGraw Hill 78  Fever 1 Fever—an abnormal elevation of body temperature Synonym: pyrexia; febrile—pertaining to fever Results from trauma, infections, drug reactions, brain tumors, and other causes Fever is an adaptive defense mechanism that, in moderation, does more good than harm Promotes interferon activity Elevates metabolic rate and accelerates tissue repair Inhibits reproduction of bacteria and viruses © McGraw Hill 79  Fever Antipyretics—fever-reducing medications; include aspirin and ibuprofen that inhibit Prostaglandin E2 synthesis Fever is usually triggered by exogenous pyrogens— fever-producing agents (for example, glycolipids on bacterial and viral surfaces) Endogenous pyrogens include polypeptides secreted by neutrophils and macrophages These raise hypothalamic set point for body temperature Neurons in the anterior hypothalamus secrete prostaglandin E2, which also raises set point Stages of fever: Onset, stadium, defervescence © McGraw Hill 80  The Course of a Fever Figure 21.17 © McGraw Hill 81 © McGraw Hill 82