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This 11 page Class Notes was uploaded by Jess Graff on Tuesday March 8, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 18 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 03/08/16
BMS 508.03 3/4/16 Chapter 22 (cont) Lymph and Immunity (cont) Structures of Body Defenses (cont) • Cytotoxic T Cells • Attack cells infected by viruses • Produce cell-mediated immunity • Memory T Cells • Formed in response to foreign substance • Remain in body to give “immunity” • Helper T Cells • Stimulate function of T cells and B cells • Suppressor T Cells • Inhibit function of T cells and B cells • Regulatory T Cells • Are helper and suppressor T cells • Control sensitivity of immune response • Other T Cells • Inflammatory T cells • Suppressor/inducer T cells • B Cells • Make up 10–15% of circulating lymphocytes • Differentiate (change) into plasma cells • Plasma cells • Produce and secrete antibodies (immunoglobulin proteins) • Antigens • Targets that identify any pathogen or foreign compound • Immunoglobulins (Antibodies) • The binding of a specific antibody to its specific target antigen initiates antibody-mediated immunity • Antibody-Mediated Immunity • A chain of events that destroys the target compound or organism • Natural Killer (NK) Cells • Also called large granular lymphocytes • Make up 5–10% of circulating lymphocytes • Responsible for immunological surveillance • Attack foreign cells, virus-infected cells, and cancer cells • Lymphocyte Distribution • Tissues maintain different T cell and B cell populations • Lymphocytes wander through tissues • Enter blood vessels or lymphatics for transport • Can survive many years • Lymphocyte Production • Also called lymphopoiesis, involves: • Bone marrow • Thymus • Peripheral lymphoid tissues • Hemocytoblasts • In bone marrow, divide into 2 types of lymphoid stem cells • Lymphoid Stem Cells • Group 1 • Remains in bone marrow and develop with help of stromal cells • Produces B cells and natural killer cells • Group 2 • Migrates to thymus • Produces T cells in environment isolated by blood– thymus barrier • T Cells and B Cells • Migrate throughout the body • To defend peripheral tissues • Retaining their ability to divide • Essential to immune system function • Differentiation • B cells differentiate • With exposure to hormone called cytokine (interleukin- 7) • T cells differentiate • With exposure to several thymic hormones • Lymphoid Tissues • Connective tissues dominated by lymphocytes • Lymphoid Nodules • Areolar tissue with densely packed lymphocytes • Germinal center contains dividing lymphocytes • Distribution of Lymphoid Nodules • Lymph nodes • Spleen • Respiratory tract (tonsils) • Along digestive, urinary, and reproductive tracts • Mucosa-Associated Lymphoid Tissue (MALT) • Lymphoid tissues associated with the digestive system • Aggregated Lymphoid Nodules • Clustered deep to intestinal epithelial lining • Appendix (Vermiform Appendix) • Contains a mass of fused lymphoid nodules • The Five Tonsils • In wall of pharynx • Left and right palatine tonsils • Pharyngeal tonsil (adenoid) • 2 lingual tonsils • Lymphoid Organs • Lymph nodes • Thymus • Spleen • Separated from surrounding tissues by a fibrous connective tissue capsule • Lymph Nodes • Trabeculae • Bundles of collagen fibers • Extend from capsule into interior of lymph node • Hilum • A shallow indentation where blood vessels and nerves reach the lymph node • Afferent lymphatics • Carry lymph • From peripheral tissues to lymph node • Efferent lymphatics • Leave lymph node at hilum • Carry lymph to venous circulation • Lymph Flow • Flows through lymph node in a network of sinuses • From subcapsular space • Contains macrophages and dendritic cells • Through outer cortex • Contains B cells within germinal centers • Through deep cortex • Dominated by T cells • Through the core (medulla) • Contains B cells and plasma cells, organized into medullary cords • Finally, into hilum and efferent lymphatics • Lymph Node Function • A filter • Purifies lymph before return to venous circulation • Removes: • Debris • Pathogens • 99% of antigens • Antigen Presentation • First step in immune response • Extracted antigens are “presented” to lymphocytes • Or attached to dendritic cells to stimulate lymphocytes • Lymphatic Functions • Lymphoid tissues and lymph nodes • Distributed to monitor peripheral infections • Respond before infections reach vital organs of trunk • Lymph nodes of gut, trachea, lungs, and thoracic duct • Protect against pathogens in digestive and respiratory systems • Lymph Nodes (Glands) • Large lymph nodes at groin and base of neck • Swell in response to inflammation • Lymphadenopathy • Chronic or excessive enlargement of lymph nodes • May indicate infections, endocrine disorders, or cancer • The Thymus • Located in mediastinum • Atrophies after puberty • Diminishing effectiveness of immune system • Divisions of the Thymus • Thymus is divided into 2 thymic lobes • Septa divide lobes into smaller lobules • A Thymic Lobule • Contains a dense outer cortex and a pale central medulla • Lymphocytes • Divide in the cortex • T cells migrate into medulla • Mature T cells leave thymus by medullary blood vessels • Thymic Epithelial Cells in the Cortex • Surround lymphocytes in cortex • Maintain blood–thymus barrier • Secrete thymic hormones that stimulate: • Stem cell divisions • T cell differentiation • Thymic Epithelial Cells in the Medulla • Form concentric layers known as thymic (Hassall’s) corpuscles • The medulla has no blood–thymus barrier • T cells can enter or leave bloodstream • Thymus Hormones • Thymosin – an extract from the thymus that promotes development of lymphocytes • Three Functions of the Spleen • Removal of abnormal blood cells and other blood components by phagocytosis • Storage of iron recycled from red blood cells • Initiation of immune responses by B cells and T cells • In response to antigens in circulating blood • Anatomy of the Spleen • Attached to stomach by gastrosplenic ligament • Contacts diaphragm and left kidney • Splenic veins, arteries, and lymphatic vessels • Communicate with spleen at hilum • Histology of the Spleen • Inside fibrous capsule • Red pulp contains many red blood cells • White pulp resembles lymphoid nodules • Trabecular Arteries • Branch and radiate toward capsule • Finer branches surrounded by white pulp • Capillaries discharge red blood cells into red pulp • Red Pulp • Contains elements of circulating blood • Plus fixed and free macrophages • Splenic Circulation • Blood passes through: • Network of reticular fibers • Then enters large sinusoids (lined by macrophages) • Which empty into trabecular veins • Spleen Function • Phagocytes and other lymphocytes in spleen • Identify and attack damaged and infected cells • In circulating blood • The Lymphatic System and Body Defenses • Body defenses provide resistance to fight infection, illness, and disease • 2 categories of defenses • Innate (nonspecific) immunity • Adaptive (specific) immunity • Innate (Nonspecific) Immunity • Always works the same way • Against any type of invading agent • Nonspecific resistance • Adaptive (Specific) Immunity • Protects against specific pathogens • Depends on activities of lymphocytes • Specific resistance (immunity) • Develops after exposure to environmental hazards Nonspecific Defenses • 7 Major Categories of Innate (Nonspecific) Immunity 1. Physical barriers 2. Phagocytes 3. Immune surveillance 4. Interferons 5. Complement 6. Inflammatory response 7. Fever • Physical Barriers 1. Keep hazardous materials outside the body • Phagocytes 1. Attack and remove dangerous microorganisms • Immune Surveillance 1. Constantly monitors normal tissues • With natural killer cells (NK cells) • Interferons 1. Chemical messengers that trigger production of antiviral proteins in normal cells 2. Antiviral proteins • Do not kill viruses • Block replication in cell • Complement 1. System of circulating proteins 2. Assists antibodies in destruction of pathogens • Inflammatory Response 1. Localized, tissue-level response that tends to limit spread of injury or infection • Fever 1. A high body temperature • Increases body metabolism • Accelerates defenses • Inhibits some viruses and bacteria • Physical Barriers 1. Outer layer of skin 2. Hair 3. Epithelial layers of internal passageways 4. Secretions that flush away materials • Sweat glands, mucus, and urine 5. Secretions that kill or inhibit microorganisms • Enzymes, antibodies, and stomach acid