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Charlotte Youngson

20,21 -The Lymphatic System Pre-lecture questions: 1. What is non-specific and specific immunity? Give one example of each. Non-we don’t care about pathogen antigen. Specific-what on blackboard picture. Khan academy picture. Made up of humoral and semadiated 2. What are class I(on all except 4) and class II MHC proteins? Sel antigen. That belong to slef. 3. What are cell-mediated and antibody-mediated immunity? Part of specific immunity. Lymphatic System • Consists of three parts 1. A network of lymphatic vessels (lymphatics) 2. Lymph – fluid within the vessels 3. Lymph nodes – cleanse the lymph Lymphatic System: Functions • Returns interstitial fluid and leaked plasma proteins back to the blood • Once interstitial fluid enters lymphatics, it is called lymph • Together with lymphoid organs and tissues, provide the structural basis of the immune system Lymph Transport • Lymph is propelled by • Pulsations of nearby arteries • Contractions of smooth muscle in the walls of the lymphatics Lymphoid Cells • Two main varieties • T cells (T lymphocytes) • WBC • B cells (B lymphocytes) • WBC Lymphocytes • T cells and B cells protect against antigens • Anything the body perceives as foreign • Bacteria (doesn’t need the host) and their toxins; viruses (small and parasitic, need the host) • Mismatched RBCs (incomplete transfusion) or cancer cells (malignant cells –start become foreign looking) • T cells • T helper • Manage the immune response • Attack and destroy foreign cells • B cells • Produce plasma cells, which secrete antibodies • Become antibody producing body • Won’t kill pathogen but will tag the pathogen • Phagocytosis kills pathogen Lymph Nodes • Functions 1. Filter lymph—macrophages destroy microorganisms and debris 2. Immune system—lymphocytes are activated and mount an attack against antigens Structure of a Lymph Node • Medullary cords extend inward from the cortex and contain B cells, T cells, and plasma cells • Lymph sinuses contain macrophages • Macrophages: powerful immune cells Spleen • Largest lymphoid organ • Fully vascularized and has sinusoidal arteries • Served by splenic artery and vein, which enter and exit at the hilus • Functions • Site of lymphocyte proliferation and immune surveillance and response (detect cancer and abnormal cells) • Cleanses the blood of aged cells and platelets and debris • You can live w.o spleen but their immune system is mildly compromised Thymus • Size decreases with age • In infants, it is found in the inferior neck and extends into the mediastinum, where it partially overlies the heart • Increases in size and is most active during childhood • Stops growing during adolescence and then gradually atrophies Tonsils • Simplest lymphoid organs • Form a ring of lymphatic tissue around the pharynx • Palatine tonsils—at posterior end of the oral cavity • Lingual tonsils—grouped at the base of the tongue • Pharyngeal tonsil—in posterior wall of the nasopharynx • Tubal tonsils—surrounding the openings of the auditory tubes into the pharynx • You’re okay w/o tonsils • Tonsils ensure we don’t get food poisoned MALT • Mucosa-associated lymphatic tissue, including • Peyer’s patches, tonsils, and the appendix (digestive tract) • Lymphoid nodules in the walls of the bronchi (respiratory tract) • Protects the digestive and respiratory systems from foreign matter • Protection in areas that open Immunity • Resistance to disease • Immune system has two intrinsic systems • Innate (nonspecific) defense system – don’t care what protein is • Adaptive (specific) defense system – care about the protein and make specific response • Neutrophils: used in acute infection – at the beginning • Lymphocytes: not phagocytic. Important in the system 1. Innate (Non-specific) defense system has two lines of defense • First line of defense is external body membranes (skin and mucosae) • Second line of defense is antimicrobial proteins, phagocytes, and other cells • Inhibit spread of invaders • Inflammation is its most important mechanism 2. Adaptive (Specific) defense system • Third line of defense attacks particular foreign substances • Takes longer to react than the innate system • Innate and adaptive defenses are deeply intertwined • Need to work together Non-Specific Immunity: Innate Defenses 1. Surface barriers – physical barrier • Skin, mucous membranes, and their secretions • Physical barrier to most microorganisms • Keratin is resistant to weak acids and bases, bacterial enzymes, and toxins • Mucosae provide similar mechanical barriers Internal Defenses: Cells and Chemicals • Necessary if microorganisms invade deeper tissues 2. Phagocytes 3. Natural killer (NK) cells 4. Inflammatory response (macrophages, mast cells, WBCs, and inflammatory chemicals) 5. Antimicrobial proteins (interferons and complement proteins) 6. Fever 1. Phagocytes: Macrophages • Macrophages develop from monocytes to become the chief phagocytic cells • Free macrophages wander through tissue spaces • E.g., alveolar macrophages • Fixed macrophages are permanent residents of some organs • E.g., Kupffer cells (liver) and microglia (brain) 2. Natural Killer (NK) Cells • Large granular lymphocytes • Target cells that lack “self” cell-surface receptors • Induce apoptosis (cell death) in cancer cells and virus-infected cells • Secrete potent chemicals that enhance the inflammatory response 3. Inflammatory Response • Triggered whenever body tissues are injured or infected • Prevents the spread of damaging agents • Disposes of cell debris and pathogens • Sets the stage for repair • Cardinal signs of acute inflammation: 1. Redness 2. Heat 3. Swelling 4. Pain 5. Antimicrobial Proteins a. Interferons (IFNs) b. complement proteins Both: • Attack microorganisms directly • Hinder microorganisms’ ability to reproduce a. Interferons • Viral-infected cells are activated to secrete IFNs • IFNs enter neighboring cells • Prevents neighbouring cells from being infected • Neighboring cells produce antiviral proteins that block viral reproduction b. Complement • ~20 blood proteins that circulate in an inactive form • Include C1–C9 • Major mechanism for destroying foreign substances 6. Fever • Systemic response to invading microorganisms • Leukocytes and macrophages exposed to foreign substances secrete pyrogens • Pyrogens reset the body’s thermostat upward Specific Immunity: Adaptive Defenses • Adaptive immune response • Is specific • Is systemic • Has memory • Two separate overlapping arms 1. Humoral (antibody-mediated) immunity 2. Cellular (cell-mediated) immunity Self-Antigens: MHC Proteins • Protein molecules (self-antigens) on the surface of cells • Antigenic to others in transfusions or grafts • Example: MHC proteins • Coded for by genes of the major histocompatibility complex (MHC) and are unique to an individual MHC Proteins • Classes of MHC proteins • Class I MHC proteins, found on virtually all body cells • Class II MHC proteins, found on antigen-presenting cells (APC) and B lymphocytes • In infected cells, MHC proteins display fragments of pathogen antigens Cells of the Specific Immune System • Two types of lymphocytes • B lymphocytes (B cells)—humoral immunity • T lymphocytes (T cells)—cell-mediated immunity • Antigen-presenting cells (APCs) • A macrophage that is presenting the pathogen antigen on it’s own cell surface together with a class II MHC Lymphocytes • Originate in red bone marrow • B cells mature
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