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The Lymphatic System and Immunity
22 The Lymphatic System and Immunity
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Functions of the Lymphatic System
Defense Lymphocytes residing in the lymphatic tissues protect the body against microorganisms and foreign substances. Such as viruses, bacteria, parasites, and fungi. Immune system – not an organ system, but a population of cells that inhabit all of our organs and defend the body from agents of disease The body harbors about 10,000 times as many bacterial cells as human cells some beneficial; some potentially disease causing Fluid balance Excess interstitial fluid enters lymphatic capillaries and becomes lymph; drains into the circulatory system. Fat Absorption absorbs fat and other substances from the intestines using specialized vessels called lacteals
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Components of the Lymphatic System
Lymph is fluid drained from interstitial spaces in all tissues. It is essential for fluid balance. Main source of lymphocytes is from lymph leaving lymph nodes Consistency of lymph determined by location. ex: after heavy fat absorption-milky color No lymph present in CNS (brain /spinal cord), cartilage, cornea, bone marrow, bone, or teeth Lymphatic capillaries and vessels transport the lymph Lymph Lymphatic Capillaries Lymphatic collecting vessels Lymph nodes 6 lymphatic trunks 2 Lymphatic ducts Drain into large veins of the body. 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 other organs by connective tissue capsules
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Lymphatic CAPILLARY Structures
Similar to blood capillaries; penetrate most tissues of the body. Increased permeability is due to: larger diameters and thinner walls Endothelial cells are loosely attached Edges overlap one another forming flap-like mini-valves Larger gaps allow bacteria and cells to entrance lymphatic capillary Increases in interstitial fluid pressure separates the flaps. Flaps push inward - fluid enters Flaps push outward –fluid remains in vessel 2) Filaments anchor endothelial cells to surrounding structures - prevents sac from collapsing 3) Lacteals - special lymphatic capillaries in small intestine -Transport lipids from digestive tract
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Higher pressure outside in interstitial fluid pushes flap open
Lower pressure inside vessel
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Lymphatic Vessels Lymph capillaries merge to form lymphatic vessels similar to veins with tunica interna (endothelial and valves), media (elastic and smooth muscle), externa (very thin) travel alongside veins/ arteries - share common connective tissue sheath one way valves prevent backflow Lymph moves through vessels by the “milking action” of the skeletal muscles and pressure changes created by the respiration similar to action of veins. Lymph from upper regions of the body flows through the help of gravity. Lymph flows at lower pressures and speed than venous blood vessels exercise significantly increases lymphatic return Vessels flow through lymph nodes: bean shaped clusters of B and T cells found along the length of the vessels; lymph fluid moves slowly thru nodes to increase filtration of microorganisms
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Lymph Trunks Jugular Subclavian Bronchiomediastinal Intercostal
Intestinal Lumbar Lymph is drained from major portions of body into six (6) lymphatic trunks: As lymphatic vessels exit from lymph nodes, they merge to form the 6 lymph trunks Each lymphatic trunk drains fluid from a certain area of the body. e.g. jugular trunks drain from the head and neck, subclavian trunks drain from the upper arms and superficial thoracic wall.
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Lymphatic trunks drain into two lymphatic ducts
Thoracic duct: Main collecting duct of the lymphatic system. Receives lymph from the left side of the head, neck, and chest, the left upper extremity, and the entire body below the ribs.
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Immune Cells of Lymphatic System
Macrophages- large, phagocytic cells of the connective tissue Formed from monocyte WBCs. Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter antigen presenting cells (APCs)-process foreign; display antigenic fragments alerting the immune system to the pathogens Neutrophils, basophils, eosinophils (WBCs) LYMPHOCYTES: (WBC) Natural killer LYMPHOCYTE (NK) cells –non-specific-INNATE large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or have turned cancerous responsible for immune surveillance T LYMPHOCYTES (T cells) specific - mature in thymus B LYMPHOCYTES (B cells) specific - differentiation into plasma cells that produce antibodies; mature in bone marrow Dendritic cells - APCs found in epidermis, mucous membranes, and lymphatic organs. Alert T cells to presences of pathogens Antimicrobial proteins - destroy bacteria Reticular cells- branched stationary cells contribute to the connective tissue framework of a lymphatic organ; act as APCs in the thymus
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Tonsils Large groups of NODULES in the mucosa of the pharynx. Protection against bacteria entering the body through the mouth or nasal cavities. Pharyngeal tonsil (adenoids) single tonsil on wall of nasopharynx Palatine tonsils on each side wall; most often infected Lingual tonsil in the back of the tongue
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Lymphatic ORGANS Areas where lymphatic tissue is concentrated
Separated from other organs by a connective tissue CAPSULE Primary Lymphatic organs: where IMMUNE cells (lymphocytes, macrophages) are produced and mature to the point where they can produce a normal immune response. (immunocompetent) e.g. red bone marrow and thymus gland Secondary Lymphatic organs: are the sites where the MATURE lymphocytes RESIDE and carry out immune response. e.g. spleen, lymph nodes
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Thymus Gland Large organ in infants but atrophied as adult.
2 lobed organ located in mediastinum Site of maturation of T cells
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Thymus Gland Surrounded by a connective tissue fibrous capsule with trabeculae divide the gland into several lobules Each lobule has cortex and medulla Cortex (numerous lymphocytes) Medulla (fewer lymphocytes) Reticular cells separate cortex from medulla and reinforce the blood-thymus barrier barrier prevents immature T cells from coming into contact with foreign antigens in the blood; contact with antigens at this stage would destroy T cells
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Lymph Nodes . Located along lymphatic vessels; most numerous
Concentrated near mammary glands, axilla, groin, thoracic cavity, throat Filter lymph through a network of sinuses Dense CT capsule surrounds outer structure and extends inwardly as trabeculae. Outer cortex contains lymphatic nodules filled with T-lymphocytes and macrophages Inner medulla lymphatic tissue called medullary cords consist of B-lymphocytes, macrophages, plasma cells, reticular cells Lymph enters the nodes via the afferent lymphatic vessel and leaves via the efferent lymphatic vessel .
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T- lymphocytes B- Lymphocytes
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Lymphatic System Metastasis – when cancerous cells break free from the original, primary tumor, travel to other sites in the body, and establish new tumors. Characteristic of malignant tumors PRIMARY SITE where cancer cells travel via blood or lymphatic system and establish new tumors where they lodge tend to lodge in the first lymph node they encounter SECONDARY TUMOR sites can be predicted by direction of lymphatic flow from primary site; prevention of metastasis by removing nodes “downstream” from originate site. Lymphoma - cancer of lymph cells that usually originate in the lymph nodes. There are multiple systems used to classify lymphoma based on cell type, prognosis, etc. Lymphedema Blockage of lymph drainage from a limb Causes severe swelling; often a consequence of surgically removing the lymph nodes in the armpit (axilla) or groin, or their damage caused by radiotherapy. Interferes with immune system function
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Largest lymphatic organ. Similar to a large lymph node - blood filter.
Spleen Largest lymphatic organ. Similar to a large lymph node - blood filter. CT Capsule; trabeculae, divide spleen into compartments Each compartment filled with: White pulp – lymphocytes and macrophages Monitors blood for pathogens Red pulp is lymphatic tissue filled with RBCs. (76%-79%). Old and deformed cells deposited, RBC “graveyard” Metabolizes (breaks down) hemoglobin recycling iron components Transfers excess plasma from blood to lymphatic system –controls blood volume. Fluid flows into spleen out into interstitial fluid. Acts as blood reserve in event of hemorrhagic shock The spleen often damaged by trauma/injury. Rupture can lead to bleeding, shock, death. Removal (splenectomy) may be required to prevent excessive bleeding.
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The hilum - depression for splenic blood vessels
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Antibodies Antibodies class of proteins called Immunoglobulins (Igs ).
Four polypeptide chains: two heavy and two light. Each light is held to a heavy by a disulfide bond. Each chain has two regions; a constant region (C) which is the same within a class of antibody and a variable region (V) which varies from one antibody to the other. V region from each chain has the antigen binding site to recognize and specifically attach to a particular antigen. Sites for complement-binding- constant area of heavy chain Antibodies
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Five Classes of Antibodies
Named for the structure of their C region IgA – plasma, mucus, saliva, tears, milk, and intestinal secretions; attack pathogens before they gain access to internal tissues; mother’s milk provides IgA antibodies to infant after birth; prevents pathogen colonization IgD - B cell transmembrane antigen receptor to increase B cell activation; also known to activate basophils and mast cells IgE - transmembrane protein on basophils and mast cells Binds to mast cells and stimulates release of histamine - inflammation and allergy IgG - constitutes 80% of circulating antibodies resistance against many viruses, bacteria, and bacterial toxins; crosses placenta to fetus, COMPLEMENT FIXATION; Anti-Rh antibodies produced by Rh-negative mothers IgM – in plasma and lymph - first class of antibody secreted after an antigen is encountered; eliminates pathogens before there is sufficient IgG available; produces anti-A and anti-B antibodies responsible for the agglutination of RBC; COMPLEMENT FIXATION. 21
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