CH_20_I.ppt

Chapter 20 - Part I The Lymphatic System Elephantiasis Hardening & thickening of skin following swelling of arms, breasts, legs, others (lymphedema) Caused by parasitic worms living in lymphatic system Source: http://www.bio.davidson.edu/Courses/immunology/Students/spring2006/Heeren/eleph_clip_image004.jpg http://www.stanford.edu/class/humbio103/ParaSites2006/Lymphatic_filariasis/Images/Wuchereria_bancrofti_1_DPDX.JPG Elephantiasis mosquitoe take a blood meal & also introduces worm larvae in saliva larvae move into lymphatic system & grow into adults ranging from 1-4? average lifespan = 7 years Filarial worm Lymphatic System Overview Lymphatic system - is a major component of immune system Consists of two semi-independent parts: 1. meandering network of lymphatic vessels returns IF & ?leaked? plasma proteins back into blood (maintains blood volume) 2. lymphoid tissues & organs scattered throughout body resident site for phagocytic cells & lymphocytes Source: www.winnetmag.com/Files/ 3966/Screen_01.GIF Tractor-trailer Interstitial fluid (IF) & Lymph IF - formed as plasma fluid is forced out of capillary bed arteriole end into surrounding tissue spaces not immediately returned to venous circulation (residual time) exchange medium for gases, nutrients, wastes between blood & cells Lymph - interstitial fluid once it has entered lymphatic vessels 3L formed each 24 hrs as interstitial fluid is returned to venous circulation flows toward heart (one-way system) Lymphatic Vessels Present in most tissues except for CNS, bones, teeth, bone marrow CSF drains fluid back into venous circulation lymph vessels are very low pressure (need help like veins) Lymph vessels include (small-to-large): lymphatic capillaries lymphatic collecting vessels lymphatic trunks lymphatic ducts Lymphatic Vessels (con?t) Types: lymphatic capillaries - microscopic, permeable, blind-ended vessels ?weaving? through capillary beds & tissues lymphatic collecting vessels - similar to veins but very thin-walled, contain more valves & anastomose more lymphatic trunks - formed by union of lymphatic vessels named for regions served (e.g. jugular, subclavian, etc.) Lymphatic Vessels (con?t) Types (con?t): lymphatic ducts - two large thoracic region ducts where all lymph is delivered 1. right lymphatic duct - drains right arm, thorax, right side of head (green area) 2. thoracic duct - arises from cisterna chyli (junction of 3 lower body trunks) right & left lumbar trunks (2) & intestinal trunk drains all other body regions (yellow area) Lymphatic Capillaries Characteristics: similar to blood capillaries? but with modifications 1. remarkably permeable 2. loosely joined endothelial overlap each other forming minivalves that are easily opened 3. anchored to collagen so ? interstitial pressure (more fluid) forces flaps open under increased pressure, closes when pressure decreases mini-valve action is one-way allows interstitial fluid to enter lymph capillaries does not allow lymph to escape from lymphatic capillaries Lymphatic Capillaries (con?t) Lymph capillaries open to absorb larger particulate matter during tissue inflammation: 1. cellular debris 2. pathogens (e.g. bacteria, fungi, etc.) 3. cancer cells Allows infectious agents to travel ?trapped? by lymph node immune cells, which cleanse &?examines? debris/cells Lacteals - specialized lymph capillaries present in intestinal mucosa absorbs digested fat in and delivers chyle (fatty lymph) to blood Lymph Transport Lymphatic system lacks an organ that acts as a pump Vessels are low-pressure conduits Uses similar methods as veins to propel lymph 1. pulsations of nearby arteries 2. smooth muscle contractions in lymphatic walls Lymphoid Cells Lymphocytes - main cells involved in immune response B cells & T cells are two main lymphocyte types protect body against foreign antigens antigen - anything body perceives as foreign (not-self) 1. bacteria (and their toxins) 2. viruses 3. incompatible RBCs (transfused) 4. cancer cells Lymphocyte Source: www.mssm.edu/medicine/hematology/lymphocyte.gif www.sirinet.net/~jgjohnso/antibodieaction2.jpg Antibodies & Antigens Lymphoid Cells (con?t) Functions: T cells - perform self-nonself recognition & can attack/destroy foreign cells once activated B cells - activate producing plasma cells, which then secrete antibodies macrophages - phagocytize foreign substances & help activate/recruit T cells dendritic cells - ?spiny cells? that perform Ag-presentation & long-term Ag recognition reticular cells - fibroblast-like cells producing stromal network supporting other cell types in lymphoid organs Dendritic cells Source: www.mayo.edu/research/bmb/esche2.jpg