The Lymphatic System Notes PDF

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Notes on Chapter 19: The Lymphatic System and Lymphoid Organs and Tissues plus images to clarify concepts. ...

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The Lymphatic System + Lymphoid Organs and Tissues: Chapter Notes

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 Provide structural basis of immune system House phagocytic cells + lymphocytes = key to body’s defense + resistance to disease

What does the lymphatic system do? Returns fluids that have leaked from the blood vascular system back from the blood vascular system back to the blood - Consists of three parts:  Network of lymphatic vessels  Lymph, fluid contained in those vessels  Lymph nodes = cleanse lymph that passes through them Lymphatic System  Once interstitial fluid enters the lymphatic vessels it is called lymph = clear water - Protein- containing fluid transported by lymphatic vessel  Blood circulates through body  nutrients, wastes, + gases exchanged btwn blood and interstitial fluid  Hydrostatic and colloid osmotic pressures operating at capillary beds force fluid out of the blood at the arterial ends of beds  “upstream” and cause it to be reabsorbed at venous ends  “downstream”  Fluid left behind? = as much as 3L of interstitial fluid  Leaked fluid + plasma proteins = returned to blood  Done via lymphatic vessels/lymphatics = drainage vessels that collect excess protein containing interstitial fluid + return it to bloodstream  Once fluid enters the lymphatic vessels it is called lymph  Lymph: Lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the interstitial fluid (the fluid which lies in the interstices of all body tissues) is collected through lymph capillaries.  Accumulated fluid = edema – impairs ability of tissue cells to make exchanges with the interstitial fluid of lymph. Vessels  Lymphatic vessels form one way sys. – lymph flows ONLY TOWARDS THE HEART - Lymphatic vessels = also called lymphatics - Function to: return excess tissue fluid to bloodstream, return leaked proteins to blood, and carry absorbed fat from intestines to blood via lacteals Lymphatic Capillaries  Lymphatic cap. = microscopic., weave btwn tissue cells and blood capill. In loose CT of body  Wide spread but NOT PRESENT IN: bones, teeth, bone marrow, and CNS  Very permeable  why? -

 Endothelial cells of walls are not tightly joined, edges overlap loosely = forming flaplike like minivalves  Collagen filaments anchors endothelial cells to surrounding structures – any increase in volume of fluid opens minivalves  Pressure in interstitial space (space between cells and a given tissue) greater than capillary?  minivalve opens allowing fluid to enter capillary  Pressure greater inside capillary?  valve flaps shut, preventing fluid from leaking out as pressure moves along vessel  Proteins in interstitial space cannot enter blood capillary so enter lymph capillary easily  Tissue inflamed? = capillaries develop opening to permit uptake of cell debris, pathogens, and cancer cells, all large molecules  threat moves through lymph and body but often at lymph nodes the debris is cleansed and examined by cells of immune system  Lacteals = special set of lymphatic capillaries = transport fats from small intestine to blood stream – chyle, fatty milky white lymph flows through them draining from villi in intestinal mucosa Larger Lymphatic Vessels  Lymph flow thru larger, thicker channels  collecting vessels, trunks, and then ducts (largest)  Collecting Lymphatic Vessels – 3 tunics like veins – have thinner walls + more internal valves + anastomose more (connect) - Lymphatic in skin travel along with superficial veins - Deep lymphatic vessels of trunk + digestive viscera travel with deep arteries  Lymphatic Trunks formed from the unification of the largest collecting vessels - Named by regions from which they drain lymph: lumbar, subclavian, bronchomediastinal, jugular on both sides and a single intestinal trunk  From here delivered to one of two large ducts – thoracic region - Right lymphatic duct = drains lymph from right upper limb and right side of head and thorax - Thoracic Duct = receives lymph from rest of body  Arises from first 2 lumbar vert. as an enlarged sac = cisterna chyli = collects lymph from two large lumbar trunks that drain the lower limbs and from intestinal trunk that drains digestive organs  As it goes superiorly receives lymphatic drainage from left side of thorax, upper limb, and head  Ducts empty lymph into venous circulation at junction of subclavian and jugular vein Transport of Lymph  Lymphatic vessels = low pressure conduits so  action of skeletal muscles, pressure changes in thorax during breathing, and valves prevent backflow + pulsations of arteries nearby promote lymph flow  Lymph. Vessels usually bundled together by CT sheaths along bvs

Smooth muscle in walls of lymph, vessels contracts rhythmically to pump lymph along  Movement inc./physical activity? = more rapid lymph flow due to impact of movement of adjacent tissues to propel lymph Lymphoid Cells and Tissues  Lymphoid cells consists of immune system cells found in lymphoid tissues together with supporting cells that form the scaffolding of those tissues  Lymphocytes = granular WBCs that arise from red bone marrow = warriors of immune system  Mature to two types: T cells (when activated manage immune response at times resulting in attacking and destroying infected cells) AND B cells (protect body by forming plasma cells, daughter cells that secrete antibodies into blood marking antigen for destruction)  Macrophages = crucial to protect body, act as phagocytes to foreign substances and aid in T cell activation  Dendritic = spiny looking cells that capture antigens and bring them back to lymph nodes  Reticular cells = fibroblast like cells that produce a reticular fiber called stroma that serves as the network to support the other cell types in the lymphoid organs and tissues  Lymphoid Tissue houses and provides a proliferation site for lymphocytes + furnishes an ideal surveillance vantage point for lymphocytes and macrophages  Largely composed of: reticular CT tissues (except thymus)- macrophages live on the fibers of the reticular CT network + vast #’s of lymphocytes squeeze through postcap. Venules and temporarily occupy space then leave to patrol body  Tissue comes in “two packages”: Diffuse lymphoid tissue and lymphoid follicles o Diffuse Tissue = loose arrangement of lymphoid cells and reticular fibers – found in virtually every body organ – larger collections in lamina proper of mucous membranes (lining of digestive tract) o Lymphoid Follicles/Nodules = solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers – form part of larger lymphoid organs (nodes) – often have germinal centers where proliferating B cells dominate, area enlarge when b cells dividing rapidly to produce plasma cells Lymph Nodes  Primary lymphoid organ = lymph nodes, small lymphoid organ that contains macrophages and lymphocytes, filters lymph  cluster along lymph. vessels of body and largest clusters at areas where trunks and collecting vessels converge  Hundreds of these organs, embedded in CT – larger clusters  Function to: 1. Filter Lymph – macrophages in lymph remove microorganisms and debris preventing from spread when delivered to blood and rest of body 2. Activate Immune System – strategic site where lymphocytes encounter antigen and mount attack 

Nodes = bean shaped and an 1 inch big – surrounded by dense fibrous capsule  CT strands called Trabeculae extend from capsule inward to divide node into compartments  Cortex and medulla areas: Cortex (outer surface layer) has follicles and houses Tcells, dendritic cells and Medulla (central area) has medullary cords, extensions of cortical lymphoid tissue containing lymphocytes  Throughout node = lymph sinuses , large capillaries spanned by reticular fibers – macrophages in these fibers phagocytize foreign matter as lymph flows by  Lymph enter node of convex side via afferent lymphatic vessels  moves through large subcapsular sinus  smaller sinuses through cortex  medulla  medullary sinuses  concave side exits via efferent lymphatic vessels : THINK I WANT ALL IN “AFFERENT”  I WANT THE EFF OUT EFFERENT Other Lymphoid Organs  Spleen, thymus, tonsils, and Peyer’s patches of small intestine – all except for thymus made up of reticular CT  Spleen – soft and blood rich, left side of abdominal cavity beneath diaphragm, curves around left side of stomach – relatively thin: Site for lymphocyte proliferation and immune surveillance and response + blood cleansing functions: removes debris, foreign matter, extracts defective or aged blood cells or platelets  Served by splenic artery and vein, enter and exit via hilum  Stores breakdown products of RBCs for later use (Fe for hemoglobin) + releases other to liver for processing  Stores platelets and monocytes for released when needed  Site of erythrocyte production in fetus  Histology of Spleen: Fibrous capsule and trabeculae + red & white pulp o White Pulp = where immune functions take place- composed of lymphocytes suspended in reticular fibers – form cuffs around central arteries (splenic) and form islands o Red pulp = where worn out RBCs and bloodborne pathogens destroyed – contains macrophages to engulf erythrocytes – consists of splenic cords, regions of reticular CT that separate splenic sinusoids filled with blood  Thymus – found in inferior neck – extends t superior thorax: T-cell precursors mature here (get “education” , become able to defend us  functions primarily in early years of life, inc. in size during first year of life, after puberty starts to atrophy slowly + becomes surrounded by fibrous and fatty tissue  has lobules, each with outer cortex and medulla – cortical regions have dividing lymphocytes and few macrophages scattered vs medullary regions have thymic corpuscles with less lymphocytes, these are concentric whorls of keratinized epithethial cells, site suggested to be involved in development of early Treg cells  has no follicles, no B cells, does not directly fight antigens  blood thymus barrier keeps bloodborne antigens out, only a site for maturation, and stroma (connective tissues) of thymus are epithelial cells versus reticular fibers providing environment for maturation 

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MALT = Mucosa Associated lymphoid tissues  set of lymphoid tissues located in mucous membranes throughout body = protection from pathogens: tonsils, Peyer’s patches, and appendix Tonsils = ring of lymphoid tissue around pharynx entrance – gather and remove any pathogens entering pharynx via food or inhaled air  Tissues have germinal centers surrounded by lymphocytes  Not fully encapsulated, epithelium overlying them invaginates into interior = tonsillar crypt that trap bacteria and other matter, then destroyed – allows for “memory” lymphocyte development pf trapped pathogens, allows us to have heightened immunity due to “traps”  Palatine tonsils = on either side of posterior end of oral cavity (common to get infected), Lingual tonsils = lumpy collection of follicles at base of tongue, Pharyngeal tonsils = in posterior wall of nasopharynx (if enlarged=adenoids), and tiny Tubal tonsils = surround auditory tubes of pharynx Peyer’s Patches = aggregated lymphoid nodules – clusters of follicles in the wall of the distal portion of the small intestine Appendix- tubular offshoot of the 1st part of large intestine with high conc. of follicles – at ideal position to destroy bacteria before reaching intestinal wall and generate “memory” lymphocytes

Clinical Apps/Imbalances  Lymphangitis = when lymphatic vessels inflamed and related vessels of vasa vasorum (network of small bvs) become congested with blood  superficial lymphatic pathway becomes visible through skin as red lines, tender to touch  Lymphedema = severe localized edema when anything prevents normal return of lymph to blood such as tumors blocking lymphatic or removal of lymphatics during cancer surgery – vessels remaining in area grow and draining eventually reestablished (short term)  Buboes = infected lymph node – when nodes overwhelmed by agent trying to destroy – ex: large number of bacteria in nodes = trapped, nodes get inflamed, swollen, tender to touch  Lymph nodes can become secondary cancer sites  metastasizing cancer cells get enter lymphatic vessels and get trapped  swollen nodes but not painful (bacterial = painful)  When spleen is ruptured, blood spilled into peritoneal cavity – spleen can be removed (splenectomy) or left alone to repair...