Lymphatic System PDF

11/7/24 Learning Objectives 1. Describe and discuss the organs of the lymphatic...

11/7/24 Learning Objectives 1. Describe and discuss the organs of the lymphatic system Lymphatic System 2. Identify and discuss the structures associated By : Marc Anthony Cueto MD with the organs of the lymphatic system using model 3. Trace the pathway of the lymph 1 2 Lymphatic System u The lymphatic system is a network of tissues, vessels and organs that work together to move a colorless, watery fluid called lymph back into your circulatory system (your bloodstream). u Some 20 liters of plasma flow through your body’s arteries and smaller arteriole blood vessels and capillaries every day. After delivering nutrients to the body’s cells and tissues and receiving their waste products, about 17 liters are returned to the circulation by way of veins. u The remaining three liters seep through the capillaries and into your body’s tissues. The lymphatic system collects this excess fluid, now called lymph, from tissues in your body and moves it along until it's ultimately returned to your bloodstream. 3 4 Lymphatic System Lymphatic Vessels u Your lymphatic system has many functions. Its key functions include: u The lymphatic vessels are the lymphatic system equivalent of the Maintains fluid levels in your body: The lymphatic blood vessels of the circulatory system and drain fluid from the system collects excess fluid that drains from cells and tissue throughout your body and returns it to your circulatory system. bloodstream, which is then recirculated through your body. u The network of lymph vessels consists of the initial collectors of Absorbs fats from the digestive tract: Lymph includes lymph fluid, which are small, valveless vessels, and goes on to fluids from your intestines that contain fats and proteins form the precollector vessels, which have rudimentary valves and transports it back to your bloodstream. Protects your body against foreign invaders: The that are not fully functional. lymphatic system is part of the immune system. It produces and releases lymphocytes (white blood cells) u These structures then form increasingly larger lymphatic vessels and other immune cells that monitor and then destroy the which form colaterals and have lymph-angions (lymph hearts). foreign invaders — such as bacteria, viruses, parasites and fungi — that may enter your body. u The larger lymph vessels contain valves that prevent the Transports and removes waste products and abnormal backflow of lymph. cells from the lymph. 5 6 1  11/7/24 Lymphatic Vessels Lymphatic Vessels : Layers u The endothelium, a general term for the inner layer of a vessel, is u The lymphatic system is an active pumping system driven by segments composed of an inner lining of single, flattened epithelial cells (simple squamous epithelium). This layer mechanically transports that have a function similar to peristalsis. fluid. u They lack a central pump (like the heart in the cardio vascular system), u The next layer is smooth muscles arranged in a circular fashion around the endothelium that alters the pressure inside the so smooth muscle tissue contracts to move lymph along through the lumen (space) inside the vessel by contracting and relaxing. The activity of smooth muscles allows lymph vessels to slowly pump vessels. lymph fluid through the body without a central pump or heart. By contrast, the smooth muscles in blood vessels are involved in u Skeletal muscle contractions also move lymph through the vessels. The vasoconstriction and vasodilation instead of fluid pumping. lymphatic vessels make their way to the lymph nodes, and from there u The outermost layer is the adventitia, consisting of fibrous tissue. It is made primarily out of collagen and serves to anchor the the vessels form into trunks. lymph vessels to structures within the body for stability. Larger lymph vessels have many more layers of adventitia than do smaller lymph vessels. u In general, the lymph vessels bring lymph fluid toward the heart and The smallest vessels, such as the lymphatic capillaries, may have above it to the subclavian veins, which enable lymph fluid to re-enter u no outer adventitia. As they proceed forward and integrate into the circulatory system through the vena cava. the larger lymph vessels, they develop adventitia and smooth muscle. Blood vessels also have adventitia, sometimes referred to as tunica. 7 8 Lymphatic Vessels : Valves Lymphatic Capillaries u Lymph capillaries are tiny, thin-walled vessels, closed at u One of the main structural features of one end and located in the spaces between cells lymph vessels is their valves, which are throughout the body. semilunar structures attached to opposite sides of the lymphatic endothelium. u Lymphatic circulation begins in the smallest type of u Valves are found in larger lymph vessels lymph vessels, the lymph capillaries. and collecting vessels and are absent in the lymphatic capillaries. u These regulate the pressure of interstitial fluid by u The valves is to prevent backflow of fluid, draining lymph from the tissues. so that lymph eventually flows forward instead of falling backwards. 9 10 Lymphatic Capillaries : Structure Lymphatic Capillaries : Functions u Lymph or lymphatic capillaries are tiny thin-walled vessels, closed at one end and located in the spaces between cells throughout the body. u These are particularly dense within connective tissue. u Lymphatic capillaries collect lymph fluid from the tissues, which u Lymphatic capillaries are slightly larger in diameter than blood capillaries and contain flap- allows them to regulate the pressure of interstitial fluid. like “minivalves” that permit interstitial fluid to flow into them but not out, under normal conditions. u Under normal conditions, lymph capillaries prevent the u Lymphatic capillaries are primarily made out of an endothelium layer that sits on a accumulation of edema (abnormal swelling) in the tissues. permeable basement membrane. The flap-like minivalves, located at gap-like junctions in the endothelium, are formed from the overlap of endothelial cells and are normally closed. u The lymphatic capillaries bring lymph further into the lymphatic Attached to the outer opening of the minivalves are anchoring filaments containing elastic u fibers. They extend out from the lymphatic capillary, attaching the endothelium to fibroblast vessels. cells in the connective tissue. u The capillaries have external valves but no internal valves or u Unlike larger lymphatic vessels, lymphatic capillaries do not contain smooth muscle nor do they have a well developed adventitia, only small elastic filaments that perform a similar smooth muscle, so the pressure of lymph accumulation itself function. must propel the fluid forward into the larger vessels. 11 12 2  11/7/24 Lymph Nodes Lymph Nodes u Lymph nodes are small oval-shaped balls of lymphatic tissue, u Lymph nodes are found throughout the body, and are typically 1 to 2 centimeters long. Humans have approximately 500–600 lymph distributed widely throughout the body and linked by a vast nodes, with clusters found in the underarms, groin, neck, chest, and abdomen. network of lymphatic vessels. u Each lymph node is surrounded by a fibrous capsule that encircles the internal cortex and medulla. u Lymph nodes are repositories of B cells, T cells, and other u The cortex is mainly composed of clusters of B cells in the outer layers and T cells in the inner layers, and may also contain antigen- immune system cells, such as dendritic cells and presenting dendritic cells. macrophages. u The medulla contains plasma cells, macrophages, and B cells as well as sinuses, which are vessel-like spaces that the lymph flows into. u They act as filters for foreign particles in the body and are u Inside each sinus cavity is a nodule, a smaller, denser bundle of one of the sites where adaptive immune responses are lymphoid tissue that usually contains a germinal center, the site of B cell proliferation during antigen presentation. triggered. u The sinuses are partially divided by capsule tissue, which causes lymph fluid to flow around the nodules in each sinus cavity on their way through the node. 13 14 Lymph Node Distribution Lymph Node Distribution u Lymph nodes are most densely distributed around the pharynx and neck, chest, armpits, groin, and around the intestines. u Lymphatic vessels are most densely distributed near lymph nodes: bundles of u Afferent and efferent lymph vessels are also most lymphoid tissue that filter the lymph fluid of pathogens and abnormal concentrated in these areas so they can filter lymph fluid close to the end of the lymphatic system, where molecules. Adaptive immune responses usually develop within lymphatic fluid is returned into the cardiovascular system. vessels. Large lymphatic vessels can be broadly characterized into two u Conversely, lymph nodes are not found in the areas of categories based on lymph node distribution. the upper central nervous system, where tissue drains into cerebrospinal fluid instead of lymph, though there Afferent lymphatic vessels flow into a lymph node and carry unfiltered are some lymph vessels in the meninges. lymph fluid. u There are few lymph nodes at the ends of the limbs. u The efferent lymph vessels in the left and lower side of Efferent lymphatic vessels flow out of a lymph node and carry filtered the body drain into the left subclavian vein through the lymph fluid. Lymph vessels that leave the thymus or spleen (which lack thoracic duct, while the efferent lymph vessels of the right side of the body drain into the right subclavian afferent vessels) also fall into this category. vein through the right lymphatic duct. 15 16 Lymphatic Trunks and Ducts Lymphatic Trunks u The lymph trunks drain into the lymph ducts, which in u A lymphatic trunk is any large lymph vessel that forms from the convergence of many efferent lymph vessels. There are four turn return lymph to the blood by emptying into the sets of lymph trunks that are paired with a right and left half, and one unpaired trunk: respective subclavian veins. Jugular lymph trunks, located in the neck, drain lymph fluid from the cervical lymph nodes of the neck. u After filtration by the lymph nodes, efferent lymphatic Subclavian lymph trunks, located beneath the clavicle, drain lymph fluid from the apical lymph nodes around the armpit, which carry lymph from the arms. vessels take lymph to the end of the lymphatic system. Bronchomediastinal lymph trunks, located in the chest, drain lymph fluid from the lungs, heart, trachea, mediastinal, and u The final goal of the lymphatic system is to recirculate mammary glands. lymph back into the plasma of the bloodstream. Lumbar lymph trunks are the lower pair of lymph trunks that drain lymph fluid from the legs, pelvic region, and kidneys. Intestinal lymph trunk is the unpaired lymph trunk that receives u There are two specialized lymphatic structures at the chyle (lymph mixed with fats) from the intestines. Chyle typically has a high fatty acid content. end of the lymphatic system, called the lymph trunks u Lymphatic trunks then drain lymph fluid into the lymph ducts, the final part of the lymphatic system. and ducts. 17 18 3  11/7/24 Cisterna Chylii u The cisterna chyli (C C ) (plural: cisternae chyli), also know n as the receptaculum chyli, is a norm al anatom ical structure in the lym phatic system. It is seen as a saccular area of dilatation in the lym phatic channels that are located in the retrocrural space, usually to the im m ediate right of the origin of the abdom inal aorta. u In general, lym phatics from the pelvis and low er extrem ities along w ith abdom inal lym phatics from the bow el and liver drain into the cisterna chyli. u Chyle (a m ilky odorless fluid) is a m ixture of chylom icrons (absorbed from the intestines) and clear lym ph from the pelvis and low er extrem ities. u The cisterna chyli is located behind the right diaphragm atic crus at the T12–L2 level (Fig 2) and gives rise to the thoracic duct.Receives lym ph from the abdom inal viscera as w ell as the abdom inal w all (below the level of the um bilicus), non- alim entary viscera and low er extrem ities. u Relations u anterior: right crus of the diaphragm u posterior: L1 and L2 vertebral bodies u left lateral: abdominal aorta u right lateral: azygos vein 19 20 Thoracic Duct Thoracic Duct u The thoracic duct is a major u The thoracic duct terminates in the lymphatic channel that begins in junction between the left internal jugular and the left subclavian veins. the abdomen, passes superiorly Near its junction with the venous through the thorax, and ends in system it is joined by: the venous channels in the neck. u the left jugular trunk, which drains It passes through the lower lymph from the left side of the head thoracic cavity in the midline and neck; with: u the left subclavian trunk, which u the thoracic aorta on the left; drains lymph from the left upper limb; and u the azygos vein on the right; u occasionally, the left and bronchomediastinal trunk, which drains lymph from the left half of u the esophagus anteriorly. the thoracic structures. 21 22 Lymphatic Duct u A similar confluence of three lymphatic trunks occurs on the right side of the body. Emptying into the junction between the right internal jugular and right subclavian veins are: u the right jugular trunk from the head and neck; u the right subclavian trunk from the right upper limb; and u occasionally, the right bronchomediastinal trunk carrying lymph from the structures in the right half of the thoracic cavity and the right upper intercostal spaces. u There is variability in how these trunks enter the veins. They may combine into a single right lymphatic duct to enter the venous system or enter as three separate trunks. 23 24 4  11/7/24 Lymph Flow u The lymphatic vessels start with the collection of lymph fluid from the interstitial fluid. u This fluid is mainly water from plasma that leaks into the intersitial space in the tissues due to pressure forces exerted by capillaries (hydrostatic pressure) or through osmotic forces from proteins (osmotic pressure). u When the pressure for interstitial fluid in the interstitial space becomes large enough it leaks into lymph capillaries, which are the site for lymph fluid collection. u Lymph flows in one direction toward the heart. Lymph vessels become larger, with better developed smooth muscle and valves to keep lymph moving forward despite the low pressure and adventia to support the lymph vessels. u As the lymph vessels become larger, their function changes from collecting fluid from the tissues to propelling fluid forward. u Lymph nodes found closer to the heart filter lymph fluid before it is returned to venous circulation through one of the two lymph ducts. 25 26 Lymphoid Tissue Mucosa Associated Lymphoid Tissue u Lymphoid tissue consists of many organs that play a role in the production and maturation of (MALT) lymphocytes in the immune response. u The main sites of entry for microbes into the body are through mucosal u The tissues of lymphoid organs are different than the tissues in most other organ systems in surfaces. that they vary considerably based on cell cycle proliferation of lymphocytes. The lymphoid u Hence, the majority (>50%) of lymphoid tissue in the human body is located tissue may be primary or secondary depending upon its stage of lymphocyte development within the lining of the respiratory, digestive and genitourinary tracts. and maturation. Specialized lymphoid tissue supports proliferation and differentiation of u Small concentrations of lymphoid tissue are also found lymphocytes. in thyroid, breast, lung, salivary glands, eye, and skin. u Central or primary lymphoid organs generate lymphocytes from immature progenitor cells u These lymphoid tissues collectively are thus referred to as mucosa associated such as lymphoblasts. The thymus gland and bone marrow contain primary lymphoid tissue lymphoid tissues (MALT). Examples include tonsils, the Peyer patches within where B and T cells are generated. the small intestine, and the verm iform appendix. u Secondary or peripheral lymphoid organs maintain mature naive lymphocytes until an u Depending upon their location, they can be sub-divided into Nasal-associated lymphoid tissue (NALT), Gut-associated lymphoid tissue (GALT), Bronchus- adaptive immune response is initiated. associated Lymphoid Tissue (BALT) and lymphoid tissue associated with the genitourinary system. 27 28 Mucosa Associated Lymphoid Tissue Mucosa Associated Lymphoid Tissue (MALT) (MALT) Gut-associated lymphoid tissue (GALT) u All mucosal lymphoid tissues although present at various sites, contain the same u It is composed of lymphoid complexes that consist of specialized epithelium, antigen- basic compartments-follicles, interfollicular regions, subepithelial dome regions, presenting cells and intraepithelial lymphocytes. and follicle-associated epithelium. u These structures occur strategically at specific areas in the digestive tract for example Peyer’s patches in the terminal ileum. Nasal-associated lymphoid tissue (NALT) u The specialized epithelial cells are called as M cells which are intimately associated with antigen presenting cells (APCs) which together carry out antigen sampling in the gut. M u It includes immune cells underlying the throat and nasal passages and especially cells sample antigen from the lumen and deliver it to the lymphoid tissue through APCs. the tonsils. Bronchus- associated lymphoid tissue (BALT) u Their structure is similar to that of lymph nodes but they are not encapsulated and u The lymphoid tissue associated with the bronchus (BALT) is structurally similar to Peyer’s are without lymphatics. patches and other lymphoid tissues of the gut. u It consists of follicles composed mainly of B cells surrounded by T cells and the u It is composed mainly of aggregates of lymphocytes organized into follicles that are germinal center. found in all lobes of the lung and along the main bronchi. u Within the follicle is the site of antigen-dependent B cell proliferation. u The majority of lymphocytes in the follicles are B cells. u Antigens and foreign particles are trapped within the deep crypts of their lympho- u Antigen sampling is carried out by epithelial cells lining the surface of the mucosa and by epithelium from where they are transported to the lymphoid follicles. way of M cells which transport antigens to underlying APCs and lymphocytes. 29 30 5  11/7/24 Thymus u The thym us is of a pinkish-gray color, soft, and lobulated on its Bone Marrow surfaces. u The organ enlarges during childhood into adolescence and begins u Bone marrow is a soft gelatinous to atrophy at puberty due to horm onal changes. After puberty, the thym us shrinks rapidly w ith age, eventually becom ing alm ost tissue that fills the inside of the indistinguishable from the surrounding fatty tissue. bones.. u The thym us consists of tw o lateral lobes placed in close contact along the m iddle line situated partly in the thorax, resting in the u In the lymphatic system, it is the red chest beneath the neck. The tw o lobes differ slightly in size, m ay be united or separated, and m ay be broken dow n into sm aller lobules. marrow that plays an important role. It is covered w ith a capsule of connective tissue that provides structural support. In contains the hematopoietic stem u The thym us provides an environm ent for T cells to m ature and cells responsible for producing RBC, proliferate, a process called lym phopoeisis. WBC and platelets. u Central tolerance is another function of the thym us. u Autoim m une diseases occur w hen central tolerance is lost, w hich u Yellow marrow stores the fats in the causes lym phocytes to recognize host m olecules as antigens and cells called adipocytes which can attack them , even if those tissues otherw ise function norm ally. The thym us sorts T cells so that they w ill be inactive towards host develop into bone, fat, cartilage or m olecules, though som etim es a few T cells evade this sorting process and m ay initiate an autoim m une disease. muscle cells. 31 32 Bone Marrow Spleen u The spleen, sim ilar to a large lym ph node, acts prim arily as a blood u Red bone marrow is an extremely important part of the lymphatic system, filter in the m ononuclear phagocyte system of the im m une system. as it produces lymphocytes – white blood cells that are responsible for u The spleen is located in the left upper quadrant of the abdom en. It identifying and destroying viruses, bacteria and other pathogens. is sim ilar to an enlarged lym ph node but is a bit m ore com plex. The spleen is m ade up of tw o distinct tissue types: u B LYMPHOCYTES are responsible for producing antibodies to fight a specific Red pulp is the site of blood filtration in the spleen. It is m ade virus, bacteria or antigen that enters the body. They mature in the red of connective tissue called the cord of Billroth that can fill bone marrow before migrating through the blood to other lymphatic organs w ith blood and contains m any m acrophages. such as the spleen and lymph nodes where they await activation. This W hite pulp is secondary lym phoid tissue that is sim ilar to that occurs when their specific antigen is picked up in the lymphatic fluid and in the adenoid tonsils. They contain large am ounts of lym phocytes and antigen -presenting cells. detected in the lymph nodes. u U nlike lym ph nodes, the spleen possesses only efferent lym phatic u T LYMPHOCYTES are also produced by red bone marrow, but mature in the vessels, because it only filters blood instead of lym ph fluid. thymus gland before migrating to other lymphatic organs. They are u The splenic artery form s its prim ary blood supply. primarily responsible for destroying infected body cells and may also help u The spleen is unique in respect to its developm ent w ithin the gut because it is derived from m esenchym al tissue rather than fight cancer. endoderm tissue during em bryonic developm ent. H ow ever, it still shares the sam e blood supply as the foregut organs in the abdom inal cavity. 33 34 Spleen Tonsils u The tonsils are small masses of secondary lymphoid tissue located in the pharynx. They function similarly to other u The primary function of the spleen is blood filtration. Blood cells have a lifespan of types of secondary lymphoid organs and also capture roughly 120 days. When blood passes through the red pulp of the spleen, healthy blood antigens from respiratory tract pathogens. cells easily pass, while older red blood cells are caught phagocytized by the u There are four pairs of tonsils located within the pharynx. macrophages within. They function similarly but have a few structural differences. u The spleen is also important for generating new red blood cells early in embryonic development, but this function stops after birth. The adenoids are located in the wall of nasopharynx. The palatine tonsils are located in the sides of the u The spleen may also function as a reservoir of blood and platelets during hypovolemic oropharynx. shock, which occurs when overall tissue perfusion falls due to severe dehydration or The tubal tonsils are located in the wall of the nasopharynx severe bleeding or hemorrhage. During hypovolemic shock, the spleen can release up near the entrance to each Eustachian tube. to a cup of extra blood to help mitigate the complications of fluid loss. The lingual tonsils are located behind the tongue. u The spleen is often removed surgically if it becomes damaged or infected. This causes u The tonsils primarily facilitate adaptive immune responses modest increases in circulating white blood cells and platelets, diminished in the upper respiratory tract, one of the most common responsiveness to some vaccines, and increased susceptibility to infection by bacteria pathways for pathogen entry in the body. In a way, the and protozoa. tonsils are the “first line of defense” against potential respiratory pathogens. 35 36 6  11/7/24 Peyer’s Patches Appendix u Peyer's patches are observable as elongated u The appendix is a pouch of lymphatic tissue that is thickenings of the intestinal attached at the end of the large intestine (cecum), located epithelium measuring a few centimeters in in the lower-right area of the abdomen. length. u The appendix has often been seen more as a nuisance u About 100 are found in humans. rather than an important part of the human anatomy, often u Microscopically, Peyer's patches appear as oval leading to its indiscriminate removal. However, it has or round lymphoid follicles (similar to lymph recently been identified as playing an important part in our immune response. nodes) located in the mucosa layer of the ileum and extend into u Lymphatic tissue starts to appear in the appendix shortly the submucosa layer. after birth and reaches a peak between the second and third decades of life, decreasing rapidly thereafter and u The number of Peyer's patches peaks at age 15– practically disappearing after the age of 60. 25 and then declines during adulthood. u During the early years of development, the appendix has u It functions by monitoring the intestinal been shown to function as a lymphoid organ, assisting with bacteria populations and prevents growth of the maturation of B-lymphocytes by exposing them to the pathogenic bacteria in the intestines. wide variety of foreign bodies (antigens) that are present in the gastro-intestinal (GI) tract thereby providing a degree of local immunity. 37 38 Thank You ! 39 7