The Lymphatic SystemIntroductionLymphatic VesselsSlide 4Distribution of Lymphatic VesselsSlide 6Slide 7Slide 8MinivalvesAnchoring FilamentsSlide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Lymph TransportSlide 20Lymphoid CellsSlide 22Slide 23Slide 24Slide 25Lymphoid TissueSlide 27Slide 28Slide 29Lymphoid OrgansSlide 31Lymph NodesSlide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Circulation in Lymph NodesSlide 44Slide 45Slide 46Lymph Nodes: ClinicalOther Lymphoid OrgansSlide 49SpleenThe SpleenSlide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59ThymusSlide 61The ThymusSlide 63TonsilsThe TonsilsSlide 66Slide 67Slide 68Slide 69Slide 70Aggregates of Lymphoid FolliclesPeyer’s PatchSlide 73Peyer’s PatchesMALTLymphatic SystemThe Lymphatic SystemChapter 21IntroductionThe lymphatic system supports the function of the cardiovascular and immune systems of the bodyThe lymphatic system consists of two semi-independent parts–A network of lymphatic vessels–Lymphoid organs scattered throughout the bodyThe lymphatic vessels transport fluids that have escaped from the cardio-vascular systemLymphatic VesselsAs blood circulates through the body, exchanges of nutrients, wastes, and gases occur between the blood and the interstitial fluidThe fluid that remains behind in the tissue spaces, as much as 3 liters a day, become part of interstitial fluidLymphatic VesselsThese leaked fluids, as well as any plasma proteins that escape from the blood-stream, must be carried back to the blood if the cardiovascular system is to sufficient blood volume to operate properlyThe lymphatics are elaborate system of drainage vessels that collects the excess protein-containing interstitial fluid and returns it to the bloodstreamOnce interstitial fluid enters the lymphatics ducts it is called lymphDistribution of Lymphatic VesselsThe lymphatic vessels form a one-way system in which lymph flows only toward the heartThe system begins with the lymph capillariesDistribution of Lymphatic VesselsLymph capillaries weave between the tissue cells and blood capillaries in the loose connective tissue of the bodyDistribution of Lymphatic VesselsLymph capillaries are widespread, occurring almost everywhere blood capillaries occurLymph capillaries are absent from bone and teeth, bone marrow, and the entire central nervous systemDistribution of Lymphatic VesselsAlthough similar to blood capillaries, lymphatic capillaries are remarkably permeableThe great permeability is due to structural modifications–Minivalves–Anchoring filamentsMinivalvesThe endothelial cells forming the walls of the lymph capillaries are not tightly joined; instead their edges loosely overlap forming easily opened, flaplike minivalvesAnchoring FilamentsBundles of fine filaments anchor the endothelial cells to surrounding structures so that any increase in interstitial fluid volume separates the cell flaps, exposing gaps in the wall and allowing fluid to enter rather than the capillary collapsingLymphatic VesselsThese structural modifications create a system where the valves gap open when fluid pressure is greater in the interstitial space, allowing fluid to enter the lymphatic capillaryPressure inside the lymphatic capillary forces the minivalve flaps together prevent-ing a leak back outLymphatic VesselsProteins present in the interstitial fluid are prevented from entering the blood capillaries but enter lymphatic capillaries In addition, when tissues are inflamed, lymphatic capillaries develop openings that permit uptake of even larger particles such as cell, pathogens, bacteria, viruses, and cancer cellsThus cancer cells can use lymphatic capillaries to travel throughout the bodyLymphatic VesselsHighly specialized lymphatic capillaries called lacteals are present in the fingerlike villa of the intestinal mucosaThe lymph draining from the digestive viscera is milky white rather than clear because the lacteals also receive digested fat from the intestineThis creamy lymph, called chyme, is also delivered to the blood via the lymphatic systemThis concept discussed further in Chap 24The Lymphatic SystemFrom the lymphatic capillaries, lymph flows through successively larger channels–Collecting vessels–Trunks–DuctsThe Lymphatic SystemCollecting vessels have the same three tunics as veins, but they are thinner-walled, have more internal valves, and anastomose moreIn general the collect- ing vessels in the skin travel along with superficial veins of the CV system while deep vessels of the trunk travel with arteriesThe Lymphatic SystemThe lymphatic trunks are formed by the union of the largest collecting vessels, and drain fairly large areas of the bodyThe trunks are named for the areas from which they collect lymph–Lumbar–Bronchomediastinal–SubclavianThe Lymphatic SystemLymph is delivered to one of two large ducts in the thoracic regionThe right lymphatic duct drains lymph from the upper arm and the right side of the head and thoraxThe larger thoracic duct receives lymph from the rest of the bodyThe Lymphatic SystemEach terminal duct empties the lymph into the venous circulation at the junction of the internal jugular vein on its side of the bodyLymph TransportUnlike the cardiovascular circulation, the lymphatic system lacks an organ that acts as a pumpUnder normal conditions, lymphatic vessels are very low pressure conduitsCompression of skeletal muscle, pressure changes associated with respiration and valves to prevent back flow, aid the movement of lymphSmooth muscle in the lymphatic duct contracts rhythmically to move lymph alongLymph TransportAbout 3 liters of lymph enters the blood- stream every 24 hours, a volume that almost equal to the amount of fluid lost to the tissue spaces from the bloodstream in the same time periodMovement of the adjacent tissues are extremely important in propelling lymph through the lymphaticsPhysical activity or passive movement increase lymph flowLymphoid CellsIn order to understand some of the basic aspects of the lymphatic system’s role in body protection and immunity it is necessary to understand the components–Lymphoid cells–Lymphoid tissuesLymphoid CellsInfectious microorganisms, such as bacteria and viruses, that manage to penetrate the body’s epithelial barrier begin to quickly proliferate in the underlying loose