The Lymphatic System - Los Angeles Mission College

The Lymphatic SystemDr. Ali Ebneshahidiebneshahidi

Functions of The Lymphatic System Lymphatic capillaries reabsorb excessive tissue fluid andtransport the fluid through the lymphatic pathway, andultimately dispose it into the blood. Lymphatic capillaries called Lacteals absorb certain fattyacids in the small intestine. Lymphatic system consists of tissues and organs that produce,mature, and store lymphocytes and macrophages, for bodydefense purposes. The lymphatic pathway is an open circuit where lymphaticcapillaries in body tissues reabsorb excessive tissue fluidwhich is derived from blood plasma. This lymph ultimatelyreturns to the blood plasma (i.e. blood plasma in capillaries interstitial fluid lymph in lymphatic pathway lymphreturns to blood plasma).ebneshahidi

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Lymphatic pathway Tissue fluid is transportedfrom lymphatic capillariesto lymphatic collectingvessels, where along thelength of these vessels,lymph nodes occur to filterthe lymph and valves occurto prevent backflow oflymph. Lymph flows fromlymphatic vessels intolymphatic trunks, andfinally into collecting ductswhere the lymph is disposedinto the subclavian veins.ebneshahidi

Lymphatic capillaries Run parallel to blood capillaries in all body tissues. Also made of simple squamous epithelium. Allows diffusion of tissue fluid from interstitial spaces into thelymphatic pathway. Also responsible for absorbing short – chain fatty acids in the smallintestine, using specialized lymphatic capillaries called lacteals.ebneshahidi

Lymphatic Vessels Lymphatic capillaries Collecting vessels LymphaticTrunksLymphatic ducts.Structurally identical to the veins – vessel wall are composedof 3 thin layers of tissues, and contain valves to preventbackflow. Form specialized lymphatic organs called lymph nodes whichstore macrophages and lymphocytes to eliminate foreignsubstances in the lymph. Lympathic trunks: Formed by the convergence of largercollecting vessels. Lymphatic trunks deliver lymph to twolymphatic ducts which eventually drain all lymph fluid back tothe blood – thoracic duct returns lymph form the left side ofthe head and body to the left subclavian vein, and rightlymphatic duct returns lymph from the right side of the headand body to the right subclavian vein.ebneshahidi

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Lymph A clear fluid composed mainly of water, electrolytes, and somesmall plasma proteins. Transported in the lymphatic pathway form the lymphaticcapillaries to the collecting ducts, and at the end disposed intothe venous blood. Reabsorbed by lymphatic capillaries in all body tissues(especially in extremities) where excessive tissue fluids occur. Because of the lack of a pumping organ in the lymphaticpathway, lymph movement is largely dependent on skeletalmuscle activity (similar to blood flow in the veins). Lymph movement is normally constant and smooth, exceptwhen obstruction (small blood clot, tumor) occurs which tendto back up the lymph, and results in edema (fluid accumulationin tissues).ebneshahidi

Lymph Nodes Specialized lymphaticorgans attached tolymphatic vessels, toproduce and store largenumbers of lymphocytesand macrophages for bodydefense, so that lymph isalmost free of foreignsubstances before it isreturned to the blood. Found mainly in the neck,armpits, and abdominalcavity (attached to themesentery membrane ofthe intestines).ebneshahidi

Absent in the central nervous system; may be because the CNS isalready well protected by the méninges and the "blood – brain barrier"(a complex network of capillaries that is impermeable to almost allforeign substances). Each lymph node is attached to an afferent lymphatic vessel wherelymph enters the lymph node, and to an efferent lymphatic vesselwhere lymph exits. Inside each lymph node, connective tissue massescalled nodules produce and stores large numbers of lymphocytes andmacrophages, while spaces called sinuses allow lymph to pass.ebneshahidi

Lymphoid organsThymus gland: a bilobed endocrine gland located at the aortic arch. slowly degenerates and shrinks after puberty; in elderly persons,thymus is mostly composed of adipose tissue. stores a large number of inactive lymphocytes called Tymphocyteswhich are activated by a thymus hormone called thymyosin in amaturation process to become T- lymphocytes (T-cells).ebneshahidi

Spleen: the largest lymphatic organ located on the left side of abdominalcavity. It is structurally identical to lymph nodes, where nodules(containing macrophages and lymphocytes) and sinuses occur. filters blood, not lymph, by allowing the entrance of blood through thesplenic artery, and after filtering blood is transported to the liver viathe hepatic portal vein, for further detoxification. 5% of blood volume enters the spleen, so it acts as a blood reservoir.ebneshahidi

Other lymphoidorgans include thetonsils, appendix,and peyer’s patches(large clusters oflymphoid tissuefound in the distalportion of smallintestine).ebneshahidi

Acquired Immunodeficiency Syndrome (AIDS) Caused by the Human Immunodeficiency Virus (HIV) whichinfects lymphocytes and suppresses immunity. Route of transmission – Africa south America Haiti north America Europe Asia. First discovered in homosexual male patients in Los Angeles andNew York , who developed rare disorders like pneumocytispneumonia and Kaposi's sarcoma. HIV infects lymphocytes (particularly helper T-cell) and someepithelial cells. The exact mechanism of pathogenesis is stillunknown, but the most popular hypothesis is that HIV directlydestroys T-cells, resulting in a strong suppression of the immunesystem. HIV can also infect macrophages or "hide" inside macrophagesand monocytes for a long time.ebneshahidi

HIV is usually spread by blood, sexual contact, drug needle,or through pregnancy; and not by food, water, coughing,sneezing, kissing, hugging, utensils, shaking hands, or toiletseats. 4 phases of symptoms:1) fever, headache, rash, weight loss, swollen lymph nodes,anti-HIV antibodies in blood (these initial symptoms areknown as "AIDS-related complex" or ARC ); 2) after yearsof ARC, T-cells and helper T-cells decline in number, nowpatients are susceptible to opportunistic infections; 3) HIV –infected macrophages cross the "blood – brain " and attackthe brain, causing severe headache, abnormal reflexes, orbrain tumor; and 4 ) patients develop cancer, usuallyKaposi's sarcoma, carcinomas of mouth and rectum, or Bcell lymphoma [note: ADIS victims are not killed directly byHIV, but by the diseases developed during the second, third,or forth phase].ebneshahidi

Functions of The Lymphatic System Lymphatic capillaries reabsorb excessive tissue fluid and transport the fluid through the lymphatic pathway, and ultimately dispose it into the blood. Lymphatic capillaries called Lacteals absorb certain fatty acids in the small intestine. Lymphatic system consists of tissues and organs that produce,