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LYMPHOID SYSTEM,LYMPHATIC VESSELS,LYMPH NODES,LYMPHOID ORGANS,RIGHT LYMPHATIC DUCT AND THORACIC DUCT,FUNCTIONS,SPREAD OF CANCER LEARNING OBJECTIVE At the end of lecture student must be able to know, Define lymphoid/lymphatic system. Define lymphatics and lymph nodes. Describe briefly the structure of lymph node. Enlist various lymphoid tissues and lymphoid organs. Identify large lymphatic channels:right lymphatic duct and thoracic duct. Identify the role of lymphatic system ininfections. Identify the role of lymphatics in the spread of cancer. Lymphoid System consists of all of the tissue aggregates and organs composed of lymphoid tissue which function together to produce our specific resistance to disease (immunity). lymphatic system The lymphatic system can be broadly divided into the conducting system and the lymphoid tissue. The conducting system carries the lymph and consists of tubular vessels that include the lymph capillaries, the lymph vessels, and the right and left thoracic ducts. The lymphoid tissue is primarily involved in immune responses and consists of lymphocytes and other white blood cells enmeshed in connective tissue through which the lymph passes. Regions of the lymphoid tissue that are densely packed with lymphocytes are known as lymphoid follicles. Lymphoid tissue can either be structurally well organized as lymph nodes or may consist of loosely organized lymphoid follicles known as the mucosaassociated lymphoid tissue (MALT) Lymphoid System The lymphatic vessels are arranged into a superficial and a deep set. On the surface of the body the superficial lymphatic vessels are placed immediately beneath the integument, accompanying the superficial veins; they join the deep lymphatic vessels in certain situations by perforating the deep fascia. In the interior of the body they lie in the submucous areolar tissue, throughout the whole length of the digestive, respiratory, and genito-urinary tracts; and in the subserous tissue of the thoracic and abdominal walls lymphatic system Lymph • Lymph is the fluid that is formed when interstitial fluid enters the initial lymphatic vessels of the lymphatic system. • The lymph is then moved along the lymphatic vessel network by either intrinsic contractions of the lymphatic vessels or by extrinsic compression of the lymphatic vessels via external tissue forces (e.g. the contractions of skeletal muscles). LYMPHATIC CHANNELS Tubular vessels transport back lymph to the blood ultimately replacing the volume lost from the blood during the formation of the interstitial fluid. These channels are the lymphatic channels or simply called lymphatics Lymphoid tissue Lymphoid tissue associated with the lymphatic system is concerned with immune functions in defending the body against the infections and spread of tumors. It consists of connective tissue with various types of white blood cells enmeshed in it, most numerous being the lymphocytes. The lymphoid tissue may be primary, secondary, or tertiary depending upon the stage of lymphocyte development and maturation it is involved in. The tertiary lymphoid tissue typically contains far fewer lymphocytes, and assumes an immune role only when challenged with antigens that result in inflammation. It achieves this by importing the lymphocytes from blood and lymph. functions It is responsible for the removal of interstitial fluid from tissues It absorbs and transports fatty acids and fats as chyle to the circulatory system It transports immune cells to and from the lymph nodes in to the bone The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated. The lymph also carries lymphocytes from the efferent lymphatics exiting the lymph nodes. Lymphoid tissue Found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the digestive system such as the tonsils. Also includes all the structures dedicated to the circulation and production of lymphocytes, which includes the spleen, thymus, bone marrow and the lymphoid tissue associated with the digestive system. consists of all of the tissue aggregates and organs composed of lymphoid tissue which function together to produce our specific resistance to disease (immunity). Lymphoid Tissue Consists primarily of two tissue components: Reticular tissue which forms the structural matrix supporting the functional tissue. It is chiefly reticular connective tissue. 2. Lymphatic tissue which is composed of lymphocytes and macrophages. Lymphoid Tissue These two components will form a diffuse, simple aggregate in many tissues of the body, for example: An infiltration of the lamina propria of mucous membranes in the alimentary canal (Peyer's patches) and respiratory tract (tonsils) 2. In regions subjected to chronic inflammatory reactions. 3. In loose connective tissue. 4. In the walls of viscera. lymphoid organ When these two tissues (lymphatic and reticular) are the predominant components in an organ, it is referred to as a lymphoid organ. Examples of lymphoid organs would be the lymph nodes, spleen and thymus. The Lymph Node An oval structure, 1 to 25mm in diameter. Enclosed by a capsule with an internal framework of trabeculae consisting of collagenous and reticular fibers. Found primarily in the proximal area of the limbs, i.e., axilla, inguinal and cervical nodes, as well as, the retroperitoneal area of the pelvis and abdomen and the surface of thoracic and abdominal organs. Contains two regions. outer:CORTEX AND inner MEDULLA. A cortex consisting of densely packed nodules of lymphocytes found just below the subscapular sinus. The nodules are called primary nodules(lymph follicles). Each one contains lymphocytes, plasma cells and macrophages. MEDULLA OF LYMPH NODE A medulla containing cords or rows of lymphocytes separated from one another by sinuses. Medullary sinuses communicate with efferent lymphatics and contain reticular cells and macrophages. Path of lymph through the node Path of lymph through the node: a. multiple afferent lymphatic empties lymph into the subcapsular sinus. b. lymph flows through sinuses around germinal centers, along side trabeculae and through the medulla. Cells of the RES line these sinuses and will phagocytize foreign material. c. lymph leaves the node through the single efferent lymphatic. d. lymphocytes move readily with the lymph. The B and T lymphocytes can leave the circulating blood through venule walls and enter lymphatic sinuses and germinal centers. Lymphocytes can also pass into the blood from lymph sinuses or travel with the lymph for reentry via the right lymphatic and thoracic ducts. e. sinusoids of the node are lymphatic not blood vascular. Path of lymph through the node Mucosa-Associated Lymphoid Tissues Lymphoid tissue located beneath the mucosal epithelial lining of the respiratory and digestive systems protects the body against pathogens that may enter the body via the mucosa. The Tonsils- The tonsils are accumulations of lymphoid tissue surrounding the openings of the digestive and respiratory tracts. Mucosa-Associated Lymphoid Tissues Palatine tonsils - are located in the lateral wall of the oropharynx and covered by a stratified squamous epithelium. Lingual tonsils - are situated in the lamina propria at the root of the tongue and also covered by a stratified squamous epithelium. Pharyngeal tonsils - are located in the upper posterior part of the throat nasopharyngnx and covered by a pseudostratified ciliated epithelium with goblet cells. PEYER’S PATCHES - Small accumulations of lymphocytes or solitary lymph follicles are found scattered beneath the mucosa throughout the gastrointestinal tract. - The most prominent accumulations occur in the ileum and appendix in the form of Peyer's patches. - In the ileum, they form dome-shaped protrusions into the lumen. - Beneath the epithelial lining of the domes, Peyer's patches extend from the lamina propria to the submucosa. Within Peyer's patches. spleen located in the upper left abdominal quadrant. Unlike the lymph node, the spleen is inserted in the blood stream. The spleen clears the blood of aged blood cells and foreign material. It is the site of an immune response to blood-borne antigens, especially in children. thymus The thymus is composed of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum. The thymus is a specialized organ in the immune system. The functions of the thymus are the "schooling" of Tlymphocytes (T cells), which are critical cells of the adaptive immune system, and the production and secretion of thymosins, hormones which control Tlymphocyte activities and various other aspects of the immune system. thoracic duct It is the largest lymphatic vessel in the body. It collects most of the lymph in the body (except that from the right arm and the right side of the chest, neck and head, which is collected by the right lymphatic duct) and drains into the systemic (blood) circulation at the left brachiocephalic vein between the left subclavian and left internal jugular veins. SPREAD OF CANCER The study of lymphatic drainage of various organs is important in diagnosis, prognosis, and treatment of cancer. The lymphatic system, because of its physical proximity to many tissues of the body, is responsible for carrying cancerous cells between the various parts of the body in a process called metastasis. The intervening lymph nodes can trap the cancer cells. If they are not successful in destroying the cancer cells the nodes may become sites of secondary tumors. Diseases and other problems of the lymphatic system can cause swelling and other symptoms. Problems with the system can impair the body's ability to fight infections. REFERENCES Internet.different sources. Grays anatomy(Henry Gray Anatomy of the Human Body) *********************************************************