Lymphatic System PDF

Lymphatic System Dr. Silvia Boyajian  Fluid balance The tissues of the body are supplied by blood Fluid similar to blood plasma, called interstitial fluid, capillaries that...

Lymphatic System Dr. Silvia Boyajian  Fluid balance The tissues of the body are supplied by blood Fluid similar to blood plasma, called interstitial fluid, capillaries that bring oxygen-rich blood and leaches from these vessels into the surrounding remove carbon dioxide-rich blood. tissue. Around 20 liters of fluid leaves the arterial Lymphatic vessels function to drain this excess fluid capillaries every day, from the tissues as lymph and return this fluid to the blood. but only 17 liters of fluid returns to the venous capillaries. Lymph returns back to the big veins (venous angle: the junction between subclavian and internal jugular veins) through the Thoracic duct and Right lymphatic duct. The lymphatic system consists of: lymphatic fluid lymphatic vessels lymphatic tissue and lymphatic organs located throughout the tissues of the body. It functions to: 1-Drain excess interstitial fluid from the tissues and return to blood stream 2-Initiate an immune response against disease by producing and transporting lymphocytes 3-Transport dietary lipids absorbed by the gastrointestinal tract into the blood. Lymph: is a colourless fluid floats in the lymphatic vessels. It is similar in composition to blood plasma Lymphatic vessels : are thin vessels that accompany arteries and veins throughout the body and transport lymph. Lymphatic tissue: Immediat is a specialized form of reticular connective tissue that is e or 1 composed of masses of lymphocytes. hypersen These either occur alone as lymph nodules (follicles) sitivity or are organized into various lymphatic organs. Lymphatic organs include the lymph nodes, spleen, thymus, and red bone marrow Immediate or type 1 hypersensitivity Lymphatic trunks and ducts All lymphatic vessels coalesce to form larger trunks which eventually converge to form the right lymphatic duct and the thoracic duct Thoracic duct (Left lymphatic duct) Is larger and drains lymph from the rest of the body. Originates in the abdomen as cisterna chyli Cisterna chyli 1- is a dilated sac 2- at the lower end of the thoracic duct (anterior to the bodies of L1 and L2) 3- formed by confluence of the right and left lumbar trunks and the intestinal trunk cisterna chyli Passes through the diaphragm at the aortic aperture Empties into the junction where left internal jugular vein joins the left subclavian vein (Lt venous angle) Left Bronchomediastinal trunk drains from: Left half of thoracic wall Anterior part of the diaphragm Left lung left half of the heart Right lymphatic duct Is formed by right jugular and right subclavian trunks Drains lymph from the upper right quadrant of the body 1- the right side of the head and neck 2- the right side of the thorax 3- the right upper limb Empties into the junction where right internal jugular vein joins the right subclavian vein (Rt venous angle) cisterna chyli Lymphatic Organs and Tissues Lymphatic organs are divided into: 1. Primary lymphatic organs Bone marrow. Thymus gland. Are sites of Lymphocyte production, maturation, selection 2. Secondary lymphatic organs Diffuse lymphatic tissue (lymphatic nodules). Spleen. Lymph nodes. Are sites to encounter pathogens and become activated  Lymphatic organs Encapsulated Not encapsulated Thymus Diffuse lymphatic system Lymph nodes M.A.L.T Spleen Mucosa-Associated Lymph Tissue GIT Resp. Urinary Lymph nodes Are kidney-shaped Lymph nodes are up to 3 cm in length located along the course of lymphatic vessels (Approximately 600 lymph nodes ) small encapsulated bodies The depression called the hilum where arteries and nerves enter and veins exit Structure of lymph nodes Lymph nodes are covered by a capsule of dense connective tissue Extensions of the capsule called trabeculae form the partitions within the lymph nodes Reticular tissue (cells and fibres) forms the stroma of the lymph node Immunocompetent B cells and T cells are suspended throughout the lymph node The lymph node consists of an outer cortex and an inner medulla, in between Paracortex  The outer cortex has lymphatic follicles that mostly contain B-cells. The inner cortex (paracortex) contains mostly T-cells. The medullary cords contain mostly plasma cells. Other cells in the lymph node:  Macrophages  Dendritic cells  Follicular dendritic cells  Reticular cells Both the macrophages, and the dendritic cells trap antigens and present them on their surfaces As B cells in lymphatic follicle are stimulated, they differentiate into plasma cells. Plasma cells move to medulla (medullary cords) The outer cortex houses lymphatic follicles (nodules) which are of two types: 1- Primary lymphoid nodules (follicles): Lymphoid follicles without a germinal centre Spherical aggregates of B lymphocytes (virgin B cells and memory cells) 2- Secondary lymphoid nodules (follicles): lymphoid follicles with a germinal centre (pale centre). Form only in response to exposure to antigens Sites for B memory cell and plasma cell generation Outer region: dense accumulation of small lymphocytes that are migrating away from their site of origin within the secondary nodule When activated by antigens (and T helper cells), B cells migrate to the centre of the follicle, forming a germinal centre. Germinal centres are the central regions of secondary follicles where activated B cells are proliferating (dividing by mitosis) and differentiating into plasma cells and memory B cells. When stimulated by antigens, lymph nodes enlarge due to the formation of germinal centres and B cell proliferation Macrophages and Dendritic cells capture antigen within tissues and transport antigen to secondary lymphoid tissue The medulla is the deep, cavitated part of the lymph node it is composed of: large tortuous lymph sinuses surrounded by lymphoid cells that are organized in clusters known as medullary cords medullary cords: contain B lymphocytes and some plasma cells Functions of lymph nodes Nodes filter the lymph, removing foreign material and microorganisms. All lymph is filtered by at least one lymph node before it returns to the blood. Antibody-mediated and cell-mediated immune responses occur in the lymph nodes Lymph nodes are production sites of antibodies and activated lymphocytes Sites for antigen recognition Afferent vessels Many afferent lymphatic vessels enter the lymph node at different points over its convex surface Each containing valves to prevent backflow of lymph. Subcapsular sinuses Each afferent vessel empties into the subcapsularsinus. Trabecular sinuses The trabecular sinuses are a continuation of the subcapsular sinuses that follow the trabeculae and drain into the medullary sinuses. Medullary sinuses Lymph slows down when it passes lymph nodes Found separating the cords. The medullary sinuses converge at the hilum into the efferent lymphatic vessel. Efferent vessels The lymph is removed from the medullary sinus via one or two efferent lymphatic vessels that leave the lymph node at the hilum. Valves in the vessels prevent lymph from flowing in the wrong direction.  Lymphocyte recirculation Lymphocyte homing Serves critical functions in adaptive immune response: 1- it enables the limited number of lymphocytes in an individual that are specific for a particular antigen to search for that antigen throughout the body 2-it ensures that particular lymphocytes are delivered to particular tissue eg. Recirculation of naive lymphocyte differ from those of effector and memory lymphocyte  specifically naive lymphocytes recirculate through peripheral lymphoid organ and effector lymphocyte migrate to peripheral tissue at sites of infection and inflammation Lymphocytes can enter lymphoid tissues in two ways: 1) Direct entry into lymph nodes via afferent lymphatics 2) Entry from blood capillaries across specialized endothelial cells present in the postcapillary venules (High Endothelial Venules= HEV) within the paracortex of the lymph node How is the process of lymphocyte recirculatioin regulated? Why naïve lymphocytes migrate preferentially to lymph node????? The structure of the post-capillary venule, in the paracortex is unusual in that it is not lined by simple squamous epithelium, but by a simple cuboidal epithelium. These are called high endothelial venules (HEVs) Lymphocytes recognize and adhere to these endothelial cells, and squeeze through them into the paracortex The process of lymphocyte recirculation is regulated by adhesion molecules on This diagram of a lymph node shows the pathways that lymphocytes can take, in and out of the lymph node. lymphocytes called Homing receptors and their ligands on vascular endothelial cells called Adressins Note: Most of the lymphocytes enter the lymph nodes via blood vessels, and about 10% enter through the lymph. Thank You