Lymphatic System PDF

Lymphatic system is formed from a) Lymph Vessels (Lympatics b)Lymphatic tissue) Closed series of channels which begin blindly in the Lymph Vessels (Lympatics tissues. Assist the cardiovascular system in the removal of tissue fluid from the interstitial spaces of the body, and then the fluid is retur...

Lymphatic system is formed from a) Lymph Vessels (Lympatics b)Lymphatic tissue) Closed series of channels which begin blindly in the Lymph Vessels (Lympatics tissues. Assist the cardiovascular system in the removal of tissue fluid from the interstitial spaces of the body, and then the fluid is returned to the blood. Lymph is the name given to the tissue fluid once it has entered a lymphatic vessel. The lymphatic system is essentially a drainage system without any circulation Lymphatics are present in most tissues No lymphatics have been demonstrated in some tissues and organs such as: cartilage, epithelia, the eye ball, CNS. The lymphatics Lymphatic capillaries Medium sized lymphatics Large Lymphatics These are small thin walled irregular wide endothelial tubes surrounded by a thin layer of delicate connective tissue. There are lymphatic anchoring filaments. carries lymph and has a blind end. Lymphatic capillaries Small and medium sized lymphatics These have an endothelial lining and a layer of connective tissue. Large lymphatics: Are similar to veins have the usual three layers of the vein. They contain valves which prevent the flow of lymph in the opposite direction. Lymhatic Nodule Rounded circumscribed masses of cells. primary nodule'' is usually used to designate a rounded mass of packed small Blymphocytes. secondary nodule is formed of a central pale area called the germinal center and a peripheral dark zone. The peripheral zone is dark due to the intense staining of the nuclei of the closely packed small lymphocytes. The germinal center is pale in staining because most of its cells are large and their cytoplasm is abundant and pale in staining. It contains large lymphocytes, a large number of medium sized lymphocytes, lymphoblasts, plasma cells and macrophages. Sites of lymphatic nodules: the lymphatic nodules are present in the lamina propria of the digestive and respiratory passages, at the The white pulp of the spleen and in the lymph nodes. The tonsils, Peyer's patches and the appendix are very rich in lymphatic nodules. Functions of the nodules: 1-The nodules produce lymphocytes. 2-They have phagocytic activity due to the presence of macrophages. 3- They produce antibodies due to their contents of plasma cells The Lymphatic Organs Primary lymphoid organs: These are responsible for the development and maturation of lymphocytes into mature, immunocompetent cells. They include bone marrow and the thymus. Secondary Lymphoid Organs: These provide the places in which immunocompetent cells can react with each other and with antigens and with other cells to build up immunological response against invading antigens. Secondary lymphoid organs include: Lymph nodes. Spleen. Tonsils. Mucosa Associated Lymphoid Tissues Thymus ▪ The thymus is a primary lymphoid organ that is the site of maturation of T-lymphocytes. normally undergoes involution during puberty. ▪ Site: it is situated in the superior mediastinum. ▪ T- cell specificity is acquired only in the thymus. Thymus ▪ The thymus is consists of 2 lobes and is covered by CT capsule sending septa dividing the lobes into incomplete lobules ▪ Each lobule is formed of dark peripheral cortex (extensive population of T lymphocytes) and pale central medulla. Thymus; cortex The cortex contains: – Epithelial reticular cells thymic epithelial cells (TECs) : branched cells connected by desmosomes. Large number of Tlymphocytes (thymocytes). – Immature T- lymphoblasts: densely packed in outer part of cortex. – Mature T-lymphocytes: in deep part of cortex. And macrophages. The medulla contains: - has the same cell population as the cortex, with a larger number of thymic epithelial cells.– Hassall’s corpuscles: They consist of concentrically arranged flattened thymic epithelial cells that become filled with keratin filaments and degenerate. - They are of unknown function. I)-The Lymph Node Ovoid or kidney-shaped bodies. Convex surface: the afferent lymphatics enter the node. Hilum: The efferent lymphatics leave the node also Both blood vessels and nerves enter or leave. A)The cortex: 1-Stroma: ❖dense connective tissue capsule ❖trabeculae ❖reticular stroma The trabeculae divide the cortex into regular compartments and divide the medulla into irregular compartments which are continuous with the cortical ones 2-The parenchyma The parenchyma of the cortex is formed of lymphatic nodules which occupy the regular compartments B)The Medulla: The medulla is formed of cords of lymphatic tissue and lymph sinuses. Functions of the lymph node: It produces lymphocytes. It is the only organ that filters lymph. It produces antibodies by the formation of the immunologically functioning plasma cells