Lymphatic System PDF 2025

Lymphatic system Assis. Prof. Dr./Noha Ramadan Elswaidy  Lymphatic (Immune) System Lymphatic system consists of lymphatic vessels & lymphatic tissues. A- Lymphatic vessels: ❑carry lymph (tissue fluid) from the interstitial spaces to the blood. ❑They have the same struct...

Lymphatic system Assis. Prof. Dr./Noha Ramadan Elswaidy  Lymphatic (Immune) System Lymphatic system consists of lymphatic vessels & lymphatic tissues. A- Lymphatic vessels: ❑carry lymph (tissue fluid) from the interstitial spaces to the blood. ❑They have the same structure as blood vessels but they have large diameter with one blind end. B- The lymphatic tissues: ❑contain aggregates of lymphocytes embedded in network of reticular fibers. ❑They are organized into organs; LYMPH NODE which are the lymph nodes, -SPLEEN -THYMUS thymus, spleen and tonsils. -TONSILS  Lymph nodes Shape: are encapsulated spherical or kidney- shaped organs, having a convex side, where the afferent lymphatic vessels enter and a concave depression called the hilum; through which arteries and nerves enter and veins and efferent lymphatic vessels leave the organ. Site: are distributed along the course of the lymphatic vessels. Structure of lymph node 1- Stroma (supportive CT): a) Capsule: dense CT thickened at hilum. b) Trabeculae (septa): divide node into incomplete compartments. c) Reticular network: of reticular cells and reticular fibers. 2- Parenchyma: A-Cortex: 1-Outer (superficial) cortex. 2-Inner (deep) cortex. 3-Cortical sinuses. B-Medulla: Medullary cords. Medullary sinuses.  A-CORTEX 1-Outer cortex Round aggregations of lymphocytes (mainly B-lymphocytes )called lymphatic follicles(nodules). 2 types of lymphatic follicles: 1ry lymphatic follicles: not exposed to antigen contains B-lymphocytes No germinal center. 2ry lymphatic follicle: exposed to antigen Having central pale area known as germinal center. Contains activated B- lymphocytes having pale nucleus.  2-Inner cortex between the outer cortex and medulla. T-lymphocytes predominate in the inner cortex, so it is called “thymus dependant area(zone)”. 3- Cortical sinuses: irregular spaces lined mainly by discontinuous endothelial cells associated with reticular cells, fibers and phagocytic macrophages. a- Subcapsular sinuses (between capsule and lymphatic follicles) b- Paratrabecular sinuses (present around trabeculae).  B- Medulla Medullary cords: formed of lymphocytes and plasma cells Medullary sinuses: connect the cortical sinuses with the efferent lymphatics through which lymph leaves the node. Functions of lymph nodes: 1- Filtration of lymph from microorganisms. 2- Immunological function (both cellular and humoral immunity).  Lymph circulation 1-afferent lymphatic vessels. 2-subcapsular sinuses. 3-intermediate, paratrabecular sinuses. 4-medullary sinuses. 5-efferent lymphatic vessels.  Capsule stroma Septa Lymph node Reticular fibers Parenchyma cortex medulla Medullary Outer cortex Inner cortex Cortical sinuses Medullary cords sinuses  TONSILS Definition: Incompletely encapsulated aggregates of lymphoid tissue Sites: Beneath mucous membrane of the mouth , pharynx and tongue. Types: palatine, pharyngeal and lingual. Palatine tonsils: They are 2 tonsils in the lateral walls of orophargnx.  Histological structure of palatine tonsil - Formed of lymphatic tissue containing secondary lymphatic follicles with germinal centers. - The lymphatic nodules are present under the epithelium and around the crypts. -They are covered by stratified squamous non-keratinized epithelium that invaginate into the lymphoid tissue forming crypts. - They are separated from the surrounding structures by dense connective tissue capsule which act as a barrier against spreading of infection. Capsule Label the diagram 1 4 2 3 Label the diagram 2 4 7 3 1 5 6  2 1 3 5 4 Choose the correct answer: - Filtration of lymph is the function of which of the following organs? a- Spleen. b- Lymph node c- Thymus. d- Liver Choose the correct answer: Palatine tonsils are covered by which of the following? a-Stratified squamous non-keratinized epithelium. b-Stratified columnar epithelium. c- Stratified squamous keratinized epithelium. d- Stratified cuboidal epithelium. Choose the correct answer: - Regarding lymph nodes ,T- lymphocytes are present in which of the following? a- Medulla. b- Outer part of cortex. c- Inner part of cortex. d- Subcapsular part.