Histology of Immune Organs PDF

TOPIC: Histology of Immune Organs LESSONS Lymphatics Lymphoid Follicles Lymph Node Spleen Lonnie Lybarger, PhD Add...

TOPIC: Histology of Immune Organs LESSONS Lymphatics Lymphoid Follicles Lymph Node Spleen Lonnie Lybarger, PhD Add faculty [email protected] photo  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly. Lymphatics and immune organs 1. Lymphatic vessels for lymph return 2. Lymphoid/immune tissues & organs Concepts and Vocabulary Lymph circulation Lymphatic capillary Lymphatic ducts Asymmetric lymph drainage Lymphatic capillaries Fluid leaks from capillaries and post‐capillary venules. Lymphatic capillaries This tissue fluid enters lymphatic capillaries and is carried back to the blood via the lymphatic drainage system… Lymph vessels and lymph return lymphatic system Lymph return is asymmetric Implications for diagnosis? Lymph from the left side above the diaphragm, and from both sides below the diaphragm, drains Right via the thoracic duct lymphatic duct Thoracic duct Jugular vein Subclavian vein Disrupted lymph flow Lymph vessels collect lymph from tissues and return it the blood vascular system by emptying into veins in the neck Disruption of lymph flow causes lymphedema elephantiasis disruption of lymph flow by surgery (sampling of axillary lymph nodes) Lymphatics and immune organs 1. Lymphatic vessels for lymph return 2. Lymphoid/immune tissues & organs Leukocyte re‐circulation White Blood Cells: Monocytes/macrophages Neutrophils Lymphocytes Eosinophils Basophils 3. Exit blood at post‐capillary venules to enter CT 2. Circulate in blood 1. Develop in bone marrow Generally, these cell function do not return to blood Lymphocyte re‐circulation Lymphocytes exit blood to enter tissues at post‐capillary venules (like any wbc). Lymphocytes exit blood to enter follicles at High Endothelial Venules (HEV) Lymphocytes exit lymphoid follicles via lymphatic capillaries, and travel via lymph vessels back to the blood vascular system. Circulation meets lymphatic system Lymph node: ‐ site where immune responses begin ‐ afferent lymphatics drain from tissues into LN ‐ lymphocytes enter from circulation Basic Imm., Fig. 1‐14 Lymphatic vessel histology? Lymphatic vessels often difficult to find in tissue sections Thin‐walled, tend to collapse Tonsil  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly.  TOPIC: Histology of Immune Organs LESSONS Lymphatics Lymphoid Follicles Lymph Node Spleen Lonnie Lybarger, PhD Add faculty [email protected] photo  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly. Concepts and Vocabulary Lymphoid follicle (nodule) Germinal center Mantle Mesenchymal reticular cell Pre‐plasma cell Plasma cell High endothelial venule (HEV) Lymphatic capillary Lymphoid organs Bone marrow Pre‐lymphocytes arise from stem cell proliferation 1° Lymphoid Maturation & deletion of organs B cells recognizing self‐antigen Thymus T Naïve, immunocompetent +antigen T & B cells enter +cytokines 2° circulating pool Proliferation & lymphoid differentiation organs effector cells memory cells (e.g. plasma cells) (enter circulating pool) Lymphoid organs Primary lymphoid organs bone marrow thymus = Generation of lymphocytes Secondary lymphoid organs solitary lymphoid follicles clusters of follicles (tonsils, MALT Peyer’s patches, appendix) lymph nodes spleen = Generation of immune responses Secondary lymphoid organs Solitary lymphoid follicles Appendix Peyer’s patches Spleen Tonsil Lymph node Lymphoid follicle (lymphoid nodule) Germinal center mantle Solitary follicles ‐ structure Fibroblastic reticular cell Centroblasts (aka mesenchymal reticular cell) Follicular Mitotic figure Dendritic Cell (in centroblast) (GC & mantle) mainly B cells (germinal center & inner mantle) Macrophage mainly T cells (outer mantle) Solitary follicles ‐ structure Mantle Germinal center macrophages Mitotic figure Germinal center lymphocytes mantle Lymphocyte traffic through follicles Lymphoid follicle capillaries drain via specialized post‐ capillary venules. High Endothelial Venule (HEV) High endothelial venules (HEV) HEV express molecules that promote naive lymphocyte binding to endothelial cells and exit from blood into the follicle. rbc lymphocytes Endothelial cells High endothelial venules HEV express molecules that promote lymphocyte binding to endothelial cells and exit from blood into the follicle. High endothelial venules HEV express molecules that promote lymphocyte binding to endothelial cells and exit from blood into the follicle. Endothelial cell nuclei lymphocytes Lymphocyte traffic through follicles Lymphocytes exit blood to enter follicles at High Endothelial Venules (HEV) Lymphocytes leave lymphoid High Endothelial follicles via lymphatic capillaries Venule (HEV)  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly.  TOPIC: Histology of Immune Organs LESSONS Lymphatics Lymphoid Follicles Lymph Node Spleen Lonnie Lybarger, PhD Add faculty [email protected] photo  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly. Concepts and Vocabulary Lymph node Capsule Trabecula/Trabeculae Cortex Medulla Lymphoid follicle Medullary cords Afferent lymphatic Efferent lymphatic Lymphatic sinuses Lymphadenopathy Lymph nodes Lymph nodes are situated in the path of lymph vessels Lymph node ‐ cortex and medulla Lymphoid follicles capsule (in cortex) trabeculae sinuses Medullary cords Lymph node Afferent lymphatics Blood capillaries Drained via HEV Naive lymphocytes enter Efferent lymphatic lymph nodes via HEV Lymph node ‐ connective tissue capsule cortex sinuses medulla Lymph node ‐ sinuses * * * * * Lymph node ‐ sinuses reticular cell Medullary cords sinus Lymph node ‐ functions Reticular cells in sinuses create turbulence which maximizes contact of lymph contents with cells in the node T and B lymphocytes encounter antigen Immune responses are generated where appropriate Pre‐plasma cells generated in germinal centers become plasma cells in medullary cords and secrete antibody there Effector T cells generated, then leave to find antigen in periphery Lymph node ‐ in harm’s way lymphadenopathy Lymph nodes swell if… 1. engaged in an immune response 2. infected with a pathogen 3. colonized by a distant cancer 4. lymphocytes become neoplastic (lymphoma) Metastasized pancreatic adenocarcinoma  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly.  TOPIC: Histology of Immune Organs LESSONS Lymphatics Lymphoid Follicles Lymph Node Spleen Lonnie Lybarger, PhD Add faculty [email protected] photo  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly. Concepts and Vocabulary Red pulp White pulp Lymphoid follicle Splenic artery and vein Trabecular artery and vein Central artery Splenic sinusoids Splenic cords Splenomegaly Spleen splenomegaly http://iheartautopsy.com/?p=1895 Spleen Trabeculae White pulp Spleen filters the blood White pulp generates immune responses against blood borne pathogens. Red pulp removes damaged or senescent red Red pulp and white blood cells from the circulation. Spleen ‐ red & white pulp White pulp White pulp Red pulp Red pulp Red pulp Spleen ‐ blood supply Red pulp White pulp Central artery Trabecular artery Splenic artery Splenic vein Spleen ‐ white pulp Central artery Spleen ‐ white pulp 1. Dendritic cells and macrophages in white pulp present antigen to lymphocytes in white pulp 2. Immune responses are generated where appropriate 3. Pre‐plasma cells become plasma cells in red pulp & secrete IgG Spleen ‐ blood supply Red pulp Splenic sinusoids White pulp Central artery Trabecular artery Splenic artery Splenic vein Spleen ‐ red pulp sinusoids and splenic cords White pulp Red pulp Spleen ‐ red pulp Splenic sinusoids arteriole Splenic sinusoid Sinusoid endothelium RBC RBC Splenic sinusoid Splenic sinusoids arteriole (Type III collagen is stained black) Spleen ‐ red pulp mac Sinusoid lumen Red pulp cord lymphocytes RBC RBC mac monocyte RBC All circulating blood cells must pass through splenic cords and into sinusoids Spleen is a major site for removal of old RBCs Splenic vein to hepatic portal vein Hepatic Splenic portal vein vein The liver conjugates and excretes bilirubin produced in the spleen Some causes of splenomegaly Red pulp: Hemolytic anemias Leukemia White pulp: Blood‐borne infection Lymphoma Metastasized cancer Extra‐splenic: Problems in the liver splenomegaly Spleen ‐ consequence of removal White pulp Spleen filters the blood, so... If the spleen is removed the risk of sepsis is greatly increased! RBC recycling function can Red pulp be taken over by the liver  Learning Objectives 1. Outline the path of lymph flow, including the major lymph vessels and the regions they drain. Explain a major clinical implication of the asymmetric pattern of lymph drainage. 2. Describe the pathways that lymphocytes use to travel between blood and tissues, and compare to pathways used by other WBCs. 3. Explain the difference between primary and secondary lymphoid organs. 4. Identify diffuse lymphoid tissue and lymphoid follicles in histological sections. Identify the following structures in follicles: high endothelial venules, mitotic figures, macrophages, lymphocytes. 5. Describe the structure of lymph nodes, spleen, and tonsils. Identify these organs in histological sections. Relate structure to function. 6. Explain the special anatomic features that reflect the function of lymph nodes as filters of lymph, and spleen as a filter of blood. Apply this information to understanding causes of lymphadenopathy and splenomegaly. Studying histology can wear you out...