Lab 14 – Lymphoid System IUSM – 2016 I. Introduction Lymphoid System II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex 3. Paracortex 4. Medulla C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary SEM of an activated macrophage. Lab 14 – Lymphoid System IUSM – 2016 I. Introduction Introduction II. Learning Objectives III. Keywords 1. The main function of the immune system is to protect the body against aberrancy: IV. Slides either foreign pathogens (e.g., bacteria, viruses, and parasites) or abnormal host cells (e.g., cancerous cells). A. Thymus 1. General Structure 2. The lymphoid system includes all cells, tissues, and organs in the body that contain 2. Cortex aggregates (accumulations) of lymphocytes (a category of leukocytes including B-cells, 3. Medulla T-cells, and natural-killer cells); while the functions of the different types of B. Lymph Nodes lymphocytes vary greatly, they generally all appear morphologically similar so cannot be 1. General Structures routinely distinguished in light microscopy. 2. Cortex 3. Lymphocytes can be found distributed throughout the lymphoid system as: (1) single 3. Paracortex cells, (2) isolated aggregates of cells, (3) distinct non-encapsulated lymphoid nodules in 4. Medulla loose CT associated with epithelium, or (4) encapsulated individual lymphoid organs. C. MALT 1. Tonsils 4. Primary lymphoid organs are sites where lymphocytes are formed and mature; they 2. BALT include the bone marrow (B-cells) and thymus (T-cells); secondary lymphoid organs are sites of lymphocyte monitoring and activation; they include lymph nodes, MALT, and 3. GALT the spleen. a. Peyer’s patches b. Vermiform appendix 5. MALT (mucosa-associated lymphoid tissue) consists of collections of lymphocytes D. Spleen and antigen-presenting cells in the lamina propria (loose CT) of the mucosa of the 1. General Structure digestive, respiratory, and genitourinary tracts; the cells may be dispersed throughout 2. White Pulp the mucosa or collected together into aggregates (lymphoid nodules). 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016 I. Introduction Learning Objectives II. Learning Objectives III. Keywords 1. Describe the cellular organization and functions of the thymus. IV. Slides A. Thymus 2. Describe the structural architecture and cellular composition of lymph nodes, their 1. General Structure function(s), and lymph and blood circulation within them. 2. Cortex 3. Medulla 3. Define the non-encapsulated collections of lymphoid tissue associated with the B. Lymph Nodes gastrointestinal tract (GALT): tonsils, Peyer's patches, and appendix. 1. General Structures 2. Cortex 4. Describe the structural architecture, cellular composition, and function of the 3. Paracortex spleen. 4. Medulla 5. Identify the characteristic structural and cellular components of defined elements of C. MALT the lymphoid system. 1. Tonsils 2. BALT 6. Identify the architectural and cellular organization of the thymus. 3. GALT a. Peyer’s patches 7. Identify the structural architecture and cellular composition of lymph nodes. b. Vermiform appendix D. Spleen 8. Identify the non-encapsulated collections of lymphoid tissue associated with the 1. General Structure gastrointestinal tract (GALT): tonsils, Peyer's patches, and appendix. 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016 I. Introduction Learning Objectives (cont.) II. Learning Objectives III. Keywords 9. Identify the connective tissue capsule, trabeculae, white and red pulp in spleen and IV. Slides components of the blood circulation in the spleen. A. Thymus 1. General Structure 10. Explain why lymphoid organs contain a network of reticular fibers or epithelial 2. Cortex tissue filled with lymphocytes and other cells of the immune system. 3. Medulla B. Lymph Nodes 11. Compare and contrast the specific unique structural features and regions of lymph 1. General Structures nodes, spleen, and thymus and the functional significance of these features. 2. Cortex 3. Paracortex 12. Describe the circulation through the lymph nodes and spleen and how these organs 4. Medulla filter lymph and blood, respectively. C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016 I. Introduction II. Learning Objectives Keywords III. Keywords IV. Slides A. Thymus Afferent lymphatic vessel Medullary cord BALT Medullary sinus 1. General Structure Central arteriole Paracortex 2. Cortex Cortex Periarteriolar lymphoid sheaths 3. Medulla Efferent lymphatic vessel Peyer’s patch B. Lymph Nodes Epitheliorecticular cell Red pulp 1. General Structures GALT Reticular network 2. Cortex Germinal center Spleen 3. Paracortex High endothelial venule Splenic cord (of Billroth) 4. Medulla Lymph node Splenic sinus C. MALT Lymphocytes Stave cells 1. Tonsils Lymphoid follicle/nodule Subcapsular sinus 2. BALT Macrophage Thymic (Hassal’s) corpuscle MALT Thymic epithelial cell 3. GALT Mantle zone Thymus a. Peyer’s patches Medulla White pulp b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016 Slide 126: Thymus, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex dense CT capsule 3. Medulla B. Lymph Nodes an individual lobule 1. General Structures consisting of an outer 2. Cortex basophilic cortex surrounding an inner 3. Paracortex eosinophilic medulla 4. Medulla C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp the thymus is the site of T-cell (lymphocyte) maturation; it is bi-lobed (seen at the gross level) and surrounded 3. Red Pulp by a vascularized dense CT capsule; trabeculae/septa arise from the capsule and divide the lobes into V. Summary incompletely-separated lobules; each lobule has a dark-staining cortex and a light-staining medulla Lab 14 – Lymphoid System IUSM – 2016 I. Introduction Slide 126: Thymus, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex capsule 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex cortex of lobule septum of CT 3. Paracortex (basophilic) extending from the 4. Medulla capsule, separating C. MALT medulla the parenchyma of 1. Tonsils of lobule the gland into 2. BALT (eosinophilic) lobules 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016 Slide 126: Thymus, H&E Slide 123: Thymus, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex 3. Paracortex 4. Medulla C. MALT 1. Tonsils 2. BALT 3. GALT non-involuted thymus has clear thymic architecture with involuted thymus lacks distinction between cortex and a. Peyer’s patches distinctive lobules with divisions into cortex and medulla regions medulla of lobules and has an abundance of adipose tissue b. Vermiform appendix D. Spleen 1. General Structure by puberty, the thymus has begun to undergo involution (degeneration) with a drop in lymphocyte production; 2. White Pulp thymic corpuscles (in the medulla) become more prominent and the parenchyma of the gland is replaced with 3. Red Pulp loose CT and adipose tissue V. Summary Lab 14 – Lymphoid System IUSM – 2016 Slide 126: Thymus, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure lymphocyte 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures epithelioreticular 2. Cortex cell (ERCs) 3. Paracortex despite the name, 4. Medulla there is no reticular C. MALT CT within the thymus 1. Tonsils 2. BALT 3. GALT macrophage a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure the basophilic cortex of each lobule is the site of positive T-cell selection; it contains an extensive population of 2. White Pulp T-cell precursor lymphocytes (thymocytes), with basophilic nuclei with little cytoplasm, as well as 3. Red Pulp macrophages and a few cortical thymic epithelial cells (epithelioreticular cells); ERCs have large round/oval V. Summary euchromatic nuclei; they around found both in the cortex and medulla and perform a variety of functions, including compartmentalizing the cortex, creating a blood-thymus barrier, and thymocyte education Lab 14 – Lymphoid System IUSM – 2016 Slide 126: Thymus, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla thymic (Hassall’s) B. Lymph Nodes corpuscle 1. General Structures 2. Cortex 3. Paracortex 4. Medulla C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure the medulla of each lobule is the site of negative T-cell selection; it is characterized by a more eosinophilic 2. White Pulp appereance due to fewer and larger lymphocytes (thymocytes) and the presence of thymic corpuscles which 3. Red Pulp are large, oval structures with whorls of keratinized, flattened cells; the corpuscles are thought to play a role in V. Summary regulatory T-cell development, though their significance remains unknown; their presence is a defining characteristic of the medulla and the thymus in general Lab 14 – Lymphoid System IUSM – 2016 Slide 42: Lymph Node, H&E I. Introduction II. Learning Objectives III. Keywords capsule (dense CT) IV. Slides A. Thymus cortex with lymphoid follicles 1. General Structure 2. Cortex paracortex 3. Medulla B. Lymph Nodes medulla 1. General Structures 2. Cortex efferent lymphatic 3. Paracortex vessel 4. Medulla a single efferent C. MALT vessel exits the 1. Tonsils lymph node 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure lymph nodes are bean-shaped, encapsulated “lymph filters” situated periodically along the length of lymphatic 2.