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Home , Mantle zone, Plasma cell, Red pulp, Trabecular arteries, White pulp

Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Lymphoid System II. Learning Objectives III. Keywords IV. Slides A. 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex 3. Paracortex 4. Medulla C. MALT 1. 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. 1. General Structure 2. White 3. V. Summary SEM of an activated . Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Introduction II. Learning Objectives III. Keywords 1. The main function of the 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 (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 . 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 (B-cells) and thymus (T-cells); secondary lymphoid organs are sites of 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 -presenting cells in the (loose CT) of the mucosa of the 1. General Structure digestive, respiratory, and genitourinary tracts; the cells may be dispersed throughout 2. 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 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 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 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 Spleen 3. Paracortex High endothelial venule Splenic cord (of Billroth) 4. Medulla 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 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 (), with basophilic nuclei with little , as well as 3. Red Pulp 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 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. White Pulp vessels (generally 400-450 total in the body); they contain lymphocytes (B-cells and T-cells) and macrophages 3. Red Pulp contained in a reticulin-fiber scaffold; all lymph passes through at least one node before returning to the venous V. Summary circulation; unlike the thymus, lymph nodes do not have lobules; instead, the entire lymph node is organized into an outer cortex and inner medulla Lab 14 – Lymphoid System IUSM – 2016 Slide 42: Lymph Node, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla cortex hilum B. Lymph Nodes (follicle) 1. General Structures 2. Cortex medulla 3. Paracortex 4. Medulla C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure lymph enters through any of the multiple afferent lymphatic vessels draining into the lymph node; the lymph 2. White Pulp passes through a series of sinuses (subcapsular  cortical  medullary) before exiting through the single 3. Red Pulp efferent lymphatic vessel (in the hilum); as the lymph passes through the sinuses, it contacts macrophage pseudopods which engulf antigen and present it to lymphocytes in the lymphoid follicles in the cortex; antigen V. Summary may also escape the sinuses and directly contact lymphocytes Lab 14 – Lymphoid System IUSM – 2016 Slide 99: Lymph Node, Silver I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure capsule 2. Cortex subcapsular sinus 3. Medulla B. Lymph Nodes cortex with lymphoid follicles 1. General Structures and cortical sinuses 2. Cortex 3. Paracortex paracortex 4. Medulla C. MALT 1. Tonsils 2. BALT medulla with 3. GALT medullary sinuses 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 99: Lymph Node, Silver I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus blood vessel with 1. General Structure lumen full of red 2. Cortex blood cells 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex 3. Paracortex 4. Medulla C. MALT 1. Tonsils reticular network 2. BALT (dark lines) 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp silver staining shows clearly the abundant reticular fibers (type III collagen), made by reticular cells, composing 3. Red Pulp the reticular network within the lymph node (and other lymphoid organs except the thymus); beyond the V. Summary reticular cells, macrophages and dendritic cells are also present within the network but can be difficult to identify in normal slide preparations Lab 14 – Lymphoid System IUSM – 2016 Slide 28 (464): Lymph Node, Giemsa I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex capsule 3. Medulla B. Lymph Nodes cortical sinus 1. General Structures 2. Cortex lymphoid follicle 3. Paracortex with eosinophilic 4. Medulla germinal center C. MALT (light-staining center) 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp the cortex contains a dense collection of lymphocytes (primarily B cells) organized into lymphoid 3. Red Pulp follicles/nodules; the follicles can be classified as either primary or secondary based upon lymphocyte V. Summary activation; upon B cells activation, a germinal center forms within the follicle (a secondary follicle); the cortical sinsues conduct lymph from the subcapsular sinuses to the medullary sinuses Lab 14 – Lymphoid System IUSM – 2016

I. Introduction II. Learning Objectives Slide 104 (NW): Lymph Node Slide 28a (464): Lymph Node 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 the paracortex (or deep cortex) is located between the cortex and medulla; most of the T cells within the lymph node are localized to the paracortex; additionally, a defining characteristic of the paracortex is the D. Spleen presence of (HEVs) (shown with arrows above); the aptly-named HEVs differ from 1. General Structure regular venules by having a simple cuboidal or columnar ; the majority of lymphocytes enter into 2. White Pulp the tissue of the lymph node by exiting the blood through the HEVs – T cells then remain in the paracortex 3. Red Pulp while B cells migrate to the cortex; HEVs are also found in other lymphoid organs, except the thymus and spleen V. Summary Lab 14 – Lymphoid System IUSM – 2016 Slide 42: Lymph Node, H&E I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla medullary B. Lymph Nodes cords 1. General Structures 2. Cortex venule 3. Paracortex 4. Medulla C. MALT medullary 1. Tonsils sinus 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure are elongated organizations of lymphocytes surrounding the lymphatic ; 2. White Pulp medullary cords medullary sinuses from the medullary sinuses, lymph will leave the node through the efferent lymphatic vessel exiting the hilum; 3. Red Pulp within the cords, plasma cells (migrated from germinal centers in secondary follicles in cortex) secrete V. Summary into the lymph which leaves the node to eventually return to the systemic circulation Lab 14 – Lymphoid System IUSM – 2016 Slide 42: Lymph Node, 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 medullary sinus 2. Cortex medullary cord 3. Paracortex (collection of cells) 4. Medulla C. MALT plasma cell 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches venule b. Vermiform appendix D. Spleen 1. General Structure plasma cells are activated B-cells that actively secrete antibodies (thousands per second); they generally have 2. White Pulp spherical nuclei (chromatin may have a “clock face” appearance) displaced to the periphery of the cell by the 3. Red Pulp cytoplasm full of -producing machinery, including abundant rER and ; the abundant rER V. Summary (basophilic) and (eosinophilic) within the cytoplasm result in an amphophilic (Gr. “both loving”) staining pattern; plasma cells may reside in the medulla or exit the node to take up residences in other organs Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 136: Palatine , H&E II. Learning Objectives III. Keywords stratified squamous IV. Slides epithelium A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes lymphoid follicle/nodule within the lamina propria of the 1. General Structures mucosa, which is greatly 2. Cortex expanded by the infiltration of 3. Paracortex all the lymphoid tissue 4. Medulla C. MALT trabecula/septum of dense CT 1. Tonsils 2. BALT dense CT forms an incomplete 3. GALT capsule, separating the tonsil a. Peyer’s patches from underlying tissues b. Vermiform appendix D. Spleen 1. General Structure tonsils are located at the entrance of the pharynx; they are specialized MALT structures composed of aggregates 2. White Pulp of lymphoid nodules within the CT of the lamina propria, under the epithelium, of the mucosa; they lack afferent 3. Red Pulp lymphatic vessels and the cortex/medulla architecture of lymph nodes, but they do have efferent lymphatic V. Summary vessels and high endothelial venules; the palatine tonsils are a pair of tonsils in the wall of the oropharynx Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 136: , H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures 2. Cortex some parts of the palatine 3. Paracortex tonsil have such extensive 4. Medulla infiltration of lymphocytes into C. MALT the mucosa that it is difficult to 1. Tonsils still appreciate the stratified 2. BALT squamous appearance of the 3. GALT overlying epithelium a. Peyer’s patches b. Vermiform appendix lymphocytes D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 136: Palatine Tonsil, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla macrophages are common B. Lymph Nodes within the lymphoid nodules of tonsils; their presence amongst 1. General Structures the darker-staining lymphocytes 2. Cortex gives a “starry night” appearance 3. Paracortex to the nodule and can be helpful 4. Medulla in distinguishing tonsils from C. MALT other lymphoid structures 1. Tonsils 2. BALT look within the germinal centers of 3. GALT the nodules to find examples of a. Peyer’s patches mitotic figures representing the b. Vermiform appendix proliferating lymphocytes D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 103 (NW): Lingual Tonsil, H&E II. Learning Objectives III. Keywords the posterior 1/3 of the tongue (pharyngeal aspect of the tongue) IV. Slides is separated from the anterior 2/3 of the tongue by the sulcus look along the posterior A. Thymus terminalis; the two parts of the tongue differ in embryologic origin aspect of the dorsum of the 1. General Structure and innervation; the are found within the tongue to find 2. Cortex lingual tonsils pharyngeal aspect 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 Posterior Anterior b. Vermiform appendix D. Spleen stratified squamous 1. General Structure epithelium 2. White Pulp posterior lingual glands 3. Red Pulp skeletal muscle V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 103 (NW): Lingual Tonsil, H&E II. Learning Objectives III. Keywords IV. Slides stratified squamous epithelium A. Thymus (non-keratinized) 1. General Structure lamina propria (CT) 2. Cortex 3. Medulla B. Lymph Nodes mantle zone of 1. General Structures lymphoid nodule 2. Cortex germinal center of 3. Paracortex lymphoid nodule 4. Medulla tonsillar crypt C. MALT adipose 1. Tonsils 2. BALT 3. GALT posterior lingual glands a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp as in the lymph node, lymphoid nodules can be classified as either primary or secondary based upon exposure 3. Red Pulp to antigen and lymphocyte activation; most nodules are secondary with an eosinophilic germinal center full of V. Summary enlarged, proliferating B cells and plasma cells; surrounding the germinal center is the mantle zone of small, heterochromatic lymphocytes Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 102 (NW): Pharyngeal Tonsil, H&E 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 stratified pseudostratified 2. BALT squamous ciliated columnar 3. GALT epithelium epithelium (PCCE) a. Peyer’s patches lymphoid b. Vermiform appendix nodule D. Spleen 1. General Structure 2. White Pulp the pharyngeal tonsil ( – Gr. “gland-like”) is a single mass of lymphoid tissue in the posterior wall of 3. Red Pulp the nasopharynx; unlike the palatine and lingual tonsils which are lined with stratified squamous epithelium, the V. Summary pharyngeal tonsil is generally covered by respiratory epithelium (pseudostratified ciliated columnar epithelium); however, it is not uncommon to see regions of the tonsil covered with stratified squamous epithelium Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 102 (NW): Pharyngeal Tonsil, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla respiratory epithelium B. Lymph Nodes (PCCE) distinguishes this as the pharyngeal tonsil 1. General Structures 2. Cortex 3. Paracortex lymphoid nodule consisting 4. Medulla of an outer mantle zone C. MALT (basophilic) surrounding the 1. Tonsils inner germinal center 2. BALT (eosinophilic) 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 Slide 97: Lung, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex branch of 3. Medulla pulmonary B. Lymph Nodes 1. General Structures accumulation 2. Cortex of lymphocytes 3. Paracortex 4. Medulla C. MALT 1. Tonsils dust cells (macrophages) 2. BALT bronchiole 3. GALT a. Peyer’s patches b. Vermiform appendix alveolus D. Spleen 1. General Structure 2. White Pulp 3. Red Pulp BALT (bronchus-associated lymphoid tissue) consists of the lymphoid tissue associated with the mucosa of the bronchi and bronchioles within the lungs V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 27: Ileum, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures look within the wall of the 2. Cortex ileum to see the collection of 3. Paracortex lymphoid nodules known 4. Medulla as Peyer’s patches (Pie-er) C. MALT 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp GALT (gut-associated lymphoid tissue) is lymphoid tissue found within the mucosa of the wall of the 3. Red Pulp alimentary canal (digestive tract); lymphoid nodules are most abundant as aggregates known as Peyer’s V. Summary patches in the ileum (most distal segment of the small intestine); in discussing the digestive tract, Peyer’s patches will serve as a distinguishing characteristic in identifying the ileum Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 27: Ileum, H&E II. Learning Objectives III. Keywords IV. Slides villi (folds) of mucosa A. Thymus consisting of simple columnar 1. General Structure epithelium, with goblet cells, 2. Cortex and an underlying lamina 3. Medulla propria of loose CT B. Lymph Nodes 1. General Structures thin layer of smooth muscle (muscularis mucosae) 2. Cortex 3. Paracortex 4. Medulla lymphoid nodule C. MALT (of Peyer’s patch) 1. Tonsils 2. BALT submucosa connective tissue 3. GALT a. Peyer’s patches muscularis externa b. Vermiform appendix (two layers of smooth muscle) D. Spleen 1. General Structure 2. White Pulp as with all MALT, lack afferent lymphatic vessel; instead, antigen gets to the nodules from the 3. Red Pulp Peyer’s patches lumen of the intestine by being transferred across the apical surfaces of M-cells, which are unique cells in the V. Summary epithelium lining the lumen directly above the Peyer’s patches (M-cells are not generally seen in light microscopy) Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 41: Appendix, H&E 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 look within the mucosa and 1. Tonsils submucosa of the wall of the 2. BALT vermiform appendix to see the 3. GALT lymphoid nodules 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 Slide 41: Appendix, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes of simple columnar 1. General Structures mucosa epithelium, with numerous 2. Cortex goblet cells, and an underlying 3. Paracortex lamina propria of loose CT, with 4. Medulla many infiltrated lymphocytes C. MALT 1. Tonsils lymphoid nodule with outer 2. BALT mantle zone (basophilic) and 3. GALT inner germinal center a. Peyer’s patches (eosinophilic) b. Vermiform appendix D. Spleen submucosa connective tissue 1. General Structure 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 41: Appendix, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex nuclei of epithelial cells 3. Medulla B. Lymph Nodes 1. General Structures goblet 2. Cortex cell 3. Paracortex 4. Medulla extensive populations of plasma C. MALT cells may be found within the loose 1. Tonsils CT of the lamina propria; they have 2. BALT a round, eccentrically-located 3. GALT nucleus and amphophilic cytoplasm a. Peyer’s patches the arrangement of b. Vermiform appendix along the periphery of the nucleus D. Spleen can produce the distinctive “clock 1. General Structure face” appearance 2. White Pulp 3. Red Pulp V. Summary Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 68: Spleen, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex capsule 3. Medulla B. Lymph Nodes trabecula 1. General Structures 2. Cortex 3. Paracortex 4. Medulla white pulp C. MALT red pulp 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure the spleen is the largest single accumulation of lymphoid tissue in the body and the main site of removal of old 2. White Pulp RBCs from the blood; it is surrounded by a capsule of dense CT with trabeculae penetrating into the 3. Red Pulp parenchyma (trabeculae from the hilum contain neurovascular bundles); the parenchyma (splenic pulp) is V. Summary divided into the white pulp (20% of the spleen), consisting of lymphoid tissue, and the red pulp (majority) where old RBCs are removed and destroyed Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 68: Spleen, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures red pulp 2. Cortex 3. Paracortex white pulp 4. Medulla C. MALT trabecula 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp unlike the other immune organs, the spleen monitors the blood – not the lymph – for ; central arterioles branch from the trabecular and carry blood into the splenic pulp: first the blood passes through the 3. Red Pulp white pulp where the vessels are encased by lymphoid cells (PALS) which can respond to antigens in the blood; from the V. Summary white pulp, blood continues into the red pulp where old RBCs are filtered out before the blood exits the spleen Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 68: Spleen, H&E II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure red pulp 2. Cortex 3. Medulla (boundary of red/white pulps) B. Lymph Nodes 1. General Structures mantle zone 2. Cortex 3. Paracortex central arteriole 4. Medulla C. MALT germinal center 1. Tonsils 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure the white pulp consists primarily of heterochromatic lymphocytes, so appears basophilic; central arteriole 2. White Pulp blood vessels, from the , are encased in concentric aggregates of lymphocytes collectively 3. Red Pulp referred to as the periarterial lymphatic sheath (PALS) (the central arteriole distinguishes the PALS from a V. Summary regular lymphoid nodule); however, upon antigen presentations, the lymphocytes can expand into lymphoid nodules, eccentrically displacing the central arteriole Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 73: Spleen, Kornhauser’s Quad II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures splenic cords red pulp 2. Cortex (of Billroth) 3. Paracortex splenic sinus 4. Medulla white pulp C. MALT 1. Tonsils trabecula 2. BALT 3. GALT a. Peyer’s patches b. Vermiform appendix D. Spleen 1. General Structure 2. White Pulp the red pulp composes the majority of the splenic parenchyma; it consists of splenic cords with reticular CT and 3. Red Pulp large aggregates of cells and splenic sinuses (or sinusoids) lined by specialized epithelial stave cells; in the red V. Summary pulp, blood exits the endothelium-lined vasculature and travels through the connective tissue cords before re- entering the vasculature Lab 14 – Lymphoid System IUSM – 2016

I. Introduction Slide 73: Spleen, Kornhauser’s Quad II. Learning Objectives III. Keywords IV. Slides A. Thymus 1. General Structure 2. Cortex 3. Medulla B. Lymph Nodes 1. General Structures splenic cord 2. Cortex (of Billroth) 3. Paracortex 4. Medulla C. MALT 1. Tonsils splenic sinus 2. BALT stave cell 3. GALT (“wood strip of barrel side”) a. Peyer’s patches b. Vermiform appendix D. Spleen in the red pulp, blood can pass through two routes: in closed circulation, the blood goes directly into the 1. General Structure splenic sinuses and then into and exits the spleen; in open circulation (maybe the only pathway in humans), the blood leaves the vasculature and enters into the ; from the cords, the plasma and 2. White Pulp splenic cords formed elements must pass between the stave cells (elongated epithelial cells) to enter into the splenic sinuses 3. Red Pulp in order to exit the spleen; old or damaged RBCs are incapable of passing between the stave cells and are V. Summary removed by macrophages; in the absence of the spleen, sinusoids in the liver and bone marrow can serve the role of removing defective RBCs Lab 14 – Lymphoid System Characteristics of Major Lymphoid Structures IUSM – 2016

I. Introduction Thymus Lymph Node Tonsil GALT Spleen II. Learning Objectives Major function: III. Keywords IV. Slides A. Thymus Location: 1. General Structure 2. Cortex CT capsule? 3. Medulla B. Lymph Nodes Cortex? 1. General Structures 2. Cortex Medulla? 3. Paracortex 4. Medulla Lymphoid C. MALT follicles? 1. Tonsils Afferent lymphatic 2. BALT vessels? 3. GALT Efferent a. Peyer’s patches lymphatic b. Vermiform appendix vessels? D. Spleen HEVs? 1. General Structure 2. White Pulp Characteristic 3. Red Pulp features: V. Summary