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Immune System I-III
UBSDM 2015 Histology
Question | Answer |
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Lymphocyte Distribution | A. Loose areolar and dense irregular connective tissue B. Solitary lymphoid nodules C. Aggregated lymphoid nodules D. Tonsils E. Lymph Nodes F. Thymus G. Spleen |
Lymphatics | Similar to valved veins that drain interstitial fluid (lymph). Filters through lymph nodes. Systemic Distribution |
Lymph Node - (LN) Distribution | Wide, ideally located to drain sites of inflammation and trap foreign particles |
Lymph Node - Capsule | Dense connective tissue. Continues into organ as Trabeculae |
Lymph Node - Hilus | Entry & Exit point of blood vessels. Site of Efferent lymphatics. Afferent lymphatics enter everywhere BUT the Hilus |
Lymph Node - Stroma | - reticular fibers associated with reticular cells - cells adherent to trabeculae and fibers form a loose, open network of sinuses - open spaces within stroma contain lymphocytes, plasma cells, macrophages |
Lymph Flow through LN | Lymph flows from afferent lymphatic to subcapsular sinus ->cortical sinus->trabecular sinus->medullary sinus->efferent lymphatic |
Lymph Node - Sinuses | Interconnected sinuses lined with endothelium like cells with processes that extend to one another. Contain Macrophages- Very numerous in the medullary sinus |
Lymph Node - Outer Cortex | Nodular Masses of Lymphocytes: Primary Nodules contain predominantly naïve lymphocytes and some memory cells. Secondary Nodules (Follicles) filled with mostly B lymphocytes & surround the germinal center. |
Lymph Node - Germinal Center | Activated B lymphocytes producing antibodies. High rate of mitosis. Maturation zone of B lymphocytes. Some T Cells present. Contain Antigen Presenting Cells. B-cells move to medulla for differentiation. Generates a clone of cells. Centers (dis)appear |
Lymph Node - Deep Cortex (Paracortical Area) | Dense, but not nodular, collection of small t-lymphocytes. Some Antigen presenting cells & macrophages. 70-90% of lymphocytes enter lymph node through "High Endothelial Venules" |
Lymph Node - Medulla | medullary cords: aggregations of lymphoid cells around blood vessels, branch and anastamose - network of sinuses separate the medullary cords from one another -composition of medullary cords: small B lymphocytes, plasma cells, Macrophages, Reticular Cel |
Lymph Node - Blood Supply | Vessels enter Hilus->trabeculae->medullary cords->Cortex->rich capillary network->postcapillary venules w/cuboidal/columnar epithelium->exit as normal veins in hilus. |
Lymph Node - Postcapillary Venules | Site of T/B lymphocyte migration out of blood into parenchyme of node. (Similar to Peyer's Patches) |
Selectins | Surface molecule of lymphoctyes that allow a cell to recognize markers on tall endothelium. Permits migration through wall of post capillary venule. |
Lymph Node Function | Allow interaction of antigen/lymphocytes Allows site for aggregation of immune tissues for fast reponse Production of antibodies Filter for unwanted materials (bacteria, tumor cells) |
Spleen | Discriminatory Filter with Specialized blood flow. Largest Lymph organ in the body. Interposed in blood stream instead of lymph. |
Spleen - White Pulp | - appears as tiny grey-white dots approx. 0.5 mm in diameter; are the splenic nodule - approximately 20% of normal spleen |
Spleen - Red Pulp | 80% of the Spleen which looks dark red due to large amount of blood |
Spleen - Central Artery | Artery seen within lymphoid nodule tissue of the spleen surrounded mostly by non-nodular t-lymphocytes |
Spleen - White Pulp Architecture | Nodular Portions are made of B lymphocytes. Non-Nodular are made of T-Lymphocytes. The B-cytes can form germinal centers. |
Spleen - Red Pulp Architecture | Made of Splenic Sinuses and Splenic Cords |
Spleen - Red Pulp Sinuses | Irregular anastomosing channels lined with fusiform endothelial cells oriented parallel to long axis of sinus. endothelial cells lie on a discontinuous basal lamina causing the latter to form rings or hoops which encircle the sinus |
Spleen - Red Pulp Splenic Cords | Intersinusoidal spaces containing reticular cells and fibers, RBCs, Macrophages, all cells of blood. Macrophages may be pigmented from eating old RBC Few WBC.splenic cords can be considered a part of the vascular pathway |
Spleen - Marginal Zone | - is a 80-100 µm wide zone of red pulp adjacent to the white pulp is the site where lymphocytes of the recirculating pool leave the blood to enter the white pulp - lymphocytes traversing this region come in contact with dendritic antigen presenting cells |
Spleen - Blood Flow | Splenic Artery->Hilus->Trabeculae->Lymphoid Sheaths(Central Arteries)->Penicillar arterioles (in red pulp)->Pulp Vein->Splenic Vein the blood reaches the sinus and exits it via a short pulp vein that is connected to the sinus. |
Spleen - Functions | Fetal: erythropoiesis, leukopoiesis, megakaryopoiesis Filters Blood Antigens Produces Lymphocytes Destroys old RBCs and Platelets Matures monocytes to Macrophage |
Signs of Splenectomy | 8. signs of splenectomy - jolly bodies in erythrocytes of circulating blood - increased number of damaged red cells in blood - increased numbers of platelets in blood(i.e. decreased destruction or sequestration) |
Mucosal-Associated Lymphoid Tissue (MALT) | Defense system of Digestive, Respiratory, urogenital systems. Organized into nodules, Peyer's Patches, Tonsils. More plasma cells than all other lymph organs. |
M-Cells | Specialized cells in MALT that present antigens across a mucous membrane. the M cell contacts the lumen with broad cytoplasmic processes. Also has a deep pocket in the basolateral plasma membrane Filled with Lymphocytes |
Thymus | Primary Lymphoid organ and source of T-lymphocytes. Reduces size over life. |
Thymus - Cortex | Darkly Staining- Lots o lympocytes. No Nodules. No germinal centers Filled with reticular cells that isolate developing lymphocytes. Stroma is made of Epithelial reticular cells. |
Thymus - Cortex - Population | 3. Cellular population: lymphocytes, epithelial reticular cells, some macrophages - mostly T lymphocytes - a few B lymphocytes also present - dendritic cells |
Thymus - Medulla | Stroma made of reticular cells. pale staining nucleus and acidophilic cytoplasm. More Reticular Cells than Cortex. |
Hassell's Corpuscles (Thymic Corpuscle) | epithelial reticular cells become flattened, are concentrically arranged and undergo keratinization. - Function of Hassell’s corpuscles: not fully understood but are functionally active. They produce thymic hormones (e.g. thymosin, thymopoietin). |
Thymus - Medulla - Population | Cellular population: lymphocytes, epithelial reticular cells, dendritic cells lymphocytes fewer in number than in cortex, hence medulla stains lighter |
Thymus - Reticular Cells' Functions | Aids in lymphocyte self/nonself development Secrete thymotaxin which calls undifferentiated lymphoblasts into thymus secrete thymulin: T-cytes make their surface markers Produce hormones that regulate t-cytes all over the body |
Thymus - Blood Supply | Arteries->interlobular septa->cortico-medullary junction->nonfenestrated Capillaries of cortex & arterioles of medulla. ->high endothelial post capillary venules. |
Thymus - Involution | - initiates at puberty - cortical and medullary concentration of lymphocytes decreases - fat cells appear - cortico-medullary distinction disappears |
Tonsils - Types | Palatine Lingual Pharyngeal |
Tonsils - Morphology | Lie within a layer of lymphocyte infiltrated epithelium with depressions (crypts) that penetrate deep into lymphoid tissue. lymphoid tissue consists of collections of lymphoid nodules in diffuse aggregates of lymphocytes, germinal centers present |
T-Lymphocyte Distrobution | Distribution: deep cortex and interfollicular area of lymph node, non nodular peri-arterial lymphoid sheath of spleen, inter-follicular region of Peyer’s patches, respiratory tract nodules; thymus ± 75% circulating (blood) lymphocytes |
B-Lymphocyte Distrobution | Distribution: lymphoid follicles (nodules) of spleen, lymph nodes, Peyer’s patches nodules, other lymphoid nodules, medullary cords of lymph nodes; bone marrow ± 15% circulating (blood) lymphocytes are B cells |
T-Lymphocyte Differentiation | lymphoid stem cell originates in bone marrow, enters blood, travels to thymus. Settles in cortex, proliferates, progeny migrate to medulla differentiate, enter blood, circulate or enter a lymphoid organ |
B-Lymphocyte Differentiation |