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Immune System I-III

UBSDM 2015 Histology

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
Created by: speedy2782



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