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56 Cards in this Set
- Front
- Back
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what is the basic structural/functional unit of lymphoid tissue?
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The lymphoid nodule
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List the various lymphoid tissues?
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-Unencapsulated lymphoid tissues (tonsils, Peyer’s patches, appendix); encapsulated lymphoid tissue (lymph node, spleen) and thymus.
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Which one of these tissues does not utilize the basic structural unit for its composition?
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-Only the thymus does not use lymphoid nodules as its structural/functional unit.
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which of these tissues are associated with lymphocyte production?
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-They are ALL associated with lymphocyte production
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what is diffuse lymphoid tissue?
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-Areas where there are large numbers of B-cells present but NOT organized into lymphoid nodules.
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what are some examples of diffuse lymphoid tissue?
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-The lamina propria of the G.I.T. or respiratory system.
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How does encapsulated lymphoid tissue differ from unencapsulated( diffuse)?
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-Encapsulated forms are completely surrounded by a connective tissue capsule.
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which type fo lympocyte is responsible for mediating the humoral antibody response?
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-The B-cell (or lymphocyte).
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what is the other type of cell involved in?
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-The cell-mediated immune response (t-cells)
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what three components comprise the thymus?
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-1. epithelial component (ERC’s); 2. lymphatic component (T-cells); and 3. C.T. component (capsule and septa).
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where do epithelial reticular cells (ERC) come from?
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-The epithelium of the oropharynx
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what does an ERC secrete and what is the function of this secretion?
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-The ERC secretes thymosin. This hormone regulates the differentiation of T-cells surrounding it
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is an ERC considered exocrine or endocrine in nature?
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Because they have no duct - endocrine (although this hormone is not specifically released into capillaries)
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what is the structural function of ERC?
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-Their stellate processes are attached by desmosomes giving them the ability to form a syncytium (meshwork) to help hold the differentiating T-cells in place.
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what are the structural/functional unit of the thymus?
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-Lobules (each composed of a cortex and medulla).
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what is the function of the thymus?
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-To act as a primary lympohoid organ in the production of T lymphocytes - it does not participate in the immune response.
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what two structural features ensure that products of the thymus are released in an unstimulated state?
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-. The blood-thymus barrier ensures developing T-cells are not exposed to circulating blood-borne antigens; 2. The lack of afferent (incoming) lymphatics ensures they are not exposed to circulating lymph-borne antigens.
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where do T-cell released by the thymus go?
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-Mature but unstimulated T-cells leave the thymus and take up residence in the spleen as well as lymph nodes.
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how long do t-cells live?
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- few days.
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name a distinguishing feature of the thymic medulla?
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-The presence of Hassal’s (thymic) corpuscles
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what is the hassal's corpuscles made of?
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-Thymic corpuscles are aggregations of closely packed ERCs - the central portion of which may keratinize.
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distinguish b/w thymic cortex and medulla by type of lymphocytes present in each?
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-The cortex is primarily T lymphocytes while the medulla is predominantly large lymphocytes (the other subset of the small lymphocyte of which T cells is one type).
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what is the blood-thymic barrier?
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-A combination of ERC and endothelial cell that prevents molecules that typically pass into other tissues from not entering the thymus.
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what structures would a potential antigen have to cross to traverse this barrier?
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-The endothelial cell, its basement membrane, a variable amount of CT, the basement membrane of the ERC and the ERC cytoplasm.
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what are the two most essential components of this barrier?
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-The ERC and the endothelial cell.
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which of these is the most selective in permeability?
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-The endothelial cell is highly impermeable
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what is a lymphoid nodule and how is it composed?
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-An accumulation of B-cells that may be classified as a secondary nodule if it exhibits a lighter germinal center surrounded by a darker corona (follicular mantle) composed of memory B-cells
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what does the presence of a germinal center (secondary nodule) reflect?
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-That the B-cells present in that area are differentiating into plasma cells
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what does the presence of a nodule in subepithelial CT indicate?
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-Penetration of an antigen through the overlying epithelial layer.
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where are they primarily found and why?
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-Under moist mucous membranes. They are thinner (than say skin) and form the luminal walls of the G.I.T. and respiratory systems - both systems exposed to numerous antigens via eating/breathing
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list three examples of aggregated (unencapsulated) lymphoid nodules?
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-Tonsils, Peyer’s patches, appendix.
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Which is the most structurally organized unencapsulated lymphoid organ?
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-The tonsil.
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which is the least?
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Peyer’s patches
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where are peyer's patches founded and why?
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-In the region of the terminal ileum. This is the most highly absorptive (penetrable) portion of the G.I.T.
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why does the appendix have a ring of lymphoid nodules?
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-It is a blind-ended, finger-like projection. Therefore, material gets caught in this region and remains here for a long them giving antigens the chance to penetrate the lining epithelium.
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what are the general functions of a lymph node? which are responsible for each function?
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1. Filter lymph of particulate matter (macrophages); and 2. site of local cell-mediated (T-cells) and humoral immune response (B-cells).
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what is cell mediated immune response?
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Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen
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what is cell humoral response?
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The Humoral Immune Response (HIR) is the aspect of immunity that is mediated by secreted antibodies (as opposed to cell-mediated immunity, which involves T lymphocytes) produced in the cells of the B lymphocyte lineage (B cell
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what structural arrangment of the lymphatics make the lymph node an effective filter?
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-The fact that numerous afferent lymphatics pierce the capsule randomly, but the efferent lymphatics exit only at the hilus - providing a one-way directional flow of lymph through the node.
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outline the passageway of a lymph-borne antigen from one side to other side (afferent to efferent)?
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-Pierce the capsule via afferent lymphatics. Pass into subcapsular (marginal) sinus. Either take cortical sinuses through the cortex or pass along the larger peritrabecular sinuses. Either way, the lymph enters the medullary sinuses which funnel it toward the efferent lymphatic vessels at the hilus
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what are dendritic reticular cells?
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Stellate-shaped cells that are mildly phagocytic to trap and present antigens on their surface - for antibodies to be made to them by the surrounding B-cell masses.
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how do they differ from the other type of reticular cell found in the lymph node?
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-The other type of reticular cell secretes the reticular fiber meshwork that organizes the parenchyma of the lynmph node.
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which lymphoid organ has no reticular fibers within it?
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-The thymus
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where is the t-cell (thymus) dependent zone in a lymph node?
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-The deep cortical (corticomedullary) region of the node
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how and why do t-cells take up residence here?
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A leaky postcapillary venule with a lining of high endothelial cells (HEVs) signal the T-cells to exit . They stick to these cells and then migrate between them into the node.
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what would happen if a thymectomy were performed early in childhood?
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-The individual would be highly deficient in resident T-cells - a probable fatal scenario.
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where are B-cells found within the lymph node?
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-Primarily within the nodules of the cortical region of the node. A few enter the T-cell (thymus) dependent zone as well as scatter within the medulla.
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where are both B and T cells found in almost equal numbers in the lymph node?
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T and B cells mix in equal number where the deep (T cell) and nodular cortex (B cell) meet
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what are the two major functional aspects of the spleen and the region responsible for carrying out each function.
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-1. Filter red blood to remove dead/dying cells (red pulp); and 2. react immunologically to blood-borne antigens (white pulp - the T/B-cell sheath around the splenic vasculature).
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outline various divisions of the splenic vasculature from splenic artery in through the parenchyma of the organ?
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Splenic a. - capsular a. - trabecular a. - central (sheathed) a. - follicular off these - the central continues down into penicillar a. - splenic sinusoids.
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identify specific lymphoid cells which might be associated with each vascular division of the spleen?
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-B cells associated with the follicular aa.; T-cells form the sheath over the central arteries forming the PALS (periarterial lymphoid sheaths).
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what are the major structural components of red pulp?
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-Vascular part = splenic sinusoids; extravascular part = splenic cords (of Bilroth)
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identify the main cell types associated with red pulp
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-Red blood cells, endothelial cells and macrophages
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what are the structural differences encounted in the open and closed circulation model for splenic vaculature?
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-In the open model the splenic arterioles empty directly into the reticular meshwork (splenic cords); in the closed model, they open into the splenic sinusoids.
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in either case, how does the strucutural and functional arrangement of the splenic sinusoids allows movement of RBCs in and out of the vascular system?
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-In both models the red blood cells “re-enter” the sinusoids (to be funnelled on into the venules etc.) via the slit-like gaps in their walls.
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be able to list various immune and hemopoietic functions of the spleen?
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-Immune fcns: proliferation of lymphocytes, production of antibodies; hemopoietic fcns: formation of rbc’s in fetal life, removal and destruction of rbc’s and retrieval of iron.
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