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12 Cards in this Set
- Front
- Back
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What is a lymphoid organ?
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Lymphoid organs are organs that contain large amounts of lymphoid tissue, which is predominantly composed of small lymphocytes |
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Name primary and secondary lymphoid organs |
Primary: Thymus and bone marrow (although due to a large proportion of non-lymphatic tissue, it's status is debatable) Secondary: Spleen, tonsils, lymph nodes, mucosa and gut associated lymphoid tissue (MALT and GALT). |
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Define primary and secondary lymphoid organs
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Primary - sites where lymphocytes mature and acquire receptors necessary for antigen recognition. Both T and B cells are produced in the bone marrow, but T cells mature in the thymus. Secondary - sites where lymphocytes are activated for an immune response in response to an antigen |
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What is the basic structure of a lymph node? |
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Where do T and B lymphocytes reside in lymph nodes? |
* Segregated into different anatomical compartments * B cells are concentrated in distinct structures, called follicles (nodules), located in the outer cortex of each node * T cells are concentrated outside but adjacent to follicles in the deep cortex (paracortex) |
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How do T and B lymphocytes get activated in lymph nodes? |
Follicular dendritic cells activate B cells, while dendritic cells in the deep cortex activate T cells |
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Where do T and B lymphocytes reside in the spleen? |
*T cells are concentrated in the periarteriolar lymphoid sheaths surrounding small arterioles *B cells are concentrated in the follicles |
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How does a lymph node filter lymph? |
There are 2 mechanisms of filtration: Lymph flows through lymphatics faster than through the lymph node itself due to differences in diameter. This causes debris to settle in the medullary sinus. * Biological - phagocytosis by macrophages. Most reside in the medullary sinus (some are fixed), where they clean out the debris. * At the efferent end of the lymph node, the lymph is clean. |
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What is the general structure of lymph organs? |
Tonsils: *Covered from stratified squamous non-keratinised epithelium. *Has specialised invaginations (tonsilar crypts) that allow more exposure to pathogens for a more enhanced immune response |
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What histological changes occur in lymph nodes during an immune response? |
*Presence of lymph nodules (follicles) |
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What are the structural features of the spleen? |
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What are the features of thymus and how does maturation of t cells occur? |
*Only active in children; replaced by fat in adults. *Site of T cell maturation, not engaged in an immune response *Has a capsule, cortex, medullary nodules and septa * Programming of T cells is done by thymic stromal epithelium in the cortex |
