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Flashcards in Lymphatic system Deck (63)
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primary organs and their function

-bone marrow
-cloacal bursa (birds only)
-aggregated lymphoid nodules in small intestines (peyer's patches)
-generate lymphocytes from progenitor cells


secondary organs and their function

-lymph nodes
-mucosal associated lymphoid tissue
-sites of lymphocyte activation/differentiation in context of immune response


function of lymphatic system

-to protect the body against pathogenic organisms and their products
-help in removal and disposal of cells undergoing natural or induced degenerations


mechanisms of action and the cells in which they occur

-phagocytosis (macrophages)
-production of immunologically competent cells (antigen presenting cells: dendritic cells, macrophages, b cells; and b/t lymphocytes)


fixed macrophages can be found in

sinusoids of the liver, spleen, and lymph nodes, as well as the reticulum of bone marrow


free macrophages can be found in

blood, lungs, and serous cavities


antigen presenting cells include what cells? what is their function

-dendritic cells, macrophages, and b-cells
-captre, process, and present fragments from extracellular antigens on MHC II


B cells are lymphoid stems cells differentiating where? Where to T cells form?

-bursa or bone marrow for b-cells
-thymus for t-cells


primary lymphatic organs functions specifics

-where t and b cells originate and their unique features established
-access by antigen is strictly controlled by barriers
-apoptotic elimination of self-reactive cells
-released to circulation to sites where antigen encountered (aka secondary lymphoid)


bone marrow is the source of

pluripotent stem cells, which become B and T cells
-background of stromal cells as well, which become macrophages


Cloacal bursa functionally equivalent to what

-dorsal wall of cloaca
-functionally equivalent to mammalian bone marrow for B cell differentiation


cloacal bursa: difference between dark cortex and light medulla

dark cortex: densely packed small lymphocytes
light medulla: lymphocytes, macrophages, reticular epithelial cells


Thymus location and function

-located in mediastinum just cranial to heart
-composed of epithelial reticulum (network) and lymphocytes
-lymphocytic stem cells migrate from bone marrow
-fill spaces btw reticular epithelial cells of developing organ
-site of T-cell development


thymic cortex

-stains much darker than thymic medulla due to greater number of lymphocytes present
-area of positive selection ("good lymphocytes")
-tingible body macrophages that frequent near the medulla to phagocytise and eliminate dead T cells


Thymic Medulla

-contains epithelial reticular cells in addition to lymphocytes
-area of negative selection ("bad" lymphocytes-autoreactive)
-some medullary reticular epithelial cells form thymic corpuscles or Hassall's corpuscles


thymic corpuscles

-large central calcified or degenerated cells surrounded by concentric circles of keratinized cells
-characteristic/notable aspect of thymus


blood supply of thymus

-arteries enter the thymus at the corticomedullary juntion within the connective tissue septa
-divides into arterioles within the septa
-branch into capillary network in the cortex


cortical capillaries of thymus

-forms the blood thymus barrier consisting of
-continuous endothelium
-perivascular connective tissue
-sheath of epithelial reticular cell processes


blood thymus barrier function

decreases antigen access to thymus, limits interference with positive T cell selection


educated T cells

-leave the thymus through postcapillary venules at the corticomeduulary junction
-enter blood, settle in T cell areas of secondary lymphatic tissue


Thymic involution

-thymus is active in young animals, involutes after sexual maturity (involution = shrinkage)
-gradual depletion of lymphocytes
-replacement by adipocytes


secondary lymphatic organs morphology/function

-network of organs, aggregated lymphatic tissue and cells
-linked by lymphatic vessels and blood vessels
-critical in innate/adaptive immunity
-filter mechanisms such as cells


lymph nodes function

-filter antigens from lymph before returning it to bloodstream
-ONLY lymphatic organ with both afferent and efferent lymph vessels and sinuses containing lymph


lymph node consists of three parts

-capsule, cortex, medulla, and hilus


lymph node cortex

-primary and secondary follicles rich in b-cells
-paracortical tissue rich in t-cells
-high endothelial blood vessels
-subcapsular sinus


lymph node medulla consists of

medullary cords and sinus



-slight indentation of lymph node
-arteries enter and efferent lymphatics and veins leave at hilus


lymph node capsule

-dense, irregular connective tissue
-(ruminants have smooth muscles cells too)
-trabeculae of capsule extend into cortex and medulla


trabeculae of lymph nodes

-extend from capsule into cortex and medulla
-structural support, contain blood vessels and nerves, and are surrounded by sinuses


lymph node stroma

-reticular cells and fibers that support lymphocytes, macrophages, and plasma cells