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52 Cards in this Set

  • Front
  • Back
Primary Lymphoid organs
- lymphocyte precursors from teh bone marrow populate these organs where they are educated to recognize and not attack self antigens and to recognize a specific foreign antigen
- bone marrow, peyer's patches, cloacal bursa, thymus
- involute after puberty
- lymphocytes that are not destroyed leave the organ and are considered both naive (have not been exposed to foreign antigen) and mature (do not self react)
Secondary Lymphoid organs
- immunocompetent lymphocytes populate these organs
- lymph node, spleen, tonsil, MALT
- antigens are either carried to the lymph node by dendritic cells or in solution
- the naive lymphocytes examine the selection of antigens and if they do not encounter their specific antigen they move on to the next lymphoid tissue and if they do they stay and are activated
Cells involved in innate immunity
- granulocytes
- mast cells (release chemotactic factors that recruit phagocytic cells)
- macrophages
Cells of acquired immunity
- B and T lymphocytes
- lymphocytes are supported by antigen presenting cells and some specialized epithelial cells and stormal cells
B lymphocytes
- develop in the Bursa of Fabricius, bone marrow, GALT
- each B lymphocyte has many copies of a unique antiody on its membrane that is specific for a unique epitope
- antigen-stimulated B lymphocytes can transform into plasma cells (effector B cells)
Plasma cells
- activated B cells
- secrete antibodies
- priminant pale goligi
-
Antibody or immunoglobulin
- large Y-shaped protein
- has binding sites at the 2 tips of the Y that specifically recognize and bind to its target antigen for its elimination
T lymphocytes
- differentiate in teh thymus
-need antigen to be presented to them by APCs
-
Antigen presenting cells
- T cells need them to present antigen to them
- they pahgocytose antigen and break it into small pepties and then they are returned to teh cell surface to activate the T lymphocyte
- includes dendritic cells, macrophages and B lymphocytes
Stromal cells
- fixed cells taht form a tissue reticulum and support the other cells of teh immune system
- Reticular and epithelioreticular cells
Reticular cells
- mesenchymal
- produce type III collagen
- provide support fo the immune reactions taht take place int eh lymphoid organs
- express surface molecules and produce substances that attract B and T lymphocytes and dendritic cells
Epithelioreticular cells
- form the scaffolding that supports developing lymphocytes in the thymus and cloacal bursa
- attached to each other and become stellate in sppearance
- do not produce reticular fibers
Organized lymphatic tissues
- encapsulated
- lymph nodes, thymus, spleen
Diffuse and nodular lymphatic tissue
- scattered through the loose CT of the gut, resp tract and UG tract
- not enclosed by a capsule
- MALT
Thymus
- primary organ responsible for the education of T cells
- epithelioreticular cells form the framework of the organ
- has lobes covered by a CT capsule and the capsule extends into trabeculae to make lobules
- each lobule has a cortex and a medulla with T cells and stromal cells
Thymic blood vessels
- arteries enter the thymus at the corticomedullary junction
- capillaries drain into postcapillary ventules at the corticomedullary junction
Hassall's corpuscles
- a type of epithelioreticular cell
- composed of calcified or degeneraed large cells, surrounded by flat, keratinized cells in a closely packed, concentric arrangement
- they are joined by desmosomes
-
Blood-Thymus barrier
- cotical capillaries have several layers along with a sheath of flattened epithelioreticular cells
- the barrier may prevent foreign antigens to enter the thymus
T Lymphocyte Education
- precursoe T cells migrate from the bone marrow to teh thymic cortex where type II epithelioreticular cells compartmentalize the cortex into isolated areas for developing thymocytes
- as T lymphocytes move through teh cortex they are tested by epithelioreticular cells and if they pass the test they move to the medulla
- if they fail, they undergo apoptosis and are removed by macrophages
- in the medulla they undergo a second selection process and those that survive leave and return to teh bloodstream by teh postcapillary venules at the corticomedullary junction and go to secondary lymphoid organs
Tingible Body Macrophages
- when macrophages are stuffed full of remnants of apoptotic cells
Cloacal bursa
- unique to birds
- develops as a sac in teh dorsal wall fo the cloaca
- looks similar to teh thymus
- B cell precursors migrate here
- lymphocytes undergo a selection process similar to that described in the thymus
- nodules are covered by pseudostratified epithelium
Ileal Peyer's patches
- young ruminants, pigs, carnivores have primary lymphoid organ peyer's patches (only B cells)
- there are also secondary lymphoid organ peyer's patches (B and T cells)
Primary lymphoid Peyer's patches
- lymphoid nodules are close and have little CT between them
- each nodule has a cortex and medulla
- lymphoid organs do not extend into the villi
- regress after puberty
- B cells only
Secondary lymphoid Peyer's patches
- B and T cells
- extend into the villi
-
Bone marrow
- in primates and rodents
- soruce of B and T cell precursors
- responsible for B-cell differentiation
-
Diffuse lymphoid tissue
- consists of unorganized collections of lymphocytes supported by a stroma made of dendritic cells and CT
Nodular tissue
- localized concentrations of lymphocytes form sharply defined, but nonencapsulated nodules int eh walls of the alimentary tract, respiratory passages and the genitourinary tract
- tonsils!
- GALT!
- primary vs secondary nodule
Primary nodule/follicle
- composed of tightly packed, small lymphocytes
- most are naive recirculating B cells
- T cell zones are in teh CT between nodules
Secondary nodule/follicle
- when a lymphocyte that has recognized an antigen returns to a primary nodule it undergoes proliferation and this reults in a light area in teh middle called a germinal center
- germinal centers are an important sign of a lymphatic tissue response to antigen
- they have a dark outer ring of small lymphocytes known as the mantle zone or corona
Tonsils
- aggregates of lymphoid nodules
- secondary lymphoid organ
- local production of antibodies is important as part of a rapid initial immune response and a subsequent more generatlized response
- epidermis depends on location
- have a CT capsule
- lack afferent lymphatic vessels
Overlying epidermis of tonsils
- oropharynx: covered by stratified squamous
- pharyngeal (in wall of nasopharynx): PSCC
- some tonsils are smooth on their surface (palatine tonsil in dogs)
Peyer's patches (secondary lymphoid)
- aggregated lymphatic nodules
- most numerous in teh ileum
- epithelium lacks villi and has M cells
- has a cap of small lymphocytes with a dense region fo dendritic cells immediately beneath teh epithelium (the dome)
M cells
- poorly developed microvilli
- lymphocytes are held within teh invagination so f the basal membrane of these cells- they endocytose a variety of protein and peptide antigens and transport them to teh underlying tissue, where they are taken up by local denritic cells and macrophages
Lymph node
- surrounded by a dense CT capsule which extends into the parenchyma as irregular trabeculae
- reticular fibers extend into the node and form a support network for lymphocytes, macrophages and dendritic cells
General structure of the lymph node
- cortex and medulla
- cortex has primary and secondary lymphatic nodules with germinal centers (B cell rich) separated by diffuse lymphatic tissue (T cell rich)
- deep cortex has diffuse lymphatic tissue drained by lympahtics (T cell rich)
- medulla is less organized
B cell response to antigen
- lymphoblasts within teh nodules proliferate and migrate toward teh medulla where, as differentiated plasma cells they secrete antibodies
T cell response to antigen
- proliferating T cells migrate to teh paracortex and differentiate
- the cells exit via the efferent lymphatics
Lymph vessels and sinuses
- multiple afferent lymphatics pierce the capsule and dump lymph into a subcapsular sinus
- cortical sinuses arise from teh subcapsular sinus and continue by following the connective tissue trabeculae and drain intot eh medullary sinuses that go out into the efferent lymph vessels
Sinus lining
- lined by flattened endothelial cells
- forms a continuous lining on teh side fo the sinus adjacent ot eh capsule and a discontinuous lining on the side facing the lymphatic parenchyma
Blood flow into lymph nodes
- major arteries enter at the hilus and travel through teh medullary cords and decrease in size as tehy do so
- capillaires extend into teh paracortex and form high endothelial vessels
- HEVs join veins in teh medullary trabeculae which drain into large veins which exit at the hilus
High Endothelial Vessels
- about 90% of lymphocytes entering the lymph arrive via HEVs (not many coem through the lymphatics)
- HEVs express receptors for lymphocytes and induce them to leave the circulation and enter into the lymph node
Spleen
- important line of defense against blood borne antigens
- functions in immune response, destruction of damaged and senescent RBCs, hematopoiesis (while you're a fetus), storage of RBCs and platelets and iron recycling
Organization of the spleen
- no afferent lymphatics
- efferent lymphatics arise in teh white pulp
- spleen is covered by a layer of mesothelium with an underlying thick CT capsule
- capsule extends into the spleen as trabeculae
- capsule has variable amounts of smooth muscle (barbituates cause muscle relaxation and epinephrine causes contraction and release of RBCs)
- parenchyma is the splenic pulp and is red or white pulp
Red pulp
- spelnic cords are composed of a 3D network of reticular fibers with a bunch fo shit in it
- dogs have splenic sinuses in tehir red pulp
- cats have a nonsinusal spleen and have venules instead of sinuses
White pulp
- has nodular and diffuse lymphoid tissue which is organized around arteries
- periarteriolar lymphatic sheaths are sleeves or sheaths of cells that surround arteries passing into the parenchyma from teh connective tissue trabeculae and T lymphocytes predominate here
-
PALS
- place where conditions required for proliferation fo B lymphocytes can be met
Marginal zone
- between red and white pulp
- receives capillaries from teh white pulp and osme terminal capillaries from teh red pulp
- capillaries empty into a marginal sinues and this is where blood borned antigen will first contact cells of teh lymphoid system
Antigen activation
- antigens elicit either a B or T cell resposne
- plasma cells generated as a result of B cell proliferation will migrate to the splenic red pulp and release antibodies into the general circulation
- Activated T cells follow the splenic drainage and exit teh organ
Splenic blood supply
- splenic artery enters at the hilus and branches into trabecular arteries
- arteries branching into the CT are the central artery of teh white pulp an these are surrounded by a sheath of lymphatic tissue
- central artery dontinues to the red pulp wher eit branches into penicillar arterioles which continue as arterial capillaries
- blood from red pulp moves into splenic sinuses or venules which drain into trabecular veins which drain into teh splenic vein
Periarterial macrophage sheats
- some arterial capillaires are srrounded by aggregates of macrophages called PAMS
- these are major sites for clerance of blood-borne particles
Open circulation
- sheathed capillaires empty into the reticulaer network of teh splenic cords rather than into teh splenic sinuses
- nonsinusal spleens
Closed circulation
- blood from teh sheathed cpaillaries pass directly to the splenic sinuses
- sinusal spleen has both open and closed circulation