Lymphatics Flashcards
What is contained in the capsule of the thymus?
blood vessels
- efferent lymphatics
- no afferent. no circulation of lymphs
What does the trabecula do?
divides teh thymus into incomplete lobules. made of delicate CT
What is made of darker outer staining cortex, with an inner lighter staining cortex?
Thymus lobules.
- dark cortex: with H&E. and epithelial reticular cells, secreting thymosin.
- The blood vessels around the thymus maintain the lymphopoiesis and separate antigens.
The inner lobe of the thymus is named, and has what characteristics?
- medulla.
- allows entry of lymphocytes in blood; has no epithelial cell lining.
What are Hassall’s corpuscles
- highly keratinized medullary epithelial cell
- produce cytokine thymic stromal lymphopoietin
- –stimulates thymic dendritic cells for maturation of single positive T cells.
Double Negative T cells characteristics?
- lack surface molecules typical of mature T cells
- enter cortex from blood, proliferate in subcapsular area.
Double Positive T cells
- confront with epithelial cells at cell surface with MHC class I&II for clone selection
- express CD4 and CD8 coreceptors and TCR Receptors
Single Positive T cells
Express TCR receptors and CD4 or CD8 coreceptors.
-found in medulla of thymus
What is the Blood thymus barrier composed of?
- endothelium
- endothelial basal lamina
- perivascular space
- basal lamina of reticular cells
- reticular cells
- thymic parenchymal cells
What are the Blood Filtering Functions of the spleen?
- store/remove RBC
- convert hemoglobin to bilirubin
- fetal blood forming
- recycles Fe
What are the spleens immunologic functions?
- screen foreign material in blood
- produce lymphocytes and plasma cells
- reduces bacterial infection in children
Billroth cords form the red pulp parenchyma with what components? What do the billroth cords do?
- various cells
- terminal capillaries open directly into substance of cords
- macrophage destroy defective RBC
Venous Sinusoids of the Red pulp
- endothelial lined sinusoids with discontinuous membrane
- store RBC
- this is the closed system
Describe innate Immunity
- lack specificity and memory
- response = inflamation
- neutrophils are first responders
What is acquired immunity
- develop in response to antigen
- more powerful than innate immunity
- takes longer to develop
- displays specificity and memory
Passive Immunity
- temporary immunity due to donated antibodies
- maternal antibodies passed to fetus
Active Immunity
-long lasting permanent immunity due to self exposure to antigen resulting in memory T cell and B cell specific for that antigen.
Humoral Immunity
-an antibody mediated by plasma cells
Cell-mediated immunity
-consists of T cells and B cells and antigen presenting cells
Lymphoid Tissue has two levels of organs…?
- primary: thymus and bone marrow. contain immunocompetent cells
- secondary: lymph nodes, spleen and tonsils
Where do the lymphocytes originate?
-primary lymphoid organs and reside in secondary organs
What are the characteristics of a lymph follicle?
- no capsule
- site for B cell localization and proliferation
- are solo or aggregated
What are primary follicles?
-spheres packed with accumulations of virgin B cells and dendritic reticular cells that have not been exposed to an antigen
What are secondary follicles?
- Derive from primary follicles that have been exposed to nonself antigens
- are not present at birth
What structure makes up the secondary lymph follicle?
- corona: densely packed B lymphocytes. Dark staining
- germinal center: B lymphocytes, memory B cells, plasma cells, dendritic reticular cells that act as antigen presenting cells. light staining
What type of vascular supply is given to the secondary follicle?
- corona has own arteriole and venule
- germinal center has own arteriole and venule
- no lymph capillaries
Diffuse Lymphatic Tissue
- subcutaneous tissue in the papillary of dermis.
- MALT, BALT, GALT: are lamina-associated
Aggregated Lymphatic Tissue
-includes various tonsils and Peyer’s patch in the ileum
Mature B cells must present what on their curface?
- IgM, IgD
- MHC II proteins
- complement receptors
- IgFc receptors
Waht are the the 5 different antibodies? and their structure.
IgA, IgD, IgG, IgM, IgE
- light and heavy chains
- heavy variable regions: Fab fragment that recognizes antigen
- Less variable region: Fc fragment; binds antibody to cell
Where are the IgA, IgD, IgG, IgM, IgE found?
- IgA: saliva, GI, respiratory tract
- IgD: surface of B cells traveling to lymphoid organ
- IgG: majority of antibody activity
- IgE: allergic response
- IgM: first class expressed by developing B cell
Major Histocompatibility Complex. Function and types.
- presents antigenic peptides to T cells
- MHC I: not expressed by trophoblast or RBC
- MHC II: on surface of B cell and antigen presenting cell
What do CD4+ T cells do?
-recognize antigens bound to MHC class II molecules.
CD8+ T Cells have what function?
- bind to an antigen presenting cell
- undergo mitosis
- release perforin and Fas ligand
- only recognize antigens bound to MHCI proteins
CD16+ T cells are also what name?
- natural killer cells
- release cytokines
What are cytokines released by Natural Killer cells?
- interleukin 2: proliferates NK cells
- interferon gamma: activate NK cell
- Macrophage activating factor
- tumor necrosis factor: directly kills tumor cells
Why do Activated T cells undergo mitosis?
- to promote daughter cells to become memory cells
- allow daughter cells to secrete interleukins
What is the process of T cell mediated immunity?
- T cell attracts B cell
- B cell now has access to free antigens
- Binding with free antigens cause mitosis
- forms plasma cell and memory cell
What does a NK cell require in order to not release perforin and cytokines?
- require the activator ligand to bind with activator receptor
- inhibitory receptor bound to the MHC I class protein
- No MHC I protein causes perforin and cytokine targeting.
- Viral and cancer cells do not contain the MHCI protein
What is the classic pathway of the complement system?
- cascade is activated by antibody binding to a pathogen
What is the alternative pathway of the complement system?
Cascade is directly activated by the pathogen
What is the purpose of the complement cascade?
- inflammatory response
- pathogen must be coated with complement to start cascade
What is the activation sequence of the complement cascade?
-C1q–>C1r–>C1s become active and initiate complement cascade
What are the final results of the cascade sequence?
- activate membrane attacking complex on pathogen, causing lysis
- produce opsonin: increase phagocytosis
- release chemokines at the inflammation area
The lymph node parenchyma consists of?
-lymphocytes and other cells that pack into lymphoid organ
The lymph node stroma is what?
-reticular fibers, cells, and free macrophages
The lymph node Hilus is what?
- entry and exit point for vessels.
- efferent are on same side as hilus
- afferent are on opposite side.
What is contained in the capsule of the lymph node?
-dense collagen fiber, elastic fiber, smooth muscle
The cortex has an outer layer with certain follicles that contain what?
- B cells, follicular dendritic cells, migrating dendritic cells
- secondary follicles: mantle and germinal center
- primary follicles: no mantle and no germinal center
The deep inner layer of teh cortex has what purpose?
- contain T helper cells, macrophages
- High endothelial venule
Explain the medulla of the Lymph node.
- irregular arrangement of loose medullary sinuses and dense medullary cords
- site for lymphocyte reentry to lymph stream
- thymic dependent area in subcortical and deeper medullary regions
What are the structure of the thymus?
- capsule
- trabecula
- lobules
Thymus capsule has what type of characteristics?
- efferent lymphs are present, no afferent
- the capsule extends trabecula into the parenchyma
The thymus trabecula do what?
- divide the thymus into incomplete lobes with delicate CT
What are the components of the lobules of the thymus
- cortex which is darker staining
- medulla which is light staining.
The cortex of the thymus has what type of cell population?
- epithelial reticular cells that secrete thymosin
- Differentiating T cells
- thymocytes migrate from cortical area to medullary area
The medulla of teh thymus houses the Hassall corpuscles which have what function?
- produce cytokine thymic stromal lymphopoietin.
- keratinized epithelial cells
- stimulate thymic dendritic cells for maturation of single positive T cells
Double Negative T cell
- lack surface molecule of mature T cells
- enter the cortex from blood vessels
- proliferate in subscapular area
Double positive T cell
- confronted with epithelial cells with cell surface MHC I&II
- express CD4&CD8 coreceptors and TC recepotrs
Single Positive T cell
-express TC receptors and either CD4 or CD8 coreceptors
Where does clonal deletion occur?
-medulla of the thymus
Thymic cortical epithelial cells that participate in clonal selection of immunocompetent T cells come from what pathway?
- thymic epithelial cells or corttex and medulla express keratin5 and keratin18 are exposed to Foxn1.
- forming, cortical thymic epithelial cells expressing keratin 18.
What pathway is responsible for the generation of APECED syndrome?
- thymic epithelial cells of the cortex and medulla express keratin 5 and keratin 18 are exposed to AIRE (transcription factor)
- forms medullary thymic epithelial cells expressing keratin 5.
- thymic medullary epithelial cells participate in clonal deletion of autoreactivated T cells.
- defective AIRE leads to APECED syndrome
What components form the blood-thymic barrier?
- endothelium
- endothelial basal lamina
- perivascular space
- basal lamina of reticular cells
- reticular cells
- thymic parenchymal cells
Where is the thymic-blood barrier located, and what job does it have?
- thymic cortex
- prevents antigens from reaching immature T cells.
- allowed to leak during fetal development to allow for self-antigen tolerance.
What is the purpose and characteristics of white pulp?
- associated with immune function.
- site for clonal expansion of antigen-stimulated lymphocytes
- the periarterial lymphatic sheath is formed by T cells around central artery.
Explain the important of the marginal zones of the spleen.
- interface between the red and white pulp with antigen presenting cells
- the site for initiating immune response, by activating B cells.
The spleen red pulp contain billroth cords that form the parenchyma of the red pulp. What is the name of the system that allows for capillaries to empty directly into the spleen, and allow RBC to be pahgocytized?
-an open system
How is the penicillus formed in the spleen?
-formation of the capillaries supply white pulp, and enter the red pulp, forming the penicillus.
