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Flashcards in Immune system Deck (35):
1

Two components of Lymphatic system

1) Secondary (Mature/active lymphocytes) and 2) Primary (Developing lymphocytes)

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Primary (Developing) lymphocytes

Bone marrow and thymus
Where cells mature/develop and take on more complex functions

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Secondary (mature) lymphocytes

Diffuse lymphatic tissue, lymphatic nodule, lymph nodes, and spleen
Where interaction with antigen and initiation of immune response occurs

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Functions of immune system

-monitor and react to the presence of potentially harmful substances
Develop lymphocytes
-Maintain fluid balance (lymphatic vessels collect interstitial fluid and filter through lymphnodes in order to identify and monitor antigens in body --> ellicit response necessary and feed it back into the blood system

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Lymphatic vessels (function

Collect fluid, large molecules, and lymphocytes from tissues and returns them to the blood.
Begin as networkds of capillaries in loose CT
More permeable than cappilaries to accept large moldcules

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Types of Immune Responses

Adaptive (specific): have a specific target; humoral (B cells) and cellular (T-cells)

Innate (non specific): barriers (skin) and chemical (areas where low pH so bacteria wont grow)

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How do Cytotoxic T Cells (CD8+) recognize and destroy foreign antigens?

-Each T-cell is specific for a unique antigen fragment
-CD8+ T cells become activated when their T-cell receptor (TCR) interacts with antigen and MHC I and co-stimulation occurs
-After activation-->differentiate and divide --> become killer cell --> produce cytokines, specifically porforin (protein that binds to cell and forms holes in cell membrane) and enzymes (travel through holes and initiate apoptosis to kill cell).

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How do Helper T cells (CD4+) recognize and destroy foreign antigens?

-CD4+ T cells become activated when their TCR ineracts with antigen and MHCII and co-stimulation occurs
-Antigen presenting cells (APC), such as macrophages, dendritic cells, and B-cells, activate CD4+ cells. They do this b phagocytosis /break cells into pieces and displays pieces hooked to MHC II, which binds to CD4 on T-cells and activates T-cells
-Once activated, CD4+ cells release interleukins and activates other cells of immune system (CD8+, B-cells, NK cells and macrophages)

9

How do B cells recognize and destroy foreign antigens?

-Can recognize native antigen via B cell receptor (antibody)
-T cells help activate B cells
1) antigen binds to antibody
2) B cell internalizes the antigen/antibody complex
3) B cell displays peptide on surfaces on MHCII
4) CD4 recognizes antigen on MHCII and activates B cell to divide and differentiate
5) activated b cells release intereukins and promote plasma and memory B cells and create more antibodies.

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Antibody structure and function

-Y-shaped
--secreted by plasma cells: antibodies found on membrane on plasma cells and secreted
-marks antigen for destruction
-2 heavy chains and two light chains with disulfide bonds
-constant region (c-terminus)
-2 identical antigen binding site (n-terminus)
-varible region on arms

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Lymphatic tissues and organs (simple to complex)

-diffuse lymphatic tissue
-lymphtic nodules
-lymph node
-thymus
-spleen

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B-cells

-represent 20 to 30 percent of circulating lymphocytes
-involved in humoral immunity: the production of antibodies that mark invaders for destruction by other immune cells--> these cells develop in the bone marrow

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T cells

-represent 60 to 80 percent of circulating lymphocytes -involved in cell-mediated immunity: the direct cell killing and the secretion of cytokins --> these cells develop in the thymus

14

Natural killer cells (NK cells)

-represent 5-10 percent of circulating lyphocytes
-they recognize transformed or virally infected cells and directly kill them

15

First barrier to microbes

Epithelium --> tight junctions!
-after penetrating the epithelium, microbes encounter diffuse lympoid aggregates in the lamina propria
-locations: alimentary canal, respiratory tract, genitourinary tract (MALT or GALT)

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Diffuse lymphatic tissue

Function: intercept antigen and initiate immune response
-composition: lymphocytes, plasma cells, eosinophils with no organized arrangement
-location: throughout lamina propria

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Lymphatic nodules

-Well organized, but non encapsulated lymphocytes
-Primary nodule: small resting lymphocytes
-Secondary nodule: Germinal center contains large proliferating lymphocytes, FDCs, and macrophages; Corona (mantle zone) is densely packed B-cells
-if you see one, an immune response is mounted there

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Aggregates of nodules

-composition: group of lymphoid nodules in lamina propria surrounded by diffuse lymphatic tissue
-location: alimentary tract
-No afferent lymphatics, lymph drains via efferent lymmphatic vessles
-tonsils: lamina propria of incomplete capsule; pharyngeal, lingual, and palatine
-Peyers patches: illeum
-Appendix

19

Lymph node (function, composition and location)

-organ that has CT capsule made of collagen
-function: filter lymph prior to its entry into the bloodstream
-Principle site of antigen dependent T and B cell activation; important site of phagocytosis and initiation of immune response to antigen
-Composition: encapsulated organ, contains lymphocytes, and a reticular meshwork with regicular cells, dendritic cells, FDCs, and macrophages
-Location intersperse along lymphatic vessel network

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Hilium

place where blood vessels are going in or out of lymph node

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Architecture: Cortex

Outer (superficial) cortex: B lymphocytes organized into nodules and lymphatic sinuses
-Deep (paracortex) cortex: T lymphocytes and HEVs

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Architecture: Medulla

Cords: reticular fibers, reticular cells, B lymph, macrophages, and dendritic
-Sinuses: macrophages and lymphocytes

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Reticular tissue

Reticular cells produce reticular fibers producing a framework that other cells can reside in
-Macrophages
Antigens can get trapped in meshwork and immune system can cause resonse

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Lymphatic circulation

-Majority of lymphocytes enter the node through the walls of HEVs (cortex)
-about 10 percent of lymphocytes enter the node through afferent lyphatic vessels
-ALL lymphocytes travel through the medulla and leave via the efferent lymphatic vessels

25

High endothelial venules

Identifying features: found in the deep cortex, lined by cuboidal cells (round nuclei), tend to stain lightly
What they do: circulate and concentrate lymph, signal lymphocytes to leave circulation, lymphocytes cross endothelium by diapedesis

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Reactive Lymphadenistis

-Occurs when the lymph nodes enlarge due to a secondary infection
-Symptoms: swollen, tender lymph nodes, fever, chills, loss of appetite, tachycardia, weekness
-Germinal centers are huge

27

Thymus

Function: develop immunocompetent T-cells
-Location: anterior to the heart
-Fully formed at birth
-As an adult=lots of fat because not constantly developing t-cells
-composition: encapsulated organ, contains lymphocytes and a reticular meshwork formed by epithelioreticular cells, deveoping t lymphocytes (thymocytes), and macrophages

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Archiecture: cortex

Densely packed T lymphocytes (thymocytes)
-Epithelioreticular cells: type I (barrier cells)--occulding jxn, type II (cellular framework)--desmosomes, type III (barrier cells)--cortex and medullla

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Architecture:Medulla

Epitheliorecticular cells: Type IV (barrier cells); type V: (cellular framework); type VI (Hassll's corpuscles)
-Blood vessels pass from trabeculae into the medulla

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T- cell development: Thymic education

maturation and differentiation of stem cells to immunocompetent t-cells

Positive selection: cortex: select for t-cells that can interact with MHC I and II; type II epithelioreticular cells

Negative selection: medulla; eliminate t-cells that bind strongly to self antigen b/c auto immune response: type V epithelioreticular cell

31

Blood-thymus barrier

physical barrier preventing thymocytes from interacting with foreign antigen

3 elements:
1) type I epithelioreticular cells
2) connective tissue: macrophages
3) continuous endothelium of capillary wall

32

Spleen (largest lymphatic organ)

-monitor/filter blood
-Location: upper lelft quadrant of abdominal cavity
-Composition: -Encapsulated connective tissue/myofibroflasts, trabeculae extend deep into organ, no afferent lymphatics, no HEVs
-Functions: 2 morphologically and functionally distinct regions: red pulp and white pulp

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Red pulp

Hemopoietic-removes aged RBCs and platelets
-rich in RBCs
-cords and sinuses
-Splenic cords (of Billroth); reticular cells/fibers, macrophages, RBCs, dendritic cells, plasma cells
-Splenic sinuses: lined with endothelial cells with prominent intercellular spaces, macrophage processes
-once the blood leaves the central arterioles, it enters the splenic sinuses of the red pulp

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White pulp

-immunologic-antibody production
-associated with splenic arteries/arterioles (PALS-t cells and splenic nodules-b cells)
-T-lymphocytes surrounding central arteriole
marginal zone: junction of nodule with red pulp

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Spleen: architecture

hilum: on medial surface; passage of splenic artery and vein; nerves and lymphatic vessles
-splenic artery enters via the trabeculae and brances off
called the central artery in the parenchyma of the spleen
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