lymphatic system, Histology Flashcards
Basic histo. structure of l.organs
1) Stroma;
a) Capsule–> gives off septa or trabecula
b) Reticulum—> Reticular tissue(in secondary l.organs)
and Reticular epithelium (in primary l.organs-Thymus)
2) Free cells:
T og B l.cytes, Macrophages and APC (dendritic cells)
L.tissue - aggregation of l.cytes. 2 forms;;
1) Diffuse l. tissue; l.cytes in muc.membrane + CT of many organs
-In body systems that open to the exterior td respiratory og digestive systems (mucosa associated L.tissue–>MALT)
2)L.nodules;
A) come and go: dense oval masses of l.cytes + macrophages, congregate in response to pathogens
B) permanent feature; in some organs like l.nodes, tonsils and appendix
-In the ileum called Peyers patches; clusters at junction of small and large intestine.
L.tissue - aggregation of l.cytes. 2 forms;;
1) Diffuse l. tissue; l.cytes in muc.membrane + CT of many organs
-In body systems that open to the exterior td respiratory og digestive systems (mucosa associated L.tissue–>MALT)
2)L.nodules;
A) come and go: dense oval masses of l.cytes + macrophages, congregate in response to pathogens
B) permanent feature; in some organs like l.nodes, tonsils and appendix
-In the ileum called Peyers patches; clusters at junction of small and large intestine.
Primary og secondary follicles (l.nodules)
1) Primary; Reticulum cells og resting naive B l.cytes
–> Antigen free enviorment (t.d intrauterine)
2) Secondary
-með Cap/Mantle zone (eins og primary follicle). Þar B-cells proliferate and hypermutation (mutation of immunoglob.gene, to enhance binding prop, of antigen/AB). Mantle zone er með memory og resting B–cells
-Germinal center með light og dark zone
a)dark zone; B-lymphoblasts (centroblasts) dividing
b)light zone; smaller B-lymphocytes (centrocytes), marcophages og follicular dendritic cells.
Classification of l.organs
1) Primary/central; thymus og bone marrow
2)
Secondary/peripheral;
A) encapsulates; lymph nodes og spleen
B) partially encapsulates; tonsils*
C) Non-capsulated: l.Nodules
Thymus
er Primary/central l.organ (lymphoepithelial organ).
-PSEUDOlobulated–>
Divided into subcapsular cortical, cortical and medullary regions w.in each lobule, created by septa coming from capsule.
-NO l.nodules
-NO l.sinuses
-Medulla has Hassals corpuscles*
-NO AFFERENT L.VESSELS ENTER!!
*Efferent l.vessels emerge from corticomedullary junction.
*Two major categories of cells in thymus:
1)Thymic epith cells (endoderm derivatives that will diff. into spec. epith w.in cortex+medulla)
2)Thymocytes
Thymus, CORTEX
-Blood thymus barrier;
Sq. thymic epith cells, pericytes og vascular epithelium
–> koma í veg f. að thymus exposed to improper angitens
-Stellate thymic epith cells; filled w keratinized tonofilament anchored saman by desmosomes.
–> This g rise to cytoreticulum of cortex (analogous collagenous reticular network of other l.tissue)
-Cytoreticular cells; APC cells, express both MHC I OG II proteins. (they take p. in thymic education og release cytokines)
-Sq cortical thymic epith. cells; eru MHC I positive. An inner layer of them extend into lobules of thymus and form—>
Corticomedullary barrier (sep. cortex from medulla)
Thymus, Medulla
-Sq. thymic epith.cells; re-inforce corticomedullary barrier
-The cytoreticulum provides the microenviorment for resident dendritic cells, macrophages + more mature thymocytes
-Hassals corpuscles; concentric congregation of thymic epith cells.—->
Release cytokines that regulate dendritic activity. (önnur kenning, they remove apoptotic thymocytes; því presence of cellular debris at the center of whorls, that are very eosinophilic and partially keratinized)
Thymus áfram
cell types:
-Myelogenous cell line:
dendritic cells, macrophages+monocytes
-Fibroblasts; mostly around vessels + in capsule og medulla.
–> prod. collagenous matter + other ct.
..monocytes mest hjá corticomedullary junction
–>they diff. into macrophages sem mest hjá cortex (og medulla)
-Dendritic cells; at corticomedullary junction + í medulla
–>the APC cells, that help with thymocytes maturation.
-Myoid cells; Large, circular cells m central nucleus og haphazardly arranged myofilaments, mostly in medulla
(they are rarely seen). Believed to do migration of l.tissue across thymus.
-Thymocytes, T-cells; enter thymus during intrauterine life.
Premature (small) thymocytes, mest í cortex, tightly packed milli cytoreticulum
-Lymphoblasts (mononuclear, large and agranular)
–> Prolymphoblasts –> Lymphocytes
Thymus, function
1) Diff. of immunocompetent T-lymphocytes from precursors from bone marrow into helper-T cells and and cytotoxic-Tcells
2) Development of self tolerance rxn
3) Secretion of polypeptides w hormonal activity by reticular epith cells, that regulate proliferation, maturation and funct of T-cells in thymus + other organs;
-Thymulin -Thymopoetin -Thymosin -Thymic humoral factor
Lymph node
1)cortex 2)paracortical region 3)medulla
-Sinuses:
1)subcapsular/marginal 2)paratrabecular/cortical 3)medullary(efferent lymphatics arise)
-Stroma;
–>capsule
–>trabeculae
–>reticular fibers –> reticular cells
Lymph node frh
1)cortex:
B-l.cytes forming nodules/follicles + macrophages + APC dendritic cells.
*L.follicles primary og secondary
2)paracortical region/paracortex: thymodependent.
T-l.cytes + macrophages + APC dendritic cells
og post-capillary venules w high cuboidal endothelium
3)medulla; in center
Irregular cords of L.tissue
-Function:
filtration of lymph
immunologic funct
B-l.cytes, after activation are transformed into plasma cells
–> ABodies-humoral immunity.
Spleen
Peripheral encapsulated l.organs
largest l.organ in the body
-Function:
prod. of l.cytes
immunologic
destruction of defective l.cytes
Spleen, microscopic structure
CT capsule, cov w simple sq epithelium(mesothelium)
Trabeculae arise from capsule
Branches of splenic artery + efferent lymphatics
*No afferent lymphatics
Stroma–> of reticular tissue
Parenchyma–> splenic pulp (white and red)
Spleen, white og red pulp
White pulp:
typical l.tissue. T and B l.cytes, their activated form
and plasma cells, macrophages and APC cells.
White pulp is in relation w. arterial blood system;
br of trabecular aa enter white pulp (are called central arterioles) *They’re surr. by periarterial lymphatic sheath
(PALS), that is thymodependent and has T-l.cytes.
-Sometimes the sheath is surr by l.nodules, w typical germinative centers and B-l.cytes
–>These nodules replace the central arteries in white pulp excentrically.
Red pulp;
composed of Bilroths cords and sinuses
1)Bilroths cord; of atypical l.tissue w B-l.cytes, their activated form, plasma cells, macrophages, erythrocytes, granulocytes, monocytes and thrombocytes.
*sinuses w wide irregular lumen–>
Endothelial cells longitudinally oriented og milli þeirra free spaces present together w discont. basement membr.
2)Sinuses:
surr by circular layer of reticular fibers and by processes of macrophages.
