lymphoid tissue Flashcards
lymphoid tissues
- contain
- provide
- structure
- masses of lymphoctyes and associated cells required to mount an immune response
- provides an environment that promotes immune cell-antigen interaction
- may exist as discrete lymphoid organs covered by epithelium or connective tissue capsule OR exist as isolated masses of cells within various organs that are in close proximity to the outside world
4 lymphoid tissues
- spleen
- tonsil
- thymus
- lymph node
primary lymphoid organs
- bone marrow and thymus
- BM = B cells
- thymus = T cells
immunocompetency
-develooping B and T cells with antigen receptors which do not recgonize self
thymus appearance
- starry sky
- continuous branched medulla
cell migration in the thymus
-migrate to superior mediastinum and differentiate into epithelioreticular cells, and form a cytoreticulum
thymic eptihelial cells
- what do they form
- what happens there
- what are these cells called
- form a cytoreticulum that becomes infiltrated by T-cell precursors (thymocytes)
- these epithelial cells are called epithelioreticular cells
epithelioreticular cells
- what do they have
- what do they support
- what do they surround and why
- s subset of…
- how can they be visualized
- connected by what
- cytokeratin positive
- surround lymphocytes and macrophages
- support thymocytes (thymus has no supporting reticular fibers),
- surround caps and contribute to blood thymus barrier thus preventing foreing antigens from entering the thymus and being considered self
- a subset from Hassal’s corpuscle
- seen with keratin IHC
- connected by desmosomes
Hassal’s corpuscles
- appearance
- where are they found
- function
- what do these diagnose
- whorls of epithelioreticular cells
- reside in thymic medulla
- poorly understood but appear to regulate T-cell (Tr) development
- these are diagnostic of the thymus
germinal centers
-what do they contain
contain proliferating b cells
diffuse area of lymphoid nodules
-what do these contain
-contain lymphocytes
nodules
-what happens here
-B cells will enter Ct and differentiate into plasma cells
mucosa associated lymphoid tissue (MALT)
-where
- lymphoid tissue found between the epithelial cells of the intestinal lumen and the muscularis mucosa
- within the lamina propria
types of tonsils (3)
- pharyngeal
- palatine
- lingual
palatine tonsils
- what do these contain
- epithelium
- germinal centers of lymphoid nodules
- glands
- lymph tissue
- striated muscle
- crypts for surface area
- stratified squamous NK epithelium
pharyngeal tonsils
-epithelium…this is diagnostic
- respiratory epithelium
- many lymphocytes
peyers patches
- where
- epithelium
- found in the lamina propria and extend to the submucosa of the ileum
- simple columnar
M (microfold) cell
- function
- appearance
- allows lymphocytes to get very close to the apical surfecr by approaching the basal surface
- the basal surface has an invagination that comes up very close to the apical surface
appendix functions
- 5
- cell type found here
- immune surveillance (abundant M cells)
- vestigal: former enlarged cecum
- endocrine organ: endocrine cells appear by 11th week in fetus
- reserve of gut microbiome : following loss due to diarrhea etc, the bacteria that live here will repopulate the gut
- surgical substitute for diseased ureters, sphincter in reconstructive bladder surgery
lymph node
- size
- where
- function
- range from 1mm to several cm
- concentrated in neck, axilla, and groin
- filtered lymph and expose antigens to immune cells
structural components of lymph nodes
- cortex
- paracortex
- medullary cords
- medullary sinuses
medullary cord
-contains
- loose CT, highly cellular
- reticular fibers
- plasma cells
- lymphocytes
- fibroblasts
- neutrophils
medullary sinus
- contains
- what type of endothelium
-venous channel running between cords, discontinuous endothelium, traversed by reticular fibers
splenic cords and sinuses
-diferences between medullary cords/sinuses
- similar to lymph nodes but:
- have blood cells in both cords and sinuses
- sinuses are not traversed by reticular fibers
- sinuses have continuous endothelium
three mechanisms assure interaction between lymphocytes and pathogens
- sinuses are lined by a discontinuous endothelium so cells can slip out
- reticular fibers traverse all sinuses
- afferent lymphatics outnumber efferent; bottleneck results
high endothelial venules
-what happens here
-this is where lymphocytes enter
lymphodenopathy
-paracortical reaction following activation of HEV’s
spleen
- function
- during fetal development
- stores what
- recycles what
- immune response, B and T cells
- destroys damaged senescent blood cells
- sequesters monocytes
- hematopoiesis (fetal development)
- storage of blood/platelets
- recylcing of iron
red pulp cords
- contains
- cellular elements
- loose Ct/reticular fibers
- cellular elements: red blood cells, platelets, macrophages, plasma cells, and lymphocytes
red pulp sinuses
- type of endothelium
- type of basal lamina
- venous channels lined by elongated, discontinuous endothelial cells
- discontinuous basal lamina
