L29 - lymphatic tissue Flashcards
describe primary lymphoid tissues
- includes bone marrow, thymus
- site of development and maturation of lymphocytes into immunocompetent cells
describe secondary lymphoid tissues
- includes lymph nodes, MALT/GALT/BALT (mucosa-, gut-, and bronchus - associated lymph tissue)
- also GU tract, tonsils, spleen
- site of immunological defense against antigens or pathogens forms
- site of confrontation with antigens and pathogens occurs here
- also sometimes present in lamina propria of GI/respiratory/GU
list lymphatic tissue from simplest to most complex form
- diffuse lymphatic tissue
- lymphatic nodules
- tonsils
- lymph nodes
- thymus
- spleen (most complex)
tell me about diffuse lymphatic tissue
- appearance
- organization
- cell types
- location
- MALT
- simplest organization
- reticular fibers present for support
- includes lymphocytes, monocytes, macrophages and plasma cells
- often present in lamina propria of GI (GALT), resp tract (BALT) or GU as sprinkled throughout OR as prominent basophilic structure
tell me about lymphatic nodules
- appearance
- organization
- structures/locations
- follicles
- non-encapsulated, spherical
- dense aggregations with some organization
- primary (homogenous) or secondary (2 zones) based on appearance
- solitary or aggregate structures
what happens when a secondary lymphatic nodule encounters an antigen?
the germinal center where immature lymphocyte are located swells & makes B lymphocytes
describe the parts of secondary lymphatic nodules
- corona/mantle zone = outside, dark staining with mature (small) lymphocytes
- germinal center = inner, light staining with immature (med/large) lymphocytes
describe difference between solitary or aggregate structures of lymphatic nodules
- plus examples of aggregates
- solitary are temporary - come and go
- aggregates are permanent and include Peyer’s patches (B/T) in ileum, lymph tissue in appendix (lamina propria and submucosa), BALT in resp tract (similar to Peyer’s patches) and lymph nodules in tonsils/nodes/spleen
tell me about tonsils
- 3 diff types
- appearance/composition
- contents
- locations
- tissue covering each type
- crypts or pleats
- collectively form ring around oropharynx
- have partial CT capsule with septa (protection)
- contain B lymphocytes
- pharyngeal = “adenoid” - single tonsil in nasopharynx, covered by pseudostratified columnar + cilia, has pleats - NO crypts
- palatine = pair in oropharynx, stratified columnar + cilia, many crypts and multiple lymph nodules (w/ germinal centers –> new B lymph)
- lingual = small bumps on posterior 1/3 tongue, stratified squamous non-keratinized, has crypts
tell me about the spleen
- function
- parts
(vascular supply comes later)
- function - filter blood, proliferation of B/T lymphocytes
- capsule = mesothelium + SMC + elastic fibers
- also has trabecula (septa) to carry splenic artery branches inward - hilum = BV and nerve passageway
- CT stroma = reticular fiber meshwork
- parenchyma composed of white and red pulp with marginal zone in between
tell me about spleen vascular supply
- what resides in white pulp
- what resides in red pulp
- open circulation
- splenic artery comes from whoknowswhere and bifurcates into trabecular artery, which enters and leaves trabecula
- once it leaves the trabecula, T lymphocytes invade the adventitia, forming the PALS. artery is now called central artery. (*this happens in white pulp)
- central artery continues past the sheath where it becomes penicillar arterioles, which enter red pulp and continue as arterial capillaries (some ensheathed by macrophages)
- capillaries empty into splenic cords where macrophages phagocytose and filter the blood
- filtered blood leaves into splenic sinus –> pulp veins –> trabecular veins –> general circulation
describe white pulp of spleen
- white pulp contains the periarterial lymphatic sheath and splenic nodules
- blue stain with H
- PALS = thymus dependent, T lympocytes with the central artery located CENTRALLY within
- splenic nodules = lymph nodes with B lymphocytes, central artery ECCentrally located and may have germinal center
describe red pulp of spleen
- red pulp includes splenic cords (of Bilroth) and splenic sinuses (sinusoids)
- stains red with E
- looks “spongy”
- splenic cords = irregularly branching splenic tissue with loose framework of reticular cells/fibers filled with blood - filtering happens here by macrophages/plasma/dendritic cells
- splenic sinuses = endothelial cells lining wide spaces for blood cell passage, drain into pulp veins, which train into trabecular veins
tell me about the thymus and movement of lymphocytes
- function
- contents/vessels
(parts ? come later)
- function = maturation site of T lymphocytes
- T lymp made in bone marrow, migrates to thymus where it matures
- T lymph becomes immunocompetent in the cortex, migrates to medulla
- leaves via postcapillary venules –> blood –> secondary lymph organs (PALS/GALT/BALT)
- NO afferent lymph vessels, reticular framework, lymphatic nodules, B lymphocytes or sinuses
- has 2 lobes, each with CT capsule and septa that divide the lobe
describe the 3 parts of the thymus lobes
- capsule - dense irregular CT with trabecula (septa), contains BV, efferent lymph vessels, nerves, collagen, plasma cells
- cortex - epithelioreticular cells protect, guard, and create antigen-free environment for maturing T lymphocytes
- medulla - lighter stain, also contains epithelioreticular cells and mature immunocompetent cells
what is DiGeorge’s syndrome?
developmental disorder thymic hypoplasia/aplasia cannot make T lymphocytes lack cell-mediated immune response death from infection no parathyroid glands - may die from tetany
describe the 6 types of epithelioreticular cells in the thymus and where they’re found
TYPE 1 - outer cortex
- barrier (seals cortex and T lymph via zonula occludens)
TYPE 2 - cortex
- stellate meshwork connected by desmosomes that suspends Tlymph
TYPE 3 - deep cortex
- isolate cortex from medulla, protein synth, forms zonula occludens
TYPE 4 - medulla
- corticomedullary barrier (same as type 3 but diff. location)
TYPE 5 - medulla
- forms 3D meshwork to suspend T-lymph in medulla
TYPE 6 - medulla
- aka Hassall’s corpuscles
- concentric eosinophilic whorls of cells important to thymus, can keratinize
describe the vascularization of thymus and the blood-thymus barrier (BTB)
- arteries enter capsule between lobules in trabeculae –> corticomedullary junction –> form capillary beds –> cortex
- cortical capillaries are continuous, covered by BL and sleeve of T1 epithelioreticular cells - forms blood-thymus barrier
- cortex capillaries empty into medulla venules
- BTB isolates T lymphocytes in cortex from molecules in blood
- layers of BTB from inside to outside are:
endothelium
BL
macrophages
T1 epithelioreticular cells
describe basic structures of lymph nodes
- hilum
- capsule
- trabeculae
- sinuses
- hilum: concave site where BV and efferent vessels enter/leave
- capsule: outer dense CT covering
- trabeculae: CT septa carrying BV and nerves
- sinuses: lined by endothelial cells and macrophages; NOT hollow, contain reticular cells on which macrophages piggyback
+ reticular tissue to suspend cells and sinuses and hilum
describe 3 types of sinuses of lymph nodes
- subcapsular (cortical) sinus = between capsule and parenchyma, drians into trabecular sinus
- trabecular = separate nodule from trabeculae whcih drains into medullary sinus
- medullary = wide, tortuous, interconnected
describe the flow of lymph!
afferent lymph vessel (+ valves) –> subcapsular sinus (has penetrated the capsule) –> trabecular sinus –> medullary sinus –> efferent lymph vessel
describe blood flow through lymph nodes!
artery –> hilum –> CT trabeculae –> medulla –> artery loses CT sheath and passes throgh medullary cords to cortex –> form capillary beds in cortex –> postcapillary venules –> veins –> exit hilum
what are the 3 parts of the parenchyma of lymph nodes?
- cortex
- paracortex
- medulla
describe the lymph node cortex
- cortex = B lymphocytes
- dendritic reticular cells in germinal centers bind Igs and present antigens to B/T lymphocytes
