Lymphoid Tissue Flashcards
primary lymphoid organs
thymus and (red) bone marrow produce lymphocytes
secondary lymphoid organs
tonsils, lymph nodes (cervical, axillary, inguinal) spleen, MALT in small intestine
diffuse, lymphocytes are activated in response to Ag
Diffuse non-encapsulated LT
Reticular CT houses lymphocytes deep to epithelium
GI tract, Genitourinary tract, respiratory passages
nodular non-encapuslated LT
primary nodule/follicle consists of only small
lymphocytes - inactive or naive, lack a germinal center
secondary nodule == activated version thats been presented - possesses germinal center - outer ring, mantle
germinal center
B cells localized to follicle, germinal center and mantle
T cells surround follicle
Tonsils: aggregate non-encapsulated LT
tonsils are large, irregular masses of LT - help protect against inhaled/ingested substances - can be partially encapsulated
palatine tonsil
stratified squamous epithelium
10-20 tonsillar crypts == deep invaginations
dense CT acts as partial capsule
contains germinal centers
pharyngeal tonsil
pseudostratified columnar ciliated
single structure at the posterior wall of nasopharynx
thin underlying capsule
shallow infoldings, no crypts
lingual tonsil
stratified squamous
base of tongue
germinal centers
lacks a capsule but has crypts
MALT: non-encapsulated aggregate nodular LT
single/clusters of nodules
found in GI tract (GALT), respiratory airways (BALT) and urinary tract
lumen open to external environment
GALT: aggregate nodular tissue
simple columnar with goblet cells gut associated lymphoid tissue - prominent in small intestine (ileum**) peyer patches characterized by an abundance of villi single or clusters of nodules
veriform appendix: aggregate nodule
simple columnar with goblet cells
short, small projection off cecum
filled with LT
crypts - no villi, no capsule
thymus
in mediastinum
lymphoblasts invade and proliferate here
lymphocytes mature into T cells
characterized by involution (decreased activity as its replaced with adipose tissue)
capsulated - lobulated by septa
contains T lymphocytes, macrophages, thymic epithelial cells
thymic epithelial cells
subcapsular (squamous) - form cortical compartment - some of these will form a sheet to separate cortex and medulla
cortical (stellate) - prdocue cytoreticulum of keratin and desmosomes - secrete cytokines for T cell development
blood-thymus barrier
in cortex - formed by TECs, basal lamina, endothelial cells
macrophages prevent circulating Ag from reacting with developing T cells
thymic medulla
houses mature T cells migrating from cortex
T cells enter postcapillary venules to exit thymus
Hassall’s corpuscles
thymic - associated with medulla
closely packed whorls of TECs
secrete cytokines that aid in maturation of T cells
thymus compartments
cortex - contain T lymphocytes - subscapular TECs, cortical TECs, macrophages
at side proximal to postcapillary venule, single-positive T cells, followed by double positive and double-negative most distal
medulla - mature T cells - medullary TECs, hassall’s corpuscles, DC, Mphage
spleen
initiates immune response to blood Ag
reservoir for platelets
hematopoiesis/RBC recycling center
spleen structure
surrounded by CT capsule - trebeculae incompletely separate
parenchyma with reticular fibers of white and red pulp
single splenic artery and vein
white pulp of spleen
T and B cells, macrophages
lymphoid nodules - central arteriole
PALS - periarteriolar lymphoid sheaths - T cells surrounding arteriole
MnA - corona/mantle - small lymphocytes surrounding GC
MgZ- marginal zone - blend of lymphocytes
red pulp of spleen
contains RBCs, platelets, macrophages, plasma cells
blood filtration/RBC turnover
splenic sinusoids and splenic cords
splenic cords
reticular tissue rich in macrophages and lymphocytes
stave cells
line sinusoids of red pulp
specialized endothelial cells that separate healthy and unhealthy RBCs
splenic blood flow
splenic artery -> trabecular arteries -> central arteriole/ PALS -> white pulp -> penicillar arteries -> splenic sinuses -> splenic cords
lymph
clear, yellow fluid comprised of interstitial fluid, solutes, foreign material
lymph nodes
encapsulated- positioned along lymphatic vessels
400-450
filter lymph - remove debris, facilitate Ab production, produce lymphocytes
