IHL I - Morphology and Function: Lymphoid Organs Flashcards
humoral immunity
B lymphocytes
produce and secrete antibodies
reticular cells
produce reticular fibers (type III)
cellular immunity
T lymphocytes
produce T cell receptors
immunoglobulin
antibody
highly specific
created by B lymphocytes
lymphocyte source?
hematopoietic stem cells
location of B lymphocytes
in bone marrow
location of T cells
thymus
location of progenitor cells for lymphocytes?
bone marrow
maturation occurs in primary lymphoid organs
-bone marrow and thymus
staining and lymphocytes?
need special staining
cannot distinguish lymphocytes without staining
immunoblast
B cell activated by antigen
goes on to proliferate (immunoblast)
-becomes plasma cells or memory cells
plasma cell
produces the antibodies
what do T cells produce?
specific T cell receptors
cell turnover of lymphocytes?
10’6 - 10’7 cells turned over daily
how many cells for each antigen?
20 cells in body for each specific antigen
**these are then activated and produced by the thousands
un-encapsulated lymphoid tissue
diffuse and nodular infiltrations
lymph nodule
collection of lymphocytes
germinal center
present in secondary lymph nodules
**primary has no germinal center
**secondary nodule has the germinal center
diffuse lymphoid infiltrations
unencapsulated collection of lymphocytes
peyer’s patch
collection of nodules in the intestine
tonsils
collections of lymphocytes in orpoharynx
in the tonsillar ring:
- palatine tonsils - pharyngeal tonsils - lingual tonsils
**partially capsulated
waldeyer’s ring
tonsillar ring
adenoids
pharyngeal tonsils
palatine tonsils
underlie stratified squamous non-keratinized cells
possess epithelial crypts
- deep chasms going down - bc lymphocytes have proliferated - have greater surface area
pharyngeal tonsils
adenoids
associated with the nose
less crypted
underlie resporatory epithlium
collagen type III (reticular fibers)
associated with the lymphoid tissue
lymphoid tonsils
underlie stratified squamous epithelial
no crypts
distinguish between palatine tonsils no glands
lymph nodes
encapsulated lymphoid tissue
hilum
singular entry of blood supply to an organ
lymph
excess intercellular fluid
can’t be absorbed into normal circulation
afferent lymphatics
toward the lymph node
-enter at the capsule
two divisions of the lymph node
cortex (outer) and medulla (inner)
subcapsular sinus
under the capsule of lymph node
where the afferent lymph dumps
trabecular sinuses
run along the trabeculae of lymph nodes
**mostly in cortex
medullary cords
lots of B lymphocytes and plasma cells
deep cortex
aka paracortex
area of cortical tissue that is not nodular in lymph node
lots of T lymphocytes
location of B lymphocytes in lymph node?
nodules
HEVs
high endothelial venules
in the deep cortex
where cells transit in and out of lymphatic tissues
-looser tight junctions
spleen function?
1 filters blood
2 generates antibodies (plasma cells)
3 salvage of iron from old RBCs (macrophage)
4 blood reservoir
5 erythropoiesis in fetus (3rd-4th month)
fibromuscular capsule
around the spleen
allow it to contract and squeeze out RBCs
splenic structure
fibro-muscular capsule
no afferent**
has hilus with splenic artery and vein and efferent lymphatic
red pulp
large concentration of RBCs
white pulp
large concentration of white blood cells
- *does have a nodular structure
- with a germinal center
PALs
peri-arteriolar lymphoid sheath
T cell sheath surrounds central arteries
three types of capillaries
continuous
fenestrated (little pores)
sinusoid - larger capillary
splenic circulation?
has open circulation and closed
capillaries dump into tissue
better filtration
pulp cords of billroth
splenic pulp cords
thymus
has cortex and medulla
**doesn’t have nodules
medulla is continuous with all other medulla in thymus
thymus cells?
prothymocytes - immature T lymphocyte
site of T cell maturation
thymic epithelial cells
differ from reticular cells
no fiber formation**
thymic circulation?
blood vessel enters and split at cortico-medullary junction
blood-thymus barrier
thymus is site “immune education”
-teaching them to not respond to self
blood thymus barrier keeps the antigens from reaching maturing T cells
formation of blood thymus barrier?
TECs and basal lamina (of endothelial)
HEVs in the thymus
so only mature T cells leave the thymus
hassals corpuscle
no real formalized function
often necrotic and calcified
produce TSLP (helps T cells mature - T regulatory cells)
only in the medulla
thymic involution
as we age, the thymus lymphocytes number decreases
space replace by fats
this is why the immune system weakens with age
thymus
- greatest relative size in infancy - greatest absolute size at puberty
CD44
prothrombocytes express this to home them to the thymus
interact with CCL21 an CCL25
then mature in the thymus
DN1
double negative
no CD4 or CD8 marker present
DN2
gain CD25
DN3
lose CD44
DN4
lose CD25
DP
become double positive when gain CD4 and CD8
**then lose one of these and become either CD4 or CD8 T cells
immune education
first branches in the cortex
the immature cells that bind to TECs are allowed to survive
-positive selection
move to the medulla (when are DP cells)
- encounter macrophages and dendritic cells - if they bind, will apoptose - negative selection
positive selection
in cortex
T lymphocytes that recognized the MCH of TECs will survive
other cells apoptose
negative selection
DP cells go to medulla
macrophages and dendritic cells bind to DP cells
-causes cells to die
HIV (AIDs)
infects and inactivates helper T cells
- binds CD4 at surface - renders individual immunocompromised
CD25
stays on T regulatory cells
-allow for inhibition of immune response
