Lymphoid Tissue Part 1 Flashcards
morphology of lymphoid tissue (2)
dense
diffuse
dense
organized into discreet structures or organs (e.g., lnn, spleen, thymus, tonsil)
diffuse
located throughout body, associated with mucous membranes
diffuse contains large numbers of
lymphocytes
diffuse is common in (2)
respiratory and digestive tracts such as MALT
primary lymphoid tissue
lymphoid tissue where b-& t-cells acquire surface receptors
bone marrow with - cells and thymus with - cells
b
t
Mature b-& t-cells 2’ migrate to all other lymphoid tissue, referred to as
2’ lymphoid tissue
Malignant tumors of immune system referred to as — when they involve solid organs & — when they involve blood
lymphomas
leukemias
lymphatic vessels are a network of
blind ended vessels in connective tissue
lymphatic vessels provide a route which allows
cells and large molecules in the ECS to reenter the bloodstream
lymphatic vessels assist circulation of
lymphocytes
lymphatic vessels concentrate – for elimination within lymph nodes
antigens
Lymph nodes
encapsulated aggregates of lymphocytes & lymphoid tissue, distributed throughout body
how is dense lymphatic tissue arranged?
in chains or clusters along vessels of lymphatic origin
examples of dense lymphatic tissue arranged in chains or clusters along vessels of lymphatic origin (6)
submandibular cervical axillary femoral popliteal hailer lnn
4 functions of lnn
- Non-specific filtering of particulate matter & microorganisms from lymph
- Interaction of circulating lymphocytes with Ag in lymph
- Aggregation, activation, & proliferation of b-cells with subsequent Ab production
- Aggregation & proliferation of t-cells & induction of cytotoxic immunity
lymphoid cell
lymphocytes of all types, derived from bone marrow
lymphoid cells enter node via
bloodstream
immune accessory cell
Ag presenting cells (macrophages, b-& t-cells; originate in
bone marrow)
follicular dendritic cells
macrophage at periphery of germinal centers; Ag-
presenting cells
Tingible body macrophage
1’ found in germinal centers; possess numerous
phagocytic vessicles
stromal cells
fibroblasts & reticular cells (fibroblast-like cells with
phagocyticcapability)
Stromal cells & extracellular products (collagen & reticular fibers), form
connective tissue skeleton of lnn
lymph node outer, fibrous capsule of
dense, irregular connective tissue
Grossly, lnn layers (2)
dense, outer, cellular cortex (contains b-cells, t-cells, & plasma cells) & less cellular inner medulla
Extensions of cortical tissue into medulla called
medullary cords
Sep by broad lymphatic channels, — —
medullary sinuses
Interspersed throughout cortex & medulla are very thin, collagenous —
trabeculae
Blood vessels enter & leave lnn at —
hilus
b-& t-cells leave bloodstream & enter node via
diapedesis
diapedesis facilitated by
complementary adhesion
molecules (=addressins)
complementary adhesion
molecules (=addressins) are present on both
endothelial cells & lymphocytes
Migrate across walls of specialized
post-capillary
venules (= high endothelial venules)
Migrate across walls of specialized post-capillary
venules(= high endothelial venules) are lined by
cuboidal to columnar endothelium
high endothelial venules are located in
paracortical zone
paracortical zone
deep,
inner cortex of node at corticomedullary junction
Corticalor subcapsular sinus
space beneath capsule where
numerous afferent lymphvessels
drain into
Endothelium of sinus on side
adjacent to capsule —, but
— on side adjacent to
parenchyma
continuous
(prevents leakage)
discontinuous
Lymphatic sinuses are not —
spaces like blood sinuses
open
what are lymphatic sinuses filled with?
reticular fibers & macrophage
processes
Sinuses in outer cortex (3)
cortical sinuses, trabecular sinuses, or peritrabecular sinuses
Medullary sinuses
broad, lymphatic channels in inner, less cellular
medulla
what do medullary sinuses contain? (3)
contain lymphocytes, plasma cells, macrophages
where do medullary sinuses converge
on hilus
Lymph drains from hilus of node via single,
efferent lymph vessel
Eventually returns to bloodstream via (2)
thoracic duct or R lymphatic duct
Lymphatic drainage to regional lnn important in
metastasis of tumor
cells
Within cortex are densely packed, highly cellular
lymphoid follicles
what do lymphoid follicles contain (2)
lymphatic nodules, 1’ follicles
May contain paler, less dense
germinal centers
if germinal centers are present, follicle then referred to as
2’ follicle
indicate node is responding to
Ag
Lymphocytes respond to Ag by increase Ab production via
clonal expansion
Sites of b-cell proliferation, (2’ hemopoiesis), contain (3)
lymphoblasts, Mφ, & immature b-& t-cells
Proliferation of lymphocytes results in (2)
lnn enlargement & “swollen glands”
Darker staining rim surrounding germinal center called
mantle zone
mantle zone
region of Ag presentation
thymus
Lobular, lymphatic organ located in
mediastinum
thymus is embryologically derived from
epithelial
outgrowth of 3rd pharyngeal pouch
the thymus is an important hematopoietic organ during
fetal development
Similar in appearance to lnn, but lacks
lymphoid follicles
medulla lacks
2
medullary cords & sinuses
thymus has a thin — of
capsule
dense, irregular
connective tissue
Slender (2) divide thymus into lobules
interlobular septa or
trabeculae
functions of the thymus (4)
- Production of mature, immunocompetent Th & Tc cells
- Clonal proliferation of Tc cells
- Clonal deletion of self-Ab’s
- Secretion of hormones regulating t-cell development & maturation
Clonal deletion of self-Ab’s results in development of
immunologic self-tolerance
Failure of clonal deletion may result in
autoimmune diseases
As t-cells mature, they express (3)`
- Ag specific t-cell receptors
- CD (cluster of differentiation) surface markers
- Class I & II HLA (human leukocyte Ag) surface markers
Thymus has highly cellular
cortex packed with
(3)
lymphocytes, mostly t-cells &
macrophages
what are absent I the thymus?
2’ follicles
thymus has limited local
clonal expansion of T cells
Less cellular, central medulla contains mostly (3)
b-cells, plasma cells & macrophages
Nurse cells
epithelial cells within thymus, provide nurse function & structural support
what do nurse cells secrete?
various hormones (thymotaxin, thymosin, & thymopoietin)
nurse cell secretion of hormones (thymotaxin, thymosin, & thymopoietin)—attract, regulate & promote t-cell proliferation & differentiation into
Tc, Ts & Th cells
Thymic or Hassal’s corpuscles are
eosinophilic, lamellated structures within both medulla & cortex, represent degenerate reticular & epithelial nurse cells
when does the thymus degenerate?
puberty
thymus is — in adults
vestigial
the thymus undergoes
fatty infiltration & lymphatic depletion (thymic involution)
inner surface of capsule has continuous epithelium to
isolate thymus
Because t-cells not fully differentiated, no — lymph vessels to thymus, only —, for lymph drainage
afferent
efferent
Thymic blood vessels also surrounded by connective tissue sheath called
blood-thymus barrier
blood-thymus barrier forms
continuous antigenic barrier
blood thymus barrier isolates
thymus from immune system
the blood thymus barrier consists of (4)
epithelioreticular cells, reticular fibers, fibroblasts, macrophages, plasma cells,
blood thymus barrier surrounds (2)
endothelium & basement membrane of blood vessels
