Lymphatic System Histology Flashcards
What tissue are all lymphocytes derived from?
stem cells in the bone marrow
Where do T lymphocytes undergo initial differentiation?
thymus
Where do B lymphocytes undergo initial differentiation?
bone marrow microenvironment
central or primary organs
where lymphocytes independently of antigen, proliferate and idfferentiate into naive or virgin cells
organs include thymus and bone marrow
peripheral or secondary organs
the site where naive or virgin cells migrate to to differentiatie
where lymphocytes interact with antigen, transform into large proliferating cells and mature into antigen specific cells
main organs are lymph nodes, spleen, MALT tissue
thymus
bilobed, pyramidal shpaed, lobulated organ
site of T cell differentiation and proliferation
at puberty it undergoes involution, though some remnants may remain
specialized epithelial cells secrete cytokines to help the thymocytes
bone marrow
T cells originate here, but this is the primary site of B cell differentiation to naive B cells
hematogone cells
immature B cells in the bone marrow
undergo various stages of maturation that can be detected by antigen profiles
major compartments of the lymph node
follicles
marginal zone
paracortical region
medulla
sinuses
What are the two major components that make up the circulation of the lymph?
1) the blood vascular component, which consists of an afferent arteriole and an efferent venule that enter and leave via the hilus
2) the lymphatic component which consists of the cortical afferent lymphatics, the subcapsular sinus, the trabecular sunuses, medullary sinuses, hilus, and efferent lymphatics
four components of MALT tissue in the GI tract
1) the unencapsulated lymphoid tissue (such as Peyer’s patches)
2) the lamina propria lymphocytes, plasma cells, and macrophages
3) the mucosal intra-epithelial lymphocytes
4) the mesenteric lymph nodes
What encapsulates the spleen, and what is it made up of?
encapsulated by dense connective tissue, which sends trabeculae into the pulp
consists of red and white pulp
white pulp
composed of the PALS (periarteriolar lymphoid sheath - T cell rich area) and nodules of cells containing germinal centers (B cell rich areas)
wide marginal zones where marginal lymphocytes are inclose proximity to the blood traversing through the spleen
red pulp
composed of splenic sinuses and cords, which acts as a filter and removal site of damaged red cells
also contains macrophages important in removing debris and foreign material as well as retrieving iron from removed red cells
chyle
a milky fluid composed of emulsified fats and lymph
joins the circulatory system at the thoracic duct
Describe the process of lymphatic development
develop from lateral plate mesoderm -> form endothelial-lined sacs -> endothelial sprouts -> branch and develop lumens -> peripheral lymphatics
developmentment of lymph nodes
primary lymph nodes develop after the lymphatic system is established
8-11 weeks - plexus of lymphatics with mesenchymal tissue
13 weeks - development of sinuses
fetus - primarily of sinuses and a capsule iwth an increasing number of lymphocytes
follicles do not appear until after birth
characteristics of lymph vessels
lined by lymphatic endothelium, very little baesment membrane
thin muscular media if diameter is >0.2mm
thoracic duct has 3 layers of smooth muscle
can be filled with lymphocytes
D2-40
marker expressed by lymphatic endothelium
CD34
vascular endothelial marker, usually not expressed on lymphatic vessels
Describe the pressure gradient from vessels of largest pressure to vessels of lowest pressure.
blood capillaries -> interstitial fluid -> small lymphatics -> large lymphatics -> lymphatic ducts -> large veins
lacteals
blind-ended lymphatic channels in the small intestine
located beneath epithelium, takes up the free faty acids and emulsified fats
areas of low pressure
Describe the movement of lymph through the nodes.
enters via afferent vessels -> subcapsular sinuses -> intermediate sinuses -> lymphatic labyrinth -> medullary sinuses -> exits via efferent vessels
Which two structures in a lymph node are lined by lymphatic endothelial cells and macrophages?
intermediate and medullary sinuses
Describe lymphocyte movement thorugh the lymph node.
enter via high endothelial venules -> traverse lymph node parenchyma -> lymphatic labyrinth -> medullary sinuses -> efferent vessels
TdT
found on immature lymphocytes, occasionally seen in myeloid cells
CD3
pan T cell markers
CD4
helper T cell marker
CD8
suppressor/cytotoxic T cell marker
PAX5
B cell marker (occurs before CD20)
CD20
B cell marker
kappa/gamma
immunoglobin light chains
CD68
macrophage marker
follicle of lymph node
mantle zone - naive cells meet antigen
germinal center - proliferating cells (centroblasts) differentiate into antigen-specific B cells
marginal zone of lymph node
memory B cells reside here
medulla of lymph node
B cell area, accumulation of plasma cells
paracortex
mainly T cell area, site of entrance of lymphoid cells and of accessory cells - T/B ce ll interaction
sinus of lymph nodes
macrophage area - “sieve” functions
functions of the spleen
filtration (debris, foreign material)
immune response
hematopoiesis
reserve of blood elements (dogs)
lamina propria
mostly T cells
CD4:CD8 = 4:1
plasmacells and preferentially IgA+
intraepithelial lymphocytes (IELs)
most are T cells
most are alpha or beta positive
m10-15% are gamma or delta positive
rarely CD56 positive
What is the main difference between mesenteric lymph nodes and regular lymph nodes?
the main difference is that the marginal zones are more prominent
Derscribe the MALT imprinting system.
