Lymphoid Organs Flashcards
what are dense lymphoid tissues and give examples
organized into discreet structures or organs
-lymph nodes, spleen, thymus, tonsil
what are diffuse lymphoid tissues
located throughout the body, associated with mucous membranes
what lymphoid structures are associated with mucous membranes
respiratory and digestive tracts such as MALT
what do diffuse and dense lymphoid tissue both contain
large numbers of lymphocytes
what happens in primary lymphoid tissues
lymphoid tissue where B and T cells acquire surface receptors
what are primary lymphoid tissues for B cells? T cells?
-B cells: bone marrow
-T cells: thymus
what happens in secondary lymphoid tissues
mature B and T cells migrate to these tissues
what are lymphomas
malignant tumors of immune system when they involve solid organs
what are leukemias
malignant tumors of the immune system when they involve blood
what are lymphatic vessels
network of blind-ended vessels in connective tissue
what are the functions of lymphatic vessels
-provide a route which allows cells and large molecules in ECS to re-enter blood stream
- assist circulation of lymphocytes, concentrate antigen for elimination within lymph nodes
what are lymph nodes
encapsulated aggregates of lymphocytes and lymphoid tissue, distributed throughout the body
what are lymph nodes arranged in
chains or clusters along vessels of lymphatic origin
what are examples of lymph nodes
submandibular, cervical, axillary, femoral, popliteal, hilar lymph node
what are the 4 functions of lymph node
-non-specific filtering of particulate matter and microorganisms from lymph
- interaction of circulating lymphocytes with antigen in lymph
- aggregation, activation and proliferation of B-cells with subsequent antibody production
- aggregation and proliferation of T cells and induction of cytotoxic immunity
what are lymphoid cells
lymphocytes of all types, derived from bone marrow; enter node via bloodstream
what are immune accessory cells and give examples
antigen presenting cells (macrophages, B cells and T cells, originate in bone marrow)
what are follicular dendritic cells and where are they found
macrophages at periphery of germinal centers; antigen presenting cells
- found in one location in the lymph node
what are tingible body macrophages and where are they found
primarily found in germinal centers; possess numerous phagocytic vesicles
what are stromal cells
fibroblasts and reticular cells
what are reticular cells
fibroblast like cells with phagocytic capability
what forms the connective tissue skeleton of lymph nodes
stromal cells and extracellular products such as collagen and reticular fibers
does the lymph node have a cortex and a medulla
yes
describe the outer capsule of the lymph node
fibrous capsule of dense irregular CT
describe the outer cortex of the lymph node
dense outer cellular cortex, containing B cells, T cells, and plasma cells
describe the inner medulla of the lymph node
less cellular inner medulla containing B cells
what are medullary cords
extensions of cortical tissue into medulla
what are medullary sinuses
broad lymphatic channels that separate medullary cords
what are trabeculae and where are they located and what is their function
-very thin and collagenous
- interspersed throughout cortex and medulla
- provide support
where do vessels enter and exit the lymph node
the hilus
what does the hilus look like in a microscope slide
indented area at the end of lymph node
how do B cells and T cells leave the bloodstream and enter the node
diapedesis
what is diapedesis facilitated by
complementary adhesion molecules (addressins) present on endothelial cells and lymphocytes
what do WBCs migrate across in diapedesis
walls of specialized post capillary venules called high endothelial venules
what are high endothelial venules lined by and where are they located
lined by cuboidal to columnar endothelium, located in deep inner cortex of node at corticomedullary junction called the paracortical zone
what is the subcapsular sinus
space beneath the capsule in lymph node where numerous afferent lymph vessels drain into
describe the endothelium of the subcapsular sinus
on the side adjacent to capsule continuous (prevents leakage) but discontinuous on side adjacent to parenchyma
what are lymphatic sinuses filled with
reticular fibers and macrophage processes
what are the sinuses in the outer cortex of lymph nodes
-cortical sinuses
-trabecular sinuses
-peritrabecular sinuses
what do sinuses in the outer cortex drain into
medullary sinuses
describe medullary sinuses and what do they contain
-broad, lymphatic channels in inner, less cellular medulla
-contain lymphocytes, plasma cells and macrophages
where do medullary sinuses converge
hilus
where does lymph drain from the hilus
a single efferent lymph vessel that eventually returns to bloodstream via thoracic duct or R lymphatic duct
what is lymphatic drainage to regional lymph nodes important in
metastasis of tumor cells
what is the cortex of the lymph node mainly made of
B cells
is the cortex of the lymph node uniform
no some areas are more dense than others
what are lymphoid follicles and where are they located
within the cortex of the lymph node they are densely packed and highly cellular
which follicles contain a germinal center
secondary follicles
what do germinal centers in follicles indicate
the node is responding to anitgens
how do lymphocytes respond to antigen
by increased antibody production via clonal expansion
what are secondary hemopoiesis and what do they contain
sites of B cell proliferation, contain lymphoblasts, macrophages and immature B cells and T cells
what is the cause of lymph node enlargement and swollen glands
proliferation of lymphocytes
what is the mantle zone
-darker staining rim surrounding germinal center
-region of antigen presentation
what is the thymus and where is it located
lobular, lymphatic organ located in mediastinum
what is the thymus embryologically derived from
epithelial outgrowth of 3rd pharyngeal pouch
what is the thymus important for in fetal development
important hematopoietic organ
what is the thymus similar in appearance to and with what exceptions
the lymph node, but lacks lymphoid follicles and medulla lacks medullary cords and sinuses
what is the capsule in the thymus made of
dense, irregular connective tissue
what divides the thymus into lobules
interlobular septa or trabeculae
what are the functions of the thymus
-production of mature, immunocompetent Th and Tc cells
-clonal proliferation of Tc cells
-clonal deletion of self antibodies
-secretion of hormones regulating t-cell development and maturation
what might the failure of clonal deletion result in
autoimmune diseases
what does clonal deletion of self antibodies do
develop immunologic self tolerance
what do t-cells express as they mature
-antigen specific t-cell receptors
- CD surface markers
- Class I and II HLA surface markers
what does the cortex in the thymus mainly contain
T cells
describe the cortex of the thymus and what it contains
highly cellular packed with lymphocytes, mostly T cells and macrophages
what follicles are in the cortex of the thymus
primary follicles only
does the cortex of the thymus have clonal expansion of t-cells
limited
describe the medulla of the thymus and what it contains
less cellular contains mostly B cells, plasma cells and macrophages
what are nurse cells and what do they do
epithelial cells within thymus (cortex and medulla),
provide nurse function and structural support
-secretes hormones that attract regulate and promote t- cell proliferation and differentiation into Tc, Ts, and Th cells
what do nurse cells secrete
thymotaxin, thymosin, thymopoietin
what are hassal’s corpuscles
eosinophilic, lamellated structures within medulla and cortex that represent degenerate reticular and epithelial nurse cells
what is a key identifier of the thymus
hassal’s corpuscles
describe the thymus at puberty and in adults
degenerates at puberty and vestigial in adults
what is thymic involution
thymus undergoes fatty infiltration and lymphatic depletion
what does the inner surface of the capsule of the thymus contain
continuous epithelium to isolate thymus
why are there no afferent lymph vessels to the thymys
because t-cells are not fully differentiated
what type of lymph vessels are present in the thymus and what do they do
only efferent to drain lymph
what is the blood thymus barrier
connective tissue sheath that surrounds thymic blood vessels
what does the blood thymus barrier do
forms continuous antigenic barrier around endothelium and basement membrane of blood vessels that isolates thymus from immune system
what makes up the blood thymus barrier
epithelioreticular cells, reticular fibers, fibroblasts, macrophages, plasma cells
what is the largest lymphoid organ in the body
the spleen
what are the immune functions of the spleen
-B and T cell replication, manufacturing of antibodies, antigen removal
-removes particulate matter and aged or defective RBC’s from circulation via phagocytosis
- recycles iron from hemoglobin
-hemopoiesis in fetus
what takes over the function of the spleen if it is removed
liver and bone marrow
describe the capsule of the spleen
dense, fibro elastic outer capsule contains smooth muscle cells and acts as a resevoir for RBCs
what are the trabeculae of the spleen made of, where are they located and what do they contain
-thick bands of dense CT
- extend in body of spleen
-contain trabecular arteries and veins
does the spleen have a cortex or medulla
no neither
what is the bulk of the spleen composed of
spongy matrix of red pulp
what is in the red pulp of the spleen
pulp cords and sinusoids
what do sinusoids contain
mostly blood
what do pulp cords contain
large numbers of macrophages and lymphocytes
are pulp cords or sinusoids more cellular
pulp cords
what are pulp cords supported by
connective tissue skeleton of reticular cells and reticular fibers
what does white pulp contain in spleen
large number of WBCs
- follicular areas that may or may not have germinal centers
what do follicular areas in white pulp contain
primarily B cells
what is in the middle of white pulp
central artery
what is the white pulp surrounded by
a thin basophilic mantle zone surrounded by paler marginal zone
what is the function of white pulp and what cells does it contain
antigen presentation, phagocytosis; contains large numbers of macrophages, plasma cells and T helper cells
what are splenic nodules
enlarged germinal centers visible to naked eye
what forms periarteriolar lymphatic sheaths (PALS)
T cells that surround the central artery
do PALS have germinal centers
no
what do PALS require for ID
immunohistochemical staining
what is another term for PALS
primary follicles in white pulp
how do branches of the splenic artery enter the spleen
within trabeculae via trabecular arteries
what do trabecular arteries branch and form in the spleen
central artery to white pulp
where do central arteries run
into red pulp where they branch into perpendicular penicillar arteries
what do penicillar arteries branch into in the spleen
arterioles and terminate into 2-3 sheathed capillaries
what do blind ending capillaries lack
endothelial lining
what surrounds blind ending capillaries
macrophages
what do sheathed capillaries form in the spleen
a non-continuous perivascular sheath or cuff that acts as part of filtering mechanism, active in phagocytosis
how do blood cells leave sheathed capillaries in the spleen
diapedesis
where do blood cells enter sinuses in the spleen
in red pulp
what are stave cells
endothelial cells that line sinusoids
what do endothelial slits between stave cells allow
free passage of blood cells
how does blood drain out of spleen
trabecular veins -> splenic vein
what are palatine tonsils and where are they located
paired structures located at the junction of oral and pharyngeal cavities within tonsillar crypts between anterior and posterior tonsillar pillars called palatoglossal and palatopharyngeal arches
where are lingual tonsils located and what are they associated with
at the base of tongue and pharyngeal tonsils in nasopharynx, associated with eustacian tubes
what are adenoids
pharyngeal tonsils
what makes up Waldeyer’s ring
palatal, lingual and pharyngeal tonsils
what makes up NALT
palatal and pharyngeal tonsils
describe the capsule of palatine tonsils
unencapsulated but supported by a cup shaped collagenous hemi capsule
do the palatine tonsils have cortex and medulla
no
describe the follicles in palatine tonsils
scattered throughout parenchyma, may or may not include germinal centers
what is the luminal surface of palatine tonsils and lingual tonsils covered by
stratified squamous nonkeratinized epithelium
what does the epithelium in palatine tonsils form
blind-ended tonsilar crypts
how do you identify lymph node
cortex with primary and secondary follicles and medulla with medullary cords and sinusoids
how do you identify thymus
mostly T cells; Hassal’s corpuscles; cortex and medulla present
how do you identify the spleen
robust capsule and trabeculae, no cortex and medulla, red and white pulp instead
how do you identify the palatine tonsil
hemicapsule and skin-like epithelium with crypts, no cortex and medulla
describe the appendix
blind-ended sac, vestigial cecum
what happens to the appendix in adults and what does it contain
atrophies, contains mostly B bells
what is the appendix used for in herbivores
important digestive organ in herbivores used for bacterial fermentation
descirbe the different components of MALT
in gut = GALT
in respiratory tract = BALT
in pharynx = NALT
what is MALT
-mucosa associated lymphoid tissue
-diffuse, unencapsulated lymphoid aggregates associated with mucosal surfaces
where is MALT located
subepithelial connective tissue of lamina propria
what does MALT mainly contain
B cells
what does MALT produce and where is it secreted
IgA that are secreted onto the mucosal surface
describe the follicles in MALT
may or may not contain germinal centers
what is the function of MALT
samples antigenic material
produces lymphoblasts
secretes antibodies
what does MALT in gut contain and where are they located
specialized M-cells- squamoid enterocytes
- located in surface epithelium with microfolds on surface
how does MALT participate in antigen sampling
transfers antigen from gut lumen into lymphoid follicles
when is MALT formed
during fetal development
when is MALT distribution at maximum
in childhood, progressively atrophies with age
what are peyers patches and where are they most common and least common
special type of MALT scattered throughout small intestine
- most common in ileum, least in duodenum
where do peyers patches project
into lumen of gut in dome areas with cuboidal mucosa
what do peyers patches contain
M-cells, B cells, and T cells
what are peyers patches histologically similar to
MALT
do peyers patches produce large amounts of IgA
no
describe the presence of germinal centers in peyers patches
frequent; associated with foci of B cells
