Lymphoid Tissues Flashcards
lymphocytes include what main subtypes?
- T-cells
- B-cells
- NK cells
innate immunity
- definition
- which immune cells are a part of innate immunity?
- immunity that does not require exposure to an antigen
- includes
- NK cells
- phagocytes - neutrophils (granulocytes), monocytes / macrophages
adaptive immunity
- definition
- includes what immune cells?
- definition: specific, and develops after exposure to an antigen
- two types of adaptive immunity
- humoral:
- antibodies made by plasma cells (B-lymphocytes)
- cell-mediated:
- Tc cells
- NK cells (also innate)
- phagocytes - neutrophils, monocytes, macrophages (also innate)
- the other granulocytes
- humoral:
what are primary lymphatic organs?
- bone marrow
- thymus
bone marrow is what kind of tissue?
reticular connective tissue?
discuss the overall histological structure of bone marrow
- venous sinuses surrounded by hematopoietic cords supported by reticular fibers
- venous sinuses - come off nutrient arteries
-
hematopoietic cords - made of
- immune cells - precursors & mature
- adipocytes
- stromal cells: fibroblasts + macrophages
what cells make up the hemopoietic cords of bone marrow?
- immune cells - precursors & mature
- adipocytes
-
stromal cells:
- fibroblasts
- macrophages
what cell types comprise the “stromal cells” in hematopoietic cords? what is their role?
- fibroblasts
- macrophages
role to secrete factors to stimulate hematopoiesis (IL-II)
what forms of B-cells are found in the bone marrow?
- precursor cells
- mature cells
discuss what stages of B-cell development happen what what tissues
- precursors arise from bone marrow
- mature to → naïve B-cells in bone marrow
- differentiated into immuno-competent B-cells in secondary lymphoid organs (nodes, spleen, MASLT) after antigen exposure
thymus
- anatomy
- embryological origins
- found in the superior mediastinum (directly posterior to the manubrium)
- embryological origin
- endodermal origins - 3rd & 4th pharyngeal pouch
- bone marrow origins
- lymphocytes
- macrophages
what main cells comprise the thymus?
what are their roles?
- T-lymphocytes → mature into naïve T-cells OR
- epithelio-reticular cells - provide a supporting framework for developing T-cells
- macrophages → phagocytize T-cells that do not mature into T-cells
summarize the gross structure of the thymus
outer CT capsule that is divided into lobules by trabeculae
summarize the histological structure of the thymus
- each lobule is divided into cortex + medulla
-
cortex
- outer portion
- densely cellular - densely packed lymphocytes at their l_east mature phase_
-
medulla
- inner portion
- less cellular - contains mature T- cells
- contains Hassall’s corpuscles - concentrically arranged epithelio-reticular cells
-
cortex
what are the roles of macrophages in each of the the primary lymphoid tissues
- bone: secrete factors to induce hematopoiesis
- thymus: phagocytosis
- phagocytizes T-cell precursors that do not mature to naïve T-cells
- phagocytizes antigens attempting to cross from the cortical capillaries into the thymus cortex
discuss the movement of T-cells throughout their maturation
- least mature - in the cortex (outer thymus)
- most mature - in the medulla (inner thymus)
what are hassali’s corpuscles?
spheres made of concentrically arranged epithelioreticular cells that support the T-cells in the medulla of the thymus
what is the blood thymus barrier? what forms the blood thymus barrier?
a barrier surrounding cortical capillaries (capillaries in the cortex - outer, densely cellular layer) that prevents antigens from escaping capillaries & contacting immature T-cells. made of
what forms the blood-thymus barrier?
- continuous capillaries - endothelial cells joined by tight junction
- perivascular CT - CT that surrounds capillaries & is loaded with macrophages that phagocytize antigens trying to escape into cortex
- epithelioreticular cells - form occluding junctions around capillaries
what is the role of the perivascular CT in the blood-thymus barrier?
loaded with macrophages to phagocytize any antigens that attempt to leave cortex capillaries into cortex
discuss the phases of T-cell education. in which location does each stage occur?
in the cortex
- double negative stage (outer cortex)- no TCR, CD3, CD4 or CD8
-
double positive stage (inner cortex)
- cells have TCR, CD3, CD4, CD8
-
positive selection occurs during this stage: T-cells presented with MCH-I & MHC-II
- cells that bind → move to medulla
- cells that bind neither → eliminated
medulla:
-
single positive stage
- cells have either CD4 or CD8
- if they bound stronger to MHC-II: have CD4
- if they bound stronger to MHC-I: have CD8
- negative selection occurs during this phase: any T-cells that bind self-MHC are eliminated (prevents autoimmunity)
- cells have either CD4 or CD8
positive selection of T-cell education
- occurs where?
- to what cells?
- has what purpose?
- inner cortex of thymus
- occurs to cells in double positive phase (TCR, CD3, CD4, CD8
- purpose: T-cells presented with both MCH-I & MHC-II to ensure viability
- cells that bind → advance to medulla
- cells that bind neither → eliminated
negative selection of T-cell education
- occurs where?
- to what cells?
- has what purpose?
- medulla of thymus
- occurs to cells in single positive phase (are either CD4+ or CD8+)
- purpose: to prevent autoimmunity - any T-cells that bind self-MHC are eliminated
secondary lymphoid tissue
- has what purpose?
- includes what forms/locations?
- lymphocytes are introduced to antigen to become → immunocompetent
- includes
-
MALT
- diffuse lymphoid tissue
- lymphoid follicles
- aggregated lymphoid follicles
- tonsils
- spleen
-
MALT
what is MALT?
in what forms is MALT found?
-
mucosa associated lymphoid tissue: secondary lymphoid tissue that is typically found in the gut, respiratory tract, and GU tract
- forms
- diffuse lymphoid tissue
- lymphoid follicles
- aggregated lymphoid follicles
- forms
diffuse lymphoid tissue
- location
- structure
- made of what cell types?
MALT (secondary lymphoid tissue)
- found in gut, respiratory tract, GU tract
- structure - loosely arranged cells + no capsule
- cell types
- B-lymphocytes
- T-lymphocytes
lymphoid follicles
- location
- structure
- made of what cell types?
MALT (secondary lymphoid tissue)
- location: gut, respiratory tract, GU tract, + lymph nodes, tonsils, spleen
- structures: well defined spherical structures + no capsule
- cell types
- mostly B-lymphocytes (B-cells > T-cells)
- follicular dendritic cells
discuss the classifications of lymphoid follicles. what makes the classifications different?
MALT (secondary lymphoid tissues)
- primary follicles: contain only non-activated B-cells
- secondary follicles: non-activated B-cells + activated B-cells
-
germinal center: contains
- large, activated lymphocytes (B-cells) that are undergoing mitosis
- dendritic cells
- mantle
- small, lymphocytes (B-cells)
-
germinal center: contains
what are germinal centers? discuss their structure.
MALT (secondary lymphoid tissue)
- the inner portion of secondary lymphoid follicles. contains
- large, activated lymphocytes (B-cells) that are undergoing mitosis
- dendritic cells
aggregated lymphoid follicles
- are located where?
- structure?
- in the ileum + appendix
- lamina propria of vermiform appendix is heavily infiltrated with aggregated lymphoid follicles
what kind of secondary lymphoid tissue does the vermiform appendix contain?
aggregated lymphoid follicles - contained within the lamina propria
tonsils
- made of what lymphoid tissue
- location?
- made of lymphoid follicles (MALT, secondary lymphoid tissue)
- locations based on type
- palatine tonsils: post part of soft palate
- pharyngeal tonsils: post part of nasopharynx
- smaller tonsils -lingual (tongue), tubal (auditory tube)
palatine tonsils
- made of what type of lymphoid tissue?
- location
- describe their structure
- made primarily of lymphoid follicles (B-lymphocytes) + scattered throughout
- location: post part of soft palate
- structure:
- covered w/ non-keratinized stratified epithelium, that
- forms multiple tonsillar crypts: “dips” infiltrated with T-cells
- rich in lymphoid follicles (containing B-cells)
-
T-cell spaces:
- in between follicles
- rich
- T-cells
- high endothelial venules: lymphocytes enter blood stream
- covered w/ non-keratinized stratified epithelium, that
pharyngeal tonsil
- made of what type of lymphoid tissue?
- location
- describe their structure
- made primarily of lymphoid follicles (MALT, secondary lymphoid tissue)
- located - post part of nasopharynx
- lined with ciliated pseudostratified columnar
small tonsils
- made of what type of lymphoid tissue?
- location?
- made primarily of lymphoid follicles
- location
- lingual - tongue
- tubal - auditory tube
palatine tonsils are covered with what type of epithelium? what are its epithelium?
- covered w/ non-keratinized stratified epithelium, that
- forms multiple tonsillar crypts: “dips” infiltrated with T-cells
what are the locations of the T-cells in the palatine tonsils?
- in the crypts of the NKSS epithelium
- in the T-cell spaces in between follicles (B-cells)
where are high endothelial venules found in the tonsils?
what is the purpose?
- in the T-cell space (space in between the lymphoid follicles) of the palatine tonsils
- role is to allow T-cells to move into blood
spleen
- general role
- general structure
- filters blood and exposes lymphocytes to blood born antigens (type of MALT, secondary lymphoid tissue)
- general structure
-
capsule: rich in myofibroblasts + forms trabeculae between parenchyma
- parenchyma
- white pulp: PALS (T-cells) + lymphoid follicles (B-cells)
- red pulps: RBCS + splenic cords + splenic sinuses
- parenchyma
-
capsule: rich in myofibroblasts + forms trabeculae between parenchyma
what is are the roles & features of the splenic capsule?
- contains myofibroblasts: allows the organ to contract & eject blood
- projects into parenchyma with trabeculae
- trabeculae contains splenic artery branches
describe the structure of the white pulp
= spleen parenchyma
- contains large number of WBCs
-
periarterial lymphatic sheath
- most T-cells
- surrounds central artery
-
lymphoid follicles
- mostly B-cells
- attach to the PALS
-
periarterial lymphatic sheath
describe the structure of the red pulp
- contains RBCS + splenic sinuses + splenic cords
-
splenic cords: made of
- dense meshwork of reticular fibers
- macrophages that phagocytize damage red blood cells
-
splenic sinuses:
- have rod shaped endothelial cells
- receive blood that has been filtered through the cords
-
splenic cords: made of
splenic cords - location / structure / role
- red pulp parenchyma)
- made of
- dense meshwork of reticular fibers
-
macrophages
- damage red blood cells
- role: to filter blood
splenic sinuses - location / structure / role
- red pulp (parenchyma)
- have rod shaped endothelial cells
- role; receive blood that has been filtered from the cords
discuss the arteries of the spleen
- what are the name of the branches & where in the spleen are they found?
- splenic artery: moves through capsule, and becomes
- trabecular arteries: travel through trabeculae (formed by capsule), then become
- central artery: in the PALS of white pulp (surrounded by T-cells), then exits to become
- penicillar arteries: in the red pulps, becomes
- sheathed capillaries: surrounded by a sheath of macrophages, which empty blood into
-
open circulation
- splenic cords → splenic sinuses
what splenic arteries are NOT surrounded by lymphocytes?
trabecular arteries (in the trabeculae from the capsule) preceding the central artery
which splenic arteries are found it the white pulp?
the central artery (surrounded by PALS aka T-cells)
which splenic arteries are found in the red pulp?
penicillar arteries
which splenic arteries are surrounded by a sheath of macrophages?
where are they found?
what did they branch off of?
what do they become?
-
sheath capillaries
- found in red pulp
- came off penciller arteries
- dump blood into “open circulation”
- splenic cords (also rich in macrophages) → splenic sinuses
after reaching the splenic sinuses, how does blood travel?
collected into pulps veins (parenchyma) → trabecular veins (capsule trabeculae) → splenic vein
list the general functions of the spleen
- immune functions
- blood maintainence / hematopoiesis
what are the immune functions of the spleen?
- antigen presentation to B-cells and T-cell
- production of antibodies
- removal of encapsulated bacteria by macrophages
what are the blood maintenance / hematopoietic functions of the spleen
- removal of damaged / abnormal RBCs & platelets
