Lymphatic tissue and organs Flashcards
What are the primary lymphatic tissues?
- Bone marrow2. Thymus
What occurs at primary lymphatic tissues?
Development and maturation of lymphocytes into immunocompetent cells
What are the secondary lymphatic tissues?
- Lymph nodes2. Mucosa-associated lymphatic tissue (MALT)3. Spleen
What occurs at secondary lymphatic tissues?
Formation of immunological defense against antigens or pathogens; confrontation with antigens or pathogens
MALT consists of what other lymphatic regions?
- GALT (gut-associated lymphatic tissue)2. BALT (bronchus-associated lymphatic tissue)3. GU tract4. Tonsils
In which layer of the epithelium is GALT located?
Lamina propria
What are characteristics of diffuse lymphatic tissue (MALT)?
- Not sharply delineated2. Part of some other organ, often sprinkled through lamina propria3. Reticular fibers provide framework for cell suspension
Which cells are found in diffuse lypmhatic tissue?
Lymphocytes, monocytes, macrophages, plasma cells
What are characteristics of lymphatic nodules (follicles)?
- Non-encapsulated, spherical, dense aggregations of lymphocytes with SOME organization2. May be primary or secondary3. May be solitary or aggregate structures
What are characteristics of primary lymphatic nodules?
Appear homogeneous throughout, have mostly small lymphocytes
What are characteristics of secondary lymphatic nodules?
Have two zones - corona (mantle) zone and germinal center
What is the mantle zone?
The outer, dark-staining zone containing mature (small) lymphocytes in a secondary lymphatic nodule
What is the germinal center?
The inner, light-staining zone containing immature (medium and large) lymphocytes in a secondary lymphatic nodule
What happens to a secondary lymphatic nodule when an antigen is encountered?
Germinal center starts to swell
Are solitary lymphatic nodules temporary or permanent?
Temporary - may appear and reappear at a particular site
Are lymphatic aggregates temporary or permanent?
Permanent
What are examples of lymphatic aggregates?
- Peyer’s patches in the ileum2. Lymphatic tissue in the appendix (lamina propria and submucosa)3. BALT in respiratory tract4. Lymphatic nodules in tonsils, lymph nodes, spleen
The tonsils have what kind of lymphatic tissue organization?
Aggregations of lymphatic nodules
What type of lymphocyte predominates in the tonsils?
B lymphocyte
What kind of epithelium covers the pharyngeal tonsils?
Pseudostratified columnar epithelium with cilia
Do the pharyngeal tonsils have crypts?
No
What do the pharyngeal tonsils have instead of crypts?
Pleats
What kind of epithelium covers the palatine tonsils?
Stratified squamous nonkeratinized infiltrated by B cells
Do the palatine tonsils have crypts?
Yes
Where are B cells produced in the palatine tonsils?
Germinal centers found in the nodules
What kind of epithelium covers the lingual tonsils?
Stratified squamous nonkeratinized
Do the lingual tonsils have crypts?
Yes
What are lymph node trabeculae?
CT septa that extend from capsule into lymph node carrying vessels and nerves
What are characteristics of subcapsular sinuses?
Deep to CT capsule, drain into trabecular sinuses
What are characteristics of trabecular sinuses?
- Separate nodules from trabeculae2. Drain into medullary sinuses3. Lined by endothelial cells - allow lymphatic cells to enter or exit4. Contain reticular cells
Which lymph sinuses are lined by macrophages?
All sinuses
What are the cells of the reticular meshwork?
- Reticular cells2. Dendritic cells3. Macrophages4. Follicular dendritic cells
What is the reticular tissue?
Consists of reticular cells and reticular fibers which form a fine 3D meshwork that suspends the cells and sinuses and supports lymph node contents
What is the function of the reticular cells?
Synthesize and secrete type III collagen. Cytoplasmic processes wrap around reticular fibers to isolate them from lymphatic tissue parenchyma
What is the function of dendritic cells in a lymph node?
Ag presentation
What is the function of macrophages in lymph nodes?
Ag presentation, phagocytic
What is the function of follicular dendritic cells in lymph nodes?
Bind Ag-Ab complexes
What comprises the parenchyma of a lymph node?
- Cortex2. Paracortex3. Medulla
What type of lymphatic tissue organization is found in the cortex of the lymph node?
Nodules
What type of lymphocyte is found in the cortex of the lymph node?
B cell
What type of cells are found in the germinal center of the lymph node nodules?
Dendritic reticular cells
What type of lymphocyte is found in the paracortex of a lymph node?
T cell
Are nodules primary or secondary?
Secondary
Are nodules permanent or temporary?
Permanent
What part of the lymph node is thymus-dependent?
Paracortex
What are high endothelial venules?
- Located in the paracortex2. Lined with simple cuboidal to columnar epithelium3. B and T cells escape from bloodstream via HEVs to enter paracortex (B cells keep going to cortex)
What percentage of lymphocytes enter the lymph node via the HEVs of the paracortex?
90%
What are medullary cords?
Irregularly shaped clumps of cells containing B, T, plasma, and dendritic cells and macrophages
What is the role of the thymus?
Site where T cells mature
In what part of the thymus do T cells mature?
Cortex
What type of cells form the framework of the thymus?
Epithelioreticular cells
What are the functions of Type 1 epithelioreticular cells?
- Form seal around cortex to separate it from CT capsule and trabeculae2. Form sleeve around tunica adventitia of vessels3. Form tight junctions to seal thymic cortex from rest of the body
What is the function of Type 2 epithelioreticular cells?
- Form meshwork in midcortex2. Held together by desmosomes3. “Teachers” of thymic cell education
What is the function of Type 3 epithelioreticular cells?
- Protein synthesis2. Form tight junctions; seal between cortex and medulla
What is the function of Type 4 epithelioreticular cells?
Barrier at corticomedullary junction
What is the function of Type 5 epithelioreticular cells?
Meshwork / framework of medulla
What is the function of Type 6 epithelioreticular cells?
Form Hassall’s corpuscles
What are Hassall’s corpuscles?
Made of Type 6 epithelioreticular cells - they are concentric, eosinophilic whorls that are unique to thymic medulla. They exhibit keratinization
Where do mature T cells go once mature?
Enter bloodstream from medulla via postcapillary venules to take up residence in paracortex of lymph nodes and PALS of spleen
What makes up the blood-thymus barrier (inside-out)?
- Endothelium2. Basal lamina3. Macrophages4. Type 1 epithelioreticular cells
What is DiGeorge’s syndrome?
Individuals cannot produce T cells, may die from infection or tetany
Does the thymus have afferent lymphatic vessels?
No
What makes up the white pulp of the spleen?
- Periarterial lymphatic sheath2. Splenic nodules
What are the characteristics of the periarterial lymphatic sheath?
- Thymus-dependent zone of the splenic pulp2. Contains T cells3. Central artery is centrally located within PALS
What are the characteristics of the splenic nodules?
- Lymphatic nodules2. Contain B cells3. May contain germinal center around central artery4. Central artery is eccentrically located in nodule
What makes up the red pulp of the spleen?
- Splenic cords2. Splenic sinuses
What are the Cords of Billroth?
- Irregular and branching cords of splenic tissue2. Contain loose network of reticular cells and fibers3. Spaces between fibers are filled with blood to be filtered4. Filter blood5. Contain macrophages, plasma cells, dendritic cells
What are the splenic sinuses?
- Lined by endothelial cells with wide intercellular spaces to allow blood cells to pass in and out of sinuses2. Drain into pulp veins which in turn drain into trabecular veins
