Lymphoid Tissue Flashcards
What are the main histological features of lymphocytes and nuetrophils?
Lymphocytes will have a large dark nucleus that takes up most of the cytoplasm while neutrophils are multi nucleated (3-5) and have visible open cyotplasm along the nuclei
Lymhpoid organs contain high numbers of lymphocytes, and diffuse lymphoid tissue is also located throughout the body. How are the lymphocytes activated in the lymphoid organs?
They are activated in response to the antigens that are presented there
What consists of your primary lymphoid organs?
Thymus and red bone marrow producing lymphocytes needed to recognize antigens
What consists of your secondary lymphoid organs and what do they do?
Diffuse lymphoid tissues where lymphocytes are activated in response to antigens
What is diffuse lymphoid tissue and what does it do?
Non-encapsulated accumulations located in lamina propria of GI and respiratory (where lamina is exposed to ‘outside’ environments)
They intercep antigens and initiate an immune response
What are lymphatic nodules in nodular lymphoid tissue?
Discrete concentration of lymphocytes sharped defined but non-encapsulated (stain dark purple)
Describe a primary nodule/follicle of nodular lymphoid tissue.
Has small lymphocytes that are naive, uniform and lack germinal center
Describe a secondary nodule/follicle of nodular lymphoid tissue and the two different layers.
They are activated primary nodules that consist of two layers:
Germinal center- lighter stained due to immature cells
Mantle/Corona Zone: outer ring w small lymphocytes
What are some examples of aggregation of nodules (non-encapulated)?
Tonsils, Peyer’s patches, Veriform appendix (Large I), mucosa-associated lymphatic tissue (MALT)
What are tonsils and what do they protect against?
Large irregular masses of lymphoid tissue in 3 different locations that protect against inhaled/ingested substances
What is characteristic of palatine tonsils?
Have nonkeratinized stratified squamous epithelium with lymphocytes, have tonsillar crypts (deep invaginations) and has partial capsule made of dense connective tissue
What is characteristic of pharyngeal tonsils (nasopharynx)?
Covered in pseudostratified columnar ciliated epithelium (DIFFERENT FROM OTHER TWO), no crypts, thin capsule
What is characteristic of lingual tonsils (base of tongue)?
Covered with stratified squamous epithelium, have germinal centers, no capsule, some crypts
What is the difference between primary and secondary lymphoid organs?
Primary contain naive/inactive cells and secondary contain active cells/lymphocytes
Where can peyer’s patches be found and what is characteristic of them?
In the ileum of the small intestine, has many aggregations of lymphatic nodules with intestinal villi.
Covered in simple columnar epithelium w/ goblet cells
Where can the veriform appendix be found and what is characterist of the cells?
Found in the large intestine/ cecum, lamina propria completely infiltrated by lymphocytes, simple columnar epithelium w goblet cells, crypts! no villi
What are the different types of mucosa-associated lymphoid tissues (MALT) and what is characteristic of them?
Mucosa-Gastrointestinal-respiratory (bronchus) = MALT/GALT/BALT…
Single clusters of lymphoid tissue, lumen opened to environment, enlarges when exopsed to antigens
What is lymph and lymphatic capillaries?
Lymph is clear, yellowish fluid comprised of interstitial fluids, solutes, and foreign materials
Lymphatic capillaries are closed-ended tubes that are found amound capillary beds (lymph is collected this way)
What are lymph nodes comprised of and what are their main functions?
Encapsulated structures along lymphatic vessels comprised of reticular tissue (in axilla neck thorax and inguinal regions)
Function is to filter lymph ie: remove debris, facilitate antibody production and produce lymphocytes
What is the general process for the path of lymph through a lymph node? (5)
- lymph enters by afferent lymphatic vessels
- goes through superficial cortex
- goes through deep/para cortex
- goes through medulla
- sinuses converge at hilum/efferent lymphatic vessel where lymph will leave and neurovascular bundle will be
What is the location in the lymph node called where you can find the lymphatic nodules (prim/second), where immune cells are suspended on reticular fibers, and where germinal centers have been presented with antigen and mantle zone contains active B cells?
Superficial cortex, which cleans the lymph
What can be found in the deep cortex of lymph nodes?
no nodules and high T cell counts
What cells can be found in the reticular meshwork of lymph nodes?
Macrophages, Dendritic cells (APC), and follicular DC
What are high endothelial venules and what do they do?
post capillary venules lined by cuboidal or columnar endothelial cells, which facilitate movement of lymphocytes from circulation into the lymphnode
What leaves through high endothelial venules (HVE)?
B cells and T cells leave bloodstream by these, cross endothelium by diapedesis, similar to neutrophils
What makes up the lymph node medulla and what is its function?
Inner part of medulla made up of medullary cords and sinuses, covered by reticular cells which serve as framework for parenchyma
What do the medullary cords consist mainly of?
B lymphocytes, macrophages, dendritic cells, and plasma cells
What are dilated spaces that separate medullary cords, which contain clusters of macrophages and neutrophils. These ‘ things ‘ also converge near the hilum of the LN to drain into efferent lymphatic vessels…
Medullary Sinuses
What is another way for saying hilum?
efferent lymphatic vessels
The thymus is bilobed in located in the thoracic mediastinum. What will form in tissues to mature into T cells?
Lymphoblast invade tissue and proliferate, to lymphocytes which form T cells
What is important regarding T cell development in comparison to B cell development?
T cells are mainly made when you are young and going through puberty while B cells are made every day
What are the histological characteristics of the thymus? sometimes looks like lymph node with germinal centers
Has thin capsule with trabeculae going to parenchyma, establishing thymic domains.
Lack lymphoid nodules and germinal centers
The thymic cortex is the site of T lymphocyte maturation and usually stains dark purple/basophillically… what is the cortex mainly packed with?
Thymocytes which are immature T-lymphocytes, which occupy spaves within meshwork of epithelioreitcular cells
What do epithelioreticular cells provide in the thymic cortex?
framework for T cell development
What type of cortical epithelioreticular cells make the boudary of the cortex and capsule, between the parenchyma and trabeculae?
Type I, uses occluding junctions to keep T cells from stroma
What type of cortical epithelioreticular cells are within the cortex, with star shaped, large nucleus, cells that express MHC 1 and 2 to help in thymic cell education?
Type II
What type of cortical epithelioreticular cells are located at the boundary of the cortex and medulla, create a barrier between cortex and medulla, and express MHC 1/2?
Type III
Which type of cortical epithelioreticular cells contains macrophages that are there to kill T cells that do not educate well?
Type III
What is the inner portion of parenchyma which contains large number of epithelioreticular cells and loosely packed T cells, AND thymic corpuscles which are its distinguishing feature?
The thymic medulla
What does the thymic medulla house and transport?
Thymic medulla houses mature T cells migrating from the cortex which enter postcapillary venules to exit the thymus
What type of medullary epithelioreticular cells in thymus are located by type III cells between cortex and medulla, which contain occluding junctions between adjacent cells to form corticomedullary junction?
Type IV
What type of medullary epithelioreticular cells in the thymus are located throughout the medulla which compartmentalize groups of lymphocytes using desmosomes?
Type V
What type of medullary epithelioreticular cells in the thymus form thymic corpuscles (isolated, packed type VI cells with flattened nuclei), with keratohyalin granules, intermediate filaments and lipid droplets?
TYPE VI**
What are type VI (6) medullary epithelioreticular cells in the thymus thought to produce and what do they do?
Produces interleukins IL4/IL7 that function in thymic differentiation and T cell education
What is the blood-thymus barrier and what does it do?
Makes a barrier between T cells and lumen of blood vessels to protects developing lymphocytes in the thymus from exposure to antigens
What are the 3 layers that make up the blood thymus barrier from outward to inward?
- Endothelium lining the capillary wall (highly permeable)
- Macrophages to kill escaped Ags, w/ perivascular CT
- Type 1 epithelioreitcular cells surround capillary wall
What are the main functions of the spleen, located in the left superior quadrant? (5)
- Filtering
- Initiates immune response to blood Ags
- Reservoir for platelets
- Recycling erythrocytes
- Hematopoiesis (in fetus till BM takes over)
the spleen has dense CT capsule with trabeculae which contain myofibroblasts. What do they do?
Help to repel RBCs and produce EC fibers
The parenchyma of the spleen contains reticular fibers which makes up…?
White pulp: T/B cells and macrophages
Red pulp: venous supply, RBCs, platelets, macrophages and plasma cells
What is the identifying factor for a histological slide of the spleen?
there is no cortex or medulla!
White pulp (splenic nodules) contains a central arteriole and PALS, what does PALS stand for and what is it?
Periarteriolar lymphoid sheaths that are T cells surrounding the central arteriole
What are the two layers/zones around the germinal center in white pulp in the spleen? ***not a true nodule
Corona/mantle zone (MnZ) which are small lymphocytes surrounding the GC Marginal Zone (MgZ): blend of lymphocytes that span white to red pulp
What is red pulps’ function, what is it composed of, and what does it contain?
They make sure T cells are functioning correctly, function in blood filtration and erythrocyte turnover
Composed of splenic sinusoids and splenic chords rich in lymphocytes and macrophages and reticular fibers
Contain penicillar arteries
What are sinusoids in red pulp in the spleen lined with and why?
Lined with stave cells which are specialized endothelial cells that separate healthy vs. unhealthy RBCs
What is the flow of blood into the spleen?
Splenic A -> Trabecular A -> into parenchyma -> central arteriole/PALS -> White pulp - > Pencillar arteries -> Splenic sinuses -> Splenic cords
What is the difference in the spleen blood flow between humans and mammals?
Humans have open circulation that allows blood to freely flow into sinusoids, while they are closed in mammals