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Flashcards in Lymphoid II Deck (29):

Central Lymphoid Organs

- Thymus (T cells) and Bone Marrow (B cells)


Encapsulated Peripheral Lymphoid Organs

- Lymph Nodes - Filters Lymph
- Spleen- Filters Blood


Unencapsulated Peripheral Lymphoid Organs

- MALT, single, diffuse, transitory, aggregated
- Surveillance of antigens via mucosal surfaces
- MALT houses 85% of all lymphoid tissues


Homing Pattern

- B cells reside in the cortical nodules and medulla of the lymph nodes. As well as the lymphoid nodules in the spleen
- T cells are in the paracortex of the lymph nodes anad Periarterial lymphatic sheath (PALS) of the Spleen
- In the blood, mostly T cells
- In mucosal Tissues- mostly B cells


Nodules vs Node

- Nodules are not completely encapsulated


Circulating Lymphocytes

- Mostly T cells
- small percentage of B cells and NK cells


Diffuse Lymphoid Tissue

- small intestine
- Lamina Propria- mainly B cells
- Plasma cells secrete IgA
- IgA protects- mucosal epithelium infection


Generation and Function of IgA

- Produced by plasma cells
- secretory piece/component added by epithelial cells, protects against lysosomal degradation
- This component is clipped at surface to release IgA dimer into lumen


Solitary Nodules (follicles)

- GI and Respiratory Tracts
- contains mucosa and submucosa
- unencapsulated - no CT layer around the nodule
- Primary Nodule- naive B cell
- Secondary Nodule- has a mantle and germinal center
- Germinal center- activated immune cells ( B cells, t helper, dendritic)



- Aggregated Nodules
- No CT, therefore not fully encapsulated and therefore aggregated nodules


Peyers Patches

- Aggregated Nodules
- Occur in ileum of GI Tract
- Formed from lose lymphatic tissue and produce primary nodules, no germinal center


Microfold Cells

- In Peyers Patches
- Transport antigen to macrophages for stimulation of B and T cells
- Helps initiate an immune response


Vermiform Appendix

- Aggregated Nodule
- Contains much more lymphatic tissue in younger humans vs adult


Bone Marrow

- Central lymphoid organ
- Encapsulated by endothelial cells



- Central lymphoid organ
- site of T cell maturation- cortex
- Bilobed
- Contains cortex and medulla
- Encapsulated
- microframework of the thymus is formed by epithelial reticular cells


T cell positive and negative selection

- T cells undergo somatic recombination in the thymus
- if T cell recognizes self antigen, it is destroyed- Negative selection
- If it does not recognize self antigen, it is released into circulation
- 95% are self recognizing and are destoryed


Blood - Thymus Barrier

- Prevents formed elements of the blood coming into contact with thymocytes and other cells in those regions, stimulating an immune response


Hassall's Corpuscle

- Unique to thymus
- Found in Medulla of thymus
- derived from medullary epithelial retricular cells
- Keratinized
- secretes thymic epithelizal cytokines



- gradual deterioration of the immune system with age
- Lymphatic tissue greatly decreases


Lymph Nodes

- >500 lymph nodes
- filter of lyphatic vessels
- Rich in nodes- neck, mediastinum, retroperitonium
- Filter lymph and hold T and B cells
- Lymphatic fluid comes in through afferent lymphatics, goes down various sinuses, and then exits through efferent lymphatics in the hilum


Supericial Cortex of Lymph nodes

- B cells and APCs


Deep Cortex (paracortex)

- T cells and APCs


Postcapillary High Endothelial Venule (HEV)

- Paracortex of lymph nodes
- Lined with cuboidal endothelium
- Lymphocytes squeeze through cuboidal cells and into blood vessels



- Filters blood
- Store Platelets
- Extra medullary hematopoiesis - residual function observed in fetus
- Red pulp- red blood cells
- White pulp- abundance of leukocytes


Periarterial Lymphatic sheath

- Contains T cells
- Directly adjacent to central artery


Peripheral White pulp

- Contains B cells


Blood Circulation of the Spleen

- Passels through central artery, into white pulp, into marginal zone and back into central artery
- Then it goes into red pulp, through venous sinusoids and into hepatic portal vein


Closed vs Open Circulation

- Sinusoid Open cirulation- Filtration slow 90%
- Sinusoid closed cirulation, fast 10%


Splenic Sinusoids of Red Pulp

- Blood cells flowing though the spleen must cross the sinusoidal wall to re enter the blood.
- Only healthy blood cells can survive this fully intact
- Macrophages are here to phagocytize the older red blood cells