B12 - Reticuloendothelial system Flashcards
Thymus
generally considered part of the reticuloendothelial system, not a major component
reticuloendothelial system is
A network of phagocytic cells part of the immune system - roles in humeral and cell mediated immunity
- Eat cell debris, dead cells, bacteria, consume things that shouldn’t be there - Recognise foreign cells, break them up into pieces and distribute them to the immune system so it can respond eg. Bacterial pathogens - Key role in the immune system
Phagocytes
- A group of white blood cells (monocytic lineage mostly) that are specialised to internalise/engulf bacteria, foreign particles and damaged host cells to protect the body
- They bind to pathogens and internalise them in a phagosome, which acidifies and fuses with lysosomes in order to destroy the contents
- Most phagocytes are of myeloid lineage - mostly monocytic
Lymphatic system
- Anatomical term
- Concerned with lymphoid cells (immune system), lymphatic vessels and lymphatic fluid (circulatory system)
- The MPS and lymphatic systems are structurally and functionally intertwined
difference between mononuclear phagocytic system and lymphatic system
- Lymph nodes cluster in regions
- Lymph fluid is reabsorbed interstitial fluid (similar to plasma) and contains white blood cells (no red cells or platelets)
- Lymphatics are similar to capillaries in structure - endothelium is slightly different and expresses different cell surface markers, cannot be differentiated under microscope
- Lymphatics generally follow veins and fluid is returned to the cardiovascular system through veins in a generally predictable pathway - flow of lymph fluid goes in the same direction, used to predict spread of cancer
- The function of lymph nodes is to
a. Filter lymph
b. Receive and process antigen from circulating cells that have been picked up by macrophages
c. Stimulate B cells to produce antibodies
modern name for reticuloendothelial system
mononuclear phagocytic system
Lymph node architecture
- Capsule
○ Thin fibrous capsule - highly variable
○ Afferent vessels
○ Subcapsular sinus
§ one of the places when a lot of macrophages are found
§ Where metastases are found because that’s where the lymph fluid comes in- Cortex
○ Follicles (B cells and follicular dendritic cells - present antigens to B cells)
○ Primary follicles (quiescent) - haven’t been stimulated
○ Secondary follicles (active, have germinal centres)
○ Mantle and marginal zones - Medulla
○ Cords (plasma cells and mature B cells)
○ Sinuses - Paracortex
○ T cells
○ Clear zonation between T cells and B cells - Hilum
○ Efferent vessels
- Cortex
Lymph nodes have a blood supply - small artery and vein
capsule of lymph node
○ Thin fibrous capsule - highly variable
○ Afferent vessels
○ Subcapsular sinus
§ one of the places when a lot of macrophages are found
§ Where metastases are found because that’s where the lymph fluid comes in
cortex of lymph node
○ Follicles (B cells and follicular dendritic cells - present antigens to B cells)
○ Primary follicles (quiescent) - haven’t been stimulated
○ Secondary follicles (active, have germinal centres)
○ Mantle and marginal zones
medulla of lymph node
○ Cords (plasma cells and mature B cells)
○ Sinuses
paracortex of lymph node
○ T cells
○ Clear zonation between T cells and B cells
Hilum of lymph node
○ Efferent vessels
disease of lymph nodes
V ascular I inflammatory * T rauma A utoimmune M etabolic I nfectious * N eoplastic * C ongenital
lymphadenopathy
- Enlargement of lymph nodes (not a specific diagnosis, need to go looking for a cause)
- Could be solitary or multiple in the same node station
- Glandular fever - multiple sore lymph nodes around the neck
- Metastatic breast cancer - one or more in the axillar
- Metastatic lung cancer - around mediastinum and spread throughout the ody
mechanisms of lymphadenopathy
○ Multiplication of cells within the node
§ Lots of follicles all enlarging at the same time - enlarged lymph node
§ Potentially including lymphocytes, plasma cells, monocytes or histocytes (or pathogens within the node - bacteria can directly infect lymph nodes)
§ Can be normal (reactive lymphadenopathy) or abnormal (lymphoproliferative disorder eg. Leukaemia, lymphoma etc. )
○ Draining of increased numbers of cells into the nodes (eg. From local abscess) into local lymph nodes
§ Phagocytes will pick up lots of bacteria, dying neutrophils etc
§ Can cause capsule to stretch - painful
○ Infiltration of cells from outside the node
§ Such as malignant cells
multiplication of cells within a lymph node
§ Lots of follicles all enlarging at the same time - enlarged lymph node
§ Potentially including lymphocytes, plasma cells, monocytes or histocytes (or pathogens within the node - bacteria can directly infect lymph nodes)
§ Can be normal (reactive lymphadenopathy) or abnormal (lymphoproliferative disorder eg. Leukaemia, lymphoma etc. )
○ Draining of increased numbers of cells into the nodes (eg. From local abscess) into local lymph nodes
§ Phagocytes will pick up lots of bacteria, dying neutrophils etc
§ Can cause capsule to stretch - painful
○ Infiltration of cells from outside the node
§ Such as malignant cells
Inflammatory disorders I
- Reactive lymphadenitis
○ Acute or chronic
§ ‘normal’ function of lymph node
§ Can be exaggerated
§ Can cause secondary problems depending on site (e.g. intussusception of bowel due to enlarged Peyer’s patches, breathing/swallowing difficulties due to enlarged tonsils) - lymphoid tissue in the mucosa is reacting to pathogens - tonsils enlarge when exposed to infectious pathogens but this can cause apnoea/asphyxiation or difficulty swallowing
○ Acute lymphadenitis
§ Short time course, tender nodes
□ Follicular hyperplasia (B cells)
® Tends to be bacterial infection, also seen in rheumatoid arthritis, SLE, HIV, toxoplasmosis, others
□ Paracortical hyperplasia (T cells)
® Tends to be viral infections (including glandular fever) and chronic infections
□ Sinus histiocytosis (histiocytes)
® Tends to be nodes draining chronic infections, abscesses or cancers
Chronic lymphadenitis
§ Longer time course, usually non-tender
§ Capsule has had more time to get used to being stretched - not tender
§ Often non-specific
§ Can reflect chronic infection in region, resulting in increased drainage to node and increased antigen presentation
§ Can also occur in immune mediated and idiopathic disorders (e.g. sarcoidosis, rheumatoid arthritis etc.)
Infectious disorders
- Specific infections directly involving nodes (as opposed to reactive changes in nodes draining areas of infection)
○ Often bacterial (abscess - proliferates in the node) but other specific infections (may be viral, fungal, parasitic) common
○ Directly involve the node itself
○ Specific pathogens like to infect lymph nodes
○ Cannot always identify specific pathogen- Note special pattern: granulomatous lymphadenitis
○ Infection directly involving lymph node
○ Infectious: usually necrotising. Mycobacterial (tuberculosis and others), fungal, parasitic
○ Non-infectious granulomas: sarcoid, others, non-necrotising
○ Granulomas - structures made up of collections of histeocytes - usually with something that cant be easily phagocytosed eg. Mycobacterium which have thick cell walls, granulomas are a form of chronic inflammation, usually TB
○ Granulomas can affect other parts of the body but lymph nodes are common
- Note special pattern: granulomatous lymphadenitis
granulomatous lymphadenitis
- Note special pattern: granulomatous lymphadenitis
○ Infection directly involving lymph node
○ Infectious: usually necrotising. Mycobacterial (tuberculosis and others), fungal, parasitic
○ Non-infectious granulomas: sarcoid, others, non-necrotising
○ Granulomas - structures made up of collections of histeocytes - usually with something that cant be easily phagocytosed eg. Mycobacterium which have thick cell walls, granulomas are a form of chronic inflammation, usually TB
○ Granulomas can affect other parts of the body but lymph nodes are common
