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
neoplastic disorders
- Primary (haematolymphoid)
○ Lymphoma - solid mass caused by a neoplastic proliferation of lymphocytes
§ Can happen anywhere with lots of lymphoid tissue
○ Leukaemia - predominately circulating cells, but often LN involvement
○ Myeloma (plasma cells) less frequently seen in nodes, often in other tissues- Secondary
○ Come from somewhere else and spread to the lymph nodes
○ Metastases: especially carcinoma, melanoma
○ Lymph node involvement is a frequent part of cancer medicine
- Secondary
Neoplastic disorders
- Primary (haematolymphoid)
○ Lymphoma - solid mass caused by a neoplastic proliferation of lymphocytes
§ Can happen anywhere with lots of lymphoid tissue
○ Leukaemia - predominately circulating cells, but often LN involvement
○ Myeloma (plasma cells) less frequently seen in nodes, often in other tissues
Neoplastic disorders
- Secondary
○ Come from somewhere else and spread to the lymph nodes
○ Metastases: especially carcinoma, melanoma
○ Lymph node involvement is a frequent part of cancer medicine
Metastatic tumours
- Part of staging of most tumours
○ Tumour Node Metastases (TNM)
○ May stage based on lymph nodes being involve/not involved, how many nodes involved, or which node stations
○ Further the involved nodes are away from the original tumour, the more likely it has been able to spread so worse prognosis
○ More nodes involved - worse prognosis
○ Tumours usually go to nodes that are closest
Metastatic tumours
- Very important for prognosis
○ More = worse (more nodes are involved)
○ Further away from primary site = worse
Metastatic tumours
- ‘Sentinel mode’ - biopsy is used in some malignancies
○ Identification of the first draining node, if positive, indicates likely spread while if negative may allow for preservation of other lymph nodes (don’t have to remove them
○ Losing lymph nodes causes problems with lymphoid drainage - reducing circulation causes lymphedema which can be very disabling
○ Used to minimise the need to remove lymph nodes
Tumour Node Metastases (TNM)
○ May stage based on lymph nodes being involve/not involved, how many nodes involved, or which node stations
○ Further the involved nodes are away from the original tumour, the more likely it has been able to spread so worse prognosis
○ More nodes involved - worse prognosis
○ Tumours usually go to nodes that are closest
Anatomy of the spleen
- left upper quadrant
○ Beneath rib cage and up against diaphragm - well protected but close to rib cage so may get damaged in injury to rib cage
○ Posterior to stomach
○ Superior and lateral to left kidney and pancreas
○ Connected to greater curve of stomach by gastrosplenic ligament, and to left kidney by splenorenal ligament
○ Gastrosplenic ligament contains the splenic artery, which runs along the superior pancreas
§ Disease involving pancreas, splenic artery can get involved causing disease of the spleen
○ Stomach, pancreas and kidney are all connected by ligamentous tissue- Fist sized and shaped - 12cm long, 150-200 g
- Partially mobile - making it susceptible to injury, particularly blunt trauma
- Surrounded by flexible, fibroelastic capsule which has prominent notches on superior border which can be palpated when the spleen becomes enlarged
spleen is partially mobile
making it susceptible to injury, particularly blunt trauma
anatomy of the spleen surfaces
○ Diaphragmatic surface - curved
○ Splenic notches - superior edge, can be palpated in splenomegaly
§ One or multiple
splenic notches
can be palpated in splenomegaly
anatomy of vascular spleen
- Highly vascular
○ Blood supply, lymphatic drainage, venous drainage are through the hilum
○ Splenic artery (branch of celiac trunk)
○ Splenic vein (joins superior mesenteric vein to form hepatic portal vein)
§ If there is increased pressure in hepatic portal vein the spleen can be enlarged
§ If you have increased venous pressure due to right heart failure the spleen becomes enlarged
○ Lymphatics follow veins drains to -> pancreaticosplenic nodes -> celiac nodes
○ Splenic vein (joins superior mesenteric vein to form hepatic portal vein)
§ If there is increased pressure in hepatic portal vein the spleen can be enlarged
§ If you have increased venous pressure due to right heart failure the spleen becomes enlarged
Function of the Spleen
- Filter the blood, particularly removal of damaged red cells, bacterial particles
a. Red pulp macrophages- Antibody production (presentation of antigens to T lymphocytes)
a. White pulp follicles - Haematopoiesis
a. Normal during foetal development while the bone marrow is still forming
b. Compensatory in settings where increase haematopoiesis is needed (e.g. severe chronic anaemia, myeloproliferative disorders or situations where bone marrow is supressed) - Sequestration of blood (30-40mL of red cells, but 30-40% of total platelets volume)
a. Red pulp interstitium
b. If the body suddenly needs a big surge of platelets
c. In some forms of splenomegaly, can sequester up to 90% of total platelets and red cells - inappropriate
- Antibody production (presentation of antigens to T lymphocytes)
spleen filtering the blood
particularly removal of damaged red cells, bacterial particles
a. Red pulp macrophages
spleen antibody production
(presentation of antigens to T lymphocytes)
a. White pulp follicles
spleen Haematopoiesis
a. Normal during foetal development while the bone marrow is still forming
b. Compensatory in settings where increase haematopoiesis is needed (e.g. severe chronic anaemia, myeloproliferative disorders or situations where bone marrow is supressed)
- Sequestration of blood (30-40mL of red cells, but 30-40% of total platelets volume)
a. Red pulp interstitium
b. If the body suddenly needs a big surge of platelets
c. In some forms of splenomegaly, can sequester up to 90% of total platelets and red cells - inappropriate
a. Red pulp macrophages
- Filter the blood, particularly removal of damaged red cells, bacterial particles
a. White pulp follicles
- Antibody production (presentation of antigens to T lymphocytes)
a. Red pulp interstitium
- Sequestration of blood (30-40mL of red cells, but 30-40% of total platelets volume)
The spleen contains two functionally and histologically distinct components that work together
- White pulp: lymphoid aggregates and macrophages
a. Central arteries (arterioles)- Red pulp:
a. Siniosoids (specialized capillaries)
b. Cords (of Billroth) - plates of modified connective tissue cells, macrophages and monocytes - enables spleen to do blood filtering
- Red pulp:
Red and white pulp
Red and white pulp are closely intertwined allowed abnormalities in blood in red pulp to be presented to the white pulp - so the spleen can perform an immune function
Diseases of the spleen
- Congenital
○ Accessory spleen (splenunculus) - part of the spleen or a nodule of splenic tissue is found elsewhere in the abdomen
§ Important if there is another disease of the spleen
○ Hypoplasia/aplasia - doesn’t form, impact on the normal development of the immune system, often causes immunodeficiencies
Diseases of the spleen
- Acquired
○ Splenomegaly - enlarged
§ Important considerations
□ Passive enlargement - if venous pressure rises
□ Secondary to infection, inflammation - hyperplasia of lymphoid component
□ Hypersplenism (overactive spleen - leads to cytopaenias of red cells and platelets) - phagocytic works to fast - removing too many red cells and platelets from circulation - thrombocytopaenia
□ Growth disorders (usually neoplasms) - usually leukaemic involvement of the spleen spread by blood
○ Trauma (rupture) - one of the most commonly injured intraabdominal organs, especially if enlarged, especially blunt trauma
§ Broken ribs can lacerate spleen - highly vascular so there can be a lot of blood loss
○ Infarct (usually embolus from heart in setting of mural thrombus, via systematic circulation)
§ Anything circulating that can be lodged in a branch of the spleen
§ Embolus - something detaches and moves downstream
§ Thromboemboli - origin commonly from the heart
§ Emboli in the heart due to atrial fibrillation, previous myocardial infarction, infective endocarditis, ventricular aneurism
§ Spleen is a common site
○ Neoplasms: leukaemia, myeloma, lymphoma relatively common
§ Also: haemoangioma/angiosarcoma. Others uncommon
Splenomegaly - enlarged
§ Important considerations
□ Passive enlargement - if venous pressure rises
□ Secondary to infection, inflammation - hyperplasia of lymphoid component
□ Hypersplenism (overactive spleen - leads to cytopaenias of red cells and platelets) - phagocytic works to fast - removing too many red cells and platelets from circulation - thrombocytopaenia
□ Growth disorders (usually neoplasms) - usually leukaemic involvement of the spleen spread by blood
Trauma (rupture)
one of the most commonly injured intraabdominal organs, especially if enlarged, especially blunt trauma
§ Broken ribs can lacerate spleen - highly vascular so there can be a lot of blood loss
○ Infarct (usually embolus from heart in setting of mural thrombus, via systematic circulation)
§ Anything circulating that can be lodged in a branch of the spleen
§ Embolus - something detaches and moves downstream
§ Thromboemboli - origin commonly from the heart
§ Emboli in the heart due to atrial fibrillation, previous myocardial infarction, infective endocarditis, ventricular aneurism
§ Spleen is a common site
Accessory spleens
- Common 20-30%
- Usually single, functional, if patient has hypersplenism then accessory spleen also needs to be removed or symptoms wont resolve
- Hypersplenism - accessory splenic tissue must be removed or problems will continue - increased splenic activity will still take place even though accessory spleen is not connected
- Common site - surface of spleen, stomach, mesentery, pelvis and occasionally attached to pelvic organs, ovaries and uterus in women
Splenomegaly
- Worldwide Malaria is the most common reason - not a concern in Australia
- Infectious mononucleosis - glandular fever - infective cause in Australia
- Hepatitis infections
- Chronic heart failure/cirrhosis
- Primary causes of the spleen
○ Hypersplenic states - If the spleen doubles in size
○ No longer protected by the rib cage
○ Displacing the kidney
○ Seatbelt can injure in motor vehicle accident
Hypersplenism
- Essentially an overactive spleen
○ Hypersplenism usually causes splenomegaly, but not all splenomegaly causes hypersplenism- Causes peripheral cytopaenias (too much filtering and/or increased sequestration)
- Red pulp predominantly affected
○ Massive expansion of the red pulp - Primary hypersplenism (idiopathic)
- Secondary hypersplenism due to (more common)
○ Infection, alcohol, portal hypertension, systemic inflammatory disorders, malignancy of the spleen, autoimmune haemolytic anaemia, immune thrombocytopaenic purpura, hemophagocytic syndrome
○ Starts causing anaemia
hypersplenism leads to
- Causes peripheral cytopaenias (too much filtering and/or increased sequestration)
anaemia
hypsersplenism can be caused by
- Primary hypersplenism (idiopathic)
- Secondary hypersplenism due to (more common)
○ Infection, alcohol, portal hypertension, systemic inflammatory disorders, malignancy of the spleen, autoimmune haemolytic anaemia, immune thrombocytopaenic purpura, hemophagocytic syndrome
○ Starts causing anaemia
- Secondary hypersplenism due to (more common)
if the spleen doubles in size
○ No longer protected by the rib cage
○ Displacing the kidney
○ Seatbelt can injure in motor vehicle accident
most common reason for splenomegaly
malaria
accessory spleens causing hypersplenism
- Hypersplenism - accessory splenic tissue must be removed or problems will continue - increased splenic activity will still take place even though accessory spleen is not connected
