what are lymphoid organs?
specialized tissues where lymphocytes (immune cells) are produced, mature, and are activated
they are connected with the lymphatic system
what is the lymphatic system?
a network of vessels and nodes that drains interstitial fluid (“lymph”) from tissues, filters it for pathogens or foreign matter, and returns it to the bloodstream
what are components of the lymphatic system?
lymphatic vessels/capillaries
lymph nodes
primary, secondary, tertiary lymphoid organs
what is a primary lymphoid organs?
sites of lymphocyte formation and maturation (bone marrow, thymus)
lymphocytes generated here become immunocompetent before entering circulation
what is a secondary lymphoid organs?
sites where mature lymphocytes encounter antigens and mount immune responses
e.g. lymph nodes, spleen, tonsils, mucosa-associated lymphoid tissue (MALT))
function: trap antigens from the lymph (nodes) or blood (spleen); facilitate activation and proliferation of T and B cells
what are tertiary lymphoid organs?
ectopic lymphoid structures that form in peripheral sites (often at sites of chronic inflammation or infection)
not present in healthy individuals—arise in tissue; associated with chronic autoimmune disease, infection, and some cancers
function: provide local sites for ongoing immune responses outside traditional organs
how do primary, secondary & tertiary lymphoid organs work together?
primary organs generate a repertoire of diverse lymphocytes - cells circulate to secondary organs where they are poised to respond to pathogen exposure
secondary organs act as immune “hubs”
tertiary structures may arise in tissues when persistent immune response is needed
what is the reticuloendothelial system? how does it differ from lymphoid organs?
RES - a network of phagocytic - mainly monocyte/macrophage lineage - cells within reticular connective tissues (e.g. liver Kupffer cells, spleen, bone marrow, lymph nodes)
function: engulfs and removes pathogens, dead cells, debris + processes antigens for presentation to immune cells
compared to lymphoid organs:
- lymphoid organs house and organize lymphocytes, including places for maturation (primary) and immune response activation (secondary)
- RES focuses on phagocytosis and innate defence
overlap - macrophages reside within lymphoid tissues
what is lymphoma?
cancer of lymphoid tissues, either B or T cell origin, can affect any lymphoid organ or tissue (lymph nodes, MALT, spleen, etc.)
what is Virchow’s Node? significance in metastasis?
Virchow’s node = a palpable, enlarged lymph node in the left supraclavicular area; Troisier’s sign
significant clinical indicator of metastasis from gastric or other abdominal cancers when enlarged - signifies secondary disease in a lymph node
what is MALT as a secondary lymphoid organ?
mucosa-associated lymphoid tissue; aggregates of lymphoid tissue in mucosal sites (GI tract, respiratory, genitourinary)
what is GALT as a secondary lymphoid organ?
gut-associated lymphoid tissue; subset of MALT in the gut:
- tonsils, adenoids
- oesophageal lymphoid tissue
- Peyer’s patches (mainly in ileum)
- appendix
- colonic/LI lymphoid aggregates
examples of GALT-associated disease - infection? tumours? inflammatory conditions?
infection - appendicitis, TB
tumours - lymphoma (arises from Peyer’s patches, appendix, or other gut lymphoid tissue)
inflammation - Crohn’s
what is Crohn’s disease?
a chronic lifelong IBD that causes inflammation and ulcers in the lining of the digestive system (esp. intestines) - involves GALT with granulomatous changes, skip lesions, and lymph node enlargement
what diseases are linked to lymphoid organs?
lymphoma
leukaemia
infection
autoimmunity
how does portal hypertension have splenic effects?
portal hypertension (from cirrhosis etc.) causes:
- impaired blood flow from spleen into portal vein = congestive splenomegaly
- sequestering + destruction of blood cells = hypersplenism
- further risk of cytopenias
causes congestive splenomegaly from back-pressure and leads to hypersplenism → sequestration and destruction of blood cells + platelets → cytopenias
infectious mononucleosis - what is it? how does it have splenic effects?
clinical syndrome caused by EBV - classified by triad: fever, pharyngitis, lymphadenopathy
splenomegaly - EBV infects B-cells = lymphoid infiltration, + congestion, with risk of splenic rupture
malaria - what is it? how does it have splenic effects?
life-threatening parasitic infection transmitted by female mosquitos - parasite infect RBCs → cyclic haemolysis and systemic illness
spleen filters abnormal RBCs and parasitised cells = persistent haemolysis + immune stimulation = splenic congestion, hypersplenism, and fragility
(autoimmune) haemolytic anaemia - what is it? how does it have splenic effects?
anaemia caused by premature destruction of RBCs (haemolysis), leading to shortened RBC lifespan
spleen destroys RBCs → splenomegaly & hypersplenism
