lymphoid System Flashcards
origin of lymphoid cells?
haemopoietic stem cells > precursor lymphoid cells > either become T cells in thymus or B cells in bone marrow > secondary lymphoid organs
what are the 2 primary lymphoid tissues?
bone marrow
thymus
what the 5 peripheral (secondary) lymphoid tissues?
lymph nodes spleen tonsils (waldeyers ring) epithelia-lymphoid tissues bone marrow
2 main roles of lymphatic system?
filtration of circulatory fluids
location for cells of the immune system (lymphoid and accessory)
importance of lymphatic system in circulation?
returns lymph to the circulation
important in fluid homeostasis and prevents excessive accumulation of fluid in tissues causing oedema
what does the lymphatic system permit?
cell traffic
cell trapping
interacting of cells and molecules with cells of the immune system (protective function)
main palpable lymph node groups?
cervical nodes
axillary nodes
inguinal nodes
non-palpable lymph node groups?
mediastinal
para-aortic
normal lymph node size?
up to 2.5cm
oval shaped
where are lymph nodes found?
located along course of lymphatic vessels
general structure and function of lymph nodes?
blind-ended vascular channels that collect fluid from tissues and return to blood stream
allow passive movement of fluid
have valves which ensure direction of flow
describe the movement of fluid in a lymph node
afferent channels bring fluid in through the capsule and into the peripheral sinus of the node
lymph filters through the node then leaves via efferent vessel in the hilum
where does lymph fluid go after leaving node?
cisterna chyli/thoracic duct
or
left jugular/subclavian/bronchomediastinal trunks
or
right “”
then goes to venous system at junction of left or right subclavian and jugular veins
where do arterial and venous vessels serving the node enter/exit the node?
hilum
how is lymph filtered in the node?
within the parenchyma
traffic of cells between lymph and the parenchyma
interactions between cells in the node and cells/substances contained within the lymph fluid
how does the lymphoid system act as defence system?
houses cells of innate immune system
traffic of antigen presenting cells (APCs) links innate and adaptive immune response
features of adaptive immune response?
specific
inducible
has memory
enhanced secondary reaction
what cell populations are found within lymph nodes?
lymphocytes macrophages antigen presenting cells dendritic cells endothelial cells
markers of B cell and T cell populations in lymph nodes?
B cells = CD20
T cells = CD3
how can lymph node enlargement be described in clinic?
localised or wide-spread and generalised
peripheral or central (internal)
types of lymphadenopathy?
local inflammation (infection, vaccination) systemic inflammation (infection, autoimmune) malignancy (haem - lymphoma/leukaemia or metastatic) others (sarcoidosis, IgG4 disease etc)
what is sarcoidosis?
generalised granulomatous condition with a wide differential
why are sarcoid like reactions a problem in lymphadenopathy?
may mask a malignancy
what is lymphangitis?
regional lymphadenopathy where there is inflammation of the lymphatic drainage system from a region to the node
(seen as red lines extending from an inflamed region)
superficial regional lymphadenopathy may be the first sign of what?
underlying malignancy
what does generalised lymphadenopathy suggest?
systemic inflammatory process or widespread malignancy (lymphoma/leukaemia)
what do you look for in lymph node enlargement?
evidence of underlying pathology (draining sites)
reactive processes (B/T cell response have different patterns on microscopy)
evidence of neoplastic disorders
how do you assess reactive processes in enlarged lymph node?
stimulate immune reaction in node
mainly B cell response = autoimmune condition or infection
mainly phagocyte response = draining tumour site
mainly T cell response = viral infection or drugs (phenytoin)
normal size and position of spleen?
usually in LUQ
normally 150-200g
shouldn’t be palpable
what are the 2 key aspects of the spleen?
diaphragmatic surface visceral surface (facing left kidney, gastric fundus, tail of pancreas and splenic flexure)
blood supply and drainage spleen?
splenic artery
drained via splenic vein (combines with superior mesenteric vein to form portal vein)
general structure of spleen?
encapsulated organ filled with parenchyma made of red pulp and white pulp
what is contained within red pulp?
sinusoids and cords
what are sinusoids?
components of red pulp which are fenestrated, lined by endothelium and supported by hoops of reticulin
what are cords?
components of red pulp which contain macrophages, some fibroblasts and cells in transit (RBCs, WBCs, PCs and some CD8 T cells)
function of spleen?
acts as a filter for blood
detects, retains and eliminates unwanted foreign/damaged material
also facilitates immune response to blood borne antigens
describe circulation in the spleen
blood enters via trabecular artery > continues in central artery > branches off via radial arterioles to perilymphoid sinuses > some continues up central artery and smaller branches then sheathed capillaries > splenic cords > venous sinuses > trabecular vein
components of white pulp in the spleen?
peri-arteriolar lymphoid sheath (PALS)
CD4 lymphoid cells
how does white pulp change?
expanded by lymphoid follicles (may show reactive changes as in lymph node)
how does antigen reach white pulp? what happens next?
via the blood
APCs in the white pulp then present antigen to immune reactive cells (B/T cells)
B and T cells responses then occur once stimulated by antigen
what spleen problems can be seen in clinic?
splenomegaly
splenic atrophy
features of splenomegaly?
dragging sensation in LUQ
discomfort when eating
pain if infarcted
hypersplenism
features of hypersplenism?
triad of
- splenomegaly
- fall in 1+ cellular components of blood
- correction of cytopenias by splenoectomy
what can cause splenomegaly?
infection congestion (portal) haematological diseases inflammatory conditions (RA, SLE etc) storage diseases miscellaneous (amyloid, tumours, cysts)
most common cause of hypospplenism?
splenectomy
other causes include coeliac, sickle cell, sarcoidosis, iatrogenic etc
features of hyposplenism?
due to reduced red pulp function
- Howell-jolly bodies
- red cell abnormalities
- need for immunisation and prophylaxis
- may have immune deficiency
