Structure and function of lymph nodes and spleen Flashcards
where do lymphoid cells originate from
Haemopoetic stem cells
Precursor lymphoid cells
B-cells mature in the bone marrow
T cells mature in the thymus
both then migrate to secondary lymphoid organs
what are the central (primary) lymphoid tissues
bone marrow
thymus
what are the peripheral (secondary) lymphoid tissues
lymph nodes spleen tonsils (waldeyer's ring) epithelia-lymphoid tissues bone marrow
functions of the lymphatic system
Return lymph to circulation
- important for fluid homeostasis
- prevents excessive accumulation of fluid in the tissues
Permits
- lymphoid cells to pass through
- cell trapping
- interaction with cells of the immune system - protective function
what are lymph nodes
small oval bodies up to 2.5cm located along the course of lymphatic vessels
what are lymphatic channels
blind-ending vascular channels that collect fluid from tissues and return to the blood stream
passive movement of fluid
valves ensure direction of flow
what happens inside the lymph node
lymph drains in via afferent channels into the peripheral sinus
filters through the node and an efferent vessel leaves from the hilum
cells move between the lymph nodes and the parenchyma
interactions occur between cells in the node and substances in the lymph
where does lymph enter the venous system
junction of L or R subclavian and jugular veins (right and left lymphatic ducts)
right thoracic duct drains upper right quadrant
left thoracic duct drains everything else
how does the lymphoid system work as defence
houses cells of the innate immune system
traffic of antigen presenting cells which links innate and adaptive immune responses
allows the adaptive immune response to happen
what cells are found in lymph nodes
B cells T cells NK cells Macrophages antigen presenting cells endothelial cells
what are CD20 and CD3
CD20 = B cell marker CD3 = T cell marker
what are the types of lymphadenopathy
localised or generalised
peripheral or central (internal)
what causeslymphadenopathy
local infection
systemic infection
malignancy
others (sarcoidosis, IgG4 related disease)
what is sarcoidosis
a granulomatous condition causing granuloma formation (lumps if inflammatory cells) around the body including in the lymph nodes
what is lymphangitis
in infected superficial lymph nodes you can see reg lines extending from the inflamed lesion
causes of superficial regional lymphadenopathy
often first sign of malignancy
need to know where the nodes drain to identify the primary lesion
causes of systemic lymphadenopathy
Systemic inflammation
wide spread malignancy (lymphoma/leukemia)
what causes a predominant B cell response in a lymph node
Auto-immune conditions
infections
what causes a predominantly phagocytic response in lymph nodes
draining tumour site
what causes a prodominant T cell response in lymph nodes
viral infections
drugs eg. phenytoin
what is a malignant lymph node called
lymphoma
what is the normal weight of the spleen
150-200g
what are the two key aspects (surfaces) of the liver
Diaphragmatic surface
Visceral surface
-left kidney, gastric fungus, tail of pancreas, splenic flexure colon
what is the blood supply to the spleen
splenic artery (branch of coeliac trunk)
drained by the splenic vein (with superior mesenteric vein forms the portal vein)
causes of spleen rupture
trauma
diseased spleen more prone to rupture
surgical emergency
what is the structure of the spleen
parenchyma made up of red pulp and white pulp
what is the function of the spleen
detects, retains and eliminates unwanted foreign or damaged material
facilitates immune responses to blood born antigens
what makes up the red pulp of the spleen
red pulp contains sinusoids and cords
sinusoids are:
- fenestrated (have gaps in endothelium)
- lined by endothelial cells
- supported by hoops of reticulin
cords contain:
- macrophages
- fibroblasts
- cells in transit (RBC,WBC, Platelets)
what makes up the white pulp of the spleen
peri-arteriolar lymphoid sheath
CD4+ lymphoid cells
antigen reaches white pulp via blood, APCs in the white pulp present antigens to immune reactive cells
when stimulated by antigens, T and B cell responses may occur
what are the features of splenomegaly
dragging sensation in LUQ
discomfort with eating
pain if infarction
what is the triad of hypersplenism
triad of:
- splenomegaly
- fall in one or more cellular blood components
- correction of cytopenias by splenectomy
causes of splenomegaly
Infection
(EBV, malaria, TB, typhoid etc)
Portal congestion (hepatic cirrhosis, portal/splenic vein thrombosis, cardiac failure)
haematological diseases (lymphoma/leukaemia, haemolytic anaemia, myeloproliferative disorders)
inflammatory conditions (RA, SLE)
storage diseases
Miscellaneous (amyloid, tumours, cysts)
what are the 2 types of abnormal splenic function
hypersplenism
hyposplenism
what causes hypersplenism
conditions associated with splenomegaly
what is hypersplenism
increased splenic function
only can be diagnoses if improvement after splenectomy
what causes hyposplenism
splenectomy (immunisation must be given beforehand)
coeliac disease
sickle cell disease
sarcoidosis
iatrogenic (non-surgical)
features of hyposplenism
due to reduced red pulp function
Howell-Jolly bodies
other red cell abnormalities
can cause some immune deficiency
