Lymphoid System Flashcards
Where does B-cell maturation occur?
Bone Marrow
Where does T-cell maturation occur?
Thymus
What are the central (primary) lymphoid tissues?
Bone marrow
Thymus
What are the peripheral (secondary) lymphoid tissues?
Lymph nodes Spleen Tonsils (Waldeyer’s ring) Epithelio-lymphoid tissues Bone marrow
Do lymphatic vessels have valves?
Yes
What is the size of a lymph node?
Up to 2.5cm
Where do afferent channels drain lymph to?
Through the capsule into the peripheral sinus
Filters through node
Where do efferent vessels leave the LN?
Hilum
Drains to: -cisterna chyli / thoracic duct
-L jugular, subclavian or bronchomediastinal trunks
-R jugular, subclavian or bronchomediastinal trunks
And then to venous system at junction of L or R subclavian and jugular veins
Where do arterial and venous vessels serving the node enter/exit?
Hilum
What are the functions of the lymphatic system?
Return lymph to the circulation- important function in fluid haemostasis, prevent excessive accumulation of fluid in tissues (oedema)
Filter lymph before return to circulation- cell traffic, interactions with immune competent cells (protective function)
Why is the lymphoid system a defence system?
Houses cells of the innate immune system Traffic of APCs links innate and adaptive immune responses Seat of the adaptive immune response -Specificity -Inducible -Memory -Enhanced secondary reaction
What cells are located within lymph nodes?
B cells- associated with follicles and germinal centres, interfollicular, plasma cells- mainly in medulla
T cells- helper/cytotoxic
NK Cells
Mononuclear phagocytes (macrophages, APCs, dendritic cells
Endothelial cells
What are the causes of lymphadenopathy?
Local inflammation
Systemic inflammation
Malignancy
Others e.g. sarcoid, Castlemans Disease
What is lymphangitis?
Red lines extending from inflamed lesion in case of superficial infection
What is the normal weight and size of the spleen?
150-200g and 12x7x3cm
What are the two key aspects of the spleen?
Diaphragmatic surface
Visceral surface- left kidney, gastric fundus, tail of pancreas, splenic flexure of colon
What is the spleen supplied and drained by?
Splenic artery (coeliac axis branch) Splenic vein (with SMV forms portal vein)
Is a disease spleen more prone to rupture?
Yes
What is the structure of the spleen?
Encapsulated
Parenchyma contains red pulp (sinusoids and cords) and white pulp
Describe splenic sinusoids
Fenestrated
Lined by endothelial cells
Supported by hoops of reticulin
Describe splenic cords
Contain macrophages and some fibroblasts and cells in transit (RBC, WBC, PC and some CD8+ T cells)
How does the spleen filter blood?
Detect, retain and eliminate unwanted, foreign or damaged material
Facilitate immune responses to blood borne antigens
What does the white pulp of the spleen contain?
Peri-arteriolar lymphoid sheath (PALS)- CD4+ lymphoid cells
This is expanded by lymphoid follicles
What do APCs in the white pulp do to antigens?
Present them to immune reactive cells
When stimulated by antigen, T and B cell responses may occur
What are the features of splenomegaly?
Dragging sensation in LUQ
Discomfort when eating
Pain if infarction
Hypersplenism- triad of splenomegaly, fall in one of more cellular components of blood, correction of cytopenias by splenectomy
What are the infective causes of splenomegaly?
Wide range: EBV, Malaria, TB, Typhoid, Brucellosis, Leishmaniasis, Trypanosomiasis,
What are the congestive causes of splenomegaly?
Portal (Hepatic cirrhosis, portal/splenic vein thrombosis, cardiac failure)
What are the haematological causes of splenomegaly?
Lymphoma/leukaemia, haemolytic anaemia, ITP, Myeloproliferative disorders
What are the inflammatory causes of splenomegaly?
RA
SLE
What are the storage disease causes of splenomegaly?
Gaucher’s
Niemann Pick Disease
What are the miscellaneous causes of splenomegaly?
Amyloid
Tumours (1’ and metastatic)
Cysts
What can cause hypersplenism?
Conditions associated with splenomegaly
Relationship between size and function is complex
What is the role of splenectomy?
A key diagnostic feature of hypersplenism
Only know the answer after splenectomy
In cases of bone marrow failure may have to balance productivity of the spleen with its role in excessive removal of circulating blood cells
What is the most common cause of hyposplenism?
Splenectomy
What is needed when splenectomy is carried out?
Immunisation
What are other causes of hyposplenism?
Coeliac
Sickle cell disease
Sarcoidosis
Iatrogenic- non surgical
What are the features of hyposplenism?
Mainly from reduced red pulp function: Howell-Jolly bodies, other red cell abnormalities
