The lymphoid system Flashcards
Where does B cell maturation take place?
Bone marrow
Where does T cell maturation take place?
Thymus
What are the primary and secondary lymphoid tissues?
- Primary (central) - bone marrow and thymus
- Secondary (peripheral) - lymph nodes, spleen, tonsils (Waldeyer’s ring), epithelio-lymphoid tissues, bone marrow
What is the function of the lymphatic system?
- Return lymph to the circulation - prevent excessive accumulation of fluid in the tissues (oedema)
- Permits cell traffic, cell trapping and interaction of cells and molecules with cells of the immune system
Describe lymph nodes
- Small, oval bodies, up to 2.5cm
- Located along the course of lymphatic vessels
Lymph nodes have afferent and efferent channels, what role do each of these channel types have?
- Afferent channels drain lymph through the capsule into the peripheral sinus
- An efferent vessel leaves from the hilum and eventually drains into the venous system
Where is lymph filtered within the node?
Within the node parenchyma before return to the blood stream
How is the lymphoid system important in defence mechanisms?
- Contains cells of the innate immune system
- Traffic of APCs links innate and adaptive immune responses
- Seat of the adaptive immune response
What cell types are present in lymph nodes?
B cells, T cells, NK cells, macrophages, APCs, dendritic cells, endothelial cells
What can cause lymphadenopathy?
- Local inflammation - infection e.g. TB
- Systemic inflammation - infection e.g. viral infections., autoimmune disorders
- Malignancy - haematological (lymphoma, leukaemia), metastatic
- Sarcoidosis
What is sarcoidosis?
- A granulomatous condition
- Wide differential diagnosis
- Not a histological diagnosis
- Sarcoid like reactions are a pit fall - may mask malignancy in a lymph node
What does this diagram show in relation to stimulation of immune reaction in a lymph node and what conditions might this occur in?
- Predominant B-cell response
- Auto-immune conditions and infections
What does this diagram show in relation to stimulation of immune reaction in a lymph node and what conditions might this occur in?
- Predominant phagocytic response
- Draining a tumour site
What does this diagram show in relation to stimulation of immune reaction in a lymph node and what conditions might this occur in?
- Predominant T-cell response
- Viral infections, drugs e.g. phenytoin
Where is the spleen located?
- Located high in the LUQ of the abdomen
- Normally 150-200g and 12x7x3cm
- Not usually palpable
- Two key aspects - diaphragmatic surface and visceral surface (left kidney, gastric fundus, tail of pancreas, splenic flexure of colon)
Describe the vascular supply to the spleen
- Supplied by splenic artery (branch of coeliac artery) and drained by splenic vein (combines with superior mesenteric vein to form portal vein)
- Rupture is a surgical emergency - diseased spleen is more prone to rupture
What are the two parts of the spleen parenchyma?
- White pulp and red pulp
- Red pulp contains sinusoids and cords
- Spleen is an encapsulated organ
What is the function of the spleen?
Same as lymph nodes do for lymph fluid - filter the blood
What does the white pulp do?
- Antigen reaches white pulp via the blood
- APCs in the white pulp present antigen 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
What is the triad of hypersplenism?
- Splenomegaly
- Fall in one or more cellular components of blood
- Correction of cytopenias by splenctomy
What can cause splenomegaly?
- Infection - EBV, HIV, TB
- Congestion - hepatic cirrhosis, portal vein thombosis, HF
- Haematological diseases - lymphoma/leukaemia, haemolytic anaemia, ITP, myeloproliferative
- Inflammatory conditions - RA, SLE
What is the arrow pointing to in this diagram?
Howell-Jolly body
