The lymphoid system Flashcards
Where do B cells mature?
In the bone marrow
Where do T cells mature?
In the thymus
What are the primary/central lymphoid organs?
The bone marrow and the thymus
What are the secondary/peripheral lymphoid tissues/organs?
Lymph nodes Spleen Tonsils (Waldeyer's ring) Epithelio-lymphoid tissues Bone marrow
What are the functions of the lymphoid system?
Return lymph to the circulation (fluid homeostasis)
Filtration of circulatory fluids - bring lymph into contact with immune system
Location for cells of the immune system
How large may normal lymph nodes be?
Up to 2.5cm
What ensures the direction of flow in lymph vessels?
Valves
What cell populations are found in lymph nodes?
Lymphocytes
Macrophages and dendritic cells (antigen presenting cells)
Endothelial cells
Where in the lymph node are B cells found?
Where are T cells found?
B cells: In the follicles
T cells: the remainder of the lymph node
What causes lymphadenopathy?
Local inflammation
Systemic inflammation
Malignancy
Others
How can internal lymph node groups be viewed?
Radiologically
What are the likely causes of a predominant B-cell reactive response in a lymph node?
Autoimmune conditions
Infections
What is a likely causes of a predominant phagocytic response in a lymph node?
Draining a tumour site
What is a likely cause of a predominant T cell response in a lymphocyte?
Viral infections
Drugs e.g. phenytoin
What investigation should you do when you find generalised lymphadenopathy?
FBC
This may give the diagnosis and you may not need to do a biopsy
How big is the spleen normally?
up to 150-200g
12x7x3 cm
what vessels supply and drain the spleen?
The splenic artery (branch of coeliac trunk) and splenic vein (forms the portal vein with the superior mesenteric vein)
When might a spleen rupture?
Trauma or if it is diseased (more prone to rupture)
Briefly describe the structure of the spleen
Encapsulated
White and red pulp separated by marginal zone
White pulp: lymphoid tissue composed of periarterial lymphatic sheath containing T cells (CD4+) and lymphatic nodule/follicle containing B cells
Red pulp: contains blood. Made of sinusoids and cords containing macrophages, fibroblasts and cells in transit.
Marginal zone: mainly non-circulating B cells, also specialised macrophages which take up CHO antigens
What is the function of the spleen?
Removal of old cells, cellular debris and microorganisms from the blood
Response to bacterial and fungal infections
List three ways in which the spleen can remove old cells, debris and microorganisms from the blood
Phagocytosis
Removal of red cells which are not sufficiently deformable to pass through sinusoids
Removal of intracellular debris or organisms when the cell passes through the inter-endothelial slit.
Name three conditions in which there are RBCs which are not sufficiently deformable to pass through the sinusoids in the spleen
Hereditary spherocytosis
Malaria
Sickle cell anaemia
What type of red cells are removed by phagocytosis in the spleen?
Those coated with IgG antibody
What is the hypersplenism triad?
Splenomegaly
Fall in one or more cellular components of blood
Correction of cytopenias by splenectomy
