Lymphoid tissues Flashcards
What are lymphoid organs?
Organs where lymphocyte production, maturation and differentiation occur
What takes place at primary/central lymphoid tissues?
Lymphocytes are generated/mature
What takes pace at secondary lymphoid tissues?
Lymphocytes interact with antigen presenting cells
Give examples of primary LTs
Bone marrow Thymus Bursa of fabrics (birds) Peyer's patch (not in cat) Appendix (caecal patch in rabbits)
Give examples of secondary lymphoid tissue
Lymph nodes and vessels
MALT - mucosal associated lymphoid tissue
Spleen
In the foetus, where is the source of lymphocytes?
Yolk sac then liver
Where is the thymus? What happen where?
Small organ near the heart
T lymphocytes maturation and selection
What are T cells called as they enter and leave the thymus?
Immature thymocytes
Leave as mature T cells
In what age people is the thymus active? What happens with age?
Active in young
Shrinks and atrophies - produces fewer mature T-cells
The thymus produces thymic hormones to support the growth and differentiation required to produce T cells. What are these hormones?
Thymosin
Thymulin
Thymopoietin
What cells are found in the thymus?
Mature T- cells Thymocytes Epithelial cells Dendritic cells Hassall corpuscles Many fat areas
What are Hassall’s corpuscles composed of? Where in the body are they found?
Non-secreting epithelial cells in concentric, keratinised layers
Only in thymus
In the cortex, thymocytes mature to adult T lymphocytes. They then migrate to the medulla, what happens here?
Thymic selection - majority die
Survivors become functional T cells and go into circulation to secondary lymphoid tissue
Describe the structure of a lymph node
Afferent lymphatic vessel entering
Efferent lymphatic vessel leaving
Cortex and medulla
Germinal centre within secondary lymphoid follicle
In what stage do lymph nodes develop? What do they do?
Late foetal
Drain fluid and antigens from tissues into afferent lymphatics
Encounter antigens - activate and proliferate lymphocytes
Organs enlarge
Lymphocytes returns to circulation via efferent lymphatic and thoracic duct
What are the 3 histological areas to a lymph node? Which cells are present in each area?
Cortex (B cell area)
Paracortex (T-cell area and HEVs)
Medulla (T and B cell area)
How is lymph fluid (fluid in lymphatic vessels into lymphoid tissues) formed?
Fluid filtered out of capillaries
Drains into lymphatic vessels
What happens to lymph after passing through secondary lymphoid tissues?
Drains into venous blood
What are high endothelial venues? When are they increased?
Venules composed of tall rounded endothelial cells
Increased after antigen stimulation
What do high endothelial venues do? Where are they found?
Allow naive lymphocytes to enter lymph node but no other cells
Paracortex of lymph node
Where are naive lymphocytes found? Where is the response started? Is it a fast or slow response?
Lymph nodes, spleen
At the lymph nodes which are draining the site of exposure
Slow
Where are mature lymphocytes found? Where is the response started? Is it a fast or slow response?
MALT
Local site of antigen exposure
Fast
The spleen consists of two pulps. What are these and what do they contain?
Red pulp = open sinusoids containing RBCs
White pulp = lymphocytes
What colour does white pulp stain with H&E?
Blue
Where is MALT found?
GI tract Respiratory tract Genital urinary tract Peyer's patches Appendix Tonsils
What do mucosa associated lymphoid tissues contain? Which two areas particularly?
Very dense areas of lymphocytes
Bronchioles and SI
What cells are found in the tonsil? Is there a capsule, afferent lymphatic, lymphoid follicles and germinal centres?
Macrophages and lymphocytes
No capsule
No afferent lymphatic vessel
Yes to lymphoid follicles and germinal centres
Where are Peyer’s patches found?
Submucosa of ileum
What is the function of germinal centres of Peyer’s patches?
Sites of antibody productions
