Lymphoid Tissue Flashcards
What are the functions of the lymphatic system?
1) Draining excess interstitial fluid
2) Transporting dietary lipids and lipid-soluble vitamins from GIT
3) Protecting against microbial invasion
What are primary lymphoid tissue/organ?
Where lymphocytes originate
eg. bone marrow (B and T cells), Thymus (T cell maturation)
Where do B cells mature?
In the bone marrow
Where do T cells mature?
In the thymus
What are secondary lymphoid tissue/organs?
Where lymphocytes aggregate and respond to Ags
eg. tonsil, spleen, lymph nodes
What are examples of diffuse and dense lymphoid tissue?
Diffuse: Lamina propria of GIT and RT
Dense: (i) MALT (ii) Discrete encapsulated organs
True or False. The thymus has both efferent and afferent lymphatic vessels?
False, it only has efferent vessels (no afferent lymphatics from circulation)
What are the cell types present in the thymus?
1) T Lymphocytes
2) Epithelial reticular cells (thymic epithelial cells)
3) Macrophages
4) Endothelial cells
What is the direction of T cell movement/maturation?
Immature T cells produced in bone marrow → transported via blood to thymus
→ enter cortex (outer region) via corticomedullary junction
→ moves towards medulla (inner region) of each lobule (separated by trabeculae)
Where does positive selection of T cells occur?
In the cortex of thymus
Where does negative selection of T cells occur?
In the medulla of thymus
How do immature/naive T cells migrate into lymph nodes?
Naive T cells express L selectin and CCR7 which mediate homing to lymph nodes
Differentiated effector T cells lose expression of L selectin and CCR7 but express receptors for chemokines produces at sites of inflammation (eg. IL-2 receptor, LFA-1) → chemotaxis to sites of infection > migration to lymphoid tissue
What are the functions of epithelial reticular cells in the thymus?
1) Form the blood-thymus barrier → compartmentalise immature and mature thymocytes in cortex and medulla respectively
2) Provide structural and supportive framework for developing thymocytes (thymus lacks reticular fibres)
3) Produce hormones (eg. thymosin, thymopoietin) for thymocyte proliferation
4) Act as APCs
The medulla has ____ epithelial reticular cells and ___lymphocytes than the cortex.
more EC
less lymphocytes
Where are Hassall’s corpuscles found in the thymus?
Medulla
Which side of a lymph node is the hilum?
Concave surface
What cells are primarily in the cortex of lymph nodes?
B cells arranged in lymphatic follicles with germinal centers
Other cell types present:
1) Plasma cells
2) Macrophages
3) Dendritic cells
4) Reticular cells
