Theme 1 - tissues Flashcards
what are primary lymphoid tissues
- involved in development and differentiation of lymphocytes
- Thymus (T cells)
- Bursa equivalent tissues (foetal liver and adult bone marrow) B cells
what is the role of secondary lymphoid tissues
what do they include
- allow ANTIGEN ACCUMULATION
- allow ANTIGEN PRESENTATION to both naïve and memory lymphocytes
- include the MUCOSA, LYMPH NODES and SPLEEN
what are the tertiary lymphoid tissues
- comprise all the remaining lymphoid tissues in the body (eg skin)
- contain only a few lymphocytes normally
- may be INVADED during inflammation by unique MEMORY LYMPHOCYTES
what is the role of the thymus
what happens to it with age
structure
how do cells enter
where do they travel to in the thymus during maturation
what affects thymocyte development
what happens to those cells that don’t leave the thymus
- produces LYMPHOCYTES
- provided env for T cell MATURATION and EDUCATION
- SHRINKS with age
- 2 lobes divided into lobules by TRABECULAE
- each lobule has OUTER CORTEX & INNER MEDULLA
- cells enter as THYMOCYTES and surrounded by EPITHELIAL cells and others eg INTERDIGITATING DENDRTIC CELLS and MACROPHAGES
- cells move from CORTEX to MEDULLA while differentiating into T cells
- in cortex THYMIC NURSE cells affect thymocyte development
- if the T cell doesn’t leave, it undergoes APOPTOSIS
what % of original thymocytes make it through the thymus into circulation as naïve T cells
5%
when cells enter thymus as THYMOCYTES what do they express/not express
then what do they express in the next stage
and finally
do not express CD4 or CD8 (double neg) - then express BOTH double positive - finally express one or the other - expression of CD3 and TCR INC as they pass through thymus
what is TCR
T cell receptor
how are thymocytes educated in the thymus
how long is this process
POSITIVELY selected to bind to MHC molecules
NEGATIVELY selected if they bind to SELF peptides
- takes 1-3 weeks
how do B cells develop
what -ve and +ve selection
immature B cells mature under local influence of GROWTH factors (from stromal cells)
- EDUCATED to not bind self molecules, if it does NEGATIVE SELECTION and it will undergo apoptosis
- EDUCATED to respond to SURVIVAL factors (POSITIVE SELECTION)
- then released as naïve B cells which are functionally immature
what % of B cells do not undergo apoptosis and can leave the bone marrow
10%
what is lymoh formed from
blood components from capillaries enter tissues making extracellular fluid that provides food and gas exchange
(tissue fluid)
- extracellular fluid drains into LYMPHATIC VESSELS
what 2 things use lymphatics to migrate around the body
lymphocytes and leukocytes
how are lymphocytes transported around the vessels
bind to ADHESION MOLECULES on the endothelial cells that line blood vessels
- up and down regulation of adhesion molecules allow movement of cells
how is movement in the lymphatics aided
- smooth muscle cell movement
- arterial pressure due to close association with blood vessels
- valves prevent backflow
how are leukocytes transported around the vessels
give an example of the what binds and what it binds to
- use HOMING RECEPTORS (adhesion molecules) to bind to ENDOTHELIUM lining of blood vessels
- LFA-1 binds to ICAM-1 on endothelial cells