Structure of the immune system Flashcards
What do the primary lymphoid organs do?
sites of lymphocyte production, not activation
What are the primary lymphoid organs?
Thymus - T cells
Bone marrow - B cells
What does the thymus comprise of?
An outer cortical layer
An inner, less dense medullary layer
Describe composition of thymus layers?
Cortex = immature and proliferating thymocytes Medulla = less densely populated with thymocytes
What does the medulla do to thymocytes?
They are tested for self-reactivity and those deemed to be safe are released into the circulation
What are the components of the thymus divided into?
Lobules which are separated by strands of connective tissue - trabeculae of which each lobule is organised into an outer cortex and an inner medulla
Role of cortical epithelal cells
The cortex is the location of the earliest events in thymocyte development, where T cell
receptor gene rearrangement and positive selection takes place.
What do secondary lymphoid organs do?
Where immune responses start - sited to monitor pathogen entry
Give examples of secondary lymphoid organs
Lymph nodes - monitor solid tissues
Spleen - monitors blood
Peyers patches and equivalents - monitor mucosae
Functions spleen red and white pulp
Red pulp - concerned with removal of RBs from the circulation as well as foreign material
White pulp - concerned with recirculaion of lymphocytes and in lymphoycte activation and coordination
Describe Peyers patches
They are GALT - concered with surveillance of gut luminal contents for foreign antigens
Able to detect luminal antigens and transport them over
This is a form of mucosal immunity
What can lymph nodes be divided into?
Three regions:
- cortex (outer) - primary follicles in this region contain the naive B cells
- paracortex (middle) - naive T cells
- Medulla (inner) - contains exiting B and T cells draining into efferent lymphatics
What is a site of lymphocyte exit formt he blood?
High endothelial venules - enable lymphocytes to directly enter a lymph node (also found in the spleen)
Express adhesion molecules, mimicking inflamed endothelium at sites of infection - allow extravasion
Describe lymphocyte recirculation
Property of developed but naive (not-activated) lymphocytes which progressively circulate from the blood, to the spleen and through the lymph nodes back to the blood
