Lymphoid tissue (year 2) Flashcards
what are lymphoid tissues?
organs in which lymphocytes are produced, matured and differentiated
what happens at primary lymphoid tissue?
lymphocytes are generated and matured
what happens at secondary lymphoid tissue?
lymphocytes interact with antigen presenting cells (APCs)
list the main primary lymphoid tissue
bone marrow, thymus gland, bursa of fabrics, ileal payers patch, appendix (rabbits)
list the main secondary lymphoid tissue
lymph nodes, mucosal-associated lymphoid tissue (MALT), spleen
where is the thymus found?
thoracic organ near the heart
what happens at the thymus?
T lymphocyte maturation and selection
what happens to the thymus as you age?
atrophies and produces fewer T cells
how is the structure of the thymus divided?
outer capsule, cortex, medulla
describe the arrangement of the structure of the thymus’ cortex
densely populated with lymphocytes of various size with some macrophages to remove thymocytes that have undergone apoptosis
what are thymocytes?
immature lymphocytes
what happens to thymocytes in the cortex of the thymus?
they mature and migrate to the medulla
describe the arrangement of the medulla of the thymus
less densely populated as the cells begin to die
what happens in the medulla of the thymus?
antigen is presented to the lymphocytes they undergo thymus selection and pass into circulation
what is the aim of the process that happens in the thymus?
remove self-reactive T-lymphocytes, these cells will cause autoimmunity if not removed
describe the passage of cells through a lymph node
enter through afferent vessel travel through the cortex then medulla and out through the efferent vessel
what does the cortex of lymph nodes mainly contain?
B cells
what does the paracortex of lymph nodes contain?
T cells
what does the medulla of lymph nodes contain?
T and B cells
what do medullary cords of lymph nodes contain?
macrophages and plasma cells
what are germinal centres in lymph nodes?
clusters of proliferating lymphocytes (T or B) that are proliferating in response to an antigen - these cause lymph nodes to expand or contract
describe the route of mature lymphocytes around the body
blood lymphocytes drain into tissue which then drains via an afferent vessel into lymph nodes and back out via the efferent vessel. From here they then enter the thoracic duct where they make their way back to the blood lymphocyte pool
describe the route of immature lymphocytes around the body
drain straight from blood via high endothelial venues bypassing the tissue and afferent vessels
what are high endothelial venules?
tall rounded endothelial cells that are post capillary venues only found in secondary lymphoid tissue
when do high endothelial venules increase in numbers?
following antigen stimulation
what are two main structures of the spleen?
red and white pulp
what is red pulp in the spleen?
open sinusoids containing red blood cells
what is white pulp in the spleen?
mainly lymphocytes
how does the spleen provide systemic immunity?
has a large blood flow
where can mucosal associated lymphoid tissue be found?
GI tract respiratory tract genito-urinary tract peters patches appendix tonsils
what are MALT?
dense areas of lymphocytes and macrophages that don’t have a capsule or afferent lymphatic vessels
describe the structure of MALT
no capsule
no afferent lymphatic vessel
have lymphoid follicles
have germinal centres
where are peters patches found?
in ideal submucosa of small bowel
what do payers patches detect?
antigens that diffuse across intestinal epithelia via M-cells
