Histology of lymphoid organs Flashcards
B cell maturation occurs where in birds?
in Bursa Fabricius
in mammals - B cell maturation?
bone marrow
T cell maturation in mammals?
in thymus
ruminants - B cell proliferation and maturation?
Peyer’s patches
How do T cells and B cells proliferate?
Expansion of T cells
B cells form antibodies
what cells mature to T cells?
bone marrow derived cells traverse the medulla and mature to T cells
what happens to cells recognising self antigens?
they are removed from the thymus
what happens to lymphoid tissue with sexual maturity?
it involutes with sexual maturity and is replaced by fat q
lobules of thymus?
each have a cortex and a medulla
thymus does not just have T cells - also?
thymus is supported by unique cytoreticulum of stellate, epithelial reticular cells and only a few reticular fibres
What is the Bursa of Fabricius?
sac-like dorsal diverticulum of the proctoderm
What is the Bursa of Fabricius unique to?
birds
what epithelium lines the Bursa
pseudostratified columnar epithelium
pB of f
primary tissue mainly but has some secondary function
GALT?
gut associated lymphoid tissue
where do peyer’s patches occur?
in the wall of the small intestines, especially ileum
what do the capsule and trabeculae of the lymph nodes make up?
the connective tissue
what do the lymphatic nodules and lymphatic tissue form?
the medullary cord
what does the medullary cord contain?
lymphocytes, macrophages and plasma cells
what does the paracortex of the medulla of the lymph nodes consist of?
T cells (CD4 T-helper cells & CD8 T-cytotoxic cells) and high endothelial venules (HEVs)
what are high endothelial venules?
they are the main entry and exit site of (T and B) lymphocytes
what are HEVs lined by?
by simple cuboidal epithelium
what does the medulla of the lymph nodes express?
they express receptors (selectins) for antigen-primed lymphocytes
similar vessels are present aswell in the thymic cortex and Peyer’s patches
what is the spleen characterised by?
by smooth muscle in the capsule and as a meshwork trabeculae
what does white pulp tissue of the spleen include?
includes lymphoid tissue around arterioles
what does the red pulp tissue of the spleen consist of?
consist of a loose vascular framework
the thymus is not just supported by T cells - what else supports the thymus?
it is supported by a unique cytoreticulum of stellate, epithelial cells and only a few reticular fibres
ALSO some dendritic cells, macrophages and other WBC
Hassall’s corpuscles - location?
these are found in the medulla of each lobe of the thymus
What are Hassall’s corpuscles?
they are concentric whorls of acidophilic and flattened reticular cells that may become swollen, keratinised and calcified centrally
What is the Bursa of Fabricius?
it is a saclike dorsal diverticulum of the proctodeum
it is unique in birds
what epithelium lines the Bursa of Fabricius?
pseudostratified columnar epithelium
describe the structure of the Bursa of Fabricius?
it has thick mucosal folds - polyhedral follicles
it has a cortex and medulla
what is found between the cortex and the medulla of the Bursa of Fabricius?
a layer of undifferentiated, epithelium-derived cells - ?capillary layer?
apex of the Bursa of Fabricius?
epithelial tuft of simple columnar cells which contains lytic enzymes
function of peyer’s patches in ruminants?
they have an additional function as a primary lymphoid organ
structure of ruminant peyer’s patches?
aggregated lymphoid tissue with germinal centres (reflecting development of a specific immune response: secondary lymphoid tissue)
peyer’s patches are part of what?
part of MALT or GALT
Where do peyer’s patches occur?
in the wall of the small intestines, especially ileum
what are peyer’s patches covered by?
by a specialised follicle-associated epithelium, in which there are numerous M (micro fold) cells specialised for antigen uptake.
what cells make up peyer’s patches?
dendritic cells, macrophages, T and B cells
what are the capsule and trabeculae of the lymph nodes?
they are connective tissue
where does afferent lymph travel in lymph nodes?
travels within spaces (sinuses) which are present beneath the capsule and along trabecula of connective tissue that extends from the cortex into the medulla
what are the sinuses called that the afferent lymph travel through in the lymph nodes?
subcapsular sinus
