Organs of the Haematopoietic System Flashcards
T cells are involved in what in the immune system?
in direct cellular killing
B cells are involved in what in the immune system?
in producing antibodies
What does the body need to ‘vet’ T and B cells for?
to check that they don’t react and attack our own body’s proteins (antigens)
What do primary lymphoid tissues generate?
specific immune cell populations
Usually T or B cells rather than both
What do secondary lymphoid tissues generate?
specific immune responses
T and B cells activated and proliferate in response to foreign antigens
Expansion of T cells
B cells form antibodies
Typified by the presence of ‘germinal centres’ packed with B cells
Give examples of primary lymphoid organs?
thymus and bone marrow (Bursa of Fabricius in birds)
maturation of T and B lymphocytes
Give examples of secondary lymphoid organs?
spleen, lymph nodes, MALT/GALT, tonsils & adenoids
initiation of immune response
give examples of tertiary lymphoid organs:
ectopic lymphoid tissues that develop at sites of chronic inflammation in non-lymphoid organs
lobes of the thymus?
lobes divided into lobules by trabeculae (or connective tissue walls)
What is the thymus?
an organ that provides environment for T cell development - ‘education’
what does each lobe of the thymus have?
an outer CORTEX and inner MEDULLA
How many steps are thymocytes educated in?
2 step process by resident cells
What happens to thymocytes that are not selected to be educated?
they undergo apoptosis and are phagocytosed by macrophages
What is the major role of the spleen?
the spleen is a secondary lymphoid organ whose major role is to survey the presence of foreign antigens in blood
what does the spleen consist of?
of a capsule with fibrous partitions (TRABECULAE)
What are the two types of tissue that make up the spleen?
red and white pulp
What is red pulp?
it filters and removes damaged or aged red blood cells - phagocytosis by macrophages
extracellular fluid drains into where?
into vessels called LYMPHATICS
where are lymph nodes located?
within the lymphatic system to allow the surveillance of antigen and the initiation of adaptive immune response
where may foreign antigen/pathogens present in tissue drain to and by what?
drain into lymphatics by antigen presenting cells
structure of lymph nodes?
they are small, bean-shaped, tissue aggregates at junctions of major lymph vessels - 1-25mm diameter becoming much larger during infection
what are lymph nodes surrounded by?
by a capsule & consisting of 3 main areas: cortex, paracortex & medulla
what enters via the AFFERENT lymphatic?
Lymph carrying antigen and DCs enter via the afferent
where do lymphocytes enter blood via?
via HIGH ENDOTHELIAL VENULES (HEV)
How do lymphocytes exit the node?
they migrate through the medulla and exit the node via the EFFERENT LYMPHATIC
Where do T cells migrate?
localise in the paracortex
Where do B cells migrate to?
in the follicles within the CORTEX (B cell responses develop in germinal centres)
white pulp (of spleen) role?
to bring lymphocytes together to mount immune responses against foreign antigen
what circulates through the white pulp?
lymphocytes (B and T cells) circulate through the white pulp entering via terminal arterioles and leaving via blood vessels in the RED pulp
Where do T cells localise in the spleen’s white pulp?
within the periarteriolar sheath (PALS) whers they interact with antigen presenting cells (DCS)
Where do B cells localise in the white pulp of the spleen?
in follicles where they interact with a specialised follicular DCs (fDCs)
B cells responding to antigens form what?
form GERMINAL CENTRES in which they mature and differentiate further
What are Peyer’s patches?
aggregates of lymphocytes; B cells form follicles surrounded by T cells, DCs & macrophages
Peyer’s patches have efferent lymphatics - where do these drain into?
drain into mesenteric lymph nodes but no afferent lymphatics
what are peyer’s patches covered by?
by specialised lymphoepithelium containing M cells
what does MALT stand for?
Mucosal Associated Lymphoid Tissue
What does GALT stand for?
Gut associated lympoid tissue
What is BALT?
Bronchus associated lymphoid tissue
What is GALT made up of?
it is made up of Peyer’s patches and isolated follicles in intestinal submucosa
what is MALT?
it is diffusely distributed lymphoid tissues in lining (mucosae) of gastrointestinal, respiratory & urogenital tracts
What are Peyer’s patches?
aggregation of lymphocytes
what is the aggregation of lymphocytes that forms Peyer’s patches?
B cells form follicles surrounded by T cells, DCs and macrophages
Peyer’s patches have lymphatic drainage… explain it?
has efferent lymphatics that drain into mesenteric lymph nodes but has no afferent lymphatics
what are Peyer’s patches covered by?
covered by specialised lymphoepithelium containing M cells
how do antigens in the gut enter the Peyer’s patches?
enters via M cells that selectively take up particles and deliver them to lymphoid follicles OR by specialised DCs which ‘reach’ onto gut lumen to sample antigens
DCs are?
dendritic cells
responsible for initiating all antigen-specific immune responses
what are tonsils aka?
waldeyer’s ring
what are adenoids?
pharyngeal tonsils
what do tonsils and adenoids do?
they are other secondary lymphoid tissue and they - survery the oropharyngeal and nasal cavities for foreign antigens
what does the harderian gland do?
it is another secondary lymphoid tissue
and it surveys the oculonasal region in birds
what does the cecal tonsil do?
it is another secondary lymphoid tissue - it is a gut lymphoid tissue located in the large intestine of birds
what is the appendix - what does it do?
the appendix of humans (+ dog/cats) contains a significant amount of lymphoid tissue suggesting it may function as a GALT
