IMMUNE AND HAEMATOLOGICAL TISSUES Flashcards
describe the location of blood cell formation from foetus to adult?
blood islands in yolk sac, then liver until shortly before birth, then spleen until bones are vascularised, bone marrow of long bones in children, bone marrow of pelvis, sternum, vertbrae in adults
where are plasma proteins formed?
hepatocytes
what are primary lymphoid tissues?
sites where lymphocytes mature and differentiate to express antigen receptors so they are functionally competent to recognise foreign antigens
what are the 2 primary lymphoid tissues?
thymus (T lymphocytes) and bone marrow (B lymphocytes)
where are B and T lymphocyte precursors formed?
bone marrow (different for maturing T cells)
what are secondary lymphoid tissues?
specialised sites for turning on an acquired immune response
what are the different types of secondary lymphoid tissue?
lymph nodes, spleen, Peyer’s patches and mucosal associated lymphoid tissue
what are mucosal associated lymphoid tissues?
aggregates of lymphocytes in a reticular mesh e.g. Gut associated lymphoid tissue or Nasal associated lymphoid tissue
where is the thymus found?
in the mediastinum between the sternum and the aorta
where does the thymus originate from?
the embryo’s 3rd pharyngeal pouch
when is the thymus most active and largest? why?
most active during childhood and largest during puberty. after puberty it involutes and the amount of lymphatic tissue decreases and adipocyte content increases
what is the function of the thymus?
important in the maturation of T cells
describe the histology of the thymus?
it has a medulla which is located centrally within each follicle and has increased amounts of epithelial cells. Hassall’s corpuscles are present in this region. the cortex is located peripherally within each follicle and is largely composed of lymphocytes supported by epithelial reticular cells.
what are hassle’s corpuscles?
concentric arrangements of epithelia reticular cells
what is the arterial supply of the thymus
anterior intercostal arteries and small branches from internal thoracic arteries.
what is the venous set of up of the thymus?
the venous blood drains into the left brachiocephalic and internal thoracic veins
describe the histology of a lymph node?
they are covered in a capsule which has extensions called trabeculae. inside the capsule is a supporting network of reticular fibres and fibroblasts. the outer cortex has lymphatic nodules (mostly B cells), the inner cortex consist of mainly T cells and dendritic cells, the medulla contains B cells, plasma cells and macrophages.
what are the functions of the trabeculae of the lymph node?
compartmentalisation, provides support and provides a route for blood vessels into the interior of the node.
what is the difference between a primary and secondary lymphatic nodule?
primary lymphatic nodules are mainly B cells whilst secondary nodules form in response to an antigen and are sites of plasma cell and memory cell formation.
describe the pathway of lymph through the lymph node?
lymph enter through several afferent lymphatic vessels, enters sinuses in the node and then flow through trabecular sinuses which extend through the cortex, into the medullary sinuses which then extend through the medulla. the medullary sinus drain into 1 or 2 efferent lymphatic vessels.
how are peyer’s patches structure different to lymph nodes?
they are not surrounded by a connective tissue capsule
what special epithelial cells line the side of peers patches facing the intestinal lumen? why?
microfold cells
transcytosis of antigens
what is the function of Peyer’s patches?
to analyse and response to pathogenic microbes in the ileum. antigens from microbes in the gut are absorbed via endocytosis by microfold cells. these antigens are passed to lymphoid tissue where they are absorbed by macrophages and presented to T lymphocytes and B lymphocytes. these lymphocytes can, if needed, trigger the immune response by producing pathogen-specific antibodies, turn into cytotoxic T lymphocytes and migrate through lymphatic vessels to alert the other cells of the immune system.
where do lymphocytes enter lymph nodes?
at high endothelial venules and some enter via afferent lymphatics.
what are the functions of the lymphatic system?
to drain excess interstitial fluid, transport dietary lipids and carry out immune responses.
describe the vessel structure and organisation of the lymphatic system?
they begin as lymphatic capillaries between cells and are closed at one end, these then unite to form lymphatic vessels. at intervals along the lymphatic vessels, the lymph flows through lymph nodes.
describe the key features of lymphatic capillaries?
have a one way structure that permits interstitial fluid to flow in only. they are attached to anchoring filaments that attach them to surrounding tissues. when excess interstitial fluid accumulates and causes swelling, the anchoring filaments are pulled which makes opening between cells even larger so more fluid can flow in.
what are lacteals?
specialised lymphatic capillaries in the small intestine which carry dietary lipids into lymphatic vessels and then into the blood
what are lymphatic trunks?
as lymphatic vessels exit lymph nodes and unite they form these trunks.
what are the main lymphatic trunks?
lumbar (lower limbs/pelvis/kidneys/adrenal glands and abdominal wall), intestinal (stomach, intestines, pancreas, spleen and liver), broncho mediastinal (thoracic wall, lung and heart), subclavian (upper limbs) and jugular (head and neck).
where does lymph from the lymph trunks pass in to?
the thoracic duct and right lymphatic duct. these then drain into the blood
what is superficial lymphatic drainage?
drainage that follows superficial veins, flows into lymph nodes in axillary, inguinal or cervical areas where they then drain into deep lymphatics.
what is deep lymphatic drainage?
drainage that follows main vessels. lymph from 75% of the body drains into the left brachiocephalic vein via the thoracic duct. lymph from the upper right quadrant enters the right brachiocephalic veins.
