Lymphatic System Flashcards
what is the lymphatic system?
lymphatic system is a collection of organs & tissues that are involved in host defence.
what are lymph vessels
Lymph vessels are the main transport vessel for cells & large molecules to migrate from tissue back to blood.
what do lymph vessels drain into?
Lymph vessels drain into vena cava.
lymph vessel structure
structured similarly to capillaries
> More porous walls.
> Most numerous in skin & mucous membranes.
> Developmentally begin as blind capillaries.
> Smooth muscle surrounding lymph vessels aid in movement of fluid.
> Larger vessels also have valves.
Diffuse lymphatic tissue
found throughout the body
Unencapsulated.
Usually within the lamina propria of the tissues
example of diffuse lymphatic tissue
Mucosa associated lymphatic tissue = MALT
in the colon
cells within diffuse lymphatic tissue
Lymphocytes are free to move from the tissue into lymph vessels post-exposure. As unencapsulated
Have quite specialised cells embedded within:
> Plasma cells.
> Eosinophils.
Lymphatic nodules
Lymphatic nodules are a concentration of lymphocytes embedded around reticular cells & fibres.
some similarities between lymph nodes and lymph nodules
Germinal centres.
Mantle zones.
Locations of lymphatic nodules
Lymphatic nodules are associated with the alimentary canal. Examples include:
> Tonsils.
Adenoids (pharyngeal tonsils)
Palatine and lingual tonsils.
> Peyer’s Patches.
Ileum.
> Appendix.lymph nodes
Lymph nodes are small encapsulated organs which “filter” lymph fluid.
1mm-20mm.
locations of lymph nodes
Widely distributed throughout the body but can be found in elevated concentrations in certain locations:
> Axilla.
> Groin.
> Mesentery.
support of lymph nodes
Each lymph node is supplied by 2 lymph vessels: Afferent & efferent.
Lymphocytes are supported by the reticular network.
prognostic value of lymph nodes
Offer prognostic indications for cancer
Can see if tumour has spread to local lymph nodes
Surgically and imaging ways to check
reticular network
These are cells that support the function of lymphocytes within the node.
cells in reticular network
Reticular cells.
> Secrete reticulin.
Dendritic cells.
> Highly specialised antigen presenting cells.
> Co-express MHC 1 and MHC 2.
> Important for the activation of T-cells.
Macrophages.
Follicular dendritic cells.
> Interdigitate between B-lymphocytes within the germinal centre.
Reticulin
Reticulin fibres are a form of collagen (type III) that are secreted by reticular cells.
A form of specialised fibroblast.
Produces a supportive mesh within soft tissues.
Liver, lung, lymph etc.
Reticulin fibres are very thin and widely distributed in these tissues.
Can be very useful in studying health of a tissue.
silver stains
Reticulin can be visualised using stains containing silver.
> Argyrophilic.
In the presence of reticulin certain silver stains leave a black deposit.
Staining solution first sensitises reticulin fibres which allows the reduction of silver on the fibres.
Examples of silver stains x2
> Gordon & Sweet’s
> Jones Methenamine Silver
Histological structure of a lymph node
The lymph node parenchyma is divided into a cortex and a medulla.
Cortex contains significant amount of lymphatic tissue.
Medulla consists of medullary cords & sinuses.
Lymphocytes within the cortex are organised into nodules.
functions of the lymph node
Lymph nodes are important structures within the human immunological response.
They are responsible for phagocytosis of particulate matter.
role of lymph nodes in antibody response
They play a key role in the antibody response:
> Antigen presentation to naïve B-cells.
> Plasma cells migrate to medullary cords to secrete antibody.
swelling lymph nodes
A swelling of the lymph nodes (lymphadenitis) is a common complication of infections.
Mono, tonsilitis etc…
exudative fluid – pushed into tissues in response to inflammation
What is the pathogenesis of swollen lymph nodes?
Proliferation of lymphocytes within germinal centres.
Increase in proportion of plasma cells in the node.
Draining of exudative fluid into lymph node.
