Lymphoid system Flashcards
What is lymph ?
Interstitial fluid from capillary beds that is not picked up by venules ; this fluid is returned to the circulatory system via lymphatic vessels via subclavian veins
On the way back , the lymph drains through one or more lymph nodes and is scanned
What is lymphoedema ?
Blocked lymph vessels or nodes that prevent drainage
May be a side effect of radiotherapy
Structure of lymph nodes
Composed of a cortex and medulla supported by a reticular network (fine collagen fibres) and surrounded by a CT capsule with extension that support blood vessels called trabeculae
Superficial cortex contains lymphoid follicles which are aggregations of mainly B cells (deep cortex/paracortex does not)
Blood supply enters and leaves at the hilum (dent in centre of node)
Function of lymph nodes
Main function is to scan the lymph and identify/fight infection or cancer cells; lymph nodes contain lymphocytes (they circulate through the blood then enter nodes via high endothelial venules) and macrophages
B/T cell activation occurs in lymph nodes
Lymph enters via afferent lymphatic vessels into a network of sinuses (subcapsular → trabecular → medullary) which drain into efferent lymphatics at the hilum
Circulation of lymphocytes in the lymphatic system
Lymphocytes constantly travel between lymph nodes and other secondary lymph organisms in search of a matching antigen
majority of lymphocytes still travel in bloodstream
they enter the lymph nodes at high endothelial venules which are found in the Paracortex and have cuboidal endothelium
they then leave via the efferent lymph vessels from where they return to the bloodstream again
Lymphocyte distribution in secondary lymphoid organs
Name the antigens presenting cells (APCs) present in the lymph nodes and explain their role
Macrophages and dendritic cells
phagocytose intruders and remnants of disintegrated cells
fragment ingested proteins and present them on major histocompatibility complex (MHC) on their surface ; this only occurs once the APCs have reached a lymph node
Antigen presentation in paracortex (T cell area) leading to T cell activation and proliferation; activated T cells move to B/T cell zone interface
this allows activated T cell to activate the B cell to proliferate and mature
B cells pick up antigen in the follicle, ingest it and move to the B/T cell zone interface
activated B cell moves back to cortex to proliferate and mature = germinal centre
Lymph nodes enlarge when …
There is an infection (because they are producing T/B cells)
when they are infected
when there is a lymphoma
when a tumour mestasises to nearby lymph nodes
Features of lymphomas
The lymphomas are malignancies of mature lymphoid cells
predominantly proliferate in the lymph nodes and spleen
lymphocytes in the bone marrow and blood are sometimes involved
Function of spleen
Filters circulating blood through sinusoids to remove effete RBCs and platelets
involved in phagocytosis of blood borne microorganisms ;
unhealthy cells cannot squeeze through gaps in the sheathed capillaries so are phagocytoses
healthy cells pass into the sinuses which drain into veins
mounts an immune response to antigens in blood
A patient with splenectomy (removal of spleen post trauma/tumour) will exhibit
Infection of blood
increased number of deformed RBCs and platelets
Structure of spleen
Comprised of a collagenous capsule surrounding a reticulin network which supports many sinusoids and lymphoid aggregates
blood enters and leaves at the hilum via the splenic artery and vein
blood entering the spleen ends up in sheathed capillaries which are lined with macrophages instead of endothelial cells
What is the white pulp of the spleen
Paracortex and superficial cortex
Mucosa associated lymphoid tissue (MALT)
This refers to the lymphoid tissue in submucosal membrane sites of the body
Populated by lymphocytes
lymph follicles or nodules are found just under the epithelia ; no distinctive connective tissue capsules
principle sites of antigen presentation and T/B cell activation
kept in shape via network of fine reticular fibres that allow lymphocytes and APCs to circulate
blood vessels with broadened epithelia for entry/exit of travelling lymphocytes
Describe the tonsils
Aggregates of lymph follicles ina partial collagen capsule deep in the epithelium of the oral/nasal cavities
this forms a ring around the pharynx
