Structure of the Lymphoreticular System Flashcards
What is the function of the lymphatic system?
It is apart of the circulatory system, and consists of a network of capillaries & ducts which work to remove interstitial fluid (lymph) and carry it back to the circulating blood.
It is also key in the transportation of fats, whilst also providing a role in the immune response
What are the organs that make up the lymphoreticular system?
Thymus
Spleen
Tonsils
MALT
GALT
Bursa of Fabricius
Describe the flow of lymph in the body
Lymph is collected from the interstitial spaces into the lymphatic capillaries
It is carried through the lymphatic vessels, passing through lymph nodes and enters the lymphatic ducts
It is then drained into the cranial vena cava where it is put back into the circularity system
What is the structure & function of the thoracic duct?
Largest duct of the lymphatic system, originates from the chyle cistern in the dorsal abdomen.
It drains lymph into the cranial vena cava around the vicinity of the left brachiocephalic vein
What are the roles of circulatory and lymph capillaries in the lymphoid system?
Fluid & dissolved gases are passing out of circulatory capillaries into tissues
Overall net filtration of fluid - excess is removed from the tissue by the lymphatic system
Interstitial fluid enter lymph capillaries via openings between adjacent endothelial cells
What are the roles and structures of vessels in the lymph system?
Flow is unidirectional
Lymph vessels are similar in structure to veins but are more delicate (thinner walls)
Valves (many) prevent backflow
Flow is mainly passive and is maintained by valves, contraction of surrounding skeletal muscles and arteries and respiratory pump
List and describe the role of primary lymphoid tissues?
Where lymphocytes are produced and mature into:
B Cells: Bone Marrow, Bursa of Fabricius (birds-Birds don’t have bone marrow),
Peyer's Patches (Ruminants-Act as a primary in ruminents)
T Cells: Thymus
Outline the role of secondary lymphoid tissues?
Where lymphocytes are activated to survey and filter foreign antigens
What are the primary lymphoid organs?
Thymus
Bone Marrow
Bursa of Fabricius
What are the secondary lymphoid organs?
Spleen
Lymph nodes
Peyer’s Patches
MALT
What is the thymus, where is it located and what is its function?
Primary lymphoid organ that regresses with age and is replaced with fat tissue
It is found in the caudal neck & thoracic region and varies in appearance across species.
Its primary features are that is has a cortex, medulla and is surrounded by a connective tissue capsule. It has strands that form incomplete lobules & also contains Hassall’s corpuscle
It plays a key role in the maturation of T Lymphocytes kick starting the immune system in younger animals
What is the spleen, where is it located and what is its function?
Largest lymphoid organ
It is closely attached to the greater curvature of the stomach on the LHS of cranial abdomen. Its defining features are the smooth muscle capsule, central arteries, trabeculae and red & white pulp
Appears bean shaped in birds
It stores blood, and plays a role in the destruction of RBC
Red pulp:
Removal of particulate matter from circulation (filtering out of bacteria and foreign
particles)
White pulp:
Division of lymphocytes – secondary lymphoid organ
Where are lymph nodes located?
They are found at various points along lymph vessels. They can be superficial or deep and vary among species
Describe the structure and function of lymph nodes
Structure:
Convex surface has afferent fibres entering
Concave surface has the Hilus where artery/ veins and the efferent lymph vessels leave the node.
Within the node it is split into three areas: capsule, cortex and medulla
Flow of lymph:
Lymph enters the lymph node through afferent fibres
It passes through into the subcapsular sinus, into the trabecular sinus and then into the medullary sinus before exiting through the efferent lymphatic vessels.
As lymph passes through the node, lymphocytes are added, and macrophages act as filters to remove microorganisms in an attempt to halt the spread of infection and tumours
What are the anatomical features of lymph nodes?
Capsule and subcapsular sinus
Cortex – B-cell centres
High endothelial venules (HEVs)
-Characterised by plump endothelial cells
-Allow lymphocytes from blood to enter directly into a lymph node
