Lecture 9: The Lymphatic System Flashcards
What immune response is the lymphatic system involved in?
Adaptive and innate immune response
Name some organs/tissues that are in the lymphatic system (7 in total)
Lymphocytes
Spleen
Bone Marrow
Thymus gland
Diffuse lymphatic tissue
Lymph nodes
Lymph vessels
What is the main transport vessel for cells and large molecules to migrate from tissue back to blood?
Lymph vessels
Where can you find lymphatic tissue?
All throughout the body
What tissues specifically can you usually find lymphatic tissue?
Lamina propria of tissues
Why can you find lymph vessels surrounded by smooth muscle?
Smooth muscle helps with the movement of the lymphatic vessels.
This is because the fluid flows at a low pressure.
Why do lymph vessels need the help of skeletal muscles?
The contraction of skeletal muscle can help move the fluid along
How do lymph vessels help WBCs?
WBCs use the lymph vessels to travel around the body.
Lymphocytes will migrate out of the tissue into lymp vessels (kind of like a subway)
What are the two specialised cells embedded in lymphatic tissue/nodules called?
Plasma cells
Eosinophils
ToF: Lymphatic tissue are un-encapsulated
True
ToF: Lymphatic nodules and lymph nodes are the same
False
What is a lymphatic nodule? Describe (3 points)
Dense masses of lymphocytes and macrophages.
Not encapsulated (does not have a distinct outer boundary separating them from surrounding tissues)
Small, localised clusters of lymphatic tissue (found throughout the body)
What is a lymph node? Describe (3 points)
Small, bean-shaped structures located along the lymphatic vessels
Acts as filter for lymphatic fluid that circulates throughout the lymphatic systems, removes foreign substances/waste products
Encapsulated (surrounded by a fibrous capsule, separated from surrounding tissues)
Where are lymphatic nodules found? (4 points)
Associated with the Alimentary canal
Tonsils: Adenoids (pharyngeal tonsils), palatine and lingual tonsil
Ileum: Peyer’s Patches
Appendix
What does a lack of encapsulation in the lymphatic nodules cause?
Lymphatic nodules are more diffuse and less organised.
What are some similarities between lymphatic nodules and lymph nodes? (4 points)
Contains lymphocytes
Involved in filtering and removing foreign substances and waste products
Both can become enlarged in response to infection/inflammation
Can both be affected by lymphoma
ToF: Lymphatic nodules are encapsulated
False
ToF: Lymph nodes are encapsulated
True
ToF: Lymph nodes are un-encapsulated
False
What is the mantle zone in the lymphatic nodule?
Layer of lymphocytes that surrounds the germinal centre in a lymphatic nodule.
Comprised mainly of B-cells
Where can you find the germinal centre?
Lymph nodes
Lymphatic Nodules
What does the germinal centre do?
Site where B-cells mature and differentiate into plasma cells that produce antibodies.
What surrounds the germinal centre?
Mantle zone
What does the Mantle zone do?
Provides support for the maturation and differentiation of B-cells
Where is the mantle zone located in the lymph node?
Found on the outer edge of the lymph node.
Why is the mantle zone important in the immune response? (L)
Helps regulate the production of antibodies by B-cells by exposing B-cells. The B-cells that recognise a specific antigen, undergo clonal expansion and differentiate into plasma cells.
Therefore a large amount of specific antibodies are produced to neutralise the invading pathogen
What size are lymph nodes?
1mm-20mm
Where can lymph nodes be mostly found even if they are distributed throughout the body?
Axilla (under the shoulder joint where the arm connects to the shoulder)
Groin / (0) \
Mesentery (fold of membrane that attaches the intestine to the abdominal wall and holds it in place)
What is each lymph node supplied by?
2 lymph vessels
One afferent (carries into the node)
One efferent (carries fluid and cells away/out)
What is the name of the network that supports the lymphocytes?
Reticular network
What is the reticular network made up of?
Reticular fibres (type of collagen fibre) produced by reticular cells
What is the role of the sentinel lymph nodes?
Scans for antigens and activated lymphocytes
What does it mean if there are activated lymphocytes found in the lymph fluid?
Sign of an Infection
Why are sentinel nodes important in the context of cancer? (L)
When cancer cells break away from the primary tumour, they can enter the lymphatic system and be carried away to nearby lymph nodes.
The sentinel nodes are the first lymph nodes that these cancer cells are likely to reach.
By examining the sentinel node, it can be determined if have spread beyond the primary tumour and intro the lymphatic system
Why is sentinel node biopsy performed?
Involves removing the sentinel node and examining it under a microscope.
Determines if it contains cancer cells.
If CC found then it means the cancer has begun to spread beyond the primary tumour and may require more aggressive treatment
What three tissues that a cancer can use?
Tissue infiltration
Haematological
Lymphatic system
Describe what tissue infiltration is?
Cancer keeps growing in the tissue that it started in
Describe how cancer uses the cardiovascular system (haematological)?
Seeds cancer cells into the blood and moves through the body looking for another victim
Describe how cancer uses the lymphatic system to spread?
Tumours go into the lymphatic vessels and start to disseminate.
Can grow in the sentinel lymph nodes
What do reticular cells secrete?
Reticulin
What jobs does the reticular network do? (5 marks)
Maintains the structural integrity of the lymphatic tissue
Provides scaffold for the attachment of immune cells
Allows immune cells move freely throughout the tissues
Provides a site for proliferation/differentiation of immune cells
Lymph fluid is filtered through the reticular network (allows immune cells to trap/eliminate pathogens)
Where are dendritic cells found in lymph nodes?
T cell zone
What are the dendritic cells in the T cell zone responsible for?
Capturing and presenting antigens to T cells
Important for coordinating the immune response
What is special about dendritic cells?
Co-express MHC 1 and MHC 2
Highly specialised antigen presenting cells
Why are macrophages an important component of the reticular network? (3 points)
Responsible for removing cellular debris/dead cells/foreign particles
Antigen presentation for T cells, coordinating an immune response
Produces cytokines, signalling the immune system
Where are Follicular dendritic cells found?
Germinal centres of lymph nodes and other lymphoid tissues
ToF: Follicular dendritic and dendritic cells are the same
False
Describe the key feature of Follicular dendritic cell
Has long branching dendrites that extend into the germinal centre This helps it trap and retain antigens within the germinal centre.
The antigens of the trapped pathogen are then displayed for the B cells
What type of collagen are reticulin fibres?
Type III
Where in the body are reticulin fibres widely distributed? (3 points)
Liver
Lung
Lymph
What dye helps visualise Reticulin fibres?
Stains that contain silver (argyrophilic)
Gordon & Sweet’s
Jones Methenamine Silver
Why is it important to use staining solution for reticulin fibres?
It sensitises the reticulin fibres which allows the reduction of silver on the fibres
What is the lymph node parenchyma divided into?
Cortex
Medulla
What does the cortex in the lymph node parenchyma contain?
Significant amount of lymphatic tissue
What does the medulla in the lymph node parenchyma contain?
Medullary cords and medullary sinuses
How are lymphocytes organised in the cortex?
Nodules
What is the function of the lymph node?
Responsible for phagocytosis of particulate matter
Plays a key role in the antibody response
In terms of antibody response what does the lymph node do?
Antigen presentation to naive B-cells
Plasma cells migrate to medullary cords to secrete antibody
What is lymphadenitis?
A swelling of the lymph nodes
What commonly causes lymphadenitis?
Common complication of infections (Mono, tonsillitis, Glandular fever, etc)
What is the pathogenesis of lymphadenitis? (how the disease develops)
Proliferation of lymphocytes within germinal centres
Increase in proportion of plasma cells in the node
Draining of exudative fluid into lymph node
What is the treatment for lymphadenitis?
Antimicrobial therapy for underlying infection
Surgical removal for reoccurring episodes
The Thymus gland is an example of what kind of organ?
Lymphoepithelial organ
Anatomically where is the thymus is located?
Superior mediastinum (anterior to the heart)
At what stage of life is the thymus functional at?
Immediately after birth
At what stage of life does the thymus start to lose it’s function?
Downhill from puberty onwards
At what stage of life does the thymus stop losing it’s function?
Doesn’t exist
What is the name of the process that describes what happens to the thymus in life?
Involution
What role does the thymus play in the immune system?
T-cell education
What does the Thymus get replaced by as humans age?
Adipose tissue
What is the interior of the thymus divided by?
Thymic lobules by connective tissue
Where is the trabeculae found?
Located in the thymic capsule
What does the trabeculae contain?
Blood vessels and efferent lymph vessels
What are the sections of the thymus divided into?
Cortex
Medulla
What does the thymic cortex contain?
Significant amounts of developing T-cells
In the thymic cortex, what cell is it supported by?
Epithelioreticular cells
How many types of epithelioreticular cells are there?
6
What types of epithelioreticular cells are in the cortex?
Type I
Type II
Type III
What types of epithelioreticular cells are in the medulla?
Type IV
Type V
Type VI
Where is EC Type I found?
Boundary cells that are between the capsule and the cortex
What role does EC Type I play?
Separates the thymic parenchymal cells from the connective tissue
What MHC does EC Type II express?
Co-expresses MHC I and MHC II
Where can you find EC Type III?
Boundary cells between cortex and medulla
What MHC does EC Type III express?
Co-expresses MHC I and MHC II
Where is EC Type IV found?
Boundary cells between the medulla and cortex
What is the role of EC Type V?
Provides cellular framework/architecture for the medulla
What is the role of Type VI?
Forms thymic corpuscles
