Lymph Node & Spleen Flashcards
What type of tissue is the lymph nodes & spleen
Secondary/peripheral lymphoid tissue
What other secondary lymphoid tissue are there apart from the lymph nodes & spleen
Tonsils/ adenoids
Peyer’s patches in intestine
Describe the structure of lymph nodes
Encapsulated collections of lymphoid tissue
Ovoid/bean shaped
Where are lymph nodes found
They are distrusted along the course of lymphatic vessels
What are the two distinct groups of lymph nodes & how can they be examined
- Superficial node groups (e.g. in the cervical, axillary and inguinal regions) can be palpated.
- Internal node groups (e.g. mediastinal, para-aortic) can be viewed radiologically
What two structures make up the lymphatic system
Lymphatic vessels & lymph nodes
What is the role of the lymphatic system in the innate vs adaptive
Innate - stores innate immune cells
Links both - antigen presenting cells traffic
Adaptive - develops & activates lymphocytes & memory cells
What is the role of the afferent channels in lymph nodes
Afferent channels drain lymph through the capsule into the supcapsular sinus
What does lymphadenopathy mean
enlargement of lymph node
Lymphadenopathy aetiology
Local inflammation - TB, toxoplasma, cat scratch disease
Systemic inflammation - Viral, autoimmune, CTD
Malignancy - lymphoma, metastatic
Others e.g. sarcoidosis
What is a sentinel lymph node
The first lymph node to which cancer cells are most likely to spread
How is a sentinel lymph node identified
By dye or radioactive isotopes
What is the importance of identifying sentinel lymph nodes in malignancy
By identifying which lymph node the cancer is most likely to spread to the lymph node can be examined and check for cancer
Describe the flow of lymph through the lymph node
Afferent lymphatic vessel =>
Subcapsular sinus =>
Trabecular sinus =>
Medullary cords & sinus =>
(Merge at hilum to form…)
Efferent lymphatic vessel
Identify the structures/parts of a lymph node
Capsule & trabecula
Subcapsular & trabecular sinuses
Inner & outer cortex
Lymphatic nodule (follicle) & germinal centre
Medulla & medullary sinuses
What is the purpose of lymph draining through the node
It allows antigenic material to interact with fixed lymphoid tissue for an immune response
Where do the medullary sinuses of a lymph node merge to form efferent lymphatics
Hilum
What is the lymph node capsule made of
fibrous connective tissue
Accumulation of what cell type would you expect to see in the sinuses of reactive lymph nodes (due to infection/foreign antigens etc)
Antigen presenting cells - histiocytes & dendritic cells
What are the three main regions of a lymph node
Cortex
Paracortex
Medulla
What cell is present in the lymph node cortex and how are they arranged
B lymphocytes arranged in follicles
What cell is present in the lymph node paracortex and how are they arranged
Mainly T lymphocytes, form part of interfollicular tissue
What is the lymph node medulla
Cord & sinuses draining into the hilum
What is the germinal centre of the lymph node
It is a specialised structure within the lymph node follicle
It is where B cells proliferate & mature to produce antibodies
It produces both plasma & memory B cells
Where are B cells located in the lymph node
- B cells mainly follicles & germinal centres
- Except plasma cells that are mainly in medulla
- Some B cells can also be found in the interfollicular tissue
Where are T cells present in the lymph node
Interfollicular tissue
Summarise the cell populations found in lymph nodes
B cells, T cells, NK cells
Macrophages, APCs, dendritic cells
Endothelial cells
Primary vs secondary follicles
Primary
- Small, quiescent lymphocytes
- Unstimulated
- No germinal centre
Secondary
- Activated follicles
- Reactive
- Have germinal centre
Summarise the journey of a naive B cell in the lymph node follicle
Clonal expansion
Somatic hypermutation
Affinity maturation & positive selection
Antigen engulfing & presenting
Differentiation
How are follicular dendritic cells different from dendritic cells
They are mesenchymal in origin
What is the 3 main functions of follicular dendritic cells
- Provide architectural support to germinal centres
- Facilitate debris removal by secreting bridging factors
Note: bridging factors attract macrophages to the site - Present antigens to naive B cells (with T helper cells assist)
Describe the initial steps in the follicle that begin the formation of step mature B cells (plasma/memory)
In the follicle
- Antigen-antibody complexes captured by FDCs
- FDCs present antigens (with T helper cell assist) to naive B cells
In the dark zone of germinal centre
- B cells undergo clonal expansion
- B cells then undergo somatic hypermutation
5a. Affinity maturation is achieved => B cells enter light zone
5b. Affinity maturation not achieved => B cells apoptose
In the light zone of germinal centre
- B cell division slows down
- B cells bind & internalise the antigen of FDCs
- Antigen is then displayed on B cell MHC II molecule
- This attracts T cells that help the B cell proliferate & mature
What are the three outcome options of the positively selected B cells in the light zone of the germinal centre
- Differentiate into plasma cells
- Differentiate into memory B cells
- Renter dark zone & proliferate to regulate germinal centre formation
What is a centroblast
Proliferating B cell in the dark zone
What is a centrocyte
B cell in the light zone
Compare how the name of the B cell changes depending on the area of the follicle they are in & their stage of development
Follicle (prior to antigen presentation) - naive B cells
Dark zone (prior to positive selection) - centroblast
Light zone (prior to differentiation) - centrocyte
After differentiation - Plasma or memory B cell
What cells are likely to be in the medullary cords
Plasma cells, B cells, Macrophages
What cells are likely to be in the medullary sinuses
Histiocytes, reticular cells
What are the four tonsils
Pharyngeal tonsils
Tubal tonsils
Palatine tonsils
Lingual tonsils
How do tonsils differ from lymph nodes
No capsule, instead have a ‘crypt’ (with overlying stratified squamous epithelium)
Name 3 signs of a reactive lymph node
- Stimulated germinal centres
- Interfollicular expansion
- Distended sinuses (histiocytosis)
Lymphadenopathy vs lymphadenitis
Lymphadenopathy - swollen lymph node
Lymphadenitis - swollen lymph node due to inflammation e.g. infection
Granulomatous lymphadenitis - what is it, what causes it and why should it be approached with caution
- granulomatous inflammation of lymph nodes
- causes include TB (ceseating), sarcoidosis (non-ceseating)
- caution: can mask malignancy
What would a B cell response in lymph nodes suggest (2)
Autoimmune condition (including IgG4 RD)
Infection
What would a T cell response in lymph nodes suggest
Viral infection
Drugs e.g. phenytoin
Dermatopathic
What would a phagocytic/granulomatous response in lymph nodes suggest
Tumour related
Dermatopathic
Granulomatous disease (sarcoidosis, TB)
What does a generalised lymphadenopathy suggest
- Systemic inflammatory/ immunological process
- Widespread malignancy (severe metastatic or lymphoma)
Where is the spleen anatomically located
Left upper quadrant of abdomen
What are the two surfaces of the spleen
Diaphragmatic surface
Visceral surface
What structures/organs are in contact with the visceral surface of the spleen (4)
Left kidney
gastric fundus
Pancreas tail
Splenic flexure of colon
What artery supplies the spleen & what is it a branch of
Splenic artery
Branch of coeliac trunk
What vein drains the spleen
Splenic vein
(Forms portal vein with superior mesenteric vein)
What is the spleen parenchyma split into
Red pulp & white pulp
Is the spleen encapsulated
Yes
What does the red pulp contain
Sinusoids & cords
Describe the structure of the sinusoids in the red pulp
- Fenestrated endothelial cell lining
- Supported by hoops of reticulin
What cells do the cords of the red pulp of the spleen contain
Monocytes/ Macrophages!!!
& some fibroblasts
& cells in transit - RBCs, WBCs etc
What supports the sinusoids in spleen
Hoops of reticulin
What is the function of the red pulp of the spleen
- Filters the blood (foreign material, damaged cells etc) &
- Facilitates immune response to antigens
What is the white pulp of the spleen made up of (2)
-Peri-arteriolar lymphoid sheath (PALS) - CD4+ lymphoid cells
-Lymphoid follicles - B cells
What is the difference in antigen presentation in the lymph nodes vs spleen
Lymph node - via APCs in blood
Spleen - via blood that stimulates APCs in the white pulp
Describe the direction of blood flow through the spleen
Splenic artery =>
White pulp =>
Red pulp =>
Splenic vein
Where does B vs T cell maturation occur
B cell - bone marrow
T cell - thymus
Where does B vs T cell activation occur
Both occur in secondary lymphoid tissue e.g. spleen, lymph nodes
Name the 2 main lymph node groups in the neck & where the supply
- Cervical nodes - Located in the neck and back
- Submandibular nodes - Located below the mandible
- Supraclavicular nodes - Located just above clavicle
- Axillary nodes - Located in the armpits
- Mesenteric nodes - Located deep in abdomen (intestine membrane)
- Inguinal nodes - Located in the groin
- Popliteal nodes - Located in popliteal fossa
