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Molecular Pathology > Lymphatic System > Flashcards

Lymphatic System Flashcards

1
Q

what is the lymphatic system?

A

lymphatic system is a collection of organs & tissues that are involved in host defence.

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2
Q

what are lymph vessels

A

Lymph vessels are the main transport vessel for cells & large molecules to migrate from tissue back to blood.

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3
Q

what do lymph vessels drain into?

A

Lymph vessels drain into vena cava.

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4
Q

lymph vessel structure

A

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.

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5
Q

Diffuse lymphatic tissue

A

found throughout the body
Unencapsulated.
Usually within the lamina propria of the tissues

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6
Q

example of diffuse lymphatic tissue

A

Mucosa associated lymphatic tissue = MALT

in the colon

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7
Q

cells within diffuse lymphatic tissue

A

Lymphocytes are free to move from the tissue into lymph vessels post-exposure. As unencapsulated
Have quite specialised cells embedded within:
> Plasma cells.
> Eosinophils.

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8
Q

Lymphatic nodules

A

Lymphatic nodules are a concentration of lymphocytes embedded around reticular cells & fibres.

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9
Q

some similarities between lymph nodes and lymph nodules

A

Germinal centres.

Mantle zones.

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10
Q

Locations of lymphatic nodules

A 
Lymphatic nodules are associated with the alimentary canal. Examples include:
> Tonsils.
         Adenoids (pharyngeal tonsils)
         Palatine and lingual tonsils.
> Peyer’s Patches.
          Ileum.
> Appendix.
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11
Q

lymph nodes

A

Lymph nodes are small encapsulated organs which “filter” lymph fluid.
1mm-20mm.

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12
Q

locations of lymph nodes

A

Widely distributed throughout the body but can be found in elevated concentrations in certain locations:
> Axilla.
> Groin.
> Mesentery.

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13
Q

support of lymph nodes

A

Each lymph node is supplied by 2 lymph vessels: Afferent & efferent.
Lymphocytes are supported by the reticular network.

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14
Q

prognostic value of lymph nodes

A

Offer prognostic indications for cancer
Can see if tumour has spread to local lymph nodes
Surgically and imaging ways to check

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15
Q

reticular network

A

These are cells that support the function of lymphocytes within the node.

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16
Q

cells in reticular network

A

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.

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17
Q

Reticulin

A

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.

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18
Q

silver stains

A

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.

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19
Q

Examples of silver stains x2

A

> Gordon & Sweet’s

> Jones Methenamine Silver

20
Q

Histological structure of a lymph node

A

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.

21
Q

functions of the lymph node

A

Lymph nodes are important structures within the human immunological response.
They are responsible for phagocytosis of particulate matter.

22
Q

role of lymph nodes in antibody response

A

They play a key role in the antibody response:
> Antigen presentation to naïve B-cells.
> Plasma cells migrate to medullary cords to secrete antibody.

23
Q

swelling lymph nodes

A

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

24
Q

What is the pathogenesis of swollen lymph nodes?

A

Proliferation of lymphocytes within germinal centres.
Increase in proportion of plasma cells in the node.
Draining of exudative fluid into lymph node.

25
Q

Treatment of swollen lymph nodes

A

Antimicrobial therapy for underlying infection.
Surgical removal for reoccurring episodes.
treat pain

26
Q

thymus gland

A

The thymus is an example of a lymphoepithelial organ.
Anatomically the thymus is located in the superior mediastinum.
Anterior to the heart.
The thymus is “unique” in that it is fully functional at birth and then downhill from puberty onwards!
In a process known as involution the tissue is gradually replaced with adipose.
The thymus has a vital role in T-cell education.

27
Q

structure of thymus gland

A

The interior of the thymus is divided into thymic lobules by connective tissue.
Trabeculae emanate from the thymic capsule.
The trabeculae contain blood vessels and efferent lymph vessels.
The thymus can also be divided into the cortex & medulla.
Thymic cortex contains a significant number of developing T-cells.
Supported by epithelioreticular cells.

28
Q

3 type of epithelioreticular cells in the cortex

A

Type I
> Boundary cells between capsule and cortex.
> Separates the thymic parenchymal cells from the connective tissue.
Type II
> Stellate cells which co-express MHC I and MHC II.
Type III
> Boundary cells between cortex and medulla.
> Co-express MHC I and MHC II.

29
Q

3 type of epithelioreticular cells in the medulla

A

Type IV
> Boundary cell between medulla and cortex.
Type V
> Provides cellular framework/architecture for the medulla.
Type VI
> Form thymic corpuscles.

30
Q

Thymic medulla: Hassall’s corpuscles

A

Still not sure what they do

Correlation between activity within corpuscles and autoimmune disease, particularly type 1 diabetes

31
Q

Thymic macrophages

A

Macrophages can be found throughout the thymus gland and are thought of as the 7th epithelioreticular cell.
Within the cortex, they play a key role in removing abnormal T-cells.
98% of all T-cells produced in the thymus will meet this fate!
Within the context of the thymus they can also be known as PAS cells.
Lysosome vesicles are very visible under PAS staining.
Play an important role in the thymus-blood barrier.

32
Q

Thymus-blood barrier.

A

The blood-thymus barrier prevents inappropriate exposure of developing T-cells to antigen.

autoimmune disease is a consequence of going wrong

33
Q

what is the blood-thymus barrier is formed from

A

Continuous capillaries rather than fenestrated/sinusoidal.
Type 1 epithelioreticular cells.
Macrophages.
Basal lamina.

34
Q

T-cell education process

A

Lymphoid progenitors migrate from the bone marrow to the thymus early in development.
Multipotent and self-renewing.
T-cell development is a multi-step process:
> Double negative stage (Cells are positive for CD 2 and 7 only)
> Double positive stage (Cells are positive for CD3, 4 and 8)
> Single positive stage (Cells are positive for CD3, 4 or 8)

35
Q

Myasthenia gravis

A

An autoimmune disorder which results in a loss of neuromuscular control.
Auto-antibodies target nicotinic acetylcholine receptors.
Important in the neuromuscular junction.
Condition has several characteristic physical symptoms.
Thymus gland involvement in MG is common.
Enlargement or the development of thymoma (20% of MG patients).

36
Q

Thymoma

A

Thymoma are heterogenous but develop from the epithelial cells of the gland.

37
Q

Three main groups of thymona

A

Type A characterised by oval epithelial cells. (~15% of patients)
Type B characterised by polygonal epithelial cells (~10% of patients)
Type AB mix of the above (~45% of patients.
Thymoma will also be staged via the Masaoka staging system.

38
Q

prognosis of thymona

A

Prognosis of thymoma is generally positive (~100%) following successful resection of early stage thymoma.
40% in patients in stage III/IV

39
Q

the spleen

A

The spleen is an incredibly important organ for both immunological purposes and haematopoietic purposes.
The spleen is the largest lymphatic organ and is found in the upper left quadrant of the abdomen.

40
Q

organisation of spleen

A

The spleen has a tough connective tissue capsule of which traveculae extend into the parenchyma.
Spleen contain significant amount of reticulin fibre similar to a lymph node.
Also has some myofibroblast cells!
The parenchymal tissue is grouped into two functionally and morphologically distinct regions:
Red pulp (haematopoesis and reticuloendothelial system)
White pulp (lymphoid)

41
Q

white pulp

A

The white pulp consists of lymphocytes rich tissue.
B-lymphocytes found within nodules.
These nodules contain a germinal centre.
Germinal centres expand & develop in response to antigen exposure.
Malphigian/splenic nodules.
T-Lymphocytes can be located around branches of the splenic artery.
Periarterial lymphatic sheath.

42
Q

red pulp

A

The red pulp consists of splenic sinuses divided by splenic cords.
Splenic cords consists of mesh of reticular cells & reticulin. Embedded within this we have:
> RBC
> Macrophages
> Lymphocytes
> Granulocytes
> Dendritic cells

43
Q

Splenic sinuses

A

The splenic sinuses are special sinusoidial vessels with unique features.
> Rod shaped endothelium.
> Porous membrane.
> Discontinuous basal membrane.

44
Q

Significance of these features of splenic sinuses?

A

Allows red cells to percolate in and out of the sinuses.

Macrophages have processes which stretch into the sinuses.

45
Q

circulation within the spleen

A

Given the spleen’s vital role in both lymphatic system and haemopoietic system it has adapted two different methods of blood circulation:
> Open circulation
> Closed circulation

46
Q

spleen in disease

A

The spleen can be involved in the presentation of several diseases.
Splenomegaly.

Examples of such diseases?
The spleen can also contribute to the development of disease.
Immune thrombocytopenic purpura.

Molecular Pathology (10 decks)

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