13b - oral mucosa and buccophargyeal lymphatic ring

What is the lymphatic system?

An organ system in vertebrates that is part of both the circulatory system and the immune system.

What does the immune system consist of histologically?

A large, diverse population of leukocytes.

Where are these leukocytes located?

Within every tissue of the body and lymphoid organs.

How are these immune components interconnected?

By blood and lymphatic circulation.

What are the constituents of the lymphatic system?

Lymph, Lymph vessels and capillaries, Lymph nodes, Lymphoid organs, Diffuse lymphoid tissue, Bone marrow

What is another name for the lymphatic system?

Lymphoid system.

What are the main cells of the lymphatic system?

Lymphocytes.

Where are lymphocytes initially formed?

In primary lymphoid organs.

What are the primary lymphoid organs?

Thymus, Bone marrow

Where does most lymphocyte activation occur?

In secondary lymphoid organs.

What are the secondary lymphoid organs listed?

Lymph nodes, Spleen, Diffuse lymphoid tissue in mucosa

Where is diffuse lymphoid tissue found?

In the mucosa of the digestive, respiratory, and urinary systems.

What does MALT stand for?

Mucosa-associated lymphoid tissue.

What does NALT stand for?

Nose-associated lymphoid tissue.

What structures are included in this lymphoid system?

Tonsils, Peyer patches, Appendix

What happens in these lymphoid tissues?

Naive T and B lymphocytes encounter pathogens and antigens.

What is the result of this encounter?

Generation of an adaptive immune response

Where are lymphocytes and antigen-presenting cells (APCs) distributed?

Throughout the body in blood, lymph, and epithelial and connective tissues.

What is their role?

Adaptive immunity.

What type of connective tissue is lymphoid tissue usually composed of?

Reticular connective tissue.

What fills this connective tissue?

Large numbers of lymphocytes.

In what two forms can lymphoid tissue exist?

Diffuse within loose connective tissue, Surrounded by capsules forming discrete (secondary) lymphoid organs

What is MALT?

Diffuse lymphoid tissue found in mucosa.

Where is MALT located?

In the mucosa of the digestive, respiratory, and urinary systems.

Is MALT surrounded by a capsule?

No.

How is it described structurally?

Lymph tissue accumulations not surrounded by a capsule.

What is the function of MALT?

Intercepts antigens to generate an immune response.

How is lymphoid tissue defined on this slide?

Reticular connective tissue + many lymphocytes.

What are lymphoid organs?

Structures that house lymphocytes and other cells of the body’s immune defence system.

What is the main mechanical role of lymph nodes?

Centres for mechanical filtration of foreign substances in the lymph.

What immune processes occur in lymph nodes?

Antigen presentation, Lymphocyte activation, Differentiation, Proliferation

How are lymph nodes arranged in the body?

As a chain of well-organized and compartmentalized lymph nodes.

How are these lymph nodes grouped?

Clustered in small groups at strategic locations.

What is the significance of lymph nodes in the head and neck area?

They are an important and major component of the lymphatic system in humans.

What type of tissue are lymph nodes?

Encapsulated tissue.

What structural units are present in lymph nodes?

Numerous lymphatic lobules.

What spaces are present within lymph nodes?

Lymph-filled sinuses.

What happens in the lymph-filled sinuses?

Lymphocytes and APCs pass through them, Lymph percolates into surrounding lymphoid tissue

Where are lymph nodes located?

Distributed throughout the body along lymphatic vessels.

What are the three main areas of a lymph node?

Cortex (cortical area), Paracortex (paracortical area), Medullary area

What is found in the cortex?

Nodules.

What is the paracortex?

A deeper extension of the cortex.

Does the paracortex contain nodules?

No.

What is present in the medullary area?

Draining sinusoids.

What is the capsule composed of?

Collagen and elastin fibers with a few fibroblasts.

What extends from the capsule into the lymph node?

Trabeculae.

Where do trabeculae extend?

Into the deeper/interior areas of the lymph node.

What do capsular and trabecular fibers continue into?

Fine reticular fibers in the deeper area.

What type of lymphoid organ is a lymph node considered?

Secondary lymphoid organ.

Do tonsils have a capsule like lymph nodes?

No.

What type of lymphoid tissue are tonsils considered?

Diffuse lymphoid tissue.

What types of lymphatic vessels are associated with lymph nodes?

Afferent and efferent vessels.

What is present in the cortical (follicle) area?

Present a subcapsular sinus.

What is the function of the subcapsular sinus?

Receives the lymph from afferent lymphatic vessels.

What is the cortex made of?

Lymphoid follicles or nodules with germinal centers.

What is the role of the cortical area?

It plays a role in humoral immunity.

Which cells are seen in the cortical area?

Area where B cells are seen.

What happens when the follicle is stimulated?

The stimulation of the follicle results in “follicle center cell reaction”.

What does this reaction lead to?

This leads to differentiation of B cells.

What do these differentiated B cells become?

Direct precursor for antibody producing plasma cells and long-term memory cells.

What cells are required for this process?

Requires follicular dendritic cells, macrophages and lymphoid cells.

How is the paracortical area described?

Densely cellular area.

Where is it located?

Under the cortex and in between lymphoid follicles.

What type of lymphoid tissue is present here?

Lymphoid tissue rich in T cells.

What is the medullary area?

Active site of plasma cell proliferation and production of antibodies.

What structures are present in this area?

With prominent draining sinusoids.

Where are these sinusoids located?

Adjacent to the hilum.

What are primary lymphoid follicles?

Round nodular area composed of a homogeneous cell population of small darkly stained inactive lymphocytes.

How do secondary lymphoid follicles arise?

Arise from primary follicles due to antigenic stimuli.

What is the peripheral area of a secondary follicle called?

Mantle zone (darker).

What does the mantle zone contain?

Closely packed small lymphocytes (mature B lymphocytes).

What is the central area of a secondary follicle called?

Germinal center.

How is the germinal center described?

Central stained area.

What type of cell population is found in the germinal center?

Heterogenous population of cells.

Which cells are present in the germinal center?

Macrophages, Follicular dendritic cells (FDC), Lymphocytes in various phases of maturation

What does a primary follicle represent?

Inactive lymphocytes.

What does a secondary follicle represent?

Activation of B lymphocytes.

What is the main difference between primary and secondary follicles?

Primary → inactive lymphocytes, Secondary → activated lymphocytes with germinal center

What type of germinal center is described on this slide?

Reactive germinal center.

What are the main cells present in the germinal center?

Lymphocytes.

What is the main type of lymphocyte present?

The main are inactive B cells.

What stage are these lymphocytes in?

In various stages of differentiation.

What are follicular dendritic cells (FDCs)?

Support cells for immune response.

What is their role in antigen handling?

Antigen trapping cells (APCs) to B cells.

What structural feature do FDCs have?

Present dendritic cytoplasmic extension.

What are tingible body macrophages?

Macrophages in the germinal center.

What do they engulf?

Apoptotic bodies and nuclear debris of lymphocytes from the surrounding vicinity.

What happens to antigen proteins?

They are engulfed and presented to lymphoid cells.

What is the oropharynx?

Entrance of the alimentary and respiratory tracts.

What is the role of tonsils in this region?

Protection.

What structure do the tonsils form?

A lymphatic tissue ring called Waldeyer’s ring.

What does each lymphatic nodule contain?

Germinal centers.

What are germinal centers?

Active areas of lymphocyte formation.

How are tonsils generally structured externally?

They have a free surface covered by epithelium.

What is abundant within the epithelium of tonsils?

Intra-epithelial lymphocytes.

What is the relationship between the epithelium and tonsil grooves?

The epithelium is continuous with the clefts or grooves of the tonsils.

What surrounds each tonsil externally?

A connective tissue capsule.

What is found beneath the tonsils?

Underlying mucous or seromucous associated glands.

Do tonsils have afferent lymphatic vessels?

No.

What is the main function of tonsils?

Protection and immune response initiation.