L2- Lymph Nodes

Front 1

Back 1

-Not sharply delineated.
-No special organization
-Composition: Reticular stroma plus free cells (e.g. macrophages, lymphocytes, and plasma cells).

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Back 2

Reticular fiber network found in diffuse lymphoid tissue.
-Contains Type III collagen fibers.
-Difficult to see normally, needs special silver stain

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Back 3

Diffuse lymph tissue

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Back 4

Dense aggregations or individual solitary spherical masses.
-Always surrounded by diffuse lymphoid tissue.

-Primary nodule:
-Homogeneous in appearance
-Mainly B-lymphocytes

-Secondary nodule:
-Contains a germinal center
-Forms in response to an antigenic response
-Contains lymphoblasts and proliferating B-lymphocytes
-Transitory structure

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Back 5

Pyer's patch

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Back 6

Secondary lymph nodule

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Back 7

Secondary Nodule
-Stains paler because the cells are larger and not as densely packed.
-Cells migrate from the germinal centers (in secondary nodules) into the surrounding tissue and eventually into the vascular and circulatory system

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Back 8

Lymph node overview

-General characteristics
-Ovoid and encapsulated lymphoid organs
-Lymph flows through the organs and is filtered

-Histological organization
-Dense, collagenous capsule
-Trabeculae project into node
-Cells held in a reticular meshwork
-Lymph nodes have a distinct cortex and medulla
-Numerous lymph sinuses are present

Front 9

Back 9

Lymph Node:
Note- Inner medulla and outer cortex

Cortex is composed of the primary and secondary lymph nodules. This is the site of production of B lymphocytes

Medulla is composed of medullary cords, reticular fibers and medullary sinuses

Front 10

Lymph Node Cortex

Back 10

Outer dense mass of lymphoid cells.

-Superficial Cortex
-Contains primary and secondary nodules (nodular cortex)

-Internodular cortex
-Lies between nodules

-Tertiary Cortex
-Lies between the medulla and the remaining part of the cortex
-T-lymphocytes found in these cotical regions

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Back 11

Reticular framework of lymph node

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Back 12

Superficial cortex (with primary and secondary nodules)

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Back 13

Germinal centers in the superficial cortex

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Back 14

Regions of the cortex. Includes Superficial (with primary and secondary nodules), internodular cortex, and tertiary cortex.
Also contains the medulla

*note: white= lymph

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Back 15

Left= Secondary germinal center and site of B cell development

Right= Internodular and tertiary cortex. Sites of T cell accumulation

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Back 16

Lymph node medulla:

Lies central to the cortex and extends to the hilus
-Composed of medullary cords, reticular fibers, and medullary sinuses

-Medullary cords are branching portions of the reticular tissue, extensions of the tertiary cortex, and contain:
-Lymphocytes, macrophages, and plasma cells
-No plasma cells are normally found in the lymph

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Back 17

Macrophages are the black dots. They sit on the reticular mesh and help to break down pathogens and unwanted materials

Front 18

Lymph Node Sinuses

Back 18

-Transport lymph through then node
-Lined by reticular/endothelial cellsthat extend cytoplasmic processes across the sinus lumen

-Pathway for lymph:
1. Afferent lymphatic vessels- Pierce capsule and empty into the SUBCAPSULAR SINUSES
2. Cortical sinuses- run radially from the subcapsular through the cortex
3. Medullary sinuses
4. Efferent lymphatic vessels- convergence at the hilus

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Back 19

Functional compartments of the lymph node

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Back 20

Lymph node capsule and subcapsular sinus

Note: two different images.
Note: valve (V) in the afferent valve

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Back 21

Capsule and subcapsular sinus

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Back 22

Hilus of lymph node

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Back 23

Postcapillary venules- High Endothelia Venules

-Located in the TERTIARY CORTEX of the lymph node
-cuboidal endotheial lining

-T lymphocytes use these vessels to pass from the blood into the lymph node
-Site that B-lymphocytes exit