It is composed of cortical lymph follicles surrounded by lymph sinuses.

The cortical follicles:

Each cortical compartment is occupied by a lymph follicle which is composed mainly of lymphocytes. Some macrophages and few plasma cells are also present. These cells are suspended in the reticular C.T. stroma.

The cortical follicles have germinal centers if they are activated.

Activated follicles (nodules) which contain germinal centres are termed "secondary nodules", whereas the resting nodules which lack germinal centers are termed "primary nodules".

The lymph sinuses of the cortex:

Each cortical follicle is surrounded by a group of lymph sinuses which are spaces present between the processes of the stromal dendritic reticular cells.

The sinuses are discontinuously lined by simple squamous endothelium.

The cortical sinuses are classified into three groups, namely;

-Subcapsular sinuses, under the capsule.

-Cortical sinuses, surrounding the follicle.

-Subcortical sinuses, present deep to the follicles.

The sinuses contain lymph which is received by the subcapsular sinuses from the afferent lymphatics. Lymph, then, passes into the cortical and subcortical sinuses.

2) The Medulla:

It is composed of medullary cords of lymphoid tissue surrounded by medullary

lymph sinuses.

Figure 39. schematic diagram and photomicrograph of the lymph node

The medullary cords:

They are branching and anastomosing cords of lymphoid tissue present in between the C.T. septa.

These cords are formed of lymphoid tissue which mainly contains plasma cells with some lymphocytes and macrophages all are suspended in the reticular C.T. stroma

The medullary lymph sinuses:

They are spaces present in between the processes of the stromal dendritic reticular cells. These spaces surround the medullary cords. The sinuses are discontinuously lined by simple squamous endothelium. The medullary sinuses receive lymph from the subcortical sinuses and transport it to the efferent lymphatics which get out of the node through its hilum.

Cells of the parenchyma of the lymph node:

1) Lymphocytes:

They are more crowded in the cortical follicles.

The lymphocytes are generally of the B-type, except in the deep part of the cortex (the para cortical zone) which contains only T-lymphocytes, so it is called; the thymus dependent zone.

2) Plasma cells:

They are more crowded in the medullary cords.

3) Macrophages:

They are more crowded around the lymph sinuses.

Function of the lymph node

1) Filtration of lymph:

About 99% of the antigens carried by the lymph from any organ or tissue are phagocytized by the macrophages present in the lymph node. Lymph arising from any tissue or organ in the body must pass through lymph nodes before getting back to the blood circulation.

Lymph gets into the lymph node through its afferent lymphatics. It percolates

through the subcapsular, cortical, subcortical and lastly the medullary lymph

sinuses. It gets out of the lymph node through its efferent lymphatics.

As lymph flows through the sinuses, 99% or more of the antigens and other debris