Lymph nodes have an inner medulla and an outer cortex surrounded by a connective tissue capsule.   Extensions of the capsule into the cortex (trabeculae)  partition the cortex into subunits known as lymph nodules and lend support to the organ.  Within the lymph nodules are areas of rapidly dividing B cells (lymphocytes) that appear as a lighter area within the nodule.  These are known as germinal centers.

The medulla of the lymph node consists of reticular fibers (highly branched collagen fibers) and macrophages.

Photo taken by Theresa Carrera (50x)

Medulla indicated by the green circle, lymph nodule indicated by the yellow circle and the lighter area indicated by the blue arrow is a germinal center.  The purple arrow indicates the CT capsule.

Photo taken by Theresa Carrera (100x)

A lymph nodule indicated by the yellow circle and the lighter area indicated by the blue circle is a germinal center.  The purple arrow indicates the CT capsule.

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