Organs of the Immune System: Lymph Nodes

Among the organs that contribute to our immune response, there are two categories: primary lymphoid organs and secondary lymphoid organs.

Lymph nodes are considered secondary lymphoid organs, along with the spleen. Shaped like beans, they contain lymphocytes, macrophages and dendritic cells. Lymphocytes carrying antigen drain through the lymph nodes, leaving the antigen behind to be dealt with in the node.

Popular thinking very strongly associates lymph nodes with lymphoma, chiefly because one of the first symptoms of lymphoma is an enlarged lymph node, but this is a little misleading. A lymphocyte within the node can become cancerous, or a cancerous lymphocyte can arrive at the node from elsewhere in the body and remain there. But it is not necessary to have lymph node involvement in order to have lymphoma.

The Job of the Lymph Nodes

Lymph nodes cluster together at junctions of the lymphatic vessels of the lymph system. They filter harmful substances and other debris from the body that are collected from the tissues of the body outside of the bloodstream.

The lymphocytes, macrophages and dendritic cells in lymph nodes act as immune cells to kill the harmful substances brought there by the lymph vessels. Because lymph vessels run throughout the entire body, they drain back through lymph node clusters no matter where they are. The fluid in the vessels comes from the fingers and toes and goes all the way up to the scalp. This massive circulatory system is constantly working to clear these substances from the body's tissues before re-circulating again, always stopping at the lymph nodes to deposit what it collects so that the nodes can eliminate them from the body.

Familiar Lymph Node Clusters

Places where lymph nodes can be felt with one's fingers include:

• Armpit
• Groin
• Under the jaw/chin
• Behind the ears
• Back of the head
• Front, back and sides of the neck

Lymph Nodes in Lymphoma

Other cancers often involve the lymph nodes (when cells from tumors break away and reach the lymph nodes), but when cancers involve the B-cell lymphocytes or the T-cell lymphocytes, they are classified as lymphomas.

Lymph Node Removal

In order for a case of lymphoma to be diagnosed, a lymph node must be excised in a biopsy. This generally requires the removal of a single node. Since our bodies have several hundred lymph nodes, the loss of a single node isn't going to cause a problem.

However, when many nodes from the same cluster are removed, called either "dissection" or "lymph node sampling," this can create a big problem because lymph vessels arriving there no longer have a place to drain. Fluid back-up can occur, leading to what's called lymphedema.