Lymphatic system and lymph nodes
Lymphatic system

What are lymph and lymph nodes?

Lymph is a clear or slightly yellowish watery fluid that:

  • Removes bacteria and certain kinds of proteins from tissues
  • Transports fat from the small intestine
  • Supplies the bloodstream with the mature white blood cells (lymphocytes) that are made in bone marrow

Lymph is circulated through the body by lymphatic vessels, which are similar to blood vessels. White blood cells and the lymphatic system are important parts of the immune system, helping the body rid itself of germs, cells, or foreign matter that could cause disease.

Lymph nodes are small, bean-shaped structures near the lymphatic vessels. There are about 600 lymph nodes throughout the body, some in deep tissues and others closer to the skin. Clusters of nodes are found in the neck, armpits, abdomen, and groin. (These nodes can be felt with the fingers.) Other nodes are found in the chest, arms, and legs.

Immune cells are stored inside nodes. Fluid from surrounding tissues enter lymph nodes via lymphatic vessels or the nodes’ own tiny blood vessels. The fluid is filtered by the nodes to remove infectious germs, cells, or foreign matter. Fresh lymphocytes are supplied and the fluid is sent back to the bloodstream to distribute lymphocytes throughout the body.

The terms lymph nodes and lymph glands are often mistakenly used to mean the same thing. Lymph nodes are not actually glands because they don’t make or secrete any substances; they only act as filters.

What causes swollen lymph nodes?

Swollen lymph nodes commonly occur when the number of white blood cells inside them has increased in response to an infection or other illness. The number of disease-fighting cells builds rapidly, causing pressure and swelling inside lymph nodes.

In many cases, the lymph nodes that swell will be close to the site of an infection. For example, a person with strep throat might develop swollen lymph nodes in the neck.

In other instances, swollen lymph nodes could indicate injury, lymphoma (cancer of the lymphatic system), AIDS (acquired immune deficiency syndrome), or a cancer that has spread to the lymph nodes from another part of the body.

What are the symptoms of swollen lymph nodes?

In general, lymph nodes larger than 1 centimeter (0.4 inches) in diameter are considered abnormal. Swollen lymph nodes not only become enlarged, sometimes visibly so, but may also be painful to the touch.

A doctor should be consulted when certain symptoms are present. These include:

  • Nodes that are swollen for more than two weeks
  • Weight loss
  • Night sweats
  • Long-lasting fever
  • Fatigue
  • Nodes that are hard, fixed to the skin, or growing rapidly
  • Swollen nodes close to the collarbone or lower part of the neck. Swollen nodes in this area often indicate a cancerous condition
  • Red or inflamed skin over swollen nodes
  • Difficulty breathing

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