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Lymph nodes are small, bean-shaped glands in the body. They are part of the lymphatic system, which carries lymph fluid, nutrients, and waste material between the body tissues and the bloodstream. The lymphatic system is part of the immune system—the body's defense system against disease.

Lymph nodes are found singly or in groups. They may be as small as the head of a pin or as large as an olive. Groups of lymph nodes can be felt in the neck, groin, and underarms. Many lymph nodes in the body cannot be felt.

When a part of the body is infected, the nearby lymph nodes can become swollen. For example, if a person has a throat infection, the lymph nodes in the neck may swell and become tender.