About the Lymph System
The lymphatic system filters fluid from around cells. It is an important part of the immune system. When people refer to swollen glands in the neck, they are usually referring to swollen lymph nodes. Common areas where lymph nodes can be easily felt, especially if they are enlarged, are: the groin, armpits (axilla), above the clavicle (supraclavicular), in the neck (cervical), and the back of the head just above hairline (occipital).
Lymph is a clear-to-white fluid made of:
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Fluid from the intestines called chyle, which contains proteins and fats
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Red blood cells
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White blood cells, especially lymphocytes, the cells that attack bacteria in the blood
About the Lymph Nodes
Lymph nodes produce immune cells to help fight infection. They also filter the lymph fluid and remove foreign material, such as bacteria and cancer cells. They can become swollen from inflammatory conditions, an abscess, cancer, and most commonly from infection. Common areas where lymph nodes can be felt include the groin, armpit, behind the ears, back of the head, sides of the neck and under the jaw and chin.
Source: U.S. National Library of Medicine (NLM)