Lymph nodes are components of the lymphatic system. Clusters of lymph nodes are found in the underarms, groin, neck, chest, and abdomen. Lymph nodes act as filters, with an internal honeycomb of connective tissue filled with lymphocytes that collect and destroy bacteria and viruses. When the body is fighting an infection, these lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes.
The spleen and tonsils are large lymphoid organs that serve similar functions, though the spleen does not filter lymph but blood.
Lymph nodes of the head and neck
These nodes, both superficial and deep, lie above and beneath the sternocleidomastoid muscles. They drain the internal structures of the throat as well as part of the posterior pharynx, tonsils, and thyroid gland.
These nodes extend in a line posterior to the sternocleidomastoids but in front of the trapezius, from the level of the mastoid bone to the clavicle. They drain the skin on the back of the head. They are frequently enlarged during upper respiratory infections.
These nodes are located just below the angle of the mandible. They drain the tonsilar and posterior pharyngeal regions.
These nodes run along the underside of the jaw on either side. They drain the structures in the floor of the mouth.
These nodes are just below the chin. They drain the teeth and intra-oral cavity.
These nodes are in the hollow above the clavicle, just lateral to where it joins the sternum. They drain a part of the throacic cavity and abdomen.