A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as filters or traps for foreign particles. They are important in the proper functioning of the immune system. They are packed tightly with the white blood cells called lymphocytes and macrophages. source: http://en.wikipedia.org/wiki/Lymph_node