A small organ lying along the course of a lymphatic vessel (see lymphatic system); commonly but incorrectly called a lymph gland. Lymph nodes vary considerably in size, from microscopic to about 2.5 cm (1 in) in diameter. A lymph node consists of a thin, fibrous outer capsule and an inner mass of lymphoid tissue. Penetrating the capsule are several small lymphatic vessels (which carry lymph into the node). Each node contains sinuses (spaces), in which the lymph is filtered. The flow of the lymph slows as it moves through narrow channels in the sinuses; this reduction in flow allows macrophages (white blood cells that engulf and destroy foreign and dead material) time to filter microorganisms from the lymph. Germinal centres in the lymph node release white blood cells called lymphocytes, which also help to fight infection. A single, larger vessel carries lymph out of the node.
Lymph node |
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