Every day some fluid leaks from the capillaries into the tissues and is not taken back by the veins. The lymphatic system collects this fluid, filters it through lymph nodes and returns it to the bloodstream.
Lymphatic vessels
Lymph capillaries start as blind-ended tubes in the tissues and join into larger vessels with one-way valves. With no pump of their own, they rely on muscle movement and breathing to push lymph along.
Draining into the veins
The thoracic duct drains the legs, abdomen, left arm and left side of the head and chest into the left subclavian vein. The right lymphatic duct drains the right arm and the right side of the head and chest.
Lymph nodes
Nodes are bean-shaped filters packed with lymphocytes and macrophages that catch microbes and abnormal cells. When they fight an infection they swell and often become tender.
Main node groups
Large groups sit in the neck (cervical), above the collarbone (supraclavicular), in the armpit (axillary) and in the groin (inguinal). Each group drains a known area, which helps trace where a problem started.
At the bedside
For any enlarged node, note its size, tenderness, consistency and mobility, and examine the area it drains. A hard, fixed, painless node, or any palpable left supraclavicular node, needs workup for cancer.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).