Definition of Thoracic Duct

The largest vessel of the lymphatic system. The thoracic duct collects lymph from the cisterna chyli and the left upper body, and drains into the left subclavian vein to deliver lymph to the bloodstream.

About the diameter of a pencil, the thoracic duct extends from the cisterna chyli in the central trunk to base of the neck, a distance of about 16 inches, somewhat paralleling the aorta. Like a vein, the thoracic duct has smooth-muscle walls that rhythmically contract and contains valves to prevent its contents from backflowing.

Muscular movement, such as occurs with physical activity or exercise, massages lymph through the thoracic duct toward the subclavian vein. Several branches of lymph vessels feed into the thoracic duct as it courses through the chest, rejoining to form a single segment that intersects with the subclavian vein beneath the clavicle (collarbone).

For further discussion of blood and lymph structure and function please see the overview section “The Blood and Lymph.”


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