Thoracic duct

Function

The thoracic duct is the lymphatic system's main artery — a vessel the size of a small pen rising from the cisterna chyli at L1, climbing the aorta's right, crossing to the left at T5, and emptying 2–4 L of lymph daily into the junction of the left subclavian and internal jugular veins.

It returns the fat absorbed as chylomicrons by the gut, and every drop of lymph from the body's left half and whole lower half. Its flow is driven by breathing's pressure swings and the smooth muscle in its wall.

Blood supply

Its own tiny vasa vasorum.

Nerve supply

Sympathetic fibres control the wall's smooth muscle.

Clinical relevance

Chylothorax

Thoracic surgery or trauma tears the duct — the pleural space fills with milky lymph; milky drain fluid after oesophagectomy is the tell.

Tumour spread

The duct carries abdominal cancer to the left supraclavicular (Virchow's) node — Troisier's sign.