thoracic duct

Lymph: Thoracic duct
The thoracic and right lymphatic ducts. (Thoracic duct is thin vertical white line at center.)
Modes of origin of thoracic duct. a. Thoracic duct. a’. Cisterna chyli. b, c’ Efferent trunks from lateral aortic glands. d. An efferent vessel which pierces the left crus of the diaphragm. e. f. Lateral aortic glands. h. Retroaortic glands. i. Intestinal trunk. j. Descending branch from intercostal lymphatics.
Latin	ductus thoracicus
Gray's	subject #176 690
Source	cisterna chyli
Drains to	junction of the left subclavian vein and left internal jugular vein
MeSH	Thoracic+Duct
Dorlands/Elsevier	Thoracic duct

In human anatomy, the thoracic duct (aka left lymphatic duct) is an important part of the lymphatic system—it is the largest lymphatic vessel in the body. It is also known under various other names including the alimentary duct, chyliferous duct, the left lymphatic duct and Van Hoorne's canal.

It collects most of the lymph in the body (except that from the right arm and the right side of the chest, neck and head, and lower left lobe of the lung, which is collected by the right lymphatic duct) and drains into the systemic (blood) circulation at the left brachiocephalic vein, right between where the left subclavian vein and left internal jugular connect.

Location

In adults, the thoracic duct is typically 38-45cm in length and an average diameter of about 5mm. It usually starts from the level of the second lumbar vertebra and extends to the root of the neck.

It originates in the abdomen from the confluence of the right and left lumbar trunk and the intestinal trunk, forming a significant pathway upward called the cisterna chyli.

It extends vertically in the chest and curves posteriorly to the left carotid artery and left internal jugular vein at the C7 vertebral level to empty into the junction of the left subclavian vein and left jugular vein, below the clavicle, near the shoulders.

It traverses the diaphragm at the aortic aperture and ascends the posterior mediastinum between the descending thoracic aorta (to its left) and the azygos vein (to its right).

Volume, mechanism, and direction of flow

In adults, the thoracic duct transports up to 4 L of lymph per day.

The lymph transport in the thoracic duct is mainly caused by the action of breathing, aided by the duct's smooth muscle and by internal valves which prevent the lymph from flowing back down again.

There are also two valves at the junction of the duct with the left subclavian vein, to prevent the flow of venous blood into the duct.

Clinical significance

When the thoracic duct is blocked or damaged a large amount of lymph can quickly accumulate in the pleural cavity, this situation is called chylothorax.

The first sign of a malignancy (especially an intraabdominal one) may be an enlarged Virchow's node, a lymph node in the left supraclavicular area, in the vicinity where the thoracic duct empties into the left subclavian vein.

Additional images

Transverse section of thorax, showing relations of pulmonary artery.

The arch of the aorta, and its branches.

Deep lymph nodes and vessels of the thorax and abdomen (diagrammatic).

The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.

See also

• Lymphatic system

References

External links

• Anatomy at MUN thorax/lymph
• SUNY Figs 21:05-02 - "The thoracic duct and azygos venous network."
• SUNY Anatomy Image 8901
• Human anatomy at Dartmouth figures/chapter_24/24-5.HTM
• thoracic duct at Dorland's Medical Dictionary
• Diagram at anatomyatlases.org