In human anatomy, the thoracic duct is the larger of the two lymph ducts of the

lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...

. It is also known as the ''left lymphatic duct'', ''alimentary duct'', ''chyliferous duct'', and ''Van Hoorne's canal''. The other duct is the right lymphatic duct. The thoracic duct carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. It also collects most of the lymph in the body other than from the right thorax, arm, head, and neck (which are drained by the right lymphatic duct). The thoracic duct usually starts from the level of the twelfth thoracic vertebra (T12) and extends to the root of the neck. It drains into the systemic (blood) circulation at the junction of the left subclavian and internal jugular veins, at the commencement of the brachiocephalic vein. When the duct ruptures, the resulting flood of liquid into the pleural cavity is known as

chylothorax A chylothorax is an abnormal accumulation of chyle, a type of lipid-rich lymph, in the space surrounding the lung. The lymphatics of the digestive system normally returns lipids absorbed from the small bowel via the thoracic duct, which ascend ...

Structure

In adults, the thoracic duct is typically 38–45 cm in length and has an average diameter of about 5 mm. The vessel usually starts from the level of the twelfth thoracic vertebra (T12) and extends to the root of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

. It drains into the systemic (blood) circulation at the angle of the left subclavian and internal jugular veins as a single trunk, at the commencement of the brachiocephalic vein. The thoracic duct originates in the abdomen from the confluence of the right and left

lumbar trunks The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph nodes. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kidneys and suprarenal glands and the deep lymp ...

and the

intestinal trunk The intestinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver, and empties lymph into the cisterna chyli, which in turn drains into the thoracic duct In huma ...

, forming a significant pathway upward called the cisterna chyli. It traverses the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

at the aortic aperture, and ascends the

superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...

and posterior mediastinum between the descending thoracic aorta (to its left) and the azygos vein (to its right). The duct extends vertically in the chest and curves posteriorly to the left

carotid artery Carotid artery may refer to: * Common carotid artery, often "carotids" or "carotid", an artery on each side of the neck which divides into the external carotid artery and internal carotid artery * External carotid artery, an artery on each side of t ...

and left internal jugular vein. At the T5 vertebral level it crosses the midline to the left side. It ascends further to terminate into the systemic (blood) circulation at the venous angle of the left subclavian and internal jugular veins i.e. the commencement of the brachiocephalic vein, below the clavicle, near the shoulders.

Function

The thoracic duct collects most of the lymph in the body other than from the right thorax, arm, head, and neck. These are drained by the right lymphatic duct. Diagram showing the parts of the body the lymphatic and thoracic ducts drain CRUK 323

Diagram showing the parts of the body the lymphatic and thoracic ducts drain CRUK 323

The lymph transport, in the thoracic duct, is mainly caused by the action of breathing, aided by the duct's

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

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

Clinical significance

The first sign of a malignancy, especially an intra-abdominal one, may be an enlarged

Virchow's node Supraclavicular lymph nodes are lymph nodes found above the clavicle, that can be felt in the supraclavicular fossa. The supraclavicular lymph nodes on the left side are called Virchow's nodes.lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inclu ...

in the left supraclavicular area, in the vicinity where the thoracic duct empties into the left brachiocephalic vein, right between where the left subclavian vein and left internal jugular join (i.e., the left Pirogoff angle). When the thoracic duct is blocked or damaged a large amount of lymph can quickly accumulate in the pleural cavity, this situation is called

Additional images

File:Gray503.png, Transverse section of thorax, showing relations of pulmonary artery. File:Gray505.png, The arch of the aorta, and its branches. File:Gray621.png, Deep lymph nodes and vessels of the thorax and abdomen (diagrammatic). File:Gray1032.png, The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind. File:Photo of Ductus Thoracicus in human mediastinum.jpeg, Front photo of the Ductus Thoracicus in the Human

mediastinum The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagu ...

with the heart and part of the pericard removed.

References

External links