In human

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

, the thoracic duct is the larger of the two

lymph duct A lymph duct is a great lymphatic vessel that empties lymph into one of the subclavian veins. There are two lymph ducts in the body—the right lymphatic duct and the thoracic duct. The right lymphatic duct drains lymph from the right upper li ...

s 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 right lymphatic duct is an important lymphatic vessel that drains the right upper quadrant of the body. It forms various combinations with the right subclavian vein and right internal jugular vein. Structure The right lymphatic duct course ...

. The thoracic duct carries

chyle Chyle (from the Greek word χυλός ''chylos'', "juice") is a milky bodily fluid consisting of lymph and emulsified fats, or free fatty acids (FFAs). It is formed in the small intestine during digestion of fatty foods, and taken up by lymph v ...

, a liquid containing both lymph and emulsified fats, rather than pure

lymph Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...

. It also collects most of the

in the body other than from the right thorax, arm, head, and neck (which are drained by the

). 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 In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplie ...

and

internal jugular vein The internal jugular vein is a paired jugular vein that collects blood from the brain and the superficial parts of the face and neck. This vein runs in the carotid sheath with the common carotid artery and vagus nerve. It begins in the posteri ...

s, at the commencement of the

brachiocephalic vein The left and right brachiocephalic veins (previously called innominate veins) are major veins in the upper chest, formed by the union of each corresponding internal jugular vein and subclavian vein. This is at the level of the sternoclavicular j ...

. When the duct ruptures, the resulting flood of liquid into the

pleural cavity The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication bet ...

is known as chylothorax.

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 In Euclidean geometry, an angle is the figure formed by two Ray (geometry), rays, called the ''Side (plane geometry), sides'' of the angle, sharing a common endpoint, called the ''vertex (geometry), vertex'' of the angle. Angles formed by two ...

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 The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

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 The cisterna chyli (or cysterna chyli, and etymologically more correct, receptaculum chyli) is a dilated sac at the lower end of the thoracic duct in most mammals into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow. It ...

. It traverses the diaphragm at the

aortic aperture The aortic hiatus is a hole in the diaphragm. It is the lowest and most posterior of the large apertures. It is located approximately at the level of the twelfth thoracic vertebra (T12). Structure Strictly speaking, it is not an aperture in the ...

, and ascends the superior and

posterior 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 ...

between the descending

thoracic aorta The descending thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the aortic arch. It is located within the posterior mediastinal cavity, but frequently bulges into the left pleural cavity. The descending thoracic ...

(to its left) and the

azygos vein The azygos vein is a vein running up the right side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superior vena cava and inferior vena cava and can provide an alternative path for blood ...

(to its right). The duct extends vertically in the chest and curves

posteriorly Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

to the left carotid artery and left

. 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 The venous angle, also known as Pirogoff's angle and in Latin as angulus venosus, is the junction where the internal jugular (Latin: ''v. jugularis interna'') and subclavian (Latin: ''v. subclavia'') veins at each side of the neck merge to form t ...

of the left subclavian and internal jugular veins i.e. the commencement of the brachiocephalic vein, below the

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the rig ...

, near the

shoulders The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...

Function

The thoracic duct collects most of the

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

breath Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen. All aerobic creatures need oxygen for cellular ...

ing, 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

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...

s 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

, 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

, this situation is called chylothorax.

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 The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

and part of the pericard removed.

References

External links