Thoracic duct

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Thoracic duct
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The thoracic and right lymphatic ducts. (Thoracic duct is thin vertical white line at center.)
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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 p...
Details
System Lymphatic system
Source cisterna chyli
Drains tojunction of the left subclavian vein and left internal jugular vein
Identifiers
Latin ductus thoracicus
MeSH D013897
TA98 A12.4.01.007
TA2 5137
FMA 5031
Anatomical terminology

In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. 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). [1] The thoracic duct usually starts from the level of the twelfth thoracic vertebrae (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. [2]

Contents

When the duct ruptures, the resulting flood of liquid into the pleural cavity 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 vertebrae (T12) and extends to the root of the neck. 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. [3] [4]

The thoracic duct originates in the abdomen from the confluence of the right and left lumbar trunks and the intestinal trunk, forming a significant pathway upward called the cisterna chyli. [5] [6] It traverses the diaphragm at the aortic aperture, and ascends the superior and posterior mediastinum between the descending thoracic aorta (to its left) and the azygos vein (to its right). [5] The duct extends vertically in the chest and curves posteriorly to the left carotid artery and left internal jugular vein. [5] [7] At the T5 vertebral level, it drains into the systemic (blood) circulation at the venous angle of the left subclavian and internal jugular veins as a single trunk, at the commencement of the brachiocephalic vein, [3] [4] 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. [7] These are drained by the right lymphatic duct. [1]

Diagram showing parts of the body that drain into the right lymphatic duct. Diagram showing the parts of the body the lymphatic and thoracic ducts drain CRUK 323.svg
Diagram showing parts of the body that drain into the right lymphatic duct.

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. In adults, the thoracic duct transports up to 4 L of lymph per day. [8]

Clinical significance

The first sign of a malignancy, especially an intra-abdominal 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 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 chylothorax.

Additional images

See also

Related Research Articles

Brachiocephalic vein

The left and right brachiocephalic veins in the upper chest are formed by the union of each corresponding internal jugular vein and subclavian vein. This is at the level of the sternoclavicular joint. The left brachiocephalic vein is usually longer than the right.

Superior vena cava One of two veinous trunks bringing deoxygenated blood back to the heart

The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart. It is a large-diameter (24 mm) short length vein that receives venous return from the upper half of the body, above the diaphragm. Venous return from the lower half, below the diaphragm, flows through the inferior vena cava. The SVC is located in the anterior right superior mediastinum. It is the typical site of central venous access via a central venous catheter or a peripherally inserted central catheter. Mentions of "the cava" without further specification usually refer to the SVC.

Subclavian artery

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 supplies blood to the right arm, with some branches supplying the head and thorax. On the left side of the body, the subclavian comes directly off the aortic arch, while on the right side it arises from the relatively short brachiocephalic artery when it bifurcates into the subclavian and the right common carotid artery.

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 the right atrium when either of the venae cavae is blocked.

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.

Subclavian vein

The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption of fats and lipids, by allowing products that have been carried by lymph to enter the bloodstream, where it can enter the hepatic portal vein. The diameter of the subclavian veins is approximately 1–2 cm, depending on the individual.

Chylothorax

A chylothorax is an accumulation of lymphatic fluid in the space surrounding the lung. Lymph formed in the digestive system is called chyle and accumulates in the pleural space due to either disruption or obstruction of the thoracic duct. In people on a normal diet, this fluid collection can sometimes be identified by its turbid, milky white appearance, since chyle contains triglycerides. It is important to distinguish a chylothorax from a pseudochylothorax, which has a similar appearance, but is caused by more chronic inflammatory processes, and requires a different treatment.

Common carotid artery One of the two arteries that supply the head and neck with blood

In anatomy, the left and right common carotid arteries (carotids) are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries.

Thoracic inlet

The thoracic inlet, also known as the superior thoracic aperture, refers to the opening at the top of the thoracic cavity. It is also clinically referred to as the thoracic outlet, in the case of thoracic outlet syndrome; this refers to the superior thoracic aperture, and not to the lower, larger opening, the inferior thoracic aperture.

Cisterna chyli

The cisterna 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 receives fatty chyle from the intestines and thus acts as a conduit for the lipid products of digestion. It is the most common drainage trunk of most of the body's lymphatics. The cisterna chyli is a retro-peritoneal structure. In humans, it is located posterior to the abdominal aorta on the anterior aspect of the bodies of the first and second lumbar vertebrae. There it forms the beginning of the primary lymph vessel, the thoracic duct, which transports lymph and chyle from the abdomen via the aortic opening of the diaphragm up to the junction of left subclavian vein and internal jugular veins. In dogs, it is located to the left and often ventral to the aorta; in cats it is left and dorsal; in guinea pigs it runs to the left and drains into the left innominate vein.

Hemiazygos vein

The hemiazygos vein is a vein running superiorly in the lower thoracic region, just to the left side of the vertebral column.

Right lymphatic duct

The right lymphatic duct, about 1.25 cm. in length, courses along the medial border of the anterior scalene at the root of the neck. The right lymphatic duct forms various combinations with the right subclavian vein and right internal jugular vein. A right lymphatic duct that enters directly into the junction of the internal jugular and subclavian veins is uncommon. The discovery of this structure has been credited to Niels Stensen.

Jugular lymph trunk

The jugular trunk is a lymphatic vessel in the neck. It is formed by vessels that emerge from the superior deep cervical lymph nodes and unite to efferents of the inferior deep cervical lymph nodes.

Superior deep cervical lymph nodes

The superior deep cervical lymph nodes lie under the sternocleidomastoid muscle in close relation with the accessory nerve and the internal jugular vein.

Bronchomediastinal lymph trunk

The efferent vessels of the tracheobronchial lymph nodes ascend upon the trachea and unite with efferents of the internal mammary and anterior mediastinal glands to form the right and left bronchomediastinal trunks.

Subclavian lymph trunk

The efferent vessels of the subclavicular group unite to form the subclavian trunk, which opens either directly into the junction of the internal jugular and subclavian veins or into the jugular lymphatic trunk; on the left side it may end in the thoracic duct.

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 limb, right side of thorax and right halves of head and neck. The thoracic duct drains lymph into the circulatory system at the left brachiocephalic vein between the left subclavian and left internal jugular veins.

Lymph sacs are a part of the development of the lymphatic system, known as lymphangiogenesis. The lymph sacs are precursors of the lymph vessels. These sacs develop through the processes of vasculogenesis and angiogenesis. However, there is evidence of both of these processes in different organisms. In mice, it is thought that the lymphatic components form through an angiogenic process. But, there is evidence from bird embryos that gives rise to the idea that lymphatic vessels arise in the embryos through a vasculogenesis-like process from the lymphangioblastic endothelial precursor cells.

Venous angle is the junction of the internal jugular and subclavian veins at both sides of the neck. The external and the anterior jugular and the vertebral veins converge toward it. The left venous angle receives lymph from the thoracic duct. The right venous angle receives lymph from the right lymphatic trunk. Truncus lymphaticus is only about 1 cm long and conveys lymph from the right side of the thorax as well as the right arm and parts of the head and neck.

References

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  8. Tewfik, Ted L.; Mosenifar, Zab (7 December 2017). "Thoracic Duct Anatomy". Medscape. WebMD Health Professional Network.