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
TA A12.4.01.007
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. Thus when it ruptures, the resulting flood of liquid into the pleural cavity is known as chylothorax.

Anatomy The study of the structure of organisms and their parts

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 which deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated over immediate (embryology) and long (evolution) timescales. Anatomy and physiology, which study (respectively) the structure and function of organisms and their parts, make a natural pair of related disciplines, and they are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine.

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.

Lymphatic system a part of the defense system (immune system) of vertebrate animals against pathogens

The lymphatic system is part of the vascular system and an important part of the immune system, comprising a large network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Unlike the circulatory system, the lymphatic system is not a closed system. The human circulatory system processes an average of 20 litres of blood per day through capillary filtration, which removes plasma while leaving the blood cells. Roughly 17 litres of the filtered plasma is reabsorbed directly into the blood vessels, while the remaining three litres remain in the interstitial fluid. One of the main functions of the lymph system is to provide an accessory return route to the blood for the surplus three litres.

Contents

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. [1] [2] 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. [3]

Neck part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk

The neck is the part of the body, on many vertebrates, that separates the head from the torso. It contains blood vessels and nerves that supply structures in the head to the body. These in humans include part of the esophagus, the larynx, trachea, and thyroid gland, major blood vessels including the carotid arteries and jugular veins, and the top part of the spinal cord.

Circulatory system Organ system for circulating blood in animals

The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients, oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.

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.

Structure

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. 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). The duct extends vertically in the chest and curves posteriorly to the left carotid artery and left internal jugular vein 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, [1] [2] below the clavicle, near the shoulders.

Abdomen frontal part of the body between the thorax (chest) and pelvis

The abdomen constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the frontal part of the abdominal segment of the trunk, the dorsal part of this segment being the back of the abdomen. The region occupied by the abdomen is termed the abdominal cavity. In arthropods it is the posterior tagma of the body; it follows the thorax or cephalothorax. The abdomen stretches from the thorax at the thoracic diaphragm to the pelvis at the pelvic brim. The pelvic brim stretches from the lumbosacral joint to the pubic symphysis and is the edge of the pelvic inlet. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity. The boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear.

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.

Azygos vein

The azygos vein is a vein running up the 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.

Function

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. [4]

Smooth muscle

Smooth muscle is an involuntary non-striated muscle. It is divided into two subgroups; the single-unit (unitary) and multiunit smooth muscle. Within single-unit cells, the whole bundle or sheet contracts as a syncytium.

Valve device that regulates, directs or controls the flow of a fluid or a gas

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.

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.

Lymph node organ of the lymphatic system

A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system, and of the adaptive immune system, that is widely present throughout the body. They are linked by the lymphatic vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, and other white blood cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a detoxification function, which is primarily dealt with by the liver and kidneys.

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.

Pleural cavity thin fluid-filled space between the two pulmonary pleurae (visceral and parietal) of each lung

The pleural cavity is the thin fluid-filled space between the two pulmonary pleurae of each lung. A pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac. The outer pleura is attached to the chest wall, but is separated from it by the endothoracic fascia. The inner pleura covers the lungs and adjoining structures, including blood vessels, bronchi and nerves. The pleural cavity can be viewed as a potential space because the two pleurae adhere to each other under all normal conditions. Parietal pleura projects up to 2.5 cm above the junction of the middle and medial third of the clavicle

Additional images

Mediastinum central compartment of the thoracic cavity that separates the lungs

The mediastinum is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.

Heart organ for the circulation of blood in animal circulatory systems

The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, as well as assisting in the removal of metabolic wastes. In humans, the heart is located between the lungs, in the middle compartment of the chest.

See also

Related Research Articles

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), yet short, vein that receives venous return from the upper half of the body, above the diaphragm. The SVC is located in the anterior right superior mediastinum. It is the typical site of central venous access (CVA) 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 major arteries of the upper thorax, below the clavicle

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.

Subclavian vein paired large 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 its products that have been carried by lymph to enter the bloodstream, where it can enter the hepatic portal vein. Their diameter is approximately 1-2cm, depending on the individual.

Common carotid artery

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.

Descending thoracic aorta part of the aorta located in the thorax

The descending thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the descending aorta and contained in the posterior mediastinal cavity. The descending thoracic aorta begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth thoracic vertebra, at the aortic hiatus in the diaphragm where it becomes the abdominal aorta.

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 Scalenus anterior 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.

Aortic hiatus

The aortic hiatus is a hole in the diaphragm. It is the lowest and most posterior of the large apertures.

Intercostal arteries Arteries supplying the space between the ribs

The intercostal arteries are a group of arteries that supply the area between the ribs ("costae"), called the intercostal space. The highest intercostal artery is an artery in the human body that usually gives rise to the first and second posterior intercostal arteries, which supply blood to their corresponding intercostal space. It usually arises from the costocervical trunk, which is a branch of the subclavian artery. Some anatomists may contend that there is no supreme intercostal artery, only a supreme intercostal vein.

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 sacs are a part of the development of the human 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.

References

  1. 1 2 Knipe, Henry. "Thoracic duct | Radiology Reference Article | Radiopaedia.org". radiopaedia.org. Retrieved 2016-10-08.
  2. 1 2 Insull, Phillip (2007-10-01). "CLINICAL ANATOMY: APPLIED ANATOMY FOR STUDENTS AND JUNIOR DOCTORS. 11th EDITION - BY HAROLD ELLIS". ANZ Journal of Surgery. 77 (10): 911–912. doi:10.1111/j.1445-2197.2007.04191.x. ISSN   1445-2197.
  3. Michael Schuenke; Erik Schulte; Udo Schumacher; Lawrence M. Ross; Edward D. Lamperti; Markus Voll; Karl Wesker (24 May 2006). Thieme atlas of anatomy: Neck and internal organs. Thieme. pp. 136–. ISBN   978-3-13-142111-1 . Retrieved 1 June 2010.
  4. Tewfik, Ted L; Mosenifar, Zab (2017-12-07). "Thoracic Duct Anatomy". Medscape. WebMD Health Professional Network.