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Lymphatic vessels are thin-walled, endothelial-lined channels that originate near the capillary beds and serve as a drainage system for returning interstitial tissue fluid and inflammatory cells to the blood.
From: Pathologic Basis of Veterinary Disease (Sixth Edition) , 2017
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Adult and Fetal
Aernout Luttun , … Peter Carmeliet , in Handbook of Stem Cells , 2004
ORIGIN OF LYMPHATIC VESSELS IN THE EMBRYO
Lymphatic vessels start developing after the blood vascular system (at E9.5 in the mouse), an argument in favor of a blood vessel origin of lymphatics. In 1902, long before specific lymphatic EC markers became available, Sabin launched her theory that the first lymphatic ECs (which organize into lymph sacs) develop by budding from a certain region in the cardinal veins171 (Fig. 42-3). Almost a century later, further evidence supporting this theory was found in mouse studies with the Prox-1 homeobox gene, a specific lymphatic marker proposed to determine the lymphatic fate of a subpopulation of ECs in the cardinal veins and to induce budding from these cells.172 The rest of the lymphatic network would result from sprouting from these initial lymph vessels (lymphangiogenesis). However, an alternative theory, developed by Huntington and McClure in 1910, states that lymphatics develop independently of veins from separate mesenchymal precursors (lymphangioblasts)173 (Fig. 42-3), suggesting that the formation of the first lymphatics is the result of coalescence of lymphatic precursors, a process which could be called lymphvasculogenesis in analogy with blood vessel ontogeny.174 Quail–chick chimera experiments have proven the existence of separate mesenchymal lymphatic precursors, at least in the avian embryo, at the level of the paraxial and splanchnic mesoderm.175–177 Although the existence of lymphangioblasts in mammalian tissues needs to be demonstrated, mechanisms proposed by both theories may act together to form the lymphatic vasculature.
Like blood vessels, some lymphatic vessels (i.e., the larger collecting lymphatics) are enveloped by SMCs, particularly around the luminal valves.178,179 In mammals and birds, contractility of the collecting lymphatics is of great functional importance.180 Indeed, the autocontractile smooth muscle coat, the presence of intraluminal valves, and external factors such as skeletal muscle contraction and arterial pulsation promote unidirectional fluid transport in the lymphatic vasculature. The origin of lymphatic SMCs remains to be investigated.
Unlike the blood vasculature, which is a closed circuit (Fig. 42-1), lymphatics form an open-ended system. It is unclear whether the mechanisms determining lymphatic vessel patterning are similar to those for blood vessels. Nevertheless, lymphatic vessels are, like blood vessels, organized in a hierarchic network. First, the lymphatic capillaries (or initial lymphatics) begin as closed saccules and form a network even more extensive than the network of blood capillaries.178,181 These capillaries drain into small precollector lymphatics and large collecting lymphatics. The collecting vessels coalesce into larger vessels that run along the veins and drain into lymph nodes. The efferent lymphatics emanating from the nodes coalesce into larger collecting ducts (which may be interconnected by collateral lymphatic vessels) and finally empty into the thoracic duct (on the left) or the right lymphatic duct.178,181 The thoracic duct empties at the level of the aortic arch in the left jugulosubclavian vein junction, and the right lymphatic duct connects to the right jugulosubclavian vein junction. Just as variations in the patterning in the aortic arch and its branches occur frequently, considerable anatomic variations have been described in the connections of the lymphatic vessels to the venous system.178 However, unlike blood vessel patterning abnormalities (see previous sections), these anatomic variations do not seem to cause life-threatening complications.
It has been shown that receptor expression varies among subsets of lymphatic vessels,174,182–184 indicating that—like blood ECs—lymphatic ECs are heterogeneous. This heterogeneity may be partly determined by origin—that is, sprouting from veins or stemming from separate lymphatic precursors. Furthermore, the extent of the lymphatic network differs among organs. Although lymphatic capillaries occur frequently in cardiac muscle, they are infrequent in skeletal muscle and might even be absent in the central nervous system, BM, parenchyma of the thymus and the spleen, peri-ocular system, and placenta.180,185
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Pulmonary Circulation and Regulation of Fluid Balance
Joe G.N. Garcia MD , in Murray and Nadel's Textbook of Respiratory Medicine (Sixth Edition) , 2016
Lymphatic Insufficiency and Edema Formation
The lymphatic vessels are capable of removing excess extravascular fluid because of their effectiveness as pumps. Lymphatic propulsion is determined by the intrinsic contractility of lymphatic vessels, by the pumping action of inspiration and expiration, and by lymphatic valves, which account for the unidirectional lymph flow.207 Lymphatics, however, have a limited capacity to increase lymph flow. Beyond their critical capacity, lymph flow does not increase in direct proportion to the increase in interstitial fluid volume and may actually decrease because of compression of the lymphatic channels.214 The extent to which lymphatic insufficiency serves as an important mechanism of fluid accumulation in the lung is not clear. Some studies have indicated that surgical removal of the lymphatics predisposes the lung to edema, although the increase in water content is usually transient.215
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Natasha L. Harvey , in Heart Development and Regeneration , 2010
Lymphatic vessels are a vital but often overlooked component of the cardiovascular system. In contrast to blood vessels, lymphatic vessels do not deliver oxygen and nutrients to tissues, but instead collect and return interstitial fluid and protein (lymph) to the bloodstream. In addition, lymphatic vessels provide an important trafficking route for cells of the immune system during immune surveillance and infection, and facilitate the absorption of lipids from the digestive tract. Lymphatic vascular function is critical for both embryonic development and adult homeostasis, reflected by the fact that abnormalities in the growth and development of lymphatic vessels (lymphangiogenesis) are associated with an ever-expanding catalog of human pathologies. Defects in embryonic lymphangiogenesis that result in dysfunctional lymphatic vessels are associated with congenital lymphoedema syndromes, as well as Down, Noonan’s and Turner syndromes. It is likely that the most severe disturbances in embryonic lymphatic vascular development are incompatible with life. Aberrant postnatal lymphangiogenesis has recently been associated with inflammatory pathologies including graft rejection, asthma, psoriasis and arthritis, while the stimulation of lymphangiogenesis by tumors has been demonstrated to promote tumor metastasis in mouse models and has been correlated with poor patient prognosis in several types of human cancers. A major focus of lymphatic vascular research is to delineate the mechanisms by which the lymphatic vasculature is constructed, in order to identify opportunities to intervene in this process and thereby develop better treatments of lymphatic vascular diseases. This chapter will focus on what we currently know about the events that initiate and control construction of the lymphatic vasculature during embryonic development, and how these events are recapitulated or go wrong in disease processes.
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Hereditary Disorders of the Lymphatic System and Varicose Veins
Robert E. Ferrell , Reed E. Pyeritz , in Emery and Rimoin's Principles and Practice of Medical Genetics , 2013
Lymphatics are thin-walled vessels that carry a protein-rich fluid from the periphery back to the central circulation. As in the systemic venous system, unidirectional flow is assisted by valves throughout lymphatics of all calibers. Lymphatics draining the legs, pelvis and abdomen merge into the cisterna chyli, which passes with the aorta through the diaphragm and becomes the thoracic duct. Lymphatics comprising the left jugular, subclavian and mediastinal trunks usually join the thoracic duct as it loops over the left subclavian artery and drains into the left innominate vein. Lymphatic drainage of the right subclavian, jugular and mediastinal trunks usually merge into a right lymphatic duct, which opens into the right innominate vein. However, any of the trunks may open independently into the great veins. Arranged periodically along lymphatic trunks are lymph nodes, comprising a stroma packed with cells of the immune system, which serve as filters of the lymphatic fluid.
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Hereditary Disorders of the Lymphatic System and Varicose Veins
R.E. Ferrell , R.E. Pyeritz , in Reference Module in Biomedical Sciences , 2014
Lymphatics are thin-walled vessels that carry a protein-rich fluid from the periphery back to the central circulation. As in the systemic venous system, unidirectional flow is assisted by valves throughout lymphatics of all calibers. Lymphatics draining the legs, pelvis, and abdomen merge into the cisterna chyli, which passes with the aorta through the diaphragm and becomes the thoracic duct. Lymphatics comprising the left jugular, subclavian, and mediastinal trunks usually join the thoracic duct as it loops over the left subclavian artery and drain into the left innominate vein. Lymphatic drainage of the right subclavian, jugular, and mediastinal trunks usually merges into a right lymphatic duct, which opens into the right innominate vein. However, any of the trunks may open independently into the great veins. Arranged periodically along lymphatic trunks are lymph nodes, comprising a stroma packed with cells of the immune system, which serve as filters of the lymphatic fluid.
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Immunohistology of the Breast
Rohit Bhargava , … David J. Dabbs , in Diagnostic Immunohistochemistry (Third Edition) , 2011
DETECTION OF LYMPHATIC SPACE INVASION
Lympho-vascular space invasion in breast carcinoma is an independent predictor of axillary lymph node metastasis, which in turn is one of the most important prognostic factors in breast carcinoma.184-187 One recent study has shown that peritumoral lymphatic space invasion (and not blood vessel invasion) was determinant of lymph node metastasis.188 In addition, identification of tumor emboli within dermal lymphatics is also important for correlation purposes in cases of inflammatory carcinomas.189-191
The pitfalls of interpretation of lymphatic channels in paraffin-embedded breast tissue are well known. Retraction artifacts, ducts with misplaced epithelium, and artifactual displacement of cells commonly complicate the interpretation of biopsy samples. A recently available antibody, D2-40, shows high sensitivity and specificity for normal lymphatic channels in a variety of tissues.192,193 D2-40 stains the lymphatic endothelium crisply and intensely but does not stain the normal vascular endothelium (Fig. 19.30).194 It is highly sensitive and specific in identifying lymphatic space invasion.192 In the breast, D2-40 stains lymphatic channels with a crisp, intense membrane staining of lymphatic endothelium. D2-40 shows a smudgy immunostaining pattern with myoepithelial cells and reactive stromal myofibroblasts. This is a pitfall because the faint to occasionally moderate staining around the periphery of a small duct may be mistaken for lymphatic space invasion; however, it is important to remember that lymphatic vessels are stained very intensely with D2-40 (see Fig. 19.30C).
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Anatomic Considerations in Abdominal Contouring
Joseph P. Hunstad , Remus Repta , in Atlas of Abdominoplasty , 2009
Lymphatics (Box 2.3)
The lymphatics of the abdominal wall can be categorized into superficial and deep vessels. The superficial lymphatic vessels are located in the abdominal soft tissue above the deep muscular fascia, and the deep lymphatic vessels are those associated with the abdominal wall musculature. In large part, abdominal contouring procedures involve the superficial lymphatic vessels. Although myofascial plication involves the deep fascia, the deep lymphatics are not encroached upon by standard abdominoplasty procedures.
The superficial abdominal lymphatic system is contained within the abdominal soft tissue above the muscular/deep fascia.
Most of the lymphatics superior to the umbilicus drain to the axillary lymph node basin. Most of the lymphatics inferior to the umbilicus drain to the superficial inguinal lymph node basin.
A significant portion of the lower abdominal tissue associated with lymphatic disruption during abdominoplasty procedures is resected.
The abdominal soft tissue lymphatics are a latticework of lymph vessels that drain primarily into the axillary and superficial inguinal lymph nodes, with the umbilicus serving as the watershed between these two lymphatic tributaries6 (Fig. 2.7). Cephalic to the umbilicus the superficial lymphatic vessels coalesce and drain into the axillary lymph node basin. There is also some lymphatic flow to the parasternal lymph node basin, but this is a minor portion. Caudal to the umbilicus the lymphatic vessels coalesce and drain into the superficial inguinal lymph node basin.
Abdominal contouring procedures inevitably disturb some of these superficial lymphatic vessels. Depending on the technique used, some or most of the superficial inferior lymphatic flow may be disturbed. Fortunately, most abdominoplasty techniques also involve resection of the inferior skin and subcutaneous tissue that has undergone disruption of the lymphatics. Lymphatic preservation may be possible by performing extensive deep liposuction of the inferior abdominal region, which is then left in place during flap elevation and resection. These concepts of liposuction abdominoplasty are addressed in Chapter 6.
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Safety Assessment including Current and Emerging Issues in Toxicologic Pathology
Ann Hubbs , … Krishnan Sriram , in Haschek and Rousseaux's Handbook of Toxicologic Pathology (Third Edition) , 2013
5.4 Lymphatic Pathology
Lymphatics are difficult to see in standard histopathologic sections. In conducting NP studies, it is important to remember that the lymphatic vasculature is a circulatory system which plays a key role in fluid homeostasis, particle clearance, cellular transport, metastasis, and the immune system. The lymphatics are increasingly recognized as being dynamic structures with unique molecular signaling essential for their role in maintaining interstitial and blood capillary homeostasis. The endothelium of the lymphatic capillaries plays an active role in movement of cells into the lymphatics. Physically, the lymphatic endothelium is attenuated, the intercellular spaces between lymphatic endothelial cells are sufficient for movement of cells, and the basement membrane of the lymphatic capillaries is discontinuous. These features provide NPs with remarkable access to the lymphatic circulation. In addition, colloidal carbon and ferritin particles have been reported within vesicles in the lymphatic endothelium and alveolar Type I cells. This implies that transcellular transport may occur through the lymphatics and alveolar Type I cells of the lung as well as the vascular endothelium, and does not always require phagocytosis. In addition, instilled carbon and ferritin particles have been observed in the gaps between lymphatic endothelial cells in the pulmonary lymphatics, suggesting intercellular movement of particulates. Once within the lymphatic lumen, the lymphatic contents filter through lymph nodes and eventually empty into the vasculature at the thoracic duct. This means that the lymphatics are a potential route for delivery of NPs and inflammatory mediators to the blood. Recently, lung-deposited NPs less than 30 nm in diameter were demonstrated to first reach the draining lymph nodes and then reach the blood after a time lag not observed with low molecular weight molecules. This suggests that lymphatic drainage into the vasculature may indeed be important in vascular dissemination of some NPs.
Particles can enter the lymphatics when carried by phagocytic cells, and this appears to be the major route for transport of fine particles in the micron size range. Fine particles injected into the footpad or deposited in the alveolar region do not reach the draining lymph node as free particles. Instead, they are phagocytized by macrophages and neutrophils, which can enter the lymphatics and are transported to the draining lymph nodes within phagocytic cells. However, extracellular routes of particle transport may be important with some NPs. Small NPs (20 nm) that are injected into the footpad rapidly translocate to the draining lymph node and can be seen in the subcapsular sinuses and in the antigen-presenting cells of the lymph node, including dendritic cells and plasmacytoid dendritic cells. Recent studies demonstrate that many NPs are rapidly and widely transported through the lymphatics. For lung-deposited NPs, rapid translocation by the lymphatics is highly influenced by surface coatings and charge, but, importantly, is size-limited, with a threshold estimated to be at a functional diameter of between 34 and 48 nm. A previous study of radiolabelled iridium and carbon NPs indicated that 20-nm diameter particles, which are below this threshold, translocated from the lung to secondary target tissues more effectively than 80-nm diameter particles, which are above this threshold. Extracellular lymphatic transport of small NPs is also suggested by recent studies of NPs used in lymphangiography.
This feature of some NPs can help to map the lymphatics and lymph nodes draining critical sites, such as tumors. In addition, chemotherapeutic agents can be adsorbed onto the NP surface, carried into the lymphatics, and from there distributed to the lymph node. This suggests the potential use of NP-conjugated chemotherapeutic agents in therapy targeted to the lymphatics, which play such an important role in metastatic spread of cancer.
One important implication of the tropism of NPs for the lymphatics is that the lymphatics represent a pathway for transport of NPs from an exposed tissue to distant tissues and organs. While this feature can be used for therapeutic purpose in some situations, it is a feature that needs to be considered when toxicologic pathologists evaluate studies. Certainly, the lymph nodes play an enormous role in immune function and receive the contents from the lymphatics. Therefore, lymphatics should be considered a potential route for delivering immunotoxic and antigenic compounds to the immune system. In addition, alterations in the lymphatics themselves can play an important role in disease pathogenesis. Recently, lymphangiectasia (lymphatic dilation) was noted in the lymphatics of mice aspirating MWCNTs. This suggests that the lymphatics may not just transport NPs; they may also be damaged by them. Thus, pathologists need to recognize that the lymphatics are potential targets in NP studies and that this can have potential functional consequences. In addition, the lymphatics need to be considered as a potential route for translocation of NPs, a feature which distinguishes NPs from traditional organic pharmaceuticals. The lymphatics and the lymph nodes are, therefore, particularly important for pathologists studying NPs. Fortunately, lymphatic endothelial markers can be used to help pathologists visualize the lymphatics in tissue sections (Figure 43.15).
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Clinical Approach to Commonly Encountered Problems
Melissa T. Hines , in Equine Internal Medicine (Fourth Edition) , 2018
The lymphatics drain the interstitium of fluid and substances, notably proteins, that are not absorbed by the capillaries.311 The lymphatics represent the only means by which interstitial protein is returned to the circulation. Interstitial fluid (and, with it, protein) moves down a pressure gradient into lymphatic capillaries through clefts between the lymphatic endothelial cells. Lymphatic endothelial cells are supported, and the lymphatic capillaries maintained patent, by anchoring filaments that attach the endothelial cells to surrounding connective tissue. Lymphatic fluid progresses centripetally through progressively larger vessels before draining into the great veins of the chest. Lymphatic valves prevent the retrograde flow of fluid from the lymphatics. Lymph is propelled by factors extrinsic to the lymphatics, including muscle activity, active and passive motion, posture, respiration, and blood vessel pulsation. Exercise increases lymph flow, at least in part because of the increase in tissue pressure that is associated with muscle contraction, although passive motion also increases lymph flow. In human beings, standing results in significant diminution or cessation of lymph flow from the lower extremities, which can result in the accumulation of interstitial fluid and edema. In addition to the extrinsic factors affecting lymph flow, coordinated contractions of lymphatic vessels contribute substantially to the centripetal flow of lymph.313
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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.
|Drains to||junction of the left subclavian vein and left internal jugular vein|
| Anatomical terminology |
[ edit on Wikidata ]
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 . It 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 .
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.   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 Structure
- 2 Function
- 3 Clinical significance
- 4 Additional images
- 5 See also
- 6 References
- 7 External links
Structure[ edit ]
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,   below the clavicle , near the shoulders .
Function[ edit ]
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. 
Clinical significance[ edit ]
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[ edit ]
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.
Front photo of the Ductus Thoracicus in the Human mediastinum with the heart and part of the pericard removed.
See also[ edit ]
- Lymph duct
- Lymphatic system
References[ edit ]
- ^ a b Knipe, Henry. “Thoracic duct | Radiology Reference Article | Radiopaedia.org” . radiopaedia.org. Retrieved 2016-10-08.
- ^ a b 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 .
- ^ 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.
- ^ Tewfik, Ted L; Mosenifar, Zab. “Thoracic Duct Anatomy” . Medscape. WebMD Health Professional Network.
External links[ edit ]
- Anatomy figure: 21:05-02 at Human Anatomy Online, SUNY Downstate Medical Center—”The thoracic duct and azygos venous network”
- Anatomy image:8901 at the SUNY Downstate Medical Center
- figures/chapter_24/24-5.HTM : Basic Human Anatomy at Dartmouth Medical School
- ” thoracic duct ” at Dorland’s Medical Dictionary
- Diagram at anatomyatlases.org
- Ultrasound Imaging the thoracic duct
- Instruction video for Ultrasound examination of the thoracic duct
- Lymphatics of the torso
- Use dmy dates from April 2017
- Wikipedia articles with TA98 identifiers
- This page was last edited on 27 November 2018, at 18:37 (UTC).
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