Lymphatic vessel

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Lymphatic vessel
Illu lymph capillary.png
Lymph capillaries in the tissue spaces.
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The thoracic duct and right lymphatic duct.
Details
System Lymphatic system
Identifiers
Latin vas lymphaticum
MeSH D042601
TA98 A12.0.00.038
TA2 3915
TH H3.09.02.0.05001
FMA 30315
Anatomical terminology
A still image from a 3D medical animation showing afferent vessels 3D Medical Animation of Afferent Vessel.jpg
A still image from a 3D medical animation showing afferent vessels

The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscle, and adventitia that binds the lymph vessels to the surrounding tissue. Lymph vessels are devoted to the propulsion of the lymph from the lymph capillaries, which are mainly concerned with absorption of interstitial fluid from the tissues. Lymph capillaries are slightly bigger than their counterpart capillaries of the vascular system. Lymph vessels that carry lymph to a lymph node are called afferent lymph vessels, and those that carry it from a lymph node are called efferent lymph vessels, from where the lymph may travel to another lymph node, may be returned to a vein, or may travel to a larger lymph duct. Lymph ducts drain the lymph into one of the subclavian veins and thus return it to general circulation.

Contents

The vessels that bring lymph away from the tissues and towards the lymph nodes can be classified as afferent vessels. These afferent vessels then drain into the subscapular sinus. [1] The efferent vessels that bring lymph from the lymphatic organs to the nodes bringing the lymph to the right lymphatic duct or the thoracic duct, the largest lymph vessel in the body. These vessels drain into the right and left subclavian veins, respectively. There are far more afferent vessels bringing in lymph than efferent vessels taking it out to allow for lymphocyte and macrophages to fulfill their immune support functions. The lymphatic vessels contain valves.

Structure

The general structure of lymphatics is based on that of blood vessels. There is an inner lining of single flattened epithelial cells (simple squamous epithelium) composed of a type of epithelium that is called endothelium, and the cells are called endothelial cells. This layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous; it leaks easily. [2] The next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening (contracting) or relaxing alter the diameter (caliber) of the lumen. The outermost layer is the adventitia that consists of fibrous tissue. The general structure described here is seen only in larger lymphatics; smaller lymphatics have fewer layers. The smallest vessels (lymphatic or lymph capillaries ) lack both the muscular layer and the outer adventitia. As they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, and then smooth muscles.

The lymphatic conducting system broadly consists of two types of channels—the initial lymphatics, the prelymphatics or lymph capillaries that specialize in collection of the lymph from the ISF, and the larger lymph vessels that propel the lymph forward.

Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis (propulsion of the lymph due to alternate contraction and relaxation of smooth muscle), valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation. [3]

Propulsion of lymph through lymph vessel Lymph vessel.png
Propulsion of lymph through lymph vessel

Lymph capillaries

The lymphatic circulation begins with blind ending (closed at one end) highly permeable superficial lymph capillaries, formed by endothelial cells with button-like junctions between them that allow fluid to pass through them when the interstitial pressure is sufficiently high. [4] These button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF. This valve system involves collagen fibers attached to lymphatic endothelial cells that respond to increased interstitial fluid pressure by separating the endothelial cells and allowing the flow of lymph into the capillary for circulation. [5] There is another system of semilunar valves that prevents back-flow of lymph along the lumen of the vessel. [4] Lymph capillaries have many interconnections (anastomoses) between them and form a very fine network. [6]

Rhythmic contraction of the vessel walls through movements may also help draw fluid into the smallest lymphatic vessels, capillaries. If tissue fluid builds up the tissue will swell; this is called edema. As the circular path through the body's system continues, the fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); both ducts drain into the circulatory system at the right and left subclavian veins. The system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a secondary circulatory system.

Lymph vessels

The lymph capillaries drain into larger collecting lymphatics. These are contractile lymphatics which transport lymph using a combination of smooth muscle walls, which contract to assist in transporting lymph, as well as valves to prevent the lymph from flowing backwards. [3] As the collecting lymph vessel accumulates lymph from more and more lymph capillaries along its length, it becomes larger and eventually becomes an afferent lymph vessel as it enters a lymphs node. The lymph percolates through the lymph node tissue and exits via an efferent lymph vessel. An efferent lymph vessel may directly drain into one of the (right or thoracic) lymph ducts, or may empty into another lymph node as its afferent lymph vessel. [6] Both the lymph ducts return the lymph to the blood stream by emptying into the subclavian veins

Lymph vessels consist of functional units known as lymphangions which are segments separated by semilunar valves. These segments propel or resist the flow of lymph by the contraction of the encircling smooth muscle depending upon the ratio of its length to its radius. [7]

Function

Lymph vessels act as reservoirs for plasma and other substances including cells that have leaked from the vascular system and transport lymph fluid back from the tissues to the circulatory system. Without functioning lymph vessels, lymph cannot be effectively drained and lymphedema typically results.

Afferent vessels

The afferent lymph vessels enter at all parts of the periphery of the lymph node, and after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. It carries unfiltered lymph into the node. In doing this they lose all their coats except their endothelial lining, which is continuous with a layer of similar cells lining the lymph paths.

Afferent lymphatic vessels are only found in lymph nodes. This is in contrast to efferent lymphatic vessel which are also found in the thymus and spleen.

Efferent vessels

The efferent lymphatic vessel commences from the lymph sinuses of the medullary portion of the lymph nodes and leave the lymph nodes at the hilum, either to veins or greater nodes. It carries filtered lymph out of the node.

Efferent lymphatic vessels are also found in association with the thymus and spleen. This is in contrast to afferent lymphatic vessels, which are found only in association with lymph nodes.

Clinical significance

Lymphedema is the swelling of tissues due to insufficient fluid drainage by the lymphatic vessels. It can be the result from absent, underdeveloped or dysfunctional lymphatic vessels. In hereditary (or primary) lymphedema, the lymphatic vessels are absent, underdeveloped or dysfunctional due to genetic causes. In acquired (or secondary) lymphedema, the lymphatic vessels are damaged by injury or infection. [8] [9] Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.

See also

Additional images

Related Research Articles

Lymphedema Medical condition

Lymphedema, also known as lymphoedema and lymphatic edema, is a condition of localized swelling caused by a compromised lymphatic system. The lymphatic system functions as a critical portion of the body's immune system and returns interstitial fluid to the bloodstream. Lymphedema is most frequently a complication of cancer treatment or parasitic infections, but it can also be seen in a number of genetic disorders. Though incurable and progressive, a number of treatments can improve symptoms. Tissues with lymphedema are at high risk of infection because the lymphatic system has been compromised.

Artery Blood vessels that carry blood away from the heart

An artery is a blood vessel in humans and most other animals that takes blood away from the heart to one or more parts of the body. Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical arteries, which carry deoxygenated blood to the organs that oxygenate it. The effective arterial blood volume is that extracellular fluid which fills the arterial system.

Blood vessel Tubular structure of the circulatory system which transports blood

The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality.

Lymphatic system Organ system in vertebrates

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 organs, and lymphoid tissues. The vessels carry a clear fluid called lymph back towards the heart, for re-circulation.

Lymph node Organ of the lymphatic system

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 include B and T cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles including cancer cells, but have no detoxification function.

Thoracic duct Lymphatic vessel

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. 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.

Lymph Fluid that circulates throughout lymphatic system

Lymph 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 the central circulation. At the origin of the fluid-return process, interstitial fluid—the fluid between the cells in all body tissues—enters the lymph capillaries. This lymphatic fluid is then transported via progressively larger lymphatic vessels through lymph nodes, where substances are removed by tissue lymphocytes and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left subclavian vein, where it mixes with central venous blood.

Microcirculation Circulation of the blood in the smallest blood vessels

The microcirculation is the circulation of the blood in the smallest blood vessels, the microvessels of the microvasculature present within organ tissues. The microvessels include terminal arterioles, metarterioles, capillaries, and venules. Arterioles carry oxygenated blood to the capillaries, and blood flows out of the capillaries through venules into veins.

Venule Very small blood vessel in the microcirculation

A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to drain into the larger blood vessels, the veins. Venules range from 7μm to 1mm in diameter. Veins contain approximately 70% of total blood volume, 25% of which is contained in the venules. Many venules unite to form a vein.

Glomerulus (kidney) Functional unit of Nephron

The glomerulus is a network of small blood vessels (capillaries) known as a tuft, located at the beginning of a nephron in the kidney. Each of the two kidneys contains about one million nephrons. The tuft is structurally supported by the mesangium, composed of intraglomerular mesangial cells. The blood is filtered across the capillary walls of this tuft through the glomerular filtration barrier, which yields its filtrate of water and soluble substances to a cup-like sac known as Bowman's capsule. The filtrate then enters the renal tubule of the nephron.

Lymphangitis Medical condition

Lymphangitis is an inflammation or an infection of the lymphatic channels that occurs as a result of infection at a site distal to the channel. The most common cause of lymphangitis in humans is Streptococcus pyogenes, hemolythic streptococci, and in some cases, mononucleosis, cytomegalovirus, tuberculosis, syphilis, and the fungus Sporothrix schenckii. Lymphangitis is sometimes mistakenly called "blood poisoning". In reality, "blood poisoning" is synonymous with sepsis.

Head and neck anatomy

This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.

Axillary lymph nodes Lymph nodes in the human armpit

The axillary lymph nodes or armpit lymph nodes are lymph nodes in the human armpit. Between 20 and 49 in number, they drain lymph vessels from the lateral quadrants of the breast, the superficial lymph vessels from thin walls of the chest and the abdomen above the level of the navel, and the vessels from the upper limb. They are divided in several groups according to their location in the armpit. These lymph nodes are clinically significant in breast cancer, and metastases from the breast to the axillary lymph nodes are considered in the staging of the disease.

Lymph capillary Microvessel serving to drain and process extracellular fluid

Lymph capillaries or lymphatic capillaries are tiny, thin-walled microvessels located in the spaces between cells which serve to drain and process extracellular fluid. Upon entering the lumen of a lymphatic capillary, the collected fluid is known as lymph. Each lymphatic capillary carries lymph into a lymphatic vessel, which in turn connects to a lymph node, a small bean-shaped gland that filters and monitors the lymphatic fluid for infections. Lymph is ultimately returned to the venous circulation.

Popliteal lymph nodes

The popliteal lymph nodes, small in size and some six or seven in number, are embedded in the fat contained in the popliteal fossa, sometimes referred to as the 'knee pit'. One lies immediately beneath the popliteal fascia, near the terminal part of the small saphenous vein, and drains the region from which this vein derives its tributaries, such as superficial regions of the posterolateral aspect of the leg and the plantar aspect of the foot.

Lymph trunk is a collection of lymph vessels that carries lymph, and is formed by confluence of many efferent lymph vessels. It in turn drains into one of the two lymph ducts.

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.

Lymph node stromal cells are essential to the structure and function of the lymph node whose functions include: creating an internal tissue scaffold for the support of hematopoietic cells; the release of small molecule chemical messengers that facilitate interactions between hematopoietic cells; the facilitation of the migration of hematopoietic cells; the presentation of antigens to immune cells at the initiation of the adaptive immune system; and the homeostasis of lymphocyte numbers. Stromal cells originate from multipotent mesenchymal stem cells.

Anatomical terms of microanatomy Anatomical terminology is used to describe microanatomical (or histological) structures

Anatomical terminology is used to describe microanatomical structures. This helps describe precisely the structure, layout and position of an object, and minimises ambiguity. An internationally accepted lexicon is Terminologia Histologica.

References

  1. ↑ "19.2B: Distribution of Lymphatic Vessels". Medicine LibreTexts. 22 July 2018. Retrieved 28 November 2021.
  2. ↑ Pepper MS, Skobe M (October 2003). "Lymphatic endothelium: morphological, molecular and functional properties". The Journal of Cell Biology. 163 (2): 209–13. doi:10.1083/jcb.200308082. PMC   2173536 . PMID   14581448.
  3. 1 2 Shayan R, Achen MG, Stacker SA (September 2006). "Lymphatic vessels in cancer metastasis: bridging the gaps". Carcinogenesis. 27 (9): 1729–38. doi: 10.1093/carcin/bgl031 . PMID   16597644.
  4. 1 2 Baluk P, Fuxe J, Hashizume H, Romano T, Lashnits E, Butz S, et al. (October 2007). "Functionally specialized junctions between endothelial cells of lymphatic vessels". The Journal of Experimental Medicine. 204 (10): 2349–62. doi:10.1084/jem.20062596. PMC   2118470 . PMID   17846148.
  5. ↑ Weitman E, Cuzzone D, Mehrara BJ (September 2013). "Tissue engineering and regeneration of lymphatic structures". Future Oncology. 9 (9): 1365–74. doi:10.2217/fon.13.110. PMC   4095806 . PMID   23980683.
  6. 1 2 Rosse C, Gaddum-Rosse P (1997). "The Cardiovascular System (Chapter 8)". Hollinshead's Textbook of Anatomy (Fifth ed.). Philadelphia: Lippincott-Raven. pp. 72–73. ISBN   0-397-51256-2.
  7. ↑ Venugopal AM, Stewart RH, Rajagopalan S, Laine GA, Quick CM (2004). "Optimal Lymphatic Vessel Structure". The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. 26th Annual International Conference of the IEEE. Vol. 2. Engineering in Medicine and Biology Society. pp. 3700–3703. doi:10.1109/IEMBS.2004.1404039. ISBN   0-7803-8439-3.
  8. ↑ Alitalo K (November 2011). "The lymphatic vasculature in disease". Nature Medicine. 17 (11): 1371–80. doi:10.1038/nm.2545. PMID   22064427. S2CID   5899689.
  9. ↑ Krebs R, Jeltsch M (2013). "The lymphangiogenic growth factors VEGF-C and VEGF-D. Part 2: The role of VEGF-C and VEGF-D in lymphatic system diseases". Lymphologie in Forschung und Praxis. 17 (2): 96–104.

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