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 bind 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 larger 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.
Generally, lymph flows away from the tissues to lymph nodes and eventually to either the right lymphatic duct or the largest lymph vessel in the body, the thoracic duct. These vessels drain into the right and left subclavian veins, respectively.The lymphatic vessels contain valves.
Lymph capillaries in the tissue spaces.
The thoracic duct and right lymphatic duct.
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. 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.
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. 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. There is another system of semilunar (semi=half; lunar=related to the Moon) valves that prevents back-flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections (anastomoses) between them and form a very fine network.
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.
The lymph capillaries drain the lymph to larger contractile lymphatics, which have valves as well as smooth muscle walls. These are called the collecting lymphatics. As the collecting lymph vessel accumulates lymph from more and more lymph capillaries in its course, it becomes larger and is called the afferent lymph vessel as it enters a lymph node. Here the lymph percolates through the lymph node tissue and is removed by the 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. Both the lymph ducts return the lymph to the blood stream by emptying into the subclavian veins
The functional unit of a lymph vessel is known as a lymphangion, which is the segment between two valves. Since it is contractile, depending upon the ratio of its length to its radius, it can act either like a contractile chamber propelling the fluid ahead, or as a resistance vessel tending to stop the lymph in its place.
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 edema typically results.
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.
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.
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. Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.
Angiomas are benign tumors derived from cells of the vascular or lymphatic vessel walls (endothelium) or derived from cells of the tissues surrounding these vessels.Angiomas are a frequent occurrence as patients age, but they might be an indicator of systemic problems such as liver disease. They are not commonly associated with malignancy.Angiosarcoma
Angiosarcoma is a cancer of the cells that line the walls of blood vessels or lymphatic vessels. The lining of the vessel walls is called the endothelium. However, they should not be confused with cherry hemangiomas.
Most tumors of visceral blood and lymphatic vessel walls are cancerous (malignant). Because these cancers are carried by the blood flow or lymphatic flow, they can more easily metastasize to distant sites, particularly the liver and lungs.
Angiosarcomas show signs of hemorrhage and necrosis. Pathologically, tumor cells show increased nuclear to cytoplasm ratio, nuclear hyperchromasia, nuclear pleomorphism and high mitotic activity.In dogs, hemangiosarcoma is relatively common, with the golden retriever and Labrador retriever at higher risk of the disease than other breeds. In humans, hemangiosarcomas and lymphangiosarcomas of the skin are uncommon. Angiosarcoma of the liver, a rare fatal tumor, has been seen in workers intensively exposed to the gas vinyl chloride monomer (VCM) for prolonged periods while working in polyvinyl chloride (PVC) polymerization plants. It has also been associated with individuals exposed to arsenic-containing insecticides and Thorotrast.Edema
Edema, also spelled oedema or œdema, is an abnormal accumulation of fluid in the interstitium, located beneath the skin and in the cavities of the body, which can cause severe pain. Clinically, hyperaldosteronism, edema manifests as swelling. The amount of interstitial fluid is determined by the balance of fluid homeostasis and the increased secretion of fluid into the interstitium. The word is from Greek οἴδημα oídēma meaning "swelling". The condition is also known (mostly archaic) as dropsy.Intermammary cleft
In female human anatomy, the intermammary cleft or intermammary sulcus or sulcus intermammarius of a woman is delineated by where the fatty portions of each breast sits in relationship to the sternum (or breastbone). It divides the two mammary complexes that consist of two bodies of fatty pads, glandular tissues of mammary glands, connective tissues, and skin, as well as two duct systems (lactiferous duct of lymphatic vessel) and lobule alveoli emanating from two nipples. Lymph vessels can ventrally extend as far as the intermammary sulcus.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.
On the right side, this trunk ends in the junction of the internal jugular and subclavian veins, called the venous angle. On the left side it joins the thoracic duct.LYVE1
Lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), also known as extracellular link domain containing 1 (XLKD1) is a Link domain-containing hyaladherin, a protein capable of binding to hyaluronic acid (HA), homologous to CD44, the main HA receptor. In humans it is encoded by the LYVE1 gene.LYVE1 is a type I integral membrane glycoprotein. It acts as a receptor and binds to both soluble and immobilized hyaluronan. This protein may function in lymphatic hyaluronan transport and have a role in tumor metastasis. LYVE-1 is a cell surface receptor on lymphatic endothelial cells that can be used as a lymphatic endothelial cell marker, allowing for the isolation of these cells for experimental purposes. The physiological role for this receptor is still the subject of debate, but evolutionary conservation suggests an important role.Lipedema
Lipedema is a disorder where there is enlargement of both legs due to deposits of fat under the skin. Typically it gets worse over time, pain may be present, and sufferers bruise easily. In severe cases the trunk and upper body may be involved. Lipedema is commonly misdiagnosed.The cause is unknown but is believed to involve genetics and hormonal factors. It often runs in families. Risk factors include being overweight or obese. Other conditions that may present similarly include obesity, lipohypertrophy, chronic venous insufficiency, and lymphedema.A number of treatments may be useful including physiotherapy and exercise. Physiotherapy may help to preserve mobility for a little longer than would otherwise be the case. Exercise, only as much as the patient is able to do without causing damage to the joints, may help with overall fitness but will not prevent progression of the disease. While surgery can remove fat tissue it can also damage lymphatic vessels. Treatment does not typically result in complete resolution. It is estimated to affect up to 11% of women. Onset is typically during puberty, pregnancy, or menopause.Lymph capillary
Lymph capillaries or lymphatic capillaries are tiny, thin-walled microvessels located in the spaces between cells (except in the central nervous system and non-vascular tissues) which serve to drain and process extracellular fluid. Upon entering the lumen of a lymphatic capillary, the collected fluid and associated cells (notably white blood cells) is known as lymph. Each lymphatic capillary carries lymph into a lymphatic vessel, which in turn connects to a lymph node. Lymph is ultimately returned to the venous circulation.
Lymphatic capillaries are slightly larger in diameter than blood capillaries, and have closed ends (unlike the loop structure of blood capillaries). Their unique structure permits interstitial fluid to flow into them but not out. The ends of the endothelial cells that make up the wall of a lymphatic capillary overlap. When pressure is greater in the interstitial fluid than in lymph, the cells separate slightly, like the opening of a one-way swinging door, and interstitial fluid enters the lymphatic capillary. When pressure is greater inside the lymphatic capillary, the cells adhere more closely, and lymph cannot escape back into interstitial fluid. Attached to the lymphatic capillaries are anchoring filaments, which contain elastic fibers. They extend out from the lymphatic capillary, attaching lymphatic endothelial cells to surrounding tissues. When excess interstitial fluid accumulates and causes tissue swelling, the anchoring filaments are pulled, making the openings between cells even larger so that more fluid can flow into the lymphatic capillary.Lymph capillaries have a greater internal oncotic pressure than blood capillaries, due to the greater concentration of plasma proteins in the lymph.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.Lymphangiectasia
Lymphangiectasia is a pathologic dilation of lymph vessels. When it occurs in the intestines of dogs, and more rarely humans, it causes a disease known as "intestinal lymphangiectasia". This disease is characterized by lymphatic vessel dilation, chronic diarrhea and loss of proteins such as serum albumin and globulin. It is considered to be a chronic form of protein-losing enteropathy.
It is also known as "lymphangiectasis".Lymphangiogenesis
Lymphangiogenesis is the formation of lymphatic vessels from pre-existing lymphatic vessels in a method believed to be similar to angiogenesis (blood vessel development).Lymphangiogenesis plays an important physiological role in homeostasis, metabolism and immunity. Impaired or excessive lymphatic vessel formation has been implicated in a number of pathological conditions including neoplasm metastasis, oedema, rheumatoid arthritis, psoriasis, lymphangiomatosis and impaired wound healing.
The role of the lymphatic system in these diseases has received renewed interest largely due to the relevantly recent discovery of LEC (lymphatic endothelial cell)-specific markers such as podoplanin, LYVE-1, PROX-1, desmoplakin and VEGF-C receptor VEGFR-3. These specific markers have enabled new insights into functional and molecular lymphatic biology. There are several known pro-lymphangiogenesis inducers such as VEGF-C, hyaluronic acid and ephrin-B2.
Various mechanisms have been proposed to explain VEGFC patterning during lymphangiogenesis, including formation of Turing patterns.Lymphangioma
Lymphangiomas are malformations of the lymphatic system characterized by lesions that are thin-walled cysts; these cysts can be macroscopic, as in a cystic hygroma, or microscopic. The lymphatic system is the network of vessels responsible for returning to the venous system excess fluid from tissues as well as the lymph nodes that filter this fluid for signs of pathogens. These malformations can occur at any age and may involve any part of the body, but 90% occur in children less than 2 years of age and involve the head and neck. These malformations are either congenital or acquired. Congenital lymphangiomas are often associated with chromosomal abnormalities such as Turner syndrome, although they can also exist in isolation. Lymphangiomas are commonly diagnosed before birth using fetal ultrasonography. Acquired lymphangiomas may result from trauma, inflammation, or lymphatic obstruction.
Most lymphangiomas are benign lesions that result only in a soft, slow-growing, "doughy" mass. Since they have no chance of becoming malignant, lymphangiomas are usually treated for cosmetic reasons only. Rarely, impingement upon critical organs may result in complications, such as respiratory distress when a lymphangioma compresses the airway. It is mostly caused due to an unhealthy part of genetics in the sperm while forming the fetus. Treatment includes aspiration, surgical excision, laser and radiofrequency ablation, and sclerotherapy.Lymphangiomatosis
Lymphangiomatosis is a condition where a lymphangioma is not present in a single localised mass, but in a widespread or multifocal manner. It is a rare type of tumor which results from an abnormal development of the lymphatic system.It is thought to be the result of congenital errors of lymphatic development occurring prior to the 20th week of gestation. Lymphangiomatosis is a condition marked by the presence of cysts that result from an increase both in the size and number of thin-walled lymphatic channels that are abnormally interconnected and dilated. 75% of cases involve multiple organs. It typically presents by age 20 and, although it is technically benign, these deranged lymphatics tend to invade surrounding tissues and cause problems due to invasion and/or compression of adjacent structures. The condition is most common in the bones and lungs and shares some characteristics with Gorham’s disease. Up to 75% of patients with lymphangiomatosis have bone involvement, leading some to conclude that lymphangiomatosis and Gorham’s disease should be considered as a spectrum of disease rather than separate diseases. When it occurs in the lungs, lymphangiomatosis has serious consequences and is most aggressive in the youngest children. When the condition extends into the chest it commonly results in the accumulation of chyle in the linings of the heart and/or lungs.Chyle is composed of lymph fluid and fats that are absorbed from the small intestine by specialized lymphatic vessels called lacteals during digestion. The accumulations are described based on location: chylothorax is chyle in the chest; chylopericardium is chyle trapped inside the sack surrounding the heart; chyloascites is chyle trapped in the linings of the abdomen and abdominal organs. The presence of chyle in these places accounts for many of the symptoms and complications associated with both lymphangiomatosis and Gorham’s disease. The incidence of lymphangiomatosis is unknown and it is often misdiagnosed. It is separate and distinct from lymphangiectasis, lymphangioleiomyomatosis (LAM), pulmonary capillary hemangiomatosis, Kaposi’s sarcoma, and kaposiform hemangioendothelioma. Its unusual nature makes lymphangiomatosis (and Gorham’s disease) a diagnostic and therapeutic challenge. A multidisciplinary approach is generally necessary for optimal diagnosis and symptom management. The term literally means lymphatic system (lymph) vessel (angi) tumor or cyst (oma) condition (tosis).Lymphangiosarcoma
Lymphangiosarcoma is a rare cancer which occurs in long-standing cases of primary or secondary lymphedema. It involves either the upper or lower lymphedematous extremities but is most common in upper extremities. Although its name implies lymphatic origin, it is believed to arise from endothelial cells and may be more accurately referred to as angiosarcoma.Lymphangitis
For discussion of the condition in horses, see Equine Lymphangitis.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 (Group A strep), although it can also be caused by the fungus Sporothrix schenckii. Lymphangitis is sometimes mistakenly called "blood poisoning". In reality, "blood poisoning" is synonymous with sepsis.
Signs and symptoms include a deep reddening of the skin, warmth, lymphadenitis (inflammation of a lymphatic gland), and a raised border around the affected area. The person may also have chills and a high fever along with moderate pain and swelling. A person with lymphangitis should be hospitalized and closely monitored by medical professionals.Lymphangitis is the inflammation of the lymphatic vessels and channels. This is characterized by certain inflammatory conditions of the skin caused by bacterial infections. Thin red lines may be observed running along the course of the lymphatic vessels in the affected area, accompanied by painful enlargement of the nearby lymph nodes.
When the inferior limbs are affected, the redness of the skin runs over the great saphenous vein location and confusion can be made with a thrombophlebitis.
Chronic lymphangitis is a cutaneous condition that is the result of recurrent bouts of acute bacterial lymphangitis.Lymphedema
Lymphedema, also known as lymphoedema and lymphatic edema, is a condition of localized fluid retention and tissue 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 ameliorate symptoms. Tissues with lymphedema are at high risk of infection because the lymphatic system has been compromised.Lymphohemangioma
Lymphohemangioma, or lymphohaemangioma, (from Latin lympha, meaning 'water', Greek, Modern αίμα (haema), meaning 'blood', αγγείο (angeio), meaning 'vessel', and –ωμα (–oma), meaning 'tumor') is a disease characterized by swelling of the lymph nodes and blood vessels. It is variously described as a "mixture of clear fluid and blood-filled cysts", a mass of abnormal swollen veins and lymph nodes, or a tumorous growth of lymph and blood vessels. It is also sometimes described as a misnomer for combined lymphatic and capillary malformation.Lymphohemangioma commonly appears in and around the eyes and mouth, but may also occur in other areas, including the pelvis, urethra, bladder, and in the limbs. Amputation of extremities may be necessary if the disease renders the extremity non-functional.Schlemm's canal
Schlemm's canal is a circular lymphatic-like vessel in the eye that collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels via aqueous veins. It is named after Friedrich Schlemm (1795–1858), a German anatomist.
The canal is essentially an endothelium-lined tube, resembling that of a lymphatic vessel. On the inside of the canal, nearest to the aqueous humor, it is covered by the trabecular meshwork; this region makes the greatest contribution to outflow resistance of the aqueous humor.
Conventionally, the canal has been considered a blood vessel, but studies published in 2014 showed that the molecular identity of Schlemm's canal is very similar to the one of lymphatic vasculature.Waldmann disease
Waldmann disease is a rare disease characterized by enlargement of the lymph vessels supplying the lamina propria of the small intestine.Although its prevalence is unknown, it being classified as a "rare disease" means that less than 200,000 of the population of the United States are affected by this condition and its subtypes.
General anatomy: systems and organs, regional anatomy, planes and lines, superficial axial anatomy, superficial anatomy of limbs