Lymphatic system
Encyclopedia
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph
(from Latin lympha "water") unidirectionally toward the heart. Lymphoid tissue is found in many organs
, particularly the lymph node
s, and in the lymphoid follicles associated with the digestive system such as the tonsil
s. The system also includes all the structures dedicated to the circulation and production of lymphocyte
s, which includes the spleen
, thymus
, bone marrow
and the lymphoid tissue associated with the digestive system. The lymphatic system as we know it today was first described independently by Olaus Rudbeck
and Thomas Bartholin.
The blood
does not directly come in contact with the parenchyma
l cells
and tissues
in the body, but constituents of the blood first exit the microvascular exchange blood vessels to become interstitial fluid
, which comes into contact with the parenchymal cells of the body. Lymph is the fluid that is formed when interstitial fluid enters the initial lymphatic vessels of the lymphatic system. The lymph is then moved along the lymphatic vessel network by either intrinsic contractions of the lymphatic passages or by extrinsic compression of the lymphatic vessels via external tissue forces (e.g. the contractions of skeletal muscle
s). Eventually, the lymph vessels empty into the lymphatic ducts, which drain into one of the two subclavian veins
(near the junctions of the subclavian veins with the internal jugular veins).
Lymphatic tissue is a specialized connective tissue - reticular connective, that contains large quantities of lymphocytes.
. The intervening lymph nodes can trap the cancer cells. If they are not successful in destroying the cancer cells the nodes may become sites of secondary tumors.
s and spread of tumor
s. It consists of connective tissue
with various types of white blood cells enmeshed in it, most numerous being the lymphocyte
s.
The lymphoid tissue may be primary, secondary, or tertiary depending upon the stage of lymphocyte development and maturation it is involved in. (The tertiary lymphoid tissue typically contains far fewer lymphocytes, and assumes an immune role only when challenged with antigens that result in inflammation
. It achieves this by importing the lymphocytes from blood and lymph.)
s from immature progenitor cells.
The thymus
and the bone marrow
constitute the primary lymphoid tissues involved in the production and early selection
of lymphocytes.
Secondary lymphoid tissue provides the environment for the foreign or altered native molecules (antigen
s) to interact with the lymphocytes. It is exemplified by the lymph node
s, and the lymphoid follicles in tonsil
s, Peyer's patches, spleen
, adenoid
s, skin
, etc. that are associated with the mucosa-associated lymphoid tissue
(MALT).
A lymph node is an organized collection of lymphoid tissue, through which the lymph passes on its way to returning to the blood. Lymph nodes are located at intervals along the lymphatic system. Several afferent lymph vessel
s bring in lymph, which percolates through the substance of the lymph node, and is drained out by an efferent lymph vessel
.
The substance of a lymph node consists of lymphoid follicles in the outer portion called the "cortex
", which contains the lymphoid follicles, and an inner portion called "medulla
", which is surrounded by the cortex on all sides except for a portion known as the "hilum
". The hilum presents as a depression on the surface of the lymph node, which makes the otherwise spherical or ovoid lymph node bean-shaped. The efferent lymph vessel directly emerges from the lymph node here. The arteries and veins supplying the lymph node with blood enter and exit through the hilum.
Lymph follicles are a dense collection of lymphocytes, the number, size and configuration of which change in accordance with the functional state of the lymph node. For example, the follicles expand significantly upon encountering a foreign antigen. The selection of B cells occurs in the germinal center of the lymph nodes.
Lymph nodes are particularly numerous in the mediastinum
in the chest, neck, pelvis, axilla (armpit), inguinal (groin) region, and in association with the blood vessels of the intestines.
Tubular vessels transport back lymph to the blood ultimately replacing the volume lost from the blood during the formation of the interstitial fluid. These channels are the lymphatic channels or simply called lymphatics.
s called lacteal
s are present in the lining of the gastrointestinal tract
, predominantly in the small intestine. While most other nutrients absorbed by the small intestine
are passed on to the portal venous system to drain via the portal vein into the liver
for processing, fats (lipids) are passed on to the lymphatic system to be transported to the blood circulation via the thoracic duct
. (There are exceptions, for example medium-chain triglycerides (MCTs) are fatty acid esters of glycerol that passively diffuse from the GI tract to the portal system.) The enriched lymph originating in the lymphatics of the small intestine
is called chyle
. The nutrients that are released to the circulatory system are processed by the liver
, having passed through the systemic circulation.
is the swelling
caused by the accumulation of lymph fluid, which may occur if the lymphatic system is damaged or has malformations. It usually affects the limbs, though face, neck and abdomen may also be affected.
Some common causes of swollen lymph nodes include infection
s, infectious mononucleosis
, and cancer
, e.g. Hodgkin's
and non-Hodgkin
lymphoma
, and metastasis
of cancerous cells via the lymphatic system.
Lymphangiomatosis
is a disease involving multiple cysts or lesions formed from lymphatic vessels.
In elephantiasis
, infection of the lymphatic vessels cause a thickening of the skin and enlargement of underlying tissues, especially in the legs and genitals. It is most commonly caused by a parasitic disease
known as lymphatic filariasis.
Lymphangiosarcoma
is a malignant soft tissue tumor
, whereas lymphangioma
is a benign tumor occurring frequently in association with Turner syndrome
. Lymphangioleiomyomatosis
is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.
.
The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck and head. Some of the plexuses enlarge and form lymphatic vessels in their respective regions. Each jugular lymph sac retains at least one connection with its jugular vein, the left one developing into the superior portion of the thoracic duct.
The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine. It develops from the primitive vena cava and mesonephric veins. Capillary plexuses and lymphatic vessels spread from the retroperitoneal lymph sac to the abdominal viscera and diaphragm. The sac establishes connections with the cisterna chyli but loses its connections with neighboring veins.
The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins. The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs. The posterior lymph sacs join the cisterna chyli
and lose their connections with adjacent veins.
With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes.
The spleen
develops from mesenchymal cells between layers of the dorsal mesentery of the stomach. The thymus
arises as an outgrowth of the third pharyngeal pouch.
The specialists observed that the pulmonary complications following lymphangiography (a test which utilizes X ray technology, along with the injection of a contrast agent, to view lymphatic circulation and lymph nodes for diagnostic purposes)are more often severe in patients with lymphatic obstruction. In these cases, the contrast medium is thought to reach the vascular system via lymphovenous communications with shunt the material directly into the venous stream, bypassing those lymph nodes distal to the communications, Because less contrast agent is absorbed in lymph nodes, a greater portion of the injected volume passes into the vascular system. Since pulmonary complications are related to the amount of medium reaching the lungs area, the early recognition of lymphovenous communications is a great significance to the lymphangiographer.
Another "hint" in proving a lymph-vein communication is offered by a Robert F Dunn experiment. The passage of radioactively tagged tracers, injected at elevated pressure, through the lymph node-venous communications coincides with the increased pressures of injection and subsequent nodal palpation in dogs. The passage of iodinated I 125 serum albumen (ISA) indicates that direct lymph node-venous communications are present, whereas passage of nucleated erythrocytes requires a communication structure the size of a capillary or larger.
Moreover, the evidence suggest that in mammals under normal conditions, mostly of the lymph is returned to the blood stream through the lymphatico-venous communications at the base of the neck. When the thoracic duct-venous communication is blocked, however, the resultant raised intralymphatic pressure will usually cause other normal non-functioning communications to open and thereby allow the return of lymph to the blood stream.
was one of the first persons to mention the lymphatic system in 5th century BC. In his work "On Joints," he briefly mentioned the lymph nodes in one sentence. Rufus of Ephesus
, a Roman physician, identified the axillary, inguinal and mesenteric lymph nodes as well as the thymus during the 1st to 2nd century AD. The first mention of lymphatic vessels was in 3rd century BC by Herophilos
, a Greek anatomist living in Alexandria
, who incorrectly concluded that the "absorptive veins of the lymphatics", by which he meant the lacteal
s (lymph vessels of the intestines), drained into the hepatic portal vein
s, and thus into the liver. Findings of Ruphus and Herophilos findings were further propagated by the Greek physician Galen
, who described the lacteals and mesenteric lymph nodes which he observed in his dissection of apes and pigs in the 2nd century AD.
Until the 17th century, ideas of Galen were most prevalent. Accordingly, it was believed that the blood was produced by the liver from chyle contaminated with ailments by the intestine and stomach, to which various spirits were added by other organs, and that this blood was consumed by all the organs of the body. This theory required that the blood be consumed and produced many times over. His ideas had remained unchallenged until the 17th century, and even then were defended by some physicians.
.jpg)
In the mid 16th century Gabriele Falloppio
(discoverer of the fallopian tube
s) described what are now known as the lacteals as "coursing over the intestines full of yellow matter." In about 1563 Bartolomeo Eustachi
, a professor of anatomy, described the thoracic duct in horses as vena alba thoracis. The next breakthrough came when in 1622 a physician, Gaspare Aselli, identified lymphatic vessels of the intestines in dogs and termed them venae alba et lacteae, which is now known as simply the lacteals. The lacteals were termed the fourth kind of vessels (the other three being the artery, vein and nerve, which was then believed to be a type of vessel), and disproved Galen's assertion that chyle was carried by the veins. But, he still believed that the lacteals carried the chyle to the liver (as taught by Galen). He also identified the thoracic duct but failed to notice its connection with the lacteals. This connection was established by Jean Pecquet
in 1651, who found a white fluid mixing with blood in a dog's heart. He suspected that fluid to be chyle
as its flow increased when abdominal pressure was applied. He traced this fluid to the thoracic duct, which he then followed to a chyle-filled sac he called the chyli receptaculum, which is now known as the cisternae chyli; further investigations led him to find that lacteals' contents enter the venous system via the thoracic duct. Thus, it was proven convincingly that the lacteals did not terminate in the liver
, thus disproving Galen's second idea: that the chyle flowed to the liver. Johann Veslingius drew the earliest sketches of the lacteals in humans in 1647.
The idea that blood recirculates through the body rather than being produced anew by the liver and the heart was first accepted as a result of works of William Harvey
—a work he published in 1628. In 1652, Olaus Rudbeck
(1630–1702), a Swede, discovered certain transparent vessels in the liver that contained clear fluid (and not white), and thus named them hepatico-aqueous vessels. He also learned that they emptied into the thoracic duct, and that they had valves. He announced his findings in the court of Queen Christina of Sweden, but did not publish his findings for a year, and in the interim similar findings were published by Thomas Bartholin, who additionally published that such vessels are present everywhere in the body, and not just the liver. He is also the one to have named them "lymphatic vessels". This had resulted in a bitter dispute between one of Bartholin's pupils, Martin Bogdan, and Rudbeck, whom he accused of plagiarism
.
Lymph
Lymph is considered a part of the interstitial fluid, the fluid which lies in the interstices of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary...
(from Latin lympha "water") unidirectionally toward the heart. Lymphoid tissue is found in many organs
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
, particularly the lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
s, and in the lymphoid follicles associated with the digestive system such as the tonsil
Tonsil
Palatine tonsils, occasionally called the faucial tonsils, are the tonsils that can be seen on the left and right sides at the back of the throat....
s. The system also includes all the structures dedicated to the circulation and production of lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s, which includes the spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
, thymus
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
, bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
and the lymphoid tissue associated with the digestive system. The lymphatic system as we know it today was first described independently by Olaus Rudbeck
Olaus Rudbeck
Olaus Rudbeck was a Swedish scientist and writer, professor of medicine at Uppsala University and for several periods rector magnificus of the same university...
and Thomas Bartholin.
The blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
does not directly come in contact with the parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
l cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
and tissues
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
in the body, but constituents of the blood first exit the microvascular exchange blood vessels to become interstitial fluid
Interstitial fluid
Interstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
, which comes into contact with the parenchymal cells of the body. Lymph is the fluid that is formed when interstitial fluid enters the initial lymphatic vessels of the lymphatic system. The lymph is then moved along the lymphatic vessel network by either intrinsic contractions of the lymphatic passages or by extrinsic compression of the lymphatic vessels via external tissue forces (e.g. the contractions of skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
s). Eventually, the lymph vessels empty into the lymphatic ducts, which drain into one of the two subclavian veins
Subclavian vein
The subclavian veins are two large veins, one on either side of the body. Their diameter is approximately that of the smallest finger.-Path:Each subclavian vein is a continuation of the axillary vein and runs from the outer border of the first rib to the medial border of anterior scalene muscle...
(near the junctions of the subclavian veins with the internal jugular veins).
Functions
The lymphoid system has multiple interrelated functions:- it is responsible for the removal of interstitial fluidInterstitial fluidInterstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
from tissues
- it absorbs and transports fatty acidFatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s and fatFatFats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s as chyleChyleChyle is a milky bodily fluid consisting of lymph and emulsified fats, or free fatty acids . It is formed in the small intestine during digestion of fatty foods, and taken up by lymph vessels specifically known as lacteals...
from the digestive system
- it transports white blood cells to and from the lymph nodes into the bones
- The lymph transports antigen-presenting cellAntigen-presenting cellAn antigen-presenting cell or accessory cell is a cell that displays foreign antigen complexes with major histocompatibility complex on their surfaces. T-cells may recognize these complexes using their T-cell receptors...
s (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.
Lymphatic tissue is a specialized connective tissue - reticular connective, that contains large quantities of lymphocytes.
Clinical significance
The study of lymphatic drainage of various organs is important in diagnosis, prognosis, and treatment of cancer. The lymphatic system, because of its physical proximity to many tissues of the body, is responsible for carrying cancerous cells between the various parts of the body in a process called metastasisMetastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
. The intervening lymph nodes can trap the cancer cells. If they are not successful in destroying the cancer cells the nodes may become sites of secondary tumors.
Organization
The lymphoid system can be broadly divided into the conducting system and the lymphoid tissue.- The conducting system carries the lymph and consists of tubular vessels that include the lymph capillaries, the lymph vesselLymph vesselIn anatomy, lymph vessels are thin walled, valved structures 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 deep to that have a thin layer of smooth muscles, and adventitia that bind...
s, and the rightRight lymphatic ductThe right lymphatic duct, about 1.25 cm. in length, courses along the medial border of the Scalenus anterior at the root of the neck. In most cases it ends in the right subclavian vein, at its angle of junction with the right internal jugular vein, although the termination can be variable, however...
and left thoracicThoracic ductIn human anatomy, the thoracic duct of the lymphatic system is the largest lymphatic vessel in the body. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal....
ducts.
- The lymphoid tissue is primarily involved in immune responses and consists of lymphocyteLymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s and other white blood cellWhite blood cellWhite blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...
s enmeshed in connective tissue through which the lymph passes. Regions of the lymphoid tissue that are densely packed with lymphocytes are known as lymphoid follicles. Lymphoid tissue can either be structurally well organized as lymph nodes or may consist of loosely organized lymphoid follicles known as the mucosa-associated lymphoid tissue (MALT)Mucosa-associated lymphoid tissueThe mucosa-associated lymphoid tissue is the diffusion system of small concentrations of lymphoid tissue found in various sites of the body, such as the gastrointestinal tract, thyroid, breast, lung, salivary glands, eye, and skin.MALT is populated by lymphocytes such as T cells and B cells, as...
Lymphoid tissue
Lymphoid tissue associated with the lymphatic system is concerned with immune functions in defending the body against the infectionInfection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s and spread of tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s. It consists of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
with various types of white blood cells enmeshed in it, most numerous being the lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s.
The lymphoid tissue may be primary, secondary, or tertiary depending upon the stage of lymphocyte development and maturation it is involved in. (The tertiary lymphoid tissue typically contains far fewer lymphocytes, and assumes an immune role only when challenged with antigens that result in inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
. It achieves this by importing the lymphocytes from blood and lymph.)
Primary lymphoid organs
The central or primary lymphoid organs generate lymphocyteLymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s from immature progenitor cells.
The thymus
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
and the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
constitute the primary lymphoid tissues involved in the production and early selection
Clonal selection
The clonal selection hypothesis has become a widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens invading the body....
of lymphocytes.
Secondary lymphoid organs
Secondary or peripheral lymphoid organs maintain mature naive lymphocytes and initiate an adaptive immune response. The peripheral lymphoid organs are the sites of lymphocyte activation by antigen. Activation leads to clonal expansion and affinity maturation. Mature lymphocytes recirculate between the blood and the peripheral lymphoid organs until they encounter their specific antigen.Secondary lymphoid tissue provides the environment for the foreign or altered native molecules (antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
s) to interact with the lymphocytes. It is exemplified by the lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
s, and the lymphoid follicles in tonsil
Tonsil
Palatine tonsils, occasionally called the faucial tonsils, are the tonsils that can be seen on the left and right sides at the back of the throat....
s, Peyer's patches, spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
, adenoid
Adenoid
Adenoids are a mass of lymphoid tissue situated posterior to the nasal cavity, in the roof of the nasopharynx, where the nose blends into the throat....
s, skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, etc. that are associated with the mucosa-associated lymphoid tissue
Mucosa-associated lymphoid tissue
The mucosa-associated lymphoid tissue is the diffusion system of small concentrations of lymphoid tissue found in various sites of the body, such as the gastrointestinal tract, thyroid, breast, lung, salivary glands, eye, and skin.MALT is populated by lymphocytes such as T cells and B cells, as...
(MALT).
Lymph nodes
Afferent lymph vessel
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...
s bring in lymph, which percolates through the substance of the lymph node, and is drained out by an efferent lymph vessel
Efferent lymph vessel
The efferent lymphatic vessel commences from the lymph sinuses of the medullary portion of the lymph nodes and leave the lymph nodes either to veins or greater nodes....
.
The substance of a lymph node consists of lymphoid follicles in the outer portion called the "cortex
Cortex (anatomy)
In anatomy and zoology the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the most well-known of all cortices.The cerebellar cortex is the thin gray...
", which contains the lymphoid follicles, and an inner portion called "medulla
Medulla of lymph node
The medulla of lymph node, or medullary sinus, is the central portion of the lymph node.There are two named structures in the medulla:* The medullary cords are cords of lymphatic tissue, and include plasma cells, macrophages, and B cells...
", which is surrounded by the cortex on all sides except for a portion known as the "hilum
Hilum of lymph node
The Hilum of lymph node is the concave portion of the lymph node where the efferent vessels exit....
". The hilum presents as a depression on the surface of the lymph node, which makes the otherwise spherical or ovoid lymph node bean-shaped. The efferent lymph vessel directly emerges from the lymph node here. The arteries and veins supplying the lymph node with blood enter and exit through the hilum.
Lymph follicles are a dense collection of lymphocytes, the number, size and configuration of which change in accordance with the functional state of the lymph node. For example, the follicles expand significantly upon encountering a foreign antigen. The selection of B cells occurs in the germinal center of the lymph nodes.
Lymph nodes are particularly numerous in the mediastinum
Mediastinum
The mediastinum is a non-delineated group of structures in the thorax, surrounded by loose connective tissue. It is the central compartment of the thoracic cavity...
in the chest, neck, pelvis, axilla (armpit), inguinal (groin) region, and in association with the blood vessels of the intestines.
Lymphatics
Function of the fatty acid transport system
Lymph vesselLymph vessel
In anatomy, lymph vessels are thin walled, valved structures 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 deep to that have a thin layer of smooth muscles, and adventitia that bind...
s called lacteal
Lacteal
A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.Triglycerides are emulsified by bile and hydrolyzed by the enzyme lipase, resulting in a mixture of fatty acids and monoglycerides. These then pass from the intestinal lumen into the enterocyte, where...
s are present in the lining of the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, predominantly in the small intestine. While most other nutrients absorbed by the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
are passed on to the portal venous system to drain via the portal vein into the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
for processing, fats (lipids) are passed on to the lymphatic system to be transported to the blood circulation via the thoracic duct
Thoracic duct
In human anatomy, the thoracic duct of the lymphatic system is the largest lymphatic vessel in the body. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal....
. (There are exceptions, for example medium-chain triglycerides (MCTs) are fatty acid esters of glycerol that passively diffuse from the GI tract to the portal system.) The enriched lymph originating in the lymphatics of the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
is called chyle
Chyle
Chyle is a milky bodily fluid consisting of lymph and emulsified fats, or free fatty acids . It is formed in the small intestine during digestion of fatty foods, and taken up by lymph vessels specifically known as lacteals...
. The nutrients that are released to the circulatory system are processed by the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, having passed through the systemic circulation.
Diseases of the lymphatic system
LymphedemaLymphedema
Lymphedema , also known as lymphatic obstruction, is a condition of localized fluid retention and tissue swelling caused by a compromised lymphatic system....
is the swelling
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
caused by the accumulation of lymph fluid, which may occur if the lymphatic system is damaged or has malformations. It usually affects the limbs, though face, neck and abdomen may also be affected.
Some common causes of swollen lymph nodes include infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s, infectious mononucleosis
Infectious mononucleosis
Infectious mononucleosis is an infectious, widespread viral...
, and cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, e.g. Hodgkin's
Hodgkin's lymphoma
Hodgkin's lymphoma, previously known as Hodgkin's disease, is a type of lymphoma, which is a cancer originating from white blood cells called lymphocytes...
and non-Hodgkin
Non-Hodgkin lymphoma
The non-Hodgkin lymphomas are a diverse group of blood cancers that include any kind of lymphoma except Hodgkin's lymphomas. Types of NHL vary significantly in their severity, from indolent to very aggressive....
lymphoma
Lymphoma
Lymphoma is a cancer in the lymphatic cells of the immune system. Typically, lymphomas present as a solid tumor of lymphoid cells. Treatment might involve chemotherapy and in some cases radiotherapy and/or bone marrow transplantation, and can be curable depending on the histology, type, and stage...
, and metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
of cancerous cells via the lymphatic system.
Lymphangiomatosis
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 neoplasm which results from an abnormal development of the lymphatic system...
is a disease involving multiple cysts or lesions formed from lymphatic vessels.
In elephantiasis
Elephantiasis
Elephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...
, infection of the lymphatic vessels cause a thickening of the skin and enlargement of underlying tissues, especially in the legs and genitals. It is most commonly caused by a parasitic disease
Parasitic disease
A parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals...
known as lymphatic filariasis.
Lymphangiosarcoma
Lymphangiosarcoma
Lymphangiosarcoma is a rare malignant tumor which occurs in long-standing cases of primary or secondary lymphedema. It involves either the upper or lower lymphedemateous extremities but is most common in upper extremities.-Signs and Symptoms:...
is a malignant soft tissue tumor
Soft tissue sarcoma
A soft-tissue sarcoma is a form of sarcoma that develops in connective tissue, though the term is sometimes applied to elements of the soft tissue that are not currently considered connective tissue.-Risk factors:...
, whereas lymphangioma
Lymphangioma
Lymphangiomas are malformations of the lymphatic system, which is the network of vessels responsible for returning to the venous system excess fluid from tissues. 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...
is a benign tumor occurring frequently in association with Turner syndrome
Turner syndrome
Turner syndrome or Ullrich-Turner syndrome encompasses several conditions in human females, of which monosomy X is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent...
. Lymphangioleiomyomatosis
Lymphangioleiomyomatosis
Lymphangioleiomyomatosis is a rare lung disease that results in a proliferation of disorderly smooth muscle growth throughout the lungs, in the bronchioles, alveolar septa, perivascular spaces, and lymphatics, resulting in the obstruction of small airways and lymphatics...
is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.
Development of lymphatic tissue
Lymphatic tissues begin to develop by the end of the fifth week of embryonic development. Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesodermMesoderm
In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
.
The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck and head. Some of the plexuses enlarge and form lymphatic vessels in their respective regions. Each jugular lymph sac retains at least one connection with its jugular vein, the left one developing into the superior portion of the thoracic duct.
The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine. It develops from the primitive vena cava and mesonephric veins. Capillary plexuses and lymphatic vessels spread from the retroperitoneal lymph sac to the abdominal viscera and diaphragm. The sac establishes connections with the cisterna chyli but loses its connections with neighboring veins.
The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins. The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs. The posterior lymph sacs join the cisterna chyli
Cisterna chyli
The cisterna chyli is a dilated sac at the lower end of the thoracic duct into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow.-Flow of lymph:...
and lose their connections with adjacent veins.
With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes.
The spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
develops from mesenchymal cells between layers of the dorsal mesentery of the stomach. The thymus
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
arises as an outgrowth of the third pharyngeal pouch.
Lymphatico-Venous Communications
Present research has found cues about a lymphatico-venous communication. In mammals, lymphatico-venous communications other than those at the base of the neck are not easy to demonstrate, but described in some experiments.The specialists observed that the pulmonary complications following lymphangiography (a test which utilizes X ray technology, along with the injection of a contrast agent, to view lymphatic circulation and lymph nodes for diagnostic purposes)are more often severe in patients with lymphatic obstruction. In these cases, the contrast medium is thought to reach the vascular system via lymphovenous communications with shunt the material directly into the venous stream, bypassing those lymph nodes distal to the communications, Because less contrast agent is absorbed in lymph nodes, a greater portion of the injected volume passes into the vascular system. Since pulmonary complications are related to the amount of medium reaching the lungs area, the early recognition of lymphovenous communications is a great significance to the lymphangiographer.
Another "hint" in proving a lymph-vein communication is offered by a Robert F Dunn experiment. The passage of radioactively tagged tracers, injected at elevated pressure, through the lymph node-venous communications coincides with the increased pressures of injection and subsequent nodal palpation in dogs. The passage of iodinated I 125 serum albumen (ISA) indicates that direct lymph node-venous communications are present, whereas passage of nucleated erythrocytes requires a communication structure the size of a capillary or larger.
Moreover, the evidence suggest that in mammals under normal conditions, mostly of the lymph is returned to the blood stream through the lymphatico-venous communications at the base of the neck. When the thoracic duct-venous communication is blocked, however, the resultant raised intralymphatic pressure will usually cause other normal non-functioning communications to open and thereby allow the return of lymph to the blood stream.
History
HippocratesHippocrates
Hippocrates of Cos or Hippokrates of Kos was an ancient Greek physician of the Age of Pericles , and is considered one of the most outstanding figures in the history of medicine...
was one of the first persons to mention the lymphatic system in 5th century BC. In his work "On Joints," he briefly mentioned the lymph nodes in one sentence. Rufus of Ephesus
Ephesus
Ephesus was an ancient Greek city, and later a major Roman city, on the west coast of Asia Minor, near present-day Selçuk, Izmir Province, Turkey. It was one of the twelve cities of the Ionian League during the Classical Greek era...
, a Roman physician, identified the axillary, inguinal and mesenteric lymph nodes as well as the thymus during the 1st to 2nd century AD. The first mention of lymphatic vessels was in 3rd century BC by Herophilos
Herophilos
Herophilos , sometimes Latinized Herophilus , was a Greek physician. Born in Chalcedon, he spent the majority of his life in Alexandria. He was the first scientist to systematically perform scientific dissections of human cadavers and is deemed to be the first anatomist. Herophilos recorded his...
, a Greek anatomist living in Alexandria
Alexandria
Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...
, who incorrectly concluded that the "absorptive veins of the lymphatics", by which he meant the lacteal
Lacteal
A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.Triglycerides are emulsified by bile and hydrolyzed by the enzyme lipase, resulting in a mixture of fatty acids and monoglycerides. These then pass from the intestinal lumen into the enterocyte, where...
s (lymph vessels of the intestines), drained into the hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...
s, and thus into the liver. Findings of Ruphus and Herophilos findings were further propagated by the Greek physician Galen
Galen
Aelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
, who described the lacteals and mesenteric lymph nodes which he observed in his dissection of apes and pigs in the 2nd century AD.
Until the 17th century, ideas of Galen were most prevalent. Accordingly, it was believed that the blood was produced by the liver from chyle contaminated with ailments by the intestine and stomach, to which various spirits were added by other organs, and that this blood was consumed by all the organs of the body. This theory required that the blood be consumed and produced many times over. His ideas had remained unchallenged until the 17th century, and even then were defended by some physicians.
Gabriele Falloppio
Gabriele Falloppio , often known by his Latin name Fallopius, was one of the most important anatomists and physicians of the sixteenth century....
(discoverer of the fallopian tube
Fallopian tube
The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction...
s) described what are now known as the lacteals as "coursing over the intestines full of yellow matter." In about 1563 Bartolomeo Eustachi
Bartolomeo Eustachi
Bartolomeo Eustachi , also known by his Latin name of Eustachius, was one of the founders of the science of human anatomy.-Life:...
, a professor of anatomy, described the thoracic duct in horses as vena alba thoracis. The next breakthrough came when in 1622 a physician, Gaspare Aselli, identified lymphatic vessels of the intestines in dogs and termed them venae alba et lacteae, which is now known as simply the lacteals. The lacteals were termed the fourth kind of vessels (the other three being the artery, vein and nerve, which was then believed to be a type of vessel), and disproved Galen's assertion that chyle was carried by the veins. But, he still believed that the lacteals carried the chyle to the liver (as taught by Galen). He also identified the thoracic duct but failed to notice its connection with the lacteals. This connection was established by Jean Pecquet
Jean Pecquet
Jean Pecquet was a French scientist. He studied the expansion of air, wrote on psychology, and is also known for investigating the thoracic duct...
in 1651, who found a white fluid mixing with blood in a dog's heart. He suspected that fluid to be chyle
Chyle
Chyle is a milky bodily fluid consisting of lymph and emulsified fats, or free fatty acids . It is formed in the small intestine during digestion of fatty foods, and taken up by lymph vessels specifically known as lacteals...
as its flow increased when abdominal pressure was applied. He traced this fluid to the thoracic duct, which he then followed to a chyle-filled sac he called the chyli receptaculum, which is now known as the cisternae chyli; further investigations led him to find that lacteals' contents enter the venous system via the thoracic duct. Thus, it was proven convincingly that the lacteals did not terminate in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, thus disproving Galen's second idea: that the chyle flowed to the liver. Johann Veslingius drew the earliest sketches of the lacteals in humans in 1647.
William Harvey
William Harvey was an English physician who was the first person to describe completely and in detail the systemic circulation and properties of blood being pumped to the body by the heart...
—a work he published in 1628. In 1652, Olaus Rudbeck
Olaus Rudbeck
Olaus Rudbeck was a Swedish scientist and writer, professor of medicine at Uppsala University and for several periods rector magnificus of the same university...
(1630–1702), a Swede, discovered certain transparent vessels in the liver that contained clear fluid (and not white), and thus named them hepatico-aqueous vessels. He also learned that they emptied into the thoracic duct, and that they had valves. He announced his findings in the court of Queen Christina of Sweden, but did not publish his findings for a year, and in the interim similar findings were published by Thomas Bartholin, who additionally published that such vessels are present everywhere in the body, and not just the liver. He is also the one to have named them "lymphatic vessels". This had resulted in a bitter dispute between one of Bartholin's pupils, Martin Bogdan, and Rudbeck, whom he accused of plagiarism
Plagiarism
Plagiarism is defined in dictionaries as the "wrongful appropriation," "close imitation," or "purloining and publication" of another author's "language, thoughts, ideas, or expressions," and the representation of them as one's own original work, but the notion remains problematic with nebulous...
.
See also
- American Society of LymphologyAmerican Society of LymphologyThe American Society of Lymphology is a non-profit organization based in Kansas City, Missouri which provides current information and resources for professionals and patients interested in the healthy function and disorders of the lymphatic system, such as immune response, allergies, infectious...
- LymphangiogenesisLymphangiogenesisLymphangiogenesis is the formation of lymphatic vessels from pre-existing lymphatic vessels, in a method believed to be similar to blood vessel development or angiogenesis....
- Manual lymphatic drainageManual lymphatic drainageManual lymphatic drainage is a type of gentle massage which is intended by proponents to encourage the natural circulation of the lymph through the body...
- Reticuloendothelial systemReticuloendothelial system"Reticuloendothelial system" is an older term for the mononuclear phagocyte system. The mononuclear phagocyte system consists primarily of monocytes and macrophages. The spleen is the largest unit of the mononuclear phagocyte system. The monocyte is formed in the bone marrow and transported by the...
External links
- Lymphatic System
- Lymphatic System Overview (innerbody.com)