Lymph (from Latin, , meaning "water") is the fluid that flows through the
lymphatic system
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 o ...
, a system composed of
lymph vessel
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 vessel ...
s (channels) and intervening
lymph node
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 inclu ...
s whose function, like the
venous system
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...
, is to return fluid from the tissues to be recirculated. At the origin of the fluid-return process,
interstitial fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...
—the fluid between the cells in all
body tissue
In biology, tissue is a biological organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are ...
s—enters the
lymph capillaries
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 enterin ...
. This lymphatic fluid is then transported via progressively larger
lymphatic vessel
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 vess ...
s through
lymph node
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 inclu ...
s, where substances are removed by tissue
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left
subclavian vein
The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption ...
, where it mixes with central
venous blood
Venous blood is deoxygenated blood which travels from the peripheral blood vessels, through the venous system into the right atrium of the heart. Deoxygenated blood is then pumped by the right ventricle to the lungs via the pulmonary artery whic ...
.
Because it is derived from interstitial fluid, with which blood and surrounding cells continually exchange substances, lymph undergoes continual change in composition. It is generally similar to
blood plasma
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intra ...
, which is the fluid component of blood. Lymph returns
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s and excess interstitial fluid to the
bloodstream
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. Lymph also transports fats from the
digestive system
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
(beginning in the
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, di- and monoglycerides. These th ...
s) to the blood via
chylomicron
Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein particles that consist of triglycerides (85 ...
s.
Bacteria may enter the lymph channels and be transported to
lymph node
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 inclu ...
s, where the bacteria are destroyed.
Metastatic
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...
cancer cells can also be transported via lymph.
Etymology
The word ''lymph'' is derived from the name of the
ancient Roman deity of fresh water,
Lympha
The Lympha (plural ''Lymphae'') is an ancient Roman deity of fresh water. She is one of twelve agricultural deities listed by Varro as "leaders" (''duces'') of Roman farmers, because "without water all agriculture is dry and poor." The Lymphae ...
.
Structure
Lymph has a composition similar but not identical to that of
blood plasma
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intra ...
. Lymph that leaves a lymph node is richer in
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s than blood plasma is. The lymph formed in the
human digestive system
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
called
chyle
Chyle (from the Ancient Greek, Greek word χυλός ''chylos'', "juice") is a milky bodily fluid consisting of lymph and emulsified fats, or free fatty acids (FFAs). It is formed in the small intestine during digestion of fatty foods, and taken ...
is rich in
triglyceride
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
s (fat), and looks milky white because of its lipid content.
Development
![Capillary Microcirculation](https://upload.wikimedia.org/wikipedia/commons/3/33/Capillary_microcirculation.svg)
Blood supplies
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s and important
metabolite
In biochemistry, a metabolite is an intermediate or end product of metabolism.
The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
s to the cells of a
tissue and collects back the waste products they produce, which requires exchange of respective constituents between the blood and tissue cells. This exchange is not direct, but instead occurs through an intermediary called
interstitial fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...
, which occupies the spaces between cells. As the blood and the surrounding cells continually add and remove substances from the interstitial fluid, its composition continually changes. Water and
solutes
In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent ...
can pass between the interstitial fluid and blood via
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
across gaps in
capillary
A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
walls called
intercellular cleft
An intercellular cleft is a channel between two cells through which molecules may travel and gap junctions and tight junctions may be present. Most notably, intercellular clefts are often found between epithelial cells and the endothelium of blood ...
s; thus, the blood and interstitial fluid are in
dynamic equilibrium
In chemistry, a dynamic equilibrium exists once a reversible reaction occurs. Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate that the conc ...
with each other.
Interstitial fluid forms at the
arterial
An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
(coming from the heart) end of capillaries because of the higher pressure of blood compared to
vein
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...
s, and most of it returns to its
venous
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...
ends and
venule
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 t ...
s; the rest (up to 10%) enters the
lymph capillaries
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 enterin ...
as lymph.
Thus, lymph when formed is a watery clear liquid with the same composition as the interstitial fluid. However, as it flows through the lymph nodes it comes in contact with blood, and tends to accumulate more cells (particularly, lymphocytes) and proteins.
Functions
Components
Lymph returns
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s and excess interstitial fluid to the
bloodstream
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. Lymph may pick up bacteria and transport them to lymph nodes, where the bacteria are destroyed.
Metastatic
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...
cancer cells can also be transported via lymph. Lymph also transports fats from the
digestive system
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
(beginning in the
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, di- and monoglycerides. These th ...
s) to the blood via
chylomicron
Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein particles that consist of triglycerides (85 ...
s.
Circulation
Tubular vessels transport lymph back to the blood, ultimately replacing the volume lost during the formation of the interstitial fluid. These channels are the lymphatic channels, or simply ''lymphatics''.
Unlike the cardiovascular system, the lymphatic system is not closed. In some amphibian and
reptilian species, the lymphatic system has central pumps, called
lymph heart
A lymph heart is an organ which pumps lymph in lungfishes, amphibians, reptiles, and flightless birds back into the circulatory system. In some amphibian species, lymph hearts are in pairs, and may number as many as 200 in one animal the size of ...
s, which typically exist in pairs,
but humans and other mammals do not have a central lymph pump. Lymph transport is slow and sporadic.
[ Despite low pressure, lymph movement occurs due to ]peristalsis
Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which ...
(propulsion of the lymph due to alternate contraction and relaxation of smooth muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
tissue), valves, and compression during contraction of adjacent skeletal muscle and arterial
An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
pulsation
A pulse, in physiology, is the throbbing of arteries resulting from heartbeat.
Pulse, The Pulse or Pulses may also refer to:
Botany
* Pulse (legume), any agriculturally significant annual leguminous food crop, such as peas, beans, lentils, and ...
.
Lymph that enters the lymph vessels from the interstitial spaces usually does not flow backwards along the vessels because of the presence of valves. If excessive hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
develops within the lymph vessels, though, some fluid can leak back into the interstitial spaces and contribute to formation of edema
Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...
.
The flow of lymph in the thoracic duct
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 ...
in an average resting person usually approximates 100ml per hour. Accompanied by another ~25ml per hour in other lymph vessels, the total lymph flow in the body is about 4 to 5 litres per day. This can be elevated several fold while exercising. It is estimated that without lymphatic flow, the average resting person would die within 24 hours.
Clinical significance
Histopathological examination of the lymph system is used as a screening tool for immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
analysis in conjunction with pathological changes in other organ systems
An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in a plant or animal body, and is made up of distinct tissues.
Plants
Plants have ...
and clinical pathology
Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids, such as blood, urine, and tissue homogenates or extracts using the tools of chemistry, microbiology, ...
to assess disease status. Although histological assessment of the lymph system does not directly measure immune function, it can be combined with identification of chemical biomarker
In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, ...
s to determine underlying changes in the diseased immune system.
As a growth medium
In 1907 the zoologist Ross Granville Harrison
Ross Granville Harrison (January 13, 1870 – September 30, 1959) was an American biologist and anatomist credited for his pioneering work on animal tissue culture. His work also contributed to the understanding of embryonic development. Harrison ...
demonstrated the growth of frog nerve cell processes in a medium of clotted lymph. It is made up of lymph nodes and vessels.
In 1913, E. Steinhardt, C. Israeli, and R. A. Lambert grew vaccinia
''Vaccinia virus'' (VACV or VV) is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of the ...
virus in fragments of tissue culture
Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, su ...
from guinea pig cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...
grown in lymph.[Steinhardt, E; Israeli, C; and Lambert, R.A. (1913) "Studies on the cultivation of the virus of vaccinia" ''J. Inf Dis. 13, 294–300]
References
External links
*
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Body fluids
Lymphatic system