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Lymph

Lymph

Overview
Lymph is considered a part of the 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...

, the fluid which lies in the interstices
Interstitial space
An interstitial space is an intermediate space located between regular-use floors, commonly located in hospitals and laboratory-type buildings to allow space for the mechanical systems of the building...

 of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary
Lymph capillary
Lymph capillaries or lymphatic capillaries are tiny thin-walled vessels that are closed at one end and are located in the spaces between cells throughout the body, except in the central nervous system, and in non-vascular tissues. The main purpose of these vessels is to drain excess tissue fluids...

. The lymph then travels to at least one 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...

 before emptying ultimately into the right or the left subclavian vein
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...

, where it mixes back with blood.

Lymph returns protein and excess interstitial fluid to the circulation. Lymph picks up bacteria and brings them to lymph nodes to be destroyed.
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Encyclopedia
Lymph is considered a part of the 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...

, the fluid which lies in the interstices
Interstitial space
An interstitial space is an intermediate space located between regular-use floors, commonly located in hospitals and laboratory-type buildings to allow space for the mechanical systems of the building...

 of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary
Lymph capillary
Lymph capillaries or lymphatic capillaries are tiny thin-walled vessels that are closed at one end and are located in the spaces between cells throughout the body, except in the central nervous system, and in non-vascular tissues. The main purpose of these vessels is to drain excess tissue fluids...

. The lymph then travels to at least one 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...

 before emptying ultimately into the right or the left subclavian vein
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...

, where it mixes back with blood.

Lymph returns protein and excess interstitial fluid to the circulation. Lymph picks up bacteria and brings them to lymph nodes to be destroyed. Metastatic
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...

 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...

 cells can also be transported via lymph. Lymph also transports fats from the digestive system.

The word is derived from the name of the Roman divinity, Lympha
Lympha
The Lympha is an ancient Roman deity of fresh water. She is one of twelve agricultural deities listed by Varro as "leaders" of Roman farmers, because "without water all agriculture is dry and poor." The Lymphae are often connected to Fons, "Source" or "Font," a god of fountains and wellheads...

.

Composition


Lymph has a composition comparable to that of blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

, but it may differ slightly. Lymph contains white blood cell
White blood cell
White 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. In particular, the lymph that leaves a lymph node is richer in 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. Likewise, the lymph formed in the digestive system 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...

 is rich in triglyceride
Triglyceride
A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....

s (fat), and looks milky white.

Formation


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....

 supplies nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s and important metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...

s to the 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....

 of a tissue
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...

 and collects back the waste products they produce, which requires exchange of respective constituents between the blood and tissue cells. However, this exchange is not direct but instead is effected through an intermediary called interstitial fluid or tissue fluid that the blood forms. 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...

 (ISF) is the fluid that occupies the spaces between the cells and constitutes their immediate environment. As the blood and the surrounding cells continually add and remove substances from the ISF, its composition continually changes. Water and solutes
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

 can freely pass between the ISF and blood via diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 across capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...

 walls and thus both are in dynamic equilibrium
Dynamic equilibrium
A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state...

 with each other.

ISF forms at the arterial
Arteriole
An arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.Arterioles have muscular walls and are the primary site of vascular resistance...

 (coming from the heart) end of capillaries because of the higher pressure of blood compared to vein
Vein
In the circulatory system, veins are blood vessels 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 blood to the heart...

s, and most of it returns to its venous
Venule
A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...

 ends and venule
Venule
A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...

s; the rest (1%) enters the lymph capillaries
Lymph capillary
Lymph capillaries or lymphatic capillaries are tiny thin-walled vessels that are closed at one end and are located in the spaces between cells throughout the body, except in the central nervous system, and in non-vascular tissues. The main purpose of these vessels is to drain excess tissue fluids...

 as lymph. Thus, lymph when formed is a watery clear liquid with the same composition as the ISF. However, as it flows through the lymph nodes it comes in contact with blood, and tends to accumulate more cells (particularly, lymphocytes) and proteins.

The two primary lymph systems are the thymus gland 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...

, where the immune cells form or mature. The secondary lymph system is made up of encapsulated and unencapsulated diffuse lymphoid tissue. The encapsulated tissue 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...

 and the lymph nodes. The unencapsulated tissue includes the gut-associated lymphoid tissue
Gut-associated lymphoid tissue
The digestive tract's immune system is often referred to as gut-associated lymphoid tissue and works to protect the body from invasion. GALT is an example of mucosa-associated lymphoid tissue.-Function:...

s and 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.

Lymphatic 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 and has no central pump. Lymph transport, therefore, is slow and sporadic. Despite low pressure, lymph movement occurs due to peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 (propulsion of the lymph due to alternate contraction and relaxation of smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

), valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...

.

Lymph that enters the lymph vessels from the interstitial space usually does not flow backwards along the vessels because of the presence of valves. If excessive hydrostatic pressure develops within the lymph vessels, though, some fluid can leak back into the interstitial space and contribute to formation of edema
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...

.

As a growth medium


In 1907 the zoologist Ross Granville Harrison
Ross Granville Harrison
Ross Granville Harrison was an American biologist and anatomist credited as the first to work successfully with artificial tissue culture....

 demonstrated the growth of frog nerve cell processes in a medium of clotted lymph.

In 1913, E. Steinhardt, C. Israeli, and R. A. Lambert grew vaccinia
Vaccinia
Vaccinia virus is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, and which encodes for approximately 250 genes. The dimensions of the virion are roughly 360 × 270 × 250 nm, with a mass of...

 virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 in fragments of tissue culture
Tissue culture
Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar...

 from guinea pig cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

l grown in lymph.

See also

  • American Society of Lymphology
    American Society of Lymphology
    The 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...

  • 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...

  • Lymphatic system
    Lymphatic system
    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 unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...

  • Lymphedema
    Lymphedema
    Lymphedema , also known as lymphatic obstruction, is a condition of localized fluid retention and tissue swelling caused by a compromised lymphatic system....

  • Manual lymphatic drainage
    Manual lymphatic drainage
    Manual lymphatic drainage is a type of gentle massage which is intended by proponents to encourage the natural circulation of the lymph through the body...