The lymphatic system, also called the lymphoid system, is made up of a network of vessels, nodes and organs that are part of the immune system. Lymphatic vessels carry a clear fluid called lymph back to the heart for recirculation.
The primary purpose of lymph is immunological defense; removes foreign bacteria and other agents from the body. The lymph contains waste products, proteins, antibodies and dead cells, as well as microbes. The lymphoid organs are composed of lymphoid tissue and are the sites of production and activation of various immune cells.
Until recently, the brain and spinal cord were thought to have no lymphatic system. However, the existence of a type of cerebral lymphatic system has recently been demonstrated. This macroscopic waste disposal system is called the lymphatic system, because of its dependence on glial cells and its functions homologous to those of the lymphatic system within the central nervous system.
In this article, we explore the glymphatic systemits main functions and the implications for the treatment of neurodegenerative diseases of this discovery.
What is the glymphatic system?
The glymphatic system is a network of vessels used to remove waste products from the central nervous system or CNS This system is particularly active while we sleep, it eliminates toxins and other brain metabolic waste. Recently, research has shown that the glymphatic system can alter and diminish its function over time; this has been suggested as a possible cause of certain neurodegenerative diseases.
The glymphatic system it is the cerebral and spinal counterpart of the lymphatic system. The lymphatic system assists the immune system and provides a parallel pathway to the circulatory system, for the removal of fluids from the body. This system carries excess interstitial fluids, proteins, and waste products out of the various organs and body tissues. These substances are released to regulate fluid volume and osmotic pressure; this is fundamental because the lack of elimination of these soluble proteins can cause serious obstructions.
Any obstruction of the lymphatic channels can have dramatic consequences. In cases of elephantiasis, a disease caused by lymphatic parasites, chronic edema occurs when the elimination of lymph stops and interstitial solutes accumulate.
Paradoxically, the lymphatic system does not extend to the central nervous system: the brain and the spinal cord. Until the discovery of the gingival system, several hypotheses were made about how the brain eliminated waste.
Brain Cleansing Pattern
The brain, like all the organs of our body, produces metabolic waste, all enzymatic reactions produce waste that must be eliminated. The glymphatic system it is formed by water channels and uses cerebrospinal fluid as a transport fluid.
Cerebrospinal fluid (CSF) is a clear, colorless fluid that surrounds the brain and spinal cord. Its main function is that of protection: it cushions blows or wounds. Also is responsible for removing waste products from the nervous system. However, how different waste products were exchanged between brain tissue and cerebrospinal fluid is a recent discovery.
A 2012 study by M. Nedergaard and researchers at the University of Rochester used two-photon fluorescence imaging to observe cerebrospinal arachnoid fluid in living mice. Using in vivo two-photon excitation microscopy, the Rochester team was able to observe cerebrospinal fluid flow in real time without having to puncture the compartment.
According to their findings, the cerebrospinal fluid is exchanged with the interstitial fluid that surrounds the brain through the paravascular spaces which surround the large veins and facilitate drainage.
Normally, the cerebrospinal fluid is separated from the brain tissue, preventing the exchange of substances. However, the traditional model of cerebrospinal fluid hydrodynamics has been firmly challenged. Currently, it is known that the cerebrospinal fluid is able to enter the spaces near the smallest blood vessels that lead to the brain (Virchow’s spaces). There it can be exchanged with the interstitial fluid; this happens through a channel formed by astrocytes. The feet of these glial cells surround the space that surrounds the capillaries of the brain, forming the glymphatic ducts through which the cerebral interstitial fluid circulates.
The exchange of materials by glymphatic transport results from energy sources that are still partly unknown. Mainly, the energy is obtained from the pulsations of the arteries and the pressure created during the manufacture of cerebrospinal fluid. Waste products, such as proteins and metabolites, are removed from brain tissue and transported to the cerebrospinal fluid for elimination. About 50% of cerebrospinal fluid reaches the cervical lymph nodes for filtration.
What influences the functioning of the glymphatic system?
The ability of the lymphatic system to function properly depends on various physiological aspects of the different organs in our body. These include the immune system, cardiac system, and circulatory system. Lifestyle, disease, and inflammation can negatively affect the glymphatic system. These alterations can slow down glymphatic drainagenegatively affecting the health of the body in general and mainly the brain.
Studies have shown that the lymphatic system is more efficient and robust when the heart pumps, the blood circulates, the body is relaxed and the brain enjoys restful sleep.
The brain performs cleaning functions during sleep. This is because the glymphatic system is more active at this time. The exchange between cerebrospinal fluid and interstitial fluid is more efficient due to the increased extracellular space.
Different studies have shown that it expands by 60% during sleep. Based on these results, it is believed that increased glymphatic cleansing overnight could be one of the causes of the restorative properties of sleep.
The aging process affects glymphatic transport, particularly the astrocyte-expressed channel that performs most of the system’s exchanges. The canal can also deteriorate due to sleep deprivation. Some studies have shown that exercise can lessen these effects in mice. This suggests that physical activity may have a neuroprotective function.
Relationship between the glymphatic system and neurodegenerative diseases
Certain neurodegenerative diseases they may be caused by changes in glyphic function related to aging. These include alterations in the glial cells responsible for the creation of the glyphic vessels, decreased production of cerebrospinal fluid by the choroid plexuses, decreased flexibility and arterial pulsations which provide the necessary energy to exchange with interstitial fluid, and the reduced ability of CSF to move through the brain.
The glymphatic system removes large proteins from the brain during sleep. One of these proteins is beta-amyloid, which is the main component of brain plaques associated with Alzheimer’s disease. Deterioration of the glyph system may also be implicated in strokes and disseminated cortical depression.
Researchers believe that increasing glymphatic transport could potentially delay the onset of Alzheimer’s disease and other neurodegenerative diseases. Animal experiments show that reduced glymphatic transport often precedes sickness ; they would therefore lead to the conclusion that greater glymphatic transport could contribute to delaying the onset of the disease.
The relationship between glyphatic function and exercise opens up the possibility of new treatments for neurodegenerative diseases. These treatments are likely to be more effective if given early in the progression of dementia. Glymphatic flow assessment methods by magnetic resonance imaging or positive emission tomography are currently being developed as clinical diagnostic tools.
The glymphatic system might have more functions than waste disposal. In the future, it may also participate in the delivery of growth factors and drugs, according to the research.
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