Homeostasis is generally defined as the body’s ability to physiologically regulate its inner environment in order to ensure its stability in response to fluctuations in the outside environment, including, but not limited to one’s home, geographic location, weather bioterrain, lifestyle and stressful events, like being chased by a saber teeth tiger.
Homeostasis is one of the key regulatory mechasnims that is used by Holistic Medicine, thanks to which humans are able to either maintain health and vitality or restore balance.
“Homeostasis is the process by which a steady state of equilibrium, or constancy, in the body with respect to physiological functions and chemical compositions of fluids and tissues is maintained. Physiological set points refer to the baseline level at which functions such as heart rate, and at which chemical compositions such as plasma sodium concentration are normally maintained. These set points are represented in the brain by specific discharge rates in neurons dedicated to the monitoring and control of specific physiological processes”. (Source)
All of our organs, in particular the liver, the kidneys, and the brain (hypothalamus, the autonomic nervous system, inter alia), the joint system and the endocrine system (1) help maintain homeostasis. Among other functions, the liver is responsible for metabolizing toxic substances and maintaining carbohydrate metabolism. The kidneys are responsible for regulating blood, water levels, re-absorption of substances into the blood, maintenance of salt and ion levels in the blood, regulation of blood pH, and excretion of urea etc.
An inability to maintain homeostasis may lead to death or a disease, a condition known as homeostatic imbalance. For instance, heart failure may occur when negative feedback mechanisms become overwhelmed and destructive positive feedback mechanisms take over. (2) Other diseases which result from a homeostatic imbalance include diabetes, dehydration, hypoglycemia, hyperglycemia, gout and any disease caused by the presence of a toxin in the bloodstream. Medical and holistic intervention can help restore homeostasis and possibly prevent permanent damage to the organs.
Humans are warm-blooded, maintaining a near-constant body temperature. Thermoregulation is an important aspect of human homeostasis. Heat is mainly produced by the liver and muscle contractions. Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death. In order to deal with these climatic conditions, humans have developed physiologic and cultural modes of adaptation. Temperature may enter a circle of positive feedback, when temperature reaches extremes of 45°C (113°F), at which cellular proteins denature, causing the active site in proteins to change, thus causing metabolism stop and ultimately death. To meet these challenges, holistic regulation via sweating and other mechanisms are vital
Iron is an essential element for human beings. The control of this necessary but potentially toxic substance is an important part of many aspects of human health and disease. Hematologists have been especially interested in the system of iron metabolism because iron is essential to red blood cells. In fact, most of the human body’s iron is contained in red blood cells’ hemoglobin, and iron deficiency is the most common cause of anemia.
When body levels of iron are too low, then hepcidin in the duodenal epithelium is decreased. This causes an increase in ferroportin activity, stimulating iron uptake in the digestive system. An iron surplus will stimulate the reverse of this process. Furthermore, in individual cells, an iron deficiency causes responsive element binding protein (IRE-BP) to bind to iron responsive elements (IRE) on mRNAs for transferrin receptors, resulting in increased production of transferrin receptors. These receptors increase binding of transferrin to cells, and therefore stimulating iron uptake.
One of the problems with a non holistic lifestyle is that iron tends to build up in tissues and with age, less and less of iron overload is excreted, except for premenauposal women. As we know or should konw, having too much iron can be a significant contributing cause to cardiovascular events, as well as cancer and other diseases. This is why holistic regulation is imporant.
Energy balance is the homeostasis of energy in living systems. It is measured with the following equation: Energy intake = internal heat produced + external work + storage. It generally uses the energy unit Calorie (or kilogram calorie), which equals the energy needed to increase the temperature of 1 kg of water by 1 °C. This is about 4.184 kJ.
The balance of many blood solutes belongs to the scope of renal physiology.
Blood glucose is regluated with two hormones, insulin and glucagon, both released from the pancreas. When blood sugar levels become too high, insulin is released from the pancreas. Glucose, or sugar, is stored in body cells as glycogen, lowering the blood sugar levels. On the other hand, when blood sugar levels become too low, glucagon is released. It promotes the release of glycogen, converted back into glucose. This increases blood sugar levels. If the pancreas is for any reason unable to produce enough of these two hormones, diabetes results, inter alia.
Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body’s water content; that is it keeps the body’s fluids from becoming too dilute or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution the more water wants to go into the solution.
The kidneys are used to remove excess ions from the blood, thus affecting the osmotic pressure. These are then expelled as urine.
The renin-angiotensin system. (3)
The renin-angiotensin system (RAS) is a hormone system that helps regulate long-term blood pressure and extracellular volume in the body.
Calcium regulation in the human body. (4)
When blood calcium becomes too low, calcium-sensing receptors in the parathyroid gland become activated. This results in the release of PTH, which acts to increase blood calcium, e.g. by release from bones (increasing the activity of bone-degrading cells called osteoclasts). This hormone also causes calcium to be reabsorbed from urine and the GI tract.
Calcitonin, released from the C cells in the thyroid gland, works the opposite way, decreasing calcium levels in the blood by causing more calcium to be fixed in bone.
The kidneys maintain acid-base homeostasis by regulating the pH of the blood plasma. Gains and losses of acid and base must be balanced. The study of the acid-base reactions in the body is acid base physiology.
Volume of Fluids
The body’s homeostatic control mechanisms, which maintain a constant internal environment, ensure that a balance between fluid gain and fluid loss is maintained. The hormones ADH (Anti-diuretic Hormone, also known as vasopressin) and Aldosterone play a major role in this. If the body is becoming fluid-deficient, there will be an increase in the secretion of these hormones (ADH), causing fluid to be retained by the kidneys and urine output to be reduced.
Conversely, if fluid levels are excessive, secretion of these hormones (aldosterone) is suppressed, resulting in less retention of fluid by the kidneys and a subsequent increase in the volume of urine produced. If you have too much Carbon dioxide(CO2) in the blood, it can cause the blood to become acidic. People breath heavily not due to low oxygen(O2) content in the blood, but because they have too much CO2.
The kidneys, by regulating the blood composition, also controls the extracellular fluid homeostasis.
Hemostasis is the process whereby bleeding is halted. A major part of this is coagulation. Platelet accumulation causes blood clotting in response to a break or tear in the lining of blood vessels. Unlike the majority of control mechanisms in human body, the hemostasis utilizes positive feedback, for the more the clot grows, the more clotting occurs, until the blood stops. Another example of positive feedback is the release of oxytocin to intensify the contractions that take place during childbirth. (2)
Among other elemets, sleep timing depends upon a balance between the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode and circadian rhythms which determine the ideal timing of a correctly structured and restorative sleep episode. (5) Deep restorative sleep is thus also regulated by the homeostasis engin. (Source)
Joint and Cartilage Homeostatic Regulation in osteoarthritis
Osteoarthritis (OA) is a whole joint disease, in which thinning and disappearance of cartilage is a critical determinant in OA progression. The rupture of cartilage homeostasis whatever its cause (aging, genetic predisposition, trauma or metabolic disorder) induces profound phenotypic modifications of chondrocytes, which then promote the synthesis of a subset of factors that induce cartilage damage and target other joint tissues. Interestingly, among these factors are numerous components of the inflammatory pathways. For example, chondrocytes produce cytokines, chemokines, alarmins, prostanoids, and adipokines and express numerous cell surface receptors for cytokines and chemokines, as well as Toll-like receptors. These receptors activate intracellular signaling pathways involved in inflammatory and stress responses of chondrocytes in OA joints. In these type of health challenges, holistic restoration is key.
References and Precision Notes
(1).(http://assets.cambridge.org/97805218/45182/excerpt/9780521845182_excerpt.pdf) Reference for autonomic and endocrine system.
(2). Marieb, Elaine N. & Hoehn, Katja (2007). Human Anatomy & Physiology (Seventh ed.). San Francisco, CA: Pearson Benjamin Cummings.
(3). Page 866-867 (Integration of Salt and Water Balance) and 1059 (The Adrenal Gland) in: Walter F., PhD. Boron (2003). Medical Physiology:. A Cellular And Molecular Approaoch. Elsevier/Saunders. pp. 1300. ISBN 1-4160-2328-3.
(4). Page 1094 (The Parathyroid Glands and Vitamin D) in: Walter F., PhD. Boron (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. pp. 1300. ISBN 1-4160-2328-3.
(5). Wyatt, James K.; Ritz-De Cecco, Angela; Czeisler, Charles A.; Dijk, Derk-Jan (1 October 1999). “Circadian temperature and melatonin rhythms, sleep, and neurobehavioral function in humans living on a 20-h day” Am J Physiol 277 (4): R1152–R1163.. Retrieved 2007-11-25. “… significant homeostatic and circadian modulation of sleep structure, with the highest sleep efficiency occurring in sleep episodes bracketing the melatonin maximum and core body temperature minimum”. (Source)
(6). Homeostatic Mechanisms in Articular Cartilage and Role of Inflammation in Osteoarthritis
Homeotasis and all mechanisms
Homeostasis can be defined as the stable condition of an organism and of its internal environment; or as the maintenance or regulation of the stable condition, or its equilibrium; or simply as the balance of bodily functions. The stable condition is the condition of optimal functioning for the organism, and is dependent on many variables, such as body temperature and fluid balance, being kept within certain pre-set limits. Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium and calcium ions, as well as that of the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.
Homeostasis is brought about by a natural resistance to change in the optimal conditions, and equilibrium is maintained by many regulatory mechanisms. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control centre, and an effector. The receptor is the sensing component that monitors and responds to changes in the environment, either external or internal. Receptors include thermoreceptors, and mechanoreceptors. Control centres include the respiratory centre, and the renin-angiotensin system. An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, receptors include nuclear receptors that bring about changes in gene expression through up-regulation or down-regulation, and act in negative feedback mechanisms. An example of this is in the control of bile acids in the liver.
Some centres such as the renin-angiotensin system, control more than one variable. When the receptor senses a stimulus, it reacts by sending an action potential to a control centre. The control centre sets the maintenance range, the acceptable upper and lower limits, for the particular variable such as temperature . The control center responds to the signal by determining an appropriate response and sending signals to an effector which can be one or more muscles, an organ, or a gland. When the signal is received and acted on, negative feedback is fed back to the receptor that stops the need for further signalling.
The concept of the regulation of the internal environment was described by French physiologist Claude Bernard in 1865, and the word homeostasis was coined by Walter Bradford Cannon in 1926. Homeostasis is an almost exclusively biological term, referring to the concepts described by Bernard and Cannon, concerning the constancy of the internal environment in which the cells of the body live and survive. The term cybernetics is applied to technological control systems such as thermostats, which function as homeostatic mechanisms, but is often defined much more broadly than the biological term of homeostasis.
Blood oxygen content
The kidneys measure the oxygen content rather than the partial pressure of oxygen in the arterial blood. When the oxygen content of the blood is chronically low, oxygen-sensitive cells secrete erythropoietin (EPO) into the blood. The effector tissue is the red bone marrow which produces red blood cells (RBCs)(erythrocytes). The increase in RBCs leads to an increased hematocrit in the blood, and subsequent increase in hemoglobin that increases the oxygen carrying capacity. This is the mechanism whereby high altitude dwellers have higher hematocrits than sea-level residents, and also why persons with pulmonary insufficiency or right-to-left shunts in the heart (through which venous blood by-passes the lungs and goes directly into the systemic circulation) have similarly high hematocrits.
Regardless of the partial pressure of oxygen in the blood, the amount of oxygen that can be carried, depends on the hemoglobin content. The partial pressure of oxygen may be sufficient for example in anemia, but the hemoglobin content will be insufficient and subsequently as will be the oxygen content. Given enough supply of iron, vitamin B12 and folic acid, EPO can stimulate RBC production, and hemoglobin and oxygen content restored to normal.
Arterial blood pressure
High pressure receptors called baroreceptors in the walls of the aortic arch and carotid sinus (at the beginning of the internal carotid artery) monitor the arterial blood pressure. Rising pressure is detected when the walls of the arteries stretch due to an increase in blood volume. This causes heart muscle cells to secrete the hormone atrial natriuretic peptide (ANP) into the blood. This acts on the kidneys to inhibit the secretion of renin and aldosterone causing the release of sodium, and accompanying water into the urine, thereby reducing the blood volume. This information is then conveyed, via afferent nerve fibers, to the solitary nucleus in the medulla oblongata. From here motor nerves belonging to the autonomic nervous system are stimulated to influence the activity of chiefly the heart and the smallest diameter arteries, called arterioles. The arterioles are the main resistance vessels in the arterial tree, and small changes in diameter cause large changes in the resistance to flow through them. When the arterial blood pressure rises the arterioles are stimulated to dilate making it easier for blood to leave the arteries, thus deflating them, and bringing the blood pressure down, back to normal. At the same time the heart is stimulated via cholinergic parasympathetic nerves to beat more slowly (called bradycardia), ensuring that the inflow of blood into the arteries is reduced, thus adding to the reduction in pressure, and correction of the original error.
If the pressure in the arteries falls, the opposite reflex is elicited: constriction of the arterioles, and a speeding up of the heart rate (called tachycardia). If the drop in blood pressure is very rapid or excessive, the medulla oblongata stimulates the adrenal medulla, via “preganglionic” sympathetic nerves, to secrete epinephrine (adrenaline) into the blood. This hormone enhances the tachycardia and causes severe vasoconstriction of the arterioles to all but the essential organ in the body (especially the heart, lungs and brain). These reactions usually correct the low arterial blood pressure (hypotension) very effectively.
The plasma pH can be altered by respiratory changes in the partial pressure of carbon dioxide; or altered by metabolic changes in the carbonic acid to bicarbonate ion ratio. The bicarbonate buffer system regulates the ratio of carbonic acid to bicarbonate to be equal to 1:20, at which ratio the blood pH is 7.4 (as explained in the Henderson–Hasselbach equation). A change in the plasma pH gives an acid–base imbalance. In acid–base homeostasis there are two mechanisms that can help regulate the pH. Respiratory compensation a mechanism of the respiratory center, adjusts the partial pressure of carbon dioxide by changing the rate and depth of breathing, to bring the pH back to normal. The partial pressure of carbon dioxide also determines the concentration of carbonic acid, and the bicarbonate buffer system can also come into play. Renal compensation can help the bicarbonate buffer system. The sensor for the plasma bicarbonate concentration is not known for certain. It is very probable that the renal tubular cells of the distal convoluted tubules are themselves sensitive to the pH of the plasma. The metabolism of these cells produces carbon dioxide, which is rapidly converted to hydrogen and bicarbonate through the action of carbonic anhydrase. When the ECF pH falls (becoming more acidic) the renal tubular cells excrete hydrogen ions into the tubular fluid to leave the body via urine. Bicarbonate ions are simultaneously secreted into the blood that decreases the carbonic acid, and consequently raises the plasma pH. The converse happens when the plasma pH rises above normal: bicarbonate ions are excreted into the urine, and hydrogen ions released into the plasma.
When hydrogen ions are excreted into the urine, and bicarbonate into the blood, the latter combine with the excess hydrogen ions in the plasma that stimulated the kidneys to perform this operation. The resulting reaction in the plasma is the formation of carbonic acid which is in eqilibrium with the plasma partial pressure of carbon dioxide. This is tightly regulated to ensure that there is no excessive build-up of carbonic acid or bicarbonate. of carbonic acid or bicarbonate ions in the blood plasma. The overall effect is therefore that hydrogen ions are lost in the urine when the pH of the plasma falls. The concomitant rise in the plasma bicarbonate mops up the increased hydrogen ions (caused by the fall in plasma pH) and the resulting excess carbonic acid is disposed of in the lungs as carbon dioxide. This restores the normal ratio between bicarbonate and the partial pressure of carbon dioxide and therefore the plasma pH.
The converse happens when a high plasma pH stimulates the kidneys to secrete hydrogen ions into the blood and to excrete bicarbonate into the urine. The hydrogen ions combine with the excess bicarbonate ions in the plasma, once again forming an excess of carbonic acid which can be exhaled, as carbon dioxide, in the lungs, keeping the plasma bicarbonate ion concentration, the partial pressure of carbon dioxide and, therefore, the plasma pH, constant.
Cerebrospinal fluid (CSF) allows for regulation of the distribution of substances between cells of the brain, and neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope.
Inhibitory neurons in the central nervous system play a homeostatic role in the balance of neuronal activity between excitation and inhibition. Inhibitory neurons using GABA, make compensating changes in the neuronal networks preventing runaway levels of excitation.
The neuroendocrine system is responsible for the homeostasis of metabolism that is carried out by hypothalamic interconnections to other glands. Three endocrine glands of the hypothalamic–pituitary–gonadal axis (HPG axis) often work together and have important regulatory functions. Two other regulatory endocrine axes are the hypothalamic–pituitary–adrenal axis (HPA axis) and the hypothalamic–pituitary–thyroid axis (HPT axis).
The liver also has many regulatory functions of the metabolism. An important function is the production and control of bile acids. Too much bile acid can be toxic to cells and its synthesis can be inhibited by activation of FXR a nuclear receptor. Also at the cellular level, homeostasis is carried out by transcriptional regulation that can alter the activity of genes in response to changes.
Main article: Energy homeostasis
This section needs expansion. You can help by adding to it. (November 2017)
The amount of energy taken in through nutrition needs to match the amount of energy used.
Many diseases are the result of a homeostatic failure. Almost any homeostatic component can malfunction, either as a result of an inherited defect, or an acquired disease. Some homeostatic mechanisms have inbuilt redundancies, which ensures that life is not immediately threatened if a component malfunctions; but sometimes a homeostatic malfunction can result in serious disease, which can be fatal if not treated. A well known example of a homeostatic failure is shown in type 1 diabetes mellitus. Here blood sugar regulation is unable to function because the beta cells of the pancreatic islets are destroyed and cannot produce the necessary insulin. The blood sugar rises in a condition known as hyperglycemia.
The plasma ionized calcium homeostat can be disrupted by the constant, unchanging, over-production of parathyroid hormone by a parathyroid adenoma resulting in the typically features of hyperparathyroidism, namely high plasma ionized Ca2+ levels and the resorption of bone, which can lead to spontaneous fractures. The abnormally high plasma ionized calcium concentrations cause conformational changes in many cell-surface proteins (especially ion channels and hormone or neurotransmitter receptors) giving rise to lethargy, muscle weakness, anorexia, constipation and labile emotions.
The body water homeostat can be compromised by the inability to secrete ADH in response to even the normal daily water losses via the exhaled air, the feces, and insensible sweating. On receiving a zero blood ADH signal, the kidneys produce huge unchanging volumes of very dilute urine, causing dehydration and death if not treated.
As organisms age, the efficiency of their control systems becomes reduced. The inefficiencies gradually result in an unstable internal environment that increases the risk of illness, and leads to the physical changes associated with aging.
Chronic disease compensation and decompensation
Various chronic diseases are kept under control by homeostatic compensation, which masks a problem by compensating for it (making up for it) in another way. However, the compensating mechanisms eventually wear out or are disrupted by a new complicating factor (such as the advent of a concurrent acute viral infection), which sends the body reeling through a new cascade of events. Such decompensation unmasks the underlying disease, worsening its symptoms. Common examples include decompensated heart failure, kidney failure, and liver failure.
In the Gaia hypothesis, James Lovelock stated that the entire mass of living matter on Earth (or any planet with life) functions as a vast homeostatic superorganism that actively modifies its planetary environment to produce the environmental conditions necessary for its own survival. In this view, the entire planet maintains several homeostats (the primary one being temperature homeostasis). Whether this sort of system is present on Earth is open to debate. However, some relatively simple homeostatic mechanisms are generally accepted. For example, it is sometimes claimed that when atmospheric carbon dioxide levels rise, certain plants may be able to grow better and thus act to remove more carbon dioxide from the atmosphere. However, warming has exacerbated droughts, making water the actual limiting factor on land. When sunlight is plentiful and atmospheric temperature climbs, it has been claimed that the phytoplankton of the ocean surface waters, acting as global sunshine, and therefore heat sensors, may thrive and produce more dimethyl sulfide (DMS). The DMS molecules act as cloud condensation nuclei, which produce more clouds, and thus increase the atmospheric albedo, and this feeds back to lower the temperature of the atmosphere. However, rising sea temperature has stratified the oceans, separating warm, sunlit waters from cool, nutrient-rich waters. Thus, nutrients have become the limiting factor, and plankton levels have actually fallen over the past 50 years, not risen. As scientists discover more about Earth, vast numbers of positive and negative feedback loops are being discovered, that, together, maintain a metastable condition, sometimes within very broad range of environmental conditions.
Main article: Predictive homeostasis
Predictive homeostasis is an anticipatory response to an expected challenge in the future, such as the stimulation of insulin secretion by gut hormones which enter the blood in response to a meal. This insulin secretion occurs before the blood sugar level rises, lowering the blood sugar level in anticipation of a large influx into the blood of glucose resulting from the digestion of carbohydrates in the gut. Such anticipatory reactions are open loop systems which are based, essentially, on “guess work”, and are not self-correcting. Anticipatory responses always require a closed loop negative feedback system to correct the ‘over-shoots’ and ‘under-shoots’ to which the anticipatory systems are prone.
The term has come to be used in other fields, for example:
Main article: Risk homeostasis
An actuary may refer to risk homeostasis, where (for example) people who have anti-lock brakes have no better safety record than those without anti-lock brakes, because the former unconsciously compensates for the safer vehicle via less-safe driving habits. Previous to the innovation of anti-lock brakes, certain maneuvers involved minor skids, evoking fear and avoidance: Now the anti-lock system moves the boundary for such feedback, and behavior patterns expand into the no-longer punitive area. It has also been suggested that ecological crises are an instance of risk homeostasis in which a particular behavior continues until proven dangerous or dramatic consequences actually occur.
Sociologists and psychologists may refer to stress homeostasis, the tendency of a population or an individual to stay at a certain level of stress, often generating artificial stresses if the “natural” level of stress is not enough.
Jean-François Lyotard, a postmodern theorist, has applied this term to societal ‘power centers’ that he describes in The Postmodern Condition, as being ‘governed by a principle of homeostasis,’ for example, the scientific hierarchy, which will sometimes ignore a radical new discovery for years because it destabilizes previously accepted norms
The word homeostasis (/ˌhoʊmioʊˈsteɪsɪs/) uses combining forms of homeo- and -stasis, New Latin from Greek: ὅμοιος homoios, “similar” and στάσις stasis, “standing still”, yielding the idea of “staying the same”.
The metabolic processes of all organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the interstitial fluid bathing the cells. The best known homeostatic mechanisms in humans and other mammals are regulators that keep the composition of the extracellular fluid (or the “internal environment”) constant, especially with regard to the temperature, pH, osmolality, and the concentrations of sodium, potassium, glucose, carbon dioxide, and oxygen. However, a great many other homeostatic mechanisms, encompassing many aspects of human physiology, control other entities in the body. Where the levels of variables are higher or lower than those needed, they are often prefixed with hyper- and hypo-, respectively such as hyperthermia and hypothermia and hypertension and hypotension.
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•Banci, Lucia (Ed.), ed. (2013). “Chapter 3 Sodium/Potassium homeostasis, Chapter 5 Calcium homeostasis, Chapter 6 Manganese homeostasis”. Metallomics and the Cell. Metal Ions in Life Sciences. 12. Springer. doi:10.1007/978-94-007-5561-1_3. ISBN 978-94-007-5560-4. electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836 electronic-ISSN 1868-0402
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Authors and affiliation. By Xavier Houard Mary B. Goldring et al.
Pierre & Marie Curie University (UR-4)Paris Cedex 5 France