The ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes.
homeostatic ho'me·o·stat'ic (-stăt'ĭk) adj.
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Sci-Tech Encyclopedia:
Homeostasis
The relatively constant conditions within organisms, or the physiological processes by which such conditions are maintained in the face of external variation.
Similar homeostatic controls are used to keep factors such as temperature and blood pressure nearly constant despite changes in an organism's activity level or surroundings. Such systems operate by detecting changes in the variable that the system is designed to hold constant and initiating some action that offsets any change. All incorporate a sensor within the system that responds when the actual condition differs from the desired one, a device to ensure that any action taken will reduce the difference between actual and desired, and an effector to take the needed action as directed. The crucial aspect is that information is fed back from effector to sensor and action is taken to reduce any imbalance—hence the term negative feedback.
Blood pressure is, at least on a moment-to-moment basis, regulated by a system for which the sensors are stretch-sensitive cells located in the neck arteries that carry blood from heart to brain. An increase in blood pressure triggers sensor activity; their signal passes to the brain; and, in turn, the nerve supplying the heart (the vagus) is stimulated to release a chemical (acetylcholine) that causes the heart to beat more slowly—which decreases blood pressure.
The volume of the blood is subject to similar regulation. Fluid (mainly plasma) moves between the capillaries and the intercellular fluid in response to changes in pressure in the capillaries. A decrease in blood volume is detected by sensors at the base of the brain; the brain stimulates secretion of substances that cause contraction of tiny muscles surrounding the blood vessels that lead into the capillaries. The resulting arteriolar constriction reduces the flow of blood to, and the pressure within, the capillaries, so fluid moves from intercellular space into capillaries, thus restoring overall blood volume.
Body temperature in mammals is regulated by a sensor that consists of cells within the hypothalamus of the brain. Several effectors are involved, which vary among animals. These include increasing heat production through nonspecific muscle activity such as shivering; increasing heat loss through sweating, panting, and opening more blood vessels in the skin (vasodilation); and decreasing heat loss through thickening of fur (piloerection) and curling up. Humans sweat, but they retain only a vestige of piloerection (“goose flesh”).
While the homeostatic mechanisms described involve the neural and endocrine systems of mammals, it is clear that such arrangements pervade systems from genes to biological communities, and that they are used by the simplest and the most complex organisms.
Organisms of every kind develop, mature, and even shift physiological states periodically—between day and night, with seasons, or as internal rhythms. Thus organisms cannot be considered constant except over short periods. However, all such changes appear to involve the same basic sensing of the results of the past activity of the system and the adjusting of future activity in response to that information. Development of an organism from a fertilized egg is far from a direct implementation of a genetic program; probably no program could anticipate all the variation in the external context in which an organism must somehow successfully develop. See also Biological clocks; Nervous system (vertebrate); Servomechanism.
World of the Body:
homeostasis
Homeostasis (Greek: staying the same) is a fundamental idea in our understanding of the workings of the body. The concept had its origin in the 1870s, when the French physiologist Claude Bernard showed that, although the concentration of sugar in the blood could be raised or lowered by a number of processes, the net effect of these processes was to keep the concentration of sugar within certain limits. Bernard extended the idea to other constituents of blood — for which he had less evidence — and in a timeless phrase referred to the constancy of the internal environment (‘le milieu intérieur’): ‘La fixité du milieu intérieur est la condition de la vie libre, independante.’
Bernard contrasted this constancy with that of the changeable world that surrounded the animal (‘le milieu extérieur’). He likened the protective function of the internal milieu to that of a greenhouse, though to us this may seem rather an odd analogy. The constitution of the internal milieu (extracellular fluids, including blood and lymph) has been suggested to represent some primal sea in which vertebrates have evolved. It is a likeable hypothesis, but one which is rather difficult to test.
Bernard's proposal attracted little contemporary attention, which was hardly surprising, for it was about 50 years ahead of its time. But during the period 1915-35 two American physiologists, W. B. Cannon (1871-1945) and L. J. Henderson (1878-1942), revived it. Cannon was particularly concerned with demonstrating the importance of the autonomic nervous system in maintaining the constancy of the milieu intérieur: he realized that the constancy of blood pressure was an essential part of the maintenance. It was Cannon who actually coined the word ‘homeostasis’, and in his Wisdom of the body (1932) he described how several of the body's systems were involved in homeostatic mechanisms.
Cannon's fellow professor at Harvard, L. J. Henderson, analysed the way in which the body maintained the hydrogen ion concentration of body fluids (usually expressed as pH) within narrow limits. There is a short-term pH homeostasis which is a property of blood itself: a bicarbonate-buffering system. If this is not adequate, the kidneys cope with any larger deviation. Henderson published his findings in a classic work, Blood: a study in general physiology (1928). The kidneys are, incidentally, the homeostatic organs par excellence: every renal activity is involved in maintaining the internal milieu, whether it is the concentration of ions in blood, blood volume, blood pressure itself, or the excretion of alien substances.
How do the body's systems actually maintain the constancy? The most conspicuous mechanism is generally known as ‘negative feedback’, illustrated below.
As an example, blood glucose concentration could be the ‘regulated variable’ in the diagram. The control system for the variable is the hormone insulin, whose main action is to accelerate the entry of glucose into many of the cells of the body, thereby lowering its plasma concentration. Insulin is released from cells in the Islets of Langerhans of the pancreas (the controller), the most important stimulus for its release being a rise in blood glucose concentration, as occurs after a meal (‘disturbance’ in the diagram). The reason for this being a ‘negative’ feedback system is that the action of insulin, by lowering the blood sugar, tends to remove the stimulus for its own release. Negative feedback is a ubiquitious principle in engineering and electronics.
It is clear from this example that the mechanism does not keep glucose concentration (the regulated variable) at a fixed level. The level oscillates, because there are delays in both arms of the system — it takes a finite time for insulin to lower blood glucose concentrations, and also for elevated glucose concentrations to increase the production of insulin from the pancreas.
Another regulated variable is carbon dioxide. The control of a constant partial pressure of carbon dioxide (PCO2) in blood is a very precise feedback loop, and its control system is the act of breathing. The body produces the gas constantly, adding it to blood. The CO2 sensor in this system consists of neurons in the medullary respiratory centre of the brain; the control system consists of motor nerves passing from the brain to the diaphragm and intercostal muscles. These nerves stimulate the act of breathing, which transfers carbon dioxide from blood into the lungs, lowers the blood PCO2, and temporarily removes the stimulus to the medullary respiratory centre. Because the body is still producing carbon dioxide, the blood PCO2 begins to rise again, the medullary receptors are stimulated, and the cycle repeats itself. A CO2-sensitive electrode inserted into an artery shows small, regular oscillations whose frequency corresponds precisely to the act of breathing.
The speed of response of the carbon dioxide loop is far greater than that of the glucose loop, a difference that derives from nervous compared with hormonal mechanisms: the PCO2 varies by only about 10% around its average level, whereas glucose varies by about 40%. The concentration ranges of some other constituents of blood provide us with clues about the nature of the relevant homeostatic mechanisms. Sodium ions (135-145 mmol/litre) and chloride ions (95-105 mmol/litre) have narrow ranges; this is the result of a mixture of nervous and hormonal mechanisms; the range is wider for potassium (3.5-5.0 mmol/litre) which is adjusted by hormonal action in the kidneys. By contrast, the hormones that provide the control systems regulating these variables show far wider concentration ranges in blood, according to the changes in secretion rates stimulated by disturbances in the variable they control. Thus ACTH (adrenocorticotrophic hormone) has a range of 3.3-15.4 pmol/litre, aldosterone 100-500 pmol/litre, and insulin 0-15 mUnits/ml (unfed) and 15-100 Units/ml (after food).
Homeostasis can itself be reset or entrained by higher nervous centres. The diurnal variations shown by ACTH and cortisol demonstrate high concentrations between midnight and midday (cortisol concentration 280-700 mmol/litre) and midday and midnight (cortisol 140-280 mmol/litre). Similarly, on a longer time-scale, the changes seen in the female reproductive cycle represent a 28-day cycle of entrainment. On a longer time-scale still, the growth and development of the child must represent the ultimate homeostatic entrainment by the brain. We might envisage old age as representing a genetically programmed deterioration of homeostasis.
Claude Bernard's intuition about ‘le milieu intérieur’ has come a very long way in a century. The mechanisms of homeostasis are so ubiquitous, their patterns so subtly intertwined, that we are tempted to produce a teleological question, and ask why. What is so useful to the organism about this precision? We do not have to look far, because the workings of every cell in the body depend on the maintenance of a negative potential inside the cell. In turn, this negative potential depends upon the relative concentrations of ions inside and outside the cell: a high sodium concentration in the extracellular fluid, and a high potassium concentration inside the cell, the gradients across the cell wall being maintained by ionic pumps within the cell membrane. But these pumps could not begin to control this gradient if the ionic concentrations in blood (extracellular fluid) were not kept within narrow limits in the first place. The subject comes into sharp focus when we consider the situation in the heart, which is very dependent on a constant plasma potassium level, within the range of 3.5-5.0 mmol/litre. The elevation of this value by 1-2 mmol/litre constitutes a medical emergency: the excitable components of the heart begin to conduct nervous impulses spontaneously and, without treatment, death soon follows from uncoordinated contraction of different parts of the ventricles (ventricular fibrillation).
It soon becomes clear that the body's function involves countless homeostatic mechanisms, both within and outside cells. Not only are the mechanisms ubiquitous, but careful analysis often shows two or more feedback loops apparently serving the same function; a good example is the elaborate relationship that exists between the control of blood pressure and plasma volume. Perhaps the apparent redundancy provides the organism with back-up systems that improve evolutionary survival value. Improvement or not, such duplication makes the understanding of disease processes very much more difficult to disentangle.
— J. R. Henderson
See also acid-base homeostasis; body fluids; hormones.
Food and Fitness:
homeostasis
The maintenance of a constant physical or chemical state. Many processes in the body are under homeostatic control: deviations of output from a normal level (set point or norm) activate corrective mechanisms to bring the level back to normal.
Temperature regulation is an example of a homeostatic mechanism. The usual set point for the core temperature is 37 degrees Celsius (37°C): body temperatures above this norm result in sweating and an increase in blood flow to the skin to cool the body; low body temperatures result in an increase in basal metabolic rate (more fuel is burnt by the liver) and shivering to generate heat.
Other, homeostatic mechanisms include those controlling blood glucose levels, blood acidity, and hormone secretions. There are also suggestions that percentage fat composition and body weight have similar control systems (see adipostat and set point theory).
Dental Dictionary:
homeostasis
(hō′mē-ō-stā′sis)
n
The term used to describe the tendency toward physiologic equilibration (for example, acid-base balance, pH level of blood, blood sugar level).
Geography Dictionary:
homeostasis
In ecology, the process whereby constancy is achieved in an organism or community. Homeostatic theory is the contention that a population level remains constant in a pre-industrial society. When there is an imbalance between population growth and resources, there is a corrective response. Malthus was one exponent of this theory.
Britannica Concise Encyclopedia:
homeostasis
For more information on homeostasis, visit Britannica.com.
Sports Science and Medicine:
homeostasis
The ability or tendency to maintain a constant physical or chemical state within a system using compensatory control mechanisms. Physiological homeostasis is illustrated by the maintenance of a constant body core temperature and blood sugar levels. Psychological homeostasis is illustrated by the maintenance of self-respect through compensatory devices such as rationalization and blaming others for faults. In sociology, homeostasis has been applied to the controversial suggestion that social systems (including governing bodies of sport) tend to act in ways that are self-maintaining and self-equilibrating.
Health Dictionary:
homeostasis
(hoh-mee-oh-stay-sis)
The tendency of the body to seek and maintain a condition of balance or equilibrium within its internal environment, even when faced with external changes. A simple example of homeostasis is the body's ability to maintain an internal temperature around 98.6 degrees Fahrenheit, whatever the temperature outside.
Veterinary Dictionary:
homeostatic
Pertaining to homeostasis.
Wikipedia:
homeostasis
Homeostasis is the property of either an open system or a closed system, especially a living organism, to regulate the state of its internal environment so as to maintain a stable, constant condition. Multiple dynamic equilibrium adjustments, through regulation mechanisms, make homeostasis possible. The term was coined in 1932 by Walter Bradford Cannon from the Greek homoios (same, like, resembling) and stasis (to stand, posture).
Biological homeostasis
With regard to any given life system parameter, an organism may be a regulator or a conformer. Regulators try to maintain key state(s) of the system within a narrow range of values over possibly wide ambient environmental variations, bearing similarity to how negative feedback is used in biocybernetic control systems. This is the most common usage of the term in physiology and biomedical engineering textbooks. On the other hand, conformers allow the environment to determine the parameter. For instance, endothermic animals maintain a constant body temperature, while ectothermic animals exhibit wide body temperature variation.
This is not to say that conformers don't have behavioural adaptations allowing them to exert some control over a given parameter. For instance, reptiles often rest on sun-heated rocks in the morning to raise their body temperature. Likewise, regulators' behaviors may contribute to their internal stability: The same sun-baked rock may host a ground squirrel, also basking in the morning sun.
An advantage of homeostatic regulation is that it allows an organism to function effectively in a broad range of environmental conditions. For example, ectotherms tend to become sluggish at low temperatures, while a co-located endotherm may be fully active. That thermal stability comes at a price since an automatic regulation system requires additional energy. One reason snakes may eat only once a week is that they use much less energy to maintain homeostasis.
Control Mechanisms
All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: The receptor is the sensing component that monitors and responds to changes in the environment. When the receptor senses a stimulus, it sends information to a control center, the component that sets the range at which a variable is maintained. The control center determines an appropriate response to the stimulus. The result of that response feeds to the receptor, either enhancing it with positive feedback or depressing it with negative feedback [1]
Negative Feedback Mechanisms
Negative feedback mechanisms reduce or suppress the original stimulus, given the effector’s output. Most homeostatic control mechanisms require a negative feedback loop to keep conditions from exceeding tolerable limits. The purpose is to prevent sudden severe changes within a complex organism. There are hundreds of negative feedback mechanisms in the human body. Among the most important regulatory functions are: thermoregulation, osmoregulation, and glucoregulation. The kidneys contribute to homeostasis in four important ways: regulation of blood water levels, reabsorption of substances into the blood, maintenance of salt and ion levels in the blood, and excretion of urea and other wastes.
A negative feedback mechanism example is the typical home heating system. Its thermostat houses a thermometer, the receptor that
senses when the temperature is too low. The control center, also housed in the thermostat, senses and responds to the thermometer
when the temperature drops below a specified set point. Below that target level, the thermostat sends a message to the effector,
the furnace. The furnace then produces heat, which warms the house. Once the thermostat senses a target level of heat has been
reached, it will signal the furnace to turn off, thus maintaining a comfortable temperature - not too hot nor cold. [1]
Positive Feedback Mechanisms
Positive feedback mechanisms are designed to accelerate or enhance the output created by a stimulus that has already been activated.
Unlike negative feedback mechanisms that initiate to maintain or regulate physiological functions within a set and narrow range, the positive feedback mechanisms are designed to push levels out of normal ranges. To achieve this purpose, a series of events initiates a cascading process that builds to increase the effect of the stimulus. This process can be beneficial but is rarely used by the body due to risks of the acceleration becoming uncontrollable.
One bodily positive feedback example event is blood platelet accumulation which in turn causes
Positive feedback can also be harmful. An example being when you have a fever it causes a positive feedback within homeostasis
that pushes the temperature continually higher. Body temperature can reach extremes of 45ºC (113ºF), at which cellular proteins
denature, causing the active site in proteins to change, thus causing metabolism stop and ultimately resulting in death.
Homeostatic Imbalance
Much disease results from disturbance of homeostasis, a condition known as homeostatic imbalance. As it ages, every organism will lose efficiency in its control systems. The inefficiencies gradually result in an unstable internal environment that increases the risk for illness. In addition, homeostatic imbalance may be viewed as partially responsible for the physical changes associated with aging. Heart failure has been seen where nominal negative feedback mechanisms become overwhelmed, and destructive positive feedback (or sometimes competing negative feedback) mechanisms then take over.[1] The term allostatis is often used to capture phenomena related to physiological imbalances.
Varieties of homeostasis
The Dynamic Energy Budget theory for metabolic organisation delineates structure and (one or more) reserves in an organism. Its formulation is based on three forms of homeostasis:
- Strong homeostasis is where structure and reserve do not change in composition. Since the amount of reserve and structure can vary, this allows a particular change in the composition of the whole body (as explained by the Dynamic Energy Budget theory).
- Weak homeostasis is where the ratio of the amounts of reserve and structure becomes constant as long as food availability is constant, even when the organism grows. This means that the whole body composition is constant during growth in constant environments.
- Structural homeostasis means that the sub-individual structures grow in harmony with the whole individual; the relative proportions of the individuals remain constant.
Ecological homeostasis
Ecological homeostasis is found in a climax community of maximum permitted biodiversity, given the prevailing ecological conditions.
In disturbed ecosystems or sub-climax biological communities such as the island of Krakatoa, after its major eruption in 1883, the established stable homeostasis of the previous forest climax ecosystem was destroyed and all life eliminated from the island. In the years after the eruption, Krakatoa went through a sequence of ecological changes in which successive groups of new plant or animal species followed one another, leading to increasing biodiversity and eventually culminating in a re-established climax community. This ecological succession on Krakatoa occurred in a number of several stages, in which a sere is defined as "a stage in a sequence of events by which succession occurs". The complete chain of seres leading to a climax is called a prisere. In the case of Krakatoa, the island as reached its climax community with eight hundred different species being recorded in 1983, one hundred years after the eruption which cleared all life off the island. Evidence confirms that this number has been homeostatic for some time, with the introduction of new species rapidly leading to elimination of old ones.
The evidence of Krakatoa, and other disturbed or virgin ecosystems shows that the initial colonisation by pioneer or R strategy species occurs through positive feedback reproduction strategies, where species are weeds, producing huge numbers of possible offspring, but investing little in the success of any one. Rapid boom and bust plague or pest cycles are observed with such species. As an ecosystem starts to approach climax these species get replaced by more sophisticated climax species which through negative feedback, adapt themselves to specific environmental conditions. These species, closely controlled by carrying capacity, follow K strategies where species produce fewer numbers of potential offspring, but invest more heavily in securing the reproductive success of each one to the micro-environmental conditions of its specific ecological niche.
It begins with a pioneer community and ends with a climax community. This climax community occurs when the ultimate vegetation has become in equilibrium with the local environment.
Such ecosystems form nested communities or heterarchies, in which homeostasis at one level, contributes to homeostatic processes at another holonic level. For example, the loss of leaves on a mature rainforest tree gives a space for new growth, and contributes to the plant litter and soil humus build-up upon which such growth depends. Equally a mature rainforest tree reduces the sunlight falling on the forest floor and helps prevent invasion by other species. But trees too fall to the forest floor and a healthy forest glade is dependent upon a constant rate of forest regrowth, produced by the fall of logs, and the recycling of forest nutrients through the respiration of termites and other insect, fungal and bacterial decomposers. Similarly such forest glades contribute ecological services, such as the regulation of microclimates or of the hydrological cycle for an ecosystem, and a number of different ecosystems act together to maintain homeostasis perhaps of a number of river catchments within a bioregion. A diversity of bioregions similarly makes up a stable homeostatic biological region or biome.
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 homeostasis. Whether this sort of system is present on Earth is still open to debate. However, some relatively simple homeostatic mechanisms are generally accepted. For example, when atmospheric carbon dioxide levels rise, certain plants are able to grow better and thus act to remove more carbon dioxide from the atmosphere. When sunlight is plentiful and atmospheric temperature climbs, the phytoplankton of the ocean surface waters 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. As scientists discover more about Gaia, 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.
Reactive homeostasis
Example of use: "Reactive homeostasis is an immediate response to a homeostatic challenge such as predation."
However, any homeostasis is impossible without reaction - because homeostasis is and must be a "feedback" phenomenon.
The phrase "reactive homeostasis" is simply short for: "reactive compensation reestablishing homeostasis", that is to say, "reestablishing a point of homeostasis." - it should not be confused with a separate kind of homeostasis or a distinct phenomenon from homeostasis, it is simply the compensation (or compensatory) phase of homeostasis.
Other fields
The term has come to be used in other fields, as well.
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 they unconsciously compensate for the safer vehicle via less-safe driving habits. Previously, 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 behavior known to be dangerous continues until dramatic consequences actually occur.
Stress homeostasis
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. [citation needed]
Jean Francois Lyotard, a postmodern theorist, has applied this term to societal 'power centers' that he describes 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. (See "The Postmodern Condition: A Report on Knowledge" by J.F. Lyotard)
Waste homeostasis
Andrew Potter has used the term waste homeostasis in reference to the lack of net gain from energy saving technologies.[2]
Conversational homeostasis
A 2007 study purported to find (and show clinically) conversational homeostasis in which overly-familiar people (such as spouses) condense their speech so much that they are actually worse at communicating novel information than strangers are, while not being conscious of this problem. [3]
Metabolic homeostasis
Some herbal medicines, known as adaptogens, have been defined to function as non-toxic metabolic regulators that can enhance metabolic homeostasis during stress.[4]
See also
References
- ^ a b c d Marieb, Elaine N. & Hoehn, Katja (2007). Human Anatomy & Physiology (Seventh ed.). San Francisco, CA: Pearson Benjamin Cummings.
- ^ Potter, Andrew (2007), "Planet-friendly design? Bah, humbug.", MacLean's 120 (5): 14, <http://www.macleans.ca>
- ^ Keysar, Boaz (2007), "The Effect of Information Overlap on Communication Effectiveness", Cognitive Science, <http://www.eurekalert.org/pub_releases/2007-02/uoc-wec022007.php>
- ^ Winston, David & Maimes, Steven. “ADAPTOGENS: Herbs for Strength, Stamina, and Stress Relief,” Healing Arts Press, 2007.
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| World of the Body. The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved. Read more |
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| Food and Fitness. Food and Fitness: A Dictionary of Diet and Exercise. Copyright © 1997, 2003 by Oxford University Press. All rights reserved. Read more |
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| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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- osmoregulation
- stressor
- bicarbonate
- allostasis (psychology)
- medulla oblongata
- steady state
- allostatic load (psychology)
- metallothionein (biochemistry)
- International Society for the Study of Subtle Energies and Energy Medicine (parapsychology)
- homeo– (prefix)
- –stasis (suffix)
- Life Support: Purpose
- negative feedback
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