Homeostasis (from Greek: ὅμος, homos, "equal"; and ιστημι, histemi, "to stand" lit. "to stand equally"; coined by Walter Bradford Cannon) is the property of either an open system or a closed system, especially a living organism, that regulates its internal environment so as to maintain a stable, constant condition. Walter Bradford Cannon ( October 19, 1871 &ndash October 19, 1945) was an American Physiologist, Professor and chairman An open system is a state of a System, in which a system continuously interacts with its environment A Closed system is a System in the state of being isolated from the environment Multiple dynamic equilibrium adjustments and regulation mechanisms make homeostasis possible. A dynamic equilibrium occurs when two opposing Processes proceed at the same rate The concept was created by Claude Bernard, often considered as the father of physiology, and published in 1865. Claude Bernard ( July 12, 1813 – February 10, 1878) was a French Physiologist. Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical

Biological homeostasis

Further information: Human homeostasis

With regard to any given life system parameter, an organism may be a conformer or a regulator. Human homeostasis refers to the body's ability to regulate its internal physiology to maintain stability in response to fluctuations in the outside environment In Mathematics, Statistics, and the mathematical Sciences a parameter ( G auxiliary measure) is a quantity that defines certain characteristics Regulators try to maintain the parameter at a constant level over possibly wide ambient environmental variations. 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. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Examples of endothermic animals include mammals and birds, examples of ectothermic animals include reptiles and some sea animals. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers

This is not to say that conformers don't have behavioural adaptations allowing them to exert some control over a given parameter. Behavior or behaviour (see spelling differences) refers to the actions or Reactions of an object or Organism, usually An adaptation is a characteristic of an Organism that has been favored by Natural selection and For instance, reptiles often rest on sun-heated rocks in the morning to raise their body temperature. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers The Sun (Sol is the Star at the center of the Solar System. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Vice versa, regulators are usually responsive to external circumstances: if the same sun-baked boulder happens to host a ground squirrel, its metabolism will adjust to the lesser need for internal heat production.

Thermal image of a cold-blooded tarantula on a warm-blooded human hand

An advantage of homeostatic regulation is that it allows an organism to function effectively in a broad range of environmental conditions. Tarantula is the common name for a group of hairy and often very large Spiders belonging to the family Theraphosidae, of which approximately 900 species For example, ectotherms tend to become sluggish at low temperatures, whereas 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. A snake is an elongate Reptile of the suborder Serpentes Like all reptiles snakes are covered in scales.

Most homeostatic regulation is controlled by the release of hormones into the bloodstream. However other regulatory processes rely on simple diffusion to maintain a balance.

Homeostatic regulation extends far beyond the control of temperature. All animals also regulate their blood glucose, as well as the concentration of their blood. Blood sugar, used in a physiological context is a misnomer and misleading Mammals regulate their blood glucose with insulin and glucagon. Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Glucagon is an important Hormone involved in Carbohydrate metabolism. These hormones are released by the pancreas. If the pancreas is for any reason unable to produce enough of these two hormones diabetes results. Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc The kidneys are used to remove excess water and ions from the blood. The kidneys are complicated organs that have numerous biological roles These are then expelled as urine. Urine is a liquid waste product of the body secreted by the Kidneys by a process of filtration from Blood and Excreted through the Urethra. The kidneys perform a vital role in homeostatic regulation in mammals, removing excess water, salt, and urea from the blood. These are the body's main waste products.

Sleep timing depends upon a balance between homeostatic sleep propensity, 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. ^[1]

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 effector, either enhancing it with positive feedback or depressing it with negative feedback ^[2]

Negative Feedback Mechanisms

Negative feedback mechanisms reduce or suppress the original stimulus, given the effector’s output. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated 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. Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different 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 Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of Carbohydrates The kidneys contribute to homeostasis in five important ways: regulation of 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 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. ^[2]

Positive Feedback Mechanisms

Positive feedback is a mechanism by which an output is enhanced, such as protein levels. however, in order to avoid any fluctuation in the protein level, the mechanism is inhibited stochastically (I), therefore when the concentration of the activated protein (A) is past the threshold ([I]), the loop mechanism is activated and the concetration of A increases exponentially if d[A]=k [A]

Positive feedback mechanisms are designed to accelerate or enhance the output created by a stimulus that has already been activated. Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction

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 positive feedback example event in the body is blood platelet accumulation, which, in turn, causes blood clotting in response to a break or tear in the lining of blood vessels. Platelets, or Thrombocytes, are small cytoplasmic bodies derived from cells They circulate in the Blood of Mammals and are involved Coagulation is a complex process by which Blood forms Clots It is an important part of Hemostasis (the cessation of blood loss from a damaged vessel whereby Another example is the release of oxytocin to intensify the contractions that take place during childbirth. Oxytocin ( IPA: /ˌɔksɪˈtoʊsɪn/ (Greek "quick birth" is a Mammalian Hormone that also acts as a Neurotransmitter in the ^[2]

Positive feedback can also be harmful. One particular example is when a fever causes a positive feedback within homeostasis that pushes the temperature continually higher. Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris Body temperature can reach extremes of 45°C (113°F), at which cellular proteins denature, causing the active site in proteins to change, thus causing metabolism to stop, 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 is also responsible for the physical changes associated with aging. Even more serious than illness and other characteristics of aging, is death. Heart failure has been seen where nominal negative feedback mechanisms become overwhelmed, and destructive positive feedback mechanisms then take over. ^[2]

Diseases that result from a homeostatic imbalance include diabetes, dehydration, hypoglycemia, hyperglycemia, gout, and any disease caused by a toxin present in the bloodstream. Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc Dehydration ( hypohydration) is the removal of Water ( hydro in ancient Greek) from an object Hypoglycemia or hypoglycaemia is the medical term for a pathologic state produced by a lower than normal level of Glucose ( sugar) in the blood Hyperglycemia, hyperglycaemia, or high blood sugar is a condition in which an excessive amount of Glucose circulates in the Blood plasma Gout (also called metabolic arthritis) is a disease created by a buildup of Uric acid. All of these conditions result from the presence of an increased amount of a particular substance. In ideal circumstances, homeostatic control mechanisms should prevent this imbalance from occurring, but, in some people, the mechanisms do not work efficiently enough or the quantity of the substance exceeds the levels at which it can be managed. In these cases, medical intervention is necessary to restore the imbalance, or permanent damage to the organs may result.

Varieties of homeostasis

The Dynamic Energy Budget theory for metabolic organisation delineates structure and (one or more) reserves in an organism. Dynamic Energy Budget (DEB theory aims to identify simple quantitative rules for the organization of Metabolism of individual organisms that can be understood from basic first Its formulation is based on three forms of homeostasis:

• Strong homeostasis, wherein 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). Dynamic Energy Budget (DEB theory aims to identify simple quantitative rules for the organization of Metabolism of individual organisms that can be understood from basic first
• Weak homeostasis, wherein 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, wherein 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. The term climax community, also described as a climatic climax community, is an ecological term for a biological community of Plants and Biodiversity is the variation of Life forms within a given Ecosystem, Biome or for the entire Earth.

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. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( A biocoenosis (alternatively biocoenose or biocenose) termed by Karl Möbius in 1877 describes all the interacting Organisms living together Krakatoa ( Indonesian: Krakatau) also spelled Krakatao or Krakatowa, is a volcanic island in the Sunda Strait A forest is an area with a high density of Trees There are many definitions of a forest based on various criteria 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". Ecological succession, a fundamental concept in Ecology, refers to more-or-less predictable and orderly changes in the composition or structure of an ecological community SERE, an Acronym for S urvival E vasion R esistance and E scape is a U The complete chain of seres leading to a climax is called a prisere. A seral community (or sere) is an intermediate stage found in Ecological succession in an ecosystem advancing towards its Climax community. 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 that 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, wherein species are weeds, producing huge numbers of possible offspring, but investing little in the success of any one. In Ecology, r/K selection theory relates to the selection of traits which promote success in particular environments WEED (1390 AM) is a Radio station broadcasting a Spanish format Rapid boom and bust plague or pest cycles are observed with such species. In Economics, the term boom and bust refers to the movement of an economy through Economic cycles. A pest is an organism which has characteristics that are regarded by Humans as injurious or unwanted 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, wherein 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. The supportable Population of an Organism, given the food habitat, water and other necessities available within an environment is known as the environment's In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living

It begins with a pioneer community and ends with a climax community. This climax community occurs when the ultimate vegetation has achieved 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. A holon ( Greek: holos, "whole" is something that is simultaneously a Whole and a Part. For example, the loss of leaves on a mature rainforest tree creates space for new growth, and contributes to the plant litter and soil humus build-up upon which such growth depends. Plant litter (sometimes called leaf litter or tree litter) is dead Plant material such as leaves, Bark, and Twigs Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Humus (Origin 1790–1800 Latin: earth ground) is the organic material in Soil lending it a dark brown or black colouration Of equal importance, 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. A glade is an open area within a woodland Glades are a lot like Prairies but offer little or no soil for trees to grow on Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have In a similar manner, 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 microclimate is a local atmospheric zone where the Climate differs from the surrounding area The Earth 's Water is always in movement and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on above An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( "Riverine" redirects here For the use of that term in Maritime geography, see there A catchment is any device or structure that captures Water. An ecoregion ( ecological region) sometimes called a bioregion, is an ecologically and geographically defined area smaller than a "realm" or " A diversity of bioregions, in like manner, makes up a stable homeostatic biological region or biome. A biome is a climatically and geographically defined area of ecologically similar climatic conditions such as communities of Plants Animals and

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. The Gaia hypothesis is an ecological Hypothesis proposing that the Biosphere and the physical components of the Earth ( Atmosphere Dr James Ephraim Lovelock, CH, CBE, FRS (born 26 July 1919) is an independent scientist author researcher environmentalist and A superorganism is an Organism consisting of many organisms This is usually meant to be a Social unit of eusocial animals where Division of labour 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. Phytoplankton are the Autotrophic component of the Plankton community Dimethyl sulfide (DMS or methylthiomethane is an organosulfur compound with the formula (CH32S 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. Cloud condensation nuclei or CCN s (also known as cloud seeds) are small particles (typically 0 The albedo of an object is the extent to which it diffusely reflects light from the sun 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

Main article: risk homeostasis

An actuary may refer to risk homeostasis, where (for example) people that have anti-lock brakes have no better safety record than those without anti-lock brakes, because the former unconsciously compensate for the safer vehicle via less-safe driving habits. Risk homeostasis is a Risk theory developed by Gerald JS Wilde a professor emeritus of psychology at Queen's University, Kingston Ontario, Canada An actuary is a business professional who deals with the financial impact of risk and uncertainty 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 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.

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. The Rebel Sell Why the culture can't be jammed (US release Nation of Rebels Why Counterculture Became Consumer Culture) is a popular Non-fiction The term rebound effect is used in conservation energy economics and green marketing ^[3]

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. ^[4]

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. The term adaptogen is used by Herbalists to refer to a natural herb product that is proposed to increase the body's resistance to Stress, trauma ^[5]

See also

References