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Homeostasis

Not to be confused withhemostasis.

Homeostasis,also spelled homoeostasis(fromGreek:, hmoios, similar), is the property of a sys-tem in which variables are regulated so that internal con-ditions remain stable and relatively constant. Examplesof homeostasis include the regulation of temperature andthe balance between acidity and alkalinity (pH). It is aprocess that maintains the stability of the human bodysinternal environment in response to changes in external

conditions.The concept was described byClaude Bernardin 1865and the word was coined byWalter Bradford Cannonin1926.[1] Although the term was originally used to refer toprocesses within living organisms, it is frequently appliedto automaticcontrol systemssuch asthermostats. Home-ostasis requires a sensor to detect changes in theconditionto be regulated, an effector mechanism that can vary thatcondition; and anegative feedbackconnection betweenthe two.

1 Examples from technology

The following are all examples of familiar homeostaticmechanisms:

A thermostatoperates by switching heaters or air-conditioners on and off in response to the output ofa temperature sensor.

Cruise controladjusts a cars throttle in response tochanges in speed.

Anautopilotoperates the steering controls of an air-craft or ship in response to deviation from a pre-setcompass bearing or route.

Process control systems in a chemical plant or oil re-finerymaintain fluid levels, pressures, temperature,chemical composition, etc. by controlling heaters,pumps and valves.

Thecentrifugal governorof asteam engine, as de-signed byJames Wattin 1788, reduces the throttle

valve in response to increases in the engine speed, oropens the valve if the speed falls below the pre-setrate.

2 Biological

Further information:Human homeostasis

All living organisms depend on maintaining a complexset of interactingmetabolicchemical reactions. From thesimplest unicellular organisms to the most complex plantsand animals, internal processes operate to keep the con-ditions within tight limits to allow these reactions to pro-ceed. Homeostatic processes act at the level of the cell,thetissue, and theorgan, as well as for theorganismas awhole.

Principal Homeostatic processes include the following:

Warm-blooded (endothermic)animals(mammalsand birds) maintain a constant body temperature,whereas ectothermicanimals (almost all other an-imals) exhibit wide bodytemperature variation.[2]

An advantage of temperature regulation is that it al-lows anorganismto function effectively in a broadrange of environmental conditions. For example,

ectothermstend to become sluggish at low tempera-tures, whereas a co-located endotherm may be fullyactive. That thermal stability comes at a price, sincean automatic regulation system requires additionalenergy.[2] If the temperature rises, the body losesheat by sweating or panting, via thelatent heatofevaporation. If it falls, this is counteracted by in-creased metabolic action, by shivering, andin fur-or feather-coated creaturesby thickening the coat.

Thermal image of a cold-bloodedtarantula(ectothermic) on a

warm-blooded human hand (endothermic).

Regulation of thepHof the blood at 7.365 (a mea-sure of alkalinity and acidity).

1

https://en.wikipedia.org/wiki/PH#Living_systemshttps://en.wikipedia.org/wiki/Endothermhttps://en.wikipedia.org/wiki/Ectothermhttps://en.wikipedia.org/wiki/Tarantulahttps://en.wikipedia.org/wiki/Evaporationhttps://en.wikipedia.org/wiki/Latent_heathttps://en.wikipedia.org/wiki/Ectothermshttps://en.wikipedia.org/wiki/Organismhttps://en.wikipedia.org/wiki/Temperaturehttps://en.wikipedia.org/wiki/Ectothermhttps://en.wikipedia.org/wiki/Animalhttps://en.wikipedia.org/wiki/Endothermhttps://en.wikipedia.org/wiki/Organismhttps://en.wikipedia.org/wiki/Organ_(anatomy)https://en.wikipedia.org/wiki/Tissue_(biology)https://en.wikipedia.org/wiki/Cell_(biology)https://en.wikipedia.org/wiki/Metabolichttps://en.wikipedia.org/wiki/Human_homeostasishttps://en.wikipedia.org/wiki/James_Watthttps://en.wikipedia.org/wiki/Steam_enginehttps://en.wikipedia.org/wiki/Centrifugal_governorhttps://en.wikipedia.org/wiki/Oil_refineryhttps://en.wikipedia.org/wiki/Oil_refineryhttps://en.wikipedia.org/wiki/Chemical_planthttps://en.wikipedia.org/wiki/Process_controlhttps://en.wikipedia.org/wiki/Autopilothttps://en.wikipedia.org/wiki/Cruise_controlhttps://en.wikipedia.org/wiki/Thermostathttps://en.wikipedia.org/wiki/Negative_feedbackhttps://en.wikipedia.org/wiki/Sensorhttps://en.wikipedia.org/wiki/Thermostathttps://en.wikipedia.org/wiki/Control_systemshttps://en.wikipedia.org/wiki/Walter_Bradford_Cannonhttps://en.wikipedia.org/wiki/Claude_Bernardhttps://en.wikipedia.org/wiki/PHhttps://en.wikipedia.org/wiki/List_of_Greek_words_with_English_derivativeshttps://en.wikipedia.org/wiki/American_and_British_English_differenceshttps://en.wikipedia.org/wiki/Hemostasis

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2 2 BIOLOGICAL

All animals also regulate their blood glucosecon-centration. Mammalsregulate their blood glucosewithinsulinandglucagon. The human body main-tains glucose levels constant most of the day, evenafter a 24-hour fast. Even during long periodsof fasting, glucose levels are reduced only very

slightly.[3] Insulin, secreted by the beta cells of thepancreas, effectively transports glucose to the bodyscells by instructing those cells to keep more of theglucose for their own use (see Dynamic equilib-rium). If the glucose inside the cells is high, the cellswill convert it to the insoluble glycogento preventthe soluble glucose from interfering with cellularmetabolism. Ultimately this lowers blood glucoselevels, and insulin helps to preventhyperglycemia.When insulin is deficient or cells become resistantto it,diabetesoccurs. Glucagon, secreted by the al-pha cells of the pancreas, encourages cells to break

down stored glycogen or convert non-carbohydratecarbon sources to glucose viagluconeogenesis, thuspreventinghypoglycemia.

Thekidneysare used to remove excess water andions from the blood. These are then expelled asurine. The kidneys perform a vital role in homeo-static regulation in mammals, removing excess wa-ter, salt, andureafrom the blood.

If the water content of the blood andlymphfluidfalls, it is restored in the first instance by extractingwater from the cells. The throat and mouth become

dry, so that the symptoms of thirst motivate the an-imal to drink.

If the oxygen content of the blood falls, or thecarbon-dioxide concentration increases, blood flowis increased by more vigorous heart action and thespeed and depth of breathing increases.

Sleep timing depends upon a balance betweenhomeostatic sleep propensity, the need for sleep as afunction of the amount of time elapsed since the lastadequate sleep episode, andcircadian rhythmsthatdetermine the ideal timing of a correctly structuredand restorative sleep episode.[4]

Personality traits are often conceptualized as a per-son specific setpoint level around which mood statesfluctuate in time.[5]

2.1 Control mechanisms

All homeostatic control mechanisms have at least threeinterdependent components for the variable being regu-lated: Thereceptoris the sensing component that moni-

tors and responds to changes in the environment. Whenthe receptor senses a stimulus, it sends information toa control center, the component that sets the range at

which a variable is maintained. The control center deter-mines an appropriate response to the stimulus. The con-trol center then sends signals to an effector, which canbe muscles, organs, or other structures that receive sig-nals from the control center. After receiving the signal,a change occurs to correct the deviation by depressing it

withnegative feedback.[6]

2.1.1 Negative feedback

Negative feedback mechanisms consist of reducing theoutput or activity of any organ or system back to its nor-mal range of functioning. A good example of this isregulatingblood pressure.Blood vesselscan sense resis-tance of blood flow against the walls when blood pres-sure increases. The blood vessels act as the receptorsand they relay this message to thebrain. The brain then

sends a message to the heart and blood vessels, bothof which are the effectors. The heart rate would de-crease as the blood vessels increase indiameter(knownas vasodilation). This change would cause the blood pres-sure to fall back to its normal range. The opposite wouldhappen when blood pressure decreases, and would causevasoconstriction.

Another important example is seen when the body is de-prived of food. The body would then reset the metabolicset point to a lower than normal value. This would allowthe body to continue to function, at a slower rate, eventhough the body is starving. Therefore, people depriving

themselves of food while trying to lose weight would findit easy to shed weight initially and much harder to losemore after. This is due to the bodys readjusting itself toa lower metabolic set-point to allow the body to survivewith its low supply of energy. Exercise can change thiseffect by increasing the metabolic demand.

Another good example of negative feedback mechanismis temperature control. Thehypothalamus, which moni-tors the body temperature, is capable of determining eventhe slightest variation of normal body temperature (36.5degrees Celsius). Response to such variation could bestimulation of glands that produce sweat to reduce the

temperature or signaling various muscles to shiver to in-crease body temperature.

Both feedbacks are equally important for the healthyfunctioning of ones body. Complications can arise if anyof the two feedbacks are affected or altered in any way.

2.2 Homeostatic imbalance

Many diseases involve a disturbance of homeostasis.

As the organism ages, the efficiency in its control systemsbecomes reduced. The inefficiencies gradually result in

an unstable internal environment that increases the riskof illness, and leads to the physical changes associatedwith aging.[6]

https://en.wikipedia.org/wiki/Celsiushttps://en.wikipedia.org/wiki/Hypothalamushttps://en.wikipedia.org/wiki/Vasoconstrictionhttps://en.wikipedia.org/wiki/Vasodilationhttps://en.wikipedia.org/wiki/Diameterhttps://en.wikipedia.org/wiki/Hearthttps://en.wikipedia.org/wiki/Brainhttps://en.wikipedia.org/wiki/Blood_vesselhttps://en.wikipedia.org/wiki/Blood_pressurehttps://en.wikipedia.org/wiki/Negative_feedbackhttps://en.wiktionary.org/wiki/receptorhttps://en.wikipedia.org/wiki/Circadian_rhythmhttps://en.wikipedia.org/wiki/Lymphhttps://en.wikipedia.org/wiki/Ureahttps://en.wikipedia.org/wiki/Urinehttps://en.wikipedia.org/wiki/Kidneyhttps://en.wikipedia.org/wiki/Hypoglycemiahttps://en.wikipedia.org/wiki/Gluconeogenesishttps://en.wikipedia.org/wiki/Diabetes_mellitushttps://en.wikipedia.org/wiki/Hyperglycemiahttps://en.wikipedia.org/wiki/Glycogenhttps://en.wikipedia.org/wiki/Dynamic_equilibriumhttps://en.wikipedia.org/wiki/Dynamic_equilibriumhttps://en.wikipedia.org/wiki/Glucagonhttps://en.wikipedia.org/wiki/Insulinhttps://en.wikipedia.org/wiki/Mammalhttps://en.wikipedia.org/wiki/Blood_glucose

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[6] Marieb, Elaine N., Hoehn, Katja N. (2009). Essen-tials of Human Anatomy & Physiology (9th ed. ed.).San Francisco, CA: Pearson/Benjamin Cummings.ISBN0321513428.

[7] Mayer, Emeran A. (2011-08). Gut feelings: the emerg-ing biology of gut-brain communication. Nature ReviewsNeuroscience 12 (8): 453466. doi:10.1038/nrn3071.Check date values in: |date= (help)

[8] George Leonards Mastery / Getting Stronger

[9] Review of George Leonards Mastery: Why resolutionsfail? Role of the homeostasis | Procrastination Help

10 Further reading

Banci, Lucia (Ed.), ed. (2013). Chapter 3Sodium/Potassium homeostasis, Chapter 5 Calciumhomeostasis, Chapter 6 Manganese homeostasis.Metallomics and the Cell. Metal Ions in Life Sci-ences 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 1559-0836electronic-ISSN 1868-0402

11 External links

Homeostasis

Peristasis

http://www.danko-nikolic.com/peristasis/http://www.biology-innovation.co.uk/pages/human-biology/homeostasis/https://www.worldcat.org/search?fq=x0:jrnl&q=n2:1868-0402https://en.wikipedia.org/wiki/International_Standard_Serial_Numberhttps://www.worldcat.org/search?fq=x0:jrnl&q=n2:1559-0836https://en.wikipedia.org/wiki/International_Standard_Serial_Numberhttps://en.wikipedia.org/wiki/Special:BookSources/9789400755611https://en.wikipedia.org/wiki/Special:BookSources/978-94-007-5560-4https://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://dx.doi.org/10.1007%252F978-94-007-5561-1_3http://dx.doi.org/10.1007%252F978-94-007-5561-1_3https://en.wikipedia.org/wiki/Digital_object_identifierhttp://www.procrastinationhelp.com/procrastination/why-resolutions-fail.htmlhttp://www.procrastinationhelp.com/procrastination/why-resolutions-fail.htmlhttp://gettingstronger.org/2010/03/george-leonards-mastery/https://en.wikipedia.org/wiki/Help:CS1_errors#bad_datehttp://dx.doi.org/10.1038%252Fnrn3071https://en.wikipedia.org/wiki/Digital_object_identifierhttps://en.wikipedia.org/wiki/Special:BookSources/0321513428https://en.wikipedia.org/wiki/International_Standard_Book_Number

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