Human homeostasis 1

Human homeostasisHuman homeostasis refers to the body's ability to physiologically regulate its inner environment to ensure itsstability in response to fluctuations in the outside environment and the weather. The liver, the kidneys, and the brain(hypothalamus, the autonomic nervous system and the endocrine system[1] ) help maintain homeostasis. The liver isresponsible for metabolizing toxic substances and maintaining carbohydrate metabolism. The kidneys areresponsible for regulating blood water levels, re-absorption of substances into the blood, maintenance of salt and ionlevels in the blood, regulation of blood pH, and excretion of urea and other candies.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 destructivepositive feedback mechanisms take over.[2] Other diseases which result from a homeostatic imbalance includediabetes, dehydration, hypoglycemia, hyperglycemia, gout and any disease caused by the presence of a toxin in thebloodstream. Medical intervention can help restore homeostasis and possibly prevent permanent damage to theorgans.

TemperatureHumans are warm-blooded, maintaining a near-constant body temperature. Thermoregulation is an important aspectof human homeostasis. Heat is mainly produced by the liver and muscle contractions. Humans have been able toadapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses forthe 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 positivefeedback, when temperature reaches extremes of 45°C (113°F), at which cellular proteins denature, causing theactive site in proteins to change, thus causing metabolism stop and ultimately death.

IronIron is an essential element for human beings. The control of this necessary but potentially toxic substance is animportant part of many aspects of human health and disease. Hematologists have been especially interested in thesystem of iron metabolism because iron is essential to red blood cells. In fact, most of the human body's iron iscontained 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 increasein ferroportin activity, stimulating iron uptake in the digestive system. An iron surplus will stimulate the reverse ofthis process.In individual cells, an iron deficiency causes responsive element binding protein (IRE-BP) to bind to iron responsiveelements (IRE) on mRNAs for transferrin receptors, resulting in increased production of transferrin receptors. Thesereceptors increase binding of transferrin to cells, and therefore stimulating iron uptake.

Human homeostasis 2

EnergyEnergy 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 thetemperature of 1 kg of water by 1 °C. This is about 4.184 kJ.

Blood compositionThe balance of many blood solutes belongs to the scope of renal physiology.

SugarBlood 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 bodycells 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 sugarlevels.If the pancreas is for any reason unable to produce enough of these two hormones, diabetes results.

OsmoregulationOsmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of thebody's water content; that is it keeps the body's fluids from becoming too dilute or too concentrated. Osmoticpressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher theosmotic 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 thenexpelled as urine.

Pressure

The renin-angiotensin system.[3]

The renin-angiotensin system (RAS) is a hormone system that helps regulatelong-term blood pressure and extracellular volume in the body.

Human homeostasis 3

Calcium

Calcium regulation in the human body.[4]

When blood calcium becomes too low, calcium-sensingreceptors in the parathyroid gland become activated.This results in the release of PTH, which acts toincrease blood calcium, e.g. by release from bones(increasing the activity of bone-degrading cells calledosteoclasts). This hormone also causes calcium to bereabsorbed from urine and the GI tract.

Calcitonin, released from the C cells in the thyroidgland, works the opposite way, decreasing calciumlevels in the blood by causing more calcium to be fixedin bone.

Acid-base

The kidneys maintain acid-base homeostasis byregulating the pH of the blood plasma. Gains and lossesof acid and base must be balanced. The study of theacid-base reactions in the body is acid base physiology.

Volume

The body's homeostatic control mechanisms, which maintain a constant internal environment, ensure that a balancebetween fluid gain and fluid loss is maintained. The hormones ADH (Anti-diuretic Hormone, also known asvasopressin) 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 lessretention 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 respirateheavily not due to low oxygen(O2) content in the blood, but because they have too much CO2.

HemostasisHemostasis 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 themajority of control mechanisms in human body, the hemostasis utilizes positive feedback, for the more the clotgrows, the more clotting occurs, until the blood stops. Another example of positive feedback is the release ofoxytocin to intensify the contractions that take place during childbirth.[2]

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SleepSleep timing depends upon a balance between homeostatic sleep propensity, the need for sleep as a function of theamount of time elapsed since the last adequate sleep episode, and circadian rhythms which determine the idealtiming of a correctly structured and restorative sleep episode.[5]

Extracellular fluidThe kidneys, by regulating the blood composition, also controls the extracellular fluid homeostasis.

References[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" (http:/ / ajpregu. physiology. org/ cgi/ content/ full/ 277/ 4/R1152). Am J Physiol 277 (4): R1152–R1163. Fulltext. PMID 10516257. . Retrieved 2007-11-25. "... significant homeostatic and circadianmodulation of sleep structure, with the highest sleep efficiency occurring in sleep episodes bracketing the melatonin maximum and core bodytemperature minimum".

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Article Sources and ContributorsHuman homeostasis  Source: http://en.wikipedia.org/w/index.php?oldid=395511889  Contributors: ABF, Access Denied, Anetode, Bobo192, Bogey97, Daughter of Mímir, Denver777, ErkanYilmaz, Favonian, Fogster, Franamax, Fratrep, GrahamColm, Hordaland, Isoxyl, JCarlson486, Jbolden1517, Jeff G., Jeffq, JimVC3, Keilana, Lankiveil, LittleHow, Lova Falk, Lperez2029,Lunapaws, Marek69, Memstone, Mikael Häggström, Petiatil, Philip Trueman, Piano non troppo, Rich Farmbrough, RobertL, Skater, Tide rolls, Tommy2010, Vrenator, WikHead, 102 ,יסויanonymous edits

Image Sources, Licenses and ContributorsFile:Renin-angiotensin system in man shadow.png  Source: http://en.wikipedia.org/w/index.php?title=File:Renin-angiotensin_system_in_man_shadow.png  License: Public Domain Contributors: Mikael HäggströmFile:Calcium regulation.png  Source: http://en.wikipedia.org/w/index.php?title=File:Calcium_regulation.png  License: Public Domain  Contributors: Mikael Häggström

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