And the Digestive System

Things to know about Homeostasis

Homeostasis or homoeostasis (homeo- + -stasis) is the property of a system in which variables are regulated so that internal conditions remain stable and most of the time constant. Examples of homeostasis are regulation of temperature and the balance between acidity and alkalinity (pH). Human homeostasis is the process that keeps the stability of the human body's internal environment in response to changes in external conditions.

The concept was described by French physiologist Claude Bernard in 1865 and the word was coined by Walter Bradford Cannon in 1926.[1] Although the term was first used to refer to processes within living things, it is frequently put to automatic control systems such as thermostats. Homeostasis requires a sensor to detect changes in the condition to be regulated, an effector mechanism that can vary that condition, and a negative feedback connection between the two.All living things depend on keeping a complex set of interacting metabolic chemical reactions. From the simplest unicellular organisms to the most complex plants and animals, internal processes work to keep the conditions within tight limits to allow these reactions to work. Homeostatic processes act at the level of the cell, the tissue, and the organ, as well as for the organism as a whole.

Control mechanisms[edit]

All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: The receptor is the sensing component that sees 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 decides an appropriate response to the stimulus. The control center then sends signals to an effector, which can be muscles, organs, or other structures that receive signals from the control center. After receiving the signal, a change occurs to correct the deviation by depressing it with negative feedback.[7]

Negative feedback[edit]

Negative feedback mechanisms consist of reducing the output or activity of any organ or system back to its normal range of functioning. A good example of this is regulatingblood pressure. Blood vessels can sense resistance of blood flow against the walls when blood pressure rises. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both of which are the effectors. The heart rate would decrease as the blood vessels increase in diameter (known as vasodilation). This change would cause the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases, and would cause vasoconstriction.

Homeostatic imbalance[edit]

Many diseases involve a disturbance of homeostasis.

As the organism ages, the efficiency in its control systems becomes reduced. The inefficiencies gradually result in an unstable internal environment that increases the risk of sickness, and leads to the physical changes associated with aging.[7]

Certain homeostatic imbalances, such as high main temperature, a high concentration of salt in the blood, or low concentration of oxygen, can generate homeostatic emotions(such as warmth, thirst, or breathlessness), which motivate behavior aimed at bringing back homeostasis (such as removing a sweater, drinking or slowing down).[8]

Examples from technology[edit]

The following are all examples of familiar homeostatic mechanisms:

  • A thermostat operates by switching heaters or air-conditioners on and off in response to the output of a temperature sensor.
  • Cruise control adjusts a car's throttle in response to changes in speed.
  • An autopilot operates the steering controls of an aircraft or ship in response to deviation from a pre-set compass bearing or route.
  • Process control systems in a chemical plant or oil refinery maintain fluid levels, pressures, temperature, chemical composition, etc. by controlling heaters, pumps and valves.
  • The centrifugal governor of a steam engine, as designed by James Watt in 1788, reduces the throttle valve in response to increases in the engine speed, or opens the valve if the speed falls below the pre-set rate.


The concept of homeostasis is central to the topic of Ecological Stoichiometry. There, it refers to the relationship between the chemical composition of an organism and the chemical composition of the nutrients it consumes. Stoichiometric homeostasis helps explain nutrient recycling and population dynamics.

Throughout history, ecological succession was seen as having a stable end-stage called the climax (see Frederic Clements), sometimes referred to as the 'potential biodiversity' of a site, shaped primarily by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of how ecosystems function, as most natural ecosystems experience disturbance at a rate that makes a "climax" community unattainable.


Main article: Predictive homeostasis

Predictive homeostasis is an anticipatory response to an expected challenge in the future, such as increased melatonin release during the evening.


Reactive homeostasis is an immediate homeostatic response to a challenge, such as predation.

Other fields

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 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. 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[citation needed] that ecological crises are an instance of risk homeostasis in which a particular behavior continues until proven dangerous or 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-François Lyotard, a postmodern theorist, has put this term to societal 'power centers' that he says as being 'governed by a principle of homeostasis,' for example, the scientific hierarchy, which will sometimes ignore a rare new discovery for years because it destabilises previously accepted norms. (See The Postmodern Condition: A Report on Knowledge by Jean-François Lyotard)


how does junk food affect the body

Although low energy levels and weight gain can not be attributed solely to junk food intake, there is an association between eating high-calorie, nutrient-poor foods and poor health. While it may be tempting to rely on the vending machines to get you through an afternoon slump, or to pick up fast food on your way to your meeting, these choices add up over time and can negatively impact your weight and energy levels.

If you never eat these 5 foods, You will burn stomach fat every day

Sugar and Weight

Junk foods high in sugar are prevalent in the United States, and account for about 16 percent of total energy intake. A 2006 review of 30 studies in "The American Journal of Clinical Nutrition" found that consumption of sugar-sweetened beverages was associated with weight gain and obesity. This may be due to the fact that calorie intake from sweetened beverages has increased by 74 calories per day from 1962 to 2000, contributing to positive energy balance and weight gain.

High-Calorie Snacks and Weight

Eating snack foods that are high in fat and calories also contributes to weight gain. A 2004 study at the University of Otago in New Zealand found that regular consumption of high-calorie snacks such as chocolate or potato chips may increase the amount of time it takes for you to tire of the food and become satisfied. Mindless junk food snacking in front of the television or in the car may also lead to overeating and increased calorie intake.


Choosing a junk food diet high in fat may affect your energy levels in as little as one week, according to a 2009 study conducted at the University of Cambridge. Within nine days of adopting a high-fat diet, rats in the study were only able to run 50 percent as far on a treadmill than rats fed a more balanced diet. This study was not performed on humans, but it can be speculated that a nutrient-poor diet could result in lower energy and physical performance in humans as well.

Healthier Options

If you eat junk food, you can make simple dietary changes to improve your energy and control your weight. Choose nutritionally balanced snacks that include fiber and protein to keep you full and satisfied. Try vegetables and hummus, whole-wheat toast with peanut butter or fruit with low-fat string cheese. Drink water or unsweetened coffee or tea instead of sugar-sweetened beverages. Take some time to plan ahead so you don't have to rely on vending machines or fast food when hunger strikes. http://healthyeating.sfgate.com/junk-food-affect-weight-energy-1376.html