Homeostasis, from the Greek words for "same" and "steady," refers to any process that living things use to actively maintain fairly stable conditions necessary for survival. The term was coined in by the physician Walter Cannon. His book, The Wisdom of the Body , describes how the human body maintains steady levels of temperature and other vital conditions such as the water, salt, sugar, protein, fat, calcium and oxygen contents of the blood.
Similar processes dynamically maintain steady-state conditions in the Earth's environment. Homeostasis has found useful applications in the social sciences. It refers to how a person under conflicting stresses and motivations can maintain a stable psychological condition. A society homeostatically maintains its stability despite competing political, economic and cultural factors. A good example is the law of supply and demand, whereby the interaction of supply and demand keeps market prices reasonably stable.
Homeostatic ideas are shared by the science of cybernetics from the Greek for "steersman" , defined in by the mathematician Norbert Wiener as "the entire field of control and communication theory, whether in the machine or in the animal. Negative feedback is a central homeostatic and cybernetic concept, referring to how an organism or system automatically opposes any change imposed upon it. For example, the human body uses a number of processes to control its temperature, keeping it close to an average value or norm of One of the most obvious physical responses to overheating is sweating, which cools the body by making more moisture on the skin available for evaporation.
In homeostasis, negative feedback loops are most common, as the body is typically attempting to decrease the effect of the stimulus to get the body back to equilibrium. There are three main types of homeostatic regulation that happen in the body. Though their names might be unfamiliar, you probably experience them every day. When you think about homeostasis, temperature might come to mind first.
It is one of the most important and obvious homeostatic systems. Regulating body temperature is called thermoregulation. All organisms, from large mammals to tiny bacteria, must maintain an ideal temperature in order to survive. Some factors that influence this ability to maintain a stable body temperature include how these systems are regulated as well as the overall size of the organism.
The colloquial terms "warm-blooded" and "cold-blooded" do not actually mean that these organisms have different blood temperatures. These terms simply refer to how these creatures maintain their internal body temperatures. Thermoregulation is also influenced by an organism's size, or more specifically, the surface-to-volume ratio. Osmoregulation strives to maintain the right amount of water and electrolytes inside and outside cells in the body.
The balance of salt and water across membranes plays an important role, as in osmosis, which explains the name "osmoregulation. Osmoregulation also affects blood pressure.
Your body regulates other chemical mechanisms as well to keep systems in balance. These use hormones as chemical signals—for example, in the case of blood sugar levels. In this situation, the pancreas would release either insulin, when blood sugar levels are high, or glucagon, when blood sugars are low, to maintain homeostasis.
Homeostasis involves both physiological and behavioral responses. In terms of behavior, you might seek out warm clothes or a patch of sunlight if you start to feel chilly.
You might also curl your body inward and keep your arms tucked in close to your body to keep in the heat. As endotherms, people also have a number of internal systems that help regulate body temperature.
When your body temperature dips below normal, a number of physiological reactions respond to help restore balance.
Blood vessels in the body's extremities constrict in order to prevent heat loss. Shivering also helps the body produce more heat. Insulin causes blood glucose levels to decrease, as would be expected in a negative feedback system. However, if an animal has not eaten and blood glucose levels decrease, this is sensed in a different group of cells in the pancreas: the hormone glucagon is released, causing glucose levels to increase.
If calcium levels decrease, specialized cells in the parathyroid gland sense this and release parathyroid hormone PTH , causing an increased absorption of calcium through the intestines and kidneys. The effects of PTH are to raise blood levels of calcium. Negative feedback loops are the predominant mechanism used in homeostasis. Negatie feedback loop : Blood sugar levels are controlled by a negative feedback loop. A positive feedback loop maintains the direction of the stimulus and possibly accelerates it.
There are few examples of positive feedback loops that exist in animal bodies, but one is found in the cascade of chemical reactions that result in blood clotting, or coagulation. As one clotting factor is activated, it activates the next factor in sequence until a fibrin clot is achieved. The direction is maintained, not changed, so this is positive feedback.
Another example of positive feedback is uterine contractions during childbirth. The hormone oxytocin, made by the endocrine system, stimulates the contraction of the uterus. This produces pain sensed by the nervous system. Instead of lowering the oxytocin and causing the pain to subside, more oxytocin is produced until the contractions are powerful enough to produce childbirth.
Positive feedback loop : The birth of a human infant is the result of positive feedback. Homeostasis is performed so the body can maintain its internal set point. However, there are times when the set point must be adjusted. When this happens, the feedback loop works to maintain the new setting.
An example of changes in a set point can been seen in blood pressure. Over time, the normal or set point for blood pressure can increase as a result of continued increases in blood pressure. The body no longer recognizes the elevation as abnormal; there is no attempt made to return to the lower set point.
The result is the maintenance of an elevated blood pressure which can have harmful effects on the body. Medication can lower blood pressure and lower the set point in the system to a more healthy level through a process of alteration of the set point in a feedback loop. Changes can be made in a group of body organ systems in order to maintain a set point in another system.
This is called acclimatization. This occurs, for instance, when an animal migrates to a higher altitude than one to which it is accustomed. In order to adjust to the lower oxygen levels at the new altitude, the body increases the number of red blood cells circulating in the blood to ensure adequate oxygen delivery to the tissues. Another example of acclimatization is animals that have seasonal changes in their coats: a heavier coat in the winter ensures adequate heat retention, while a light coat in summer assists in keeping body temperature from rising to harmful levels.
Animals use different modes of thermoregulation processes to maintain homeostatic internal body temperatures. As internal body temperature rises, physiological processes are affected, such as enzyme activity. Although enzyme activity initially increases with temperature, enzymes begin to denature and lose their function at higher temperatures around C for mammals. As internal body temperature decreases below normal levels, hypothermia occurs and other physiological process are affected.
There are various thermoregulation mechanisms that animals use to regulate their internal body temperature. Thermoregulation in organisms runs along a spectrum from endothermy to ectothermy.
Since ectotherms rely on environmental heat sources, they can operate at economical metabolic rates. The term derives from Greek roots meaning "similar" and "a state of stability. Instead, homeostasis holds important physiological factors within an acceptable range of values, according to a review in the journal Appetite.
The human body, for example, regulates its internal concentrations of hydrogen, calcium, potassium and sodium, charged particles that cells rely on for normal function. Homeostatic processes also maintain water, oxygen, pH and blood sugar levels, as well as core body temperature, according to a review in Advances in Physiology Education.
In healthy organisms, homeostatic processes unfold constantly and automatically, according to Scientific American. Multiple systems often work in tandem to hold steady a single physiological factor, like body temperature.
If these measures falter or fail, an organism may succumb to disease, or even death. Many homeostatic systems listen for distress signals from the body to know when key variables fall out of their appropriate range. The nervous system detects these deviations and reports back to a control center, often based in the brain.
The control center then directs muscles, organs and glands to correct for the disturbance.
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