For what are lives looking? Call it Dynamic equilibrium, a continuous circle dance of adjustment and correction.
Maintaining this balance between a living system's internal conditions and fluctuating environmental (external) conditions is called homeostasis. Inside and outside must fit.
Living organisms are living systems. A system is a set of elements (parts) actively interacting, organized for a goal. The "goal" of living systems is to stay alive. Single organisms are living systems, but living systems can be of any size, from organism to community to ecosystem, to finally, the entire biosphere. The elements or parts of a living system include all the sub-systems it contains.
These systems are organized and dynamically interact. The ways they connect to and interact with one another are also elements (parts) of the living system. A system includes its physical parts plus its relationship parts. See essay, "Thinking in Wholes."
Living systems (organisms, ecosystems) are self-regulating. Living organisms regulate their internal conditions to balance their interiors with their exterior environments.
When this search for balance between inside and outside is successful, the living system survives. When external changes (for example, of temperature) are too quick and too severe; balance cannot be maintained and the living system dies.
|Feedback Loop, Process of Balance
Homeostasis is a dynamic, active process, not a static one. A Feedback Loop illustrates this interactive process:
To help you visualize this diagram, pretend that Any System is a bucket half full of water. The bucket has a hole in it where water is flowing out---this is Output. You are holding the bucket under a running faucet--this is Input. If the amount of water flowing out of the hole is the same as the amount entering from the faucet, the system is in balance. In this situation, the sensor is your eyesight. The feedback system is your hand on the faucet, which can turn the faucet to increase or decrease the flow based on what your eyes are telling you.
Feedback corrects the Input. Think of the time when you finally learned to ride a bicycle; when you learned to balance. Homeostasis happens without thinking--we just do it. Here are two stages of this bicycle-riding process shown as feedback loops:
In Figure One, you are just starting to lose your balance. If you don't correct it you will fall. Homeostasis is the process of correcting imbalances. Figure Two takes place about three seconds after Figure One.
Another way to think of homeostasis is that living systems try to maintain a constant internal environment. The adjustments that organisms make to keep their interior environments stable are responses to changes in the environment outside their bodies.
The most familiar regulation our own bodies do is temperature regulation. In humans, normal body temperature is about 98.6 F.
A rise in body temperature means we need to dump heat. We sweat and we breathe faster, two regulatory processes that lower the body temperature. To get rid of heat, we also reduce activity, and expand our capillaries so more blood can dump its heat near the surface of the skin. Our skin is an efficient heat-exchanger when the air around it is cooler than the body.
A decrease in body temperature, say from a chilly winter walk, leads to increased heat-producing activity such as increased metabolism or the muscular contractions of shivering. Heat loss is also reduced by decreased circulation to the skin; the capillaries shrink. Below is a feedback loop showing a response to cold:
Getting Warm Again: Regulating Blood Temperature
|Feedback loops regulate
many internal conditions.
Waste: From protozoans to worms to insects to mammals, the organ systems that get rid of unusable and excess substances work to maintain the balance between inside and outside. The principal function of the excretory system of animals is homeostasis.
Saltiness: Most animals regulate the salt content of their internal fluids. The blood of most ocean fishes, for example is not nearly as salty as the ocean itself--if it were the fish would die. So they must continuously adjust their blood to keep dissolved mineral salts out. Freshwater fishes have the opposite problem: their blood requires a higher salt content than is found in fresh water. So they must continually regulate to retain dissolved mineral salts. In both cases, the kidneys accomplish this job.
Temperature: Land animals regulate their temperatures; the salt and sugar content of their blood (fluid and electrolyte balance); and their metabolisms (energy production and use).
Sugar: Most animals regulate the sugar content of their blood; in turn the sugar content helps determine metabolism.
Hormones: The activity of endocrine glands (hormone producers) are regulated by feedback loops in the circulatory system.
Enzymes: Many enzymes are regulated by feedback loops within individual cells, and others by feedback loops in larger systems.
Closed Loops: The regulatory feedback loops above are "closed" feedback loops. A change in the outside environment is sensed, which triggers a response which opposes or corrects the change. Closed feedback loops are often called negative feedback loops, which is counter-intuitive, because their action is toward the good of the living system.
Open Loops: "Open" feedback loops (also called positive feedback loops) are often destructive. The response in an open loop says "Great! More! More!" So the change in the outside is reinforced instead of corrected. Open feedback loops accelerate change, which can lead to death. But some situations require open feedback loops.
For instance, If you cut yourself, your blood tries to clot to stop blood loss. The more the blood tries to clot, the more it does clot. This is a positive feedback loop in action, but when the bleeding ends, it stops, and a closed feedback loop takes over. If the positive feedback loop continued its "runaway" clotting, all the blood in your body would coagulate and you would die.
Feedback Spirals: In economics, open feedback loops are often described as spirals. Inflation of a money supply is good example, bankruptcy is another. The "upward spiral of inflation" and the "downward spiral of debt" are common phrases in newspapers.