Homeostasis

Homeostasis is the maintenance of stable internal conditions in a living thing. Organisms use a variety of systems and processes that help regulate and maintain a constant environment within their bodies. All organisms use a self-adjusting balance to make sure that what is going on inside their bodies is kept within certain boundaries.

One of the main characteristics of living things, or organisms, is that they have the ability to adjust to their environment. In the highly competitive struggle for survival, an organism would be at a great disadvantage if it could not adjust and be ready to cope with a changed situation. Such change can occur inside or outside an organism. Since living things are extremely complex organisms with constant energy demands, there are countless cellular reactions going on all the time. For example, chemicals are combining and breaking apart, fluids are passing in and out of membranes, and substances are being converted from one form to another. All of this constant activity means that the environment inside an organism's body is dynamic, and that it is always in a state of movement and change.

CLAUDE BERNARD DEVELOPS THE CONCEPT OF HOMEOSTASIS

The concept of homeostasis was developed by the French physiologist (a person specializing in the study of life processes, activities, and functions) Claude Bernard (1813–1878). Bernard investigated how the body keeps itself in a stable, or steady state. It was Bernard who first recognized the idea behind homeostasis—that an organism is designed and operates on the principle that it will always attempt to maintain a balance in its systems.

After Bernard, science eventually discovered that living things use two simple self-adjusting elements, input and output, as regulators. Although these elements are uncomplicated, an organism has many mechanisms and structures that it uses to maintain homeostasis. Some of these mechanisms work automatically and are under the control of the autonomic nervous system. It is this system that regulates the body's involuntary processes like internal body temperature, blood pressure, and food digestion, among other function.

Certain changes in the external environment may automatically trigger an organ to take a certain action. Under certain conditions, our bodies will perspire whether we want them to or not. Other mechanisms are controlled by the body's endocrine system. This system uses chemical messages, known as hormones, inside the body to regulate functions. A hormone is secreted by the organ that produces it when something happens to the organism that warrants regulation. Hormones then travel through the bloodstream to their target cells, which take the appropriate action.

THE FEEDBACK SYSTEM

For this system to really work, however, it must have some way of getting updated information as to what is going on inside and outside the organism. This is achieved by a feedback system that operates something like the thermostat in a house. Every thermostat has a sensor that, when set at a certain temperature, automatically turns the furnace on when the temperature gets lower than its setting, and turns it off when it reaches it. In this way, a built-in feedback "loop" regularly monitors its environment and is able to maintain a constant temperature by turning the furnace on or off.

The feedback system in our bodies works mostly with what is called negative feedback. Negative feedback operates by detecting an unwanted change and countering it in order to balance it. A typical example would be the body's use of feedback mechanisms to raise or lower its internal temperature during extremely cold or hot weather.

LEVELS OF HOMEOSTASIS

In the human body, homeostasis takes place at many different levels. These include the molecular level (in which atoms are linked together by chemical bonds), the cellular level, the organism level, and the population level. An example of homeostasis at the molecular level would be the body limiting how much of something is produced by a certain chemical reaction. At the cellular level, an example would be how certain cells

will stop dividing if they become so numerous that they touch each other. Sensations of hunger and thirst are good examples of a homeostasis mechanism at the organism level. Finally, at the population level, an increase in the number of prey animals usually results in an increase in the number of predators that eat the prey. In this way, the population size of both animals is kept in balance.

[See alsoEndocrine System; Hormones ]