Homeostasis is the ability to maintain a relatively stable internal state that persists despite changes in the world outside. All living organisms, from plants to puppies to people, must regulate their internal environment to process energy and ultimately survive. If your blood pressure skyrockets or body temperature plummets, for example, your organ systems may struggle to do their jobs and eventually fail.

How homeostasis is maintained

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. The continual loop of disturbance and adjustment is known as "negative feedback," according to the online textbook Anatomy and Physiology.

For example, the human body maintains a core temperature of about 98.6 degrees Fahrenheit (37 degrees Celsius). When overheated, thermosensors in the skin and brain sound an alarm, initiating a chain reaction that directs the body to sweat and flush. When chilled, the body responds by shivering, and reducing blood circulation to the skin. Similarly, when sodium levels spike, the body signals the kidneys to conserve water and expel excess salt in concentrated urine, according to two NIH-funded studies.

Animals will also adjust their behavior in response to negative feedback. For example, when overheated, we may shed a layer of clothing, move into the shade, or drink a cold glass of water.