Homeostasis?
WHY IS HOMEOSTASIS IMPORTANT?
Physiologist Walter Cannon coined the term “homeostasis” in the 1920s, expanding on previous work by late physiologist Claude Bernard. In the 1870s, Bernard described how complex organisms must maintain balance in their internal environment, or “milieu intérieur,” in order to lead a “free and independent life” in the world beyond.
Cannon honed the concept, and introduced homeostasis to popular audiences through his book, “The Wisdom of the Body” (The British Medical Journal, 1932).
Hailed as a core tenet of physiology, Cannon’s basic definition of homeostasis remains in use today. The term derives from Greek roots meaning “similar” and “a state of stability.”
The prefix “homeo” stresses that homeostasis doesn’t work like a thermostat or cruise control in a car, fixed at one precise temperature or speed. 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 2015 review in Advances in Physiology Education
In healthy organisms, homeostatic processes unfold constantly and automatically, according to Scientific American(opens in new tab).
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.
HOW IS HOMEOSTASIS 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
