What Is Homeostasis?
Homeostasis keeps the internal milieu of the body stable and balanced
Medically reviewed by Arno Kroner, DAOM, LAc
Homeostasis is a physiological process that keeps the internal environment of a living organism stable and balanced. The constant equilibrium created by homeostasis is vital to the survival of every species. Even when the external environment is rapidly changing, homeostasis keeps the body's internal environment constant and steady.
This article defines the meaning of homeostasis, describes how the concept originated, explains how these physiological processes work via negative feedback loops, and details why maintaining a "milieu intérieur" (constant internal environment) is essential for all living things.
Homeostasis is a term derived from the Greek words "homeo" (meaning similar to) and "stasis" (meaning standing still). In the 1920s, an American physiologist named Walter B. Cannon invented the word "homeostasis."
Cannon described homeostasis as "coordinated physiological processes" that maintain "steady states" in a living organism. He clarified that the word doesn't imply something set in stone or stagnant but instead describes an automated, self-regulating process that varies but is "relatively constant."
Cannon's concept of homeostasis can be traced back to the principles of milieu intérieur developed by a French physiologist Claude Bernard in the 1860s.
"Homeostasis" and "milieu intérieur" are similar terms that highlight the importance of living organisms having internal mechanisms that can maintain inner balance and "relatively constant" stability. Even if the external environment changes rapidly, homeostasis makes it possible for the body to keep its internal environment steady via dynamic equilibrium reactions.
The body's ability to maintain a constant internal temperature of 98.6 degrees F (37 degrees C) is a perfect example of homeostasis. When the external environment is hot, the body sweats to cool itself down and maintain a steady internal temperature. When it's cold outside, the body shivers to stay warm.
How It Works
Homeostasis typically involves negative feedback loops. Within these loops, negative stimuli automatically trigger mechanisms to help homeostasis's dynamic equilibrium process. "Dynamic equilibrium" describes the process and reactions that occur as the body makes adjustments in response to negative feedback warnings of imbalance.
Homeostasis's ultimate goal is to help the body maintain a constant and relatively stable internal environment whenever possible. For example, being in hot weather triggers cooling mechanisms, such as sweat, that keep the body's core temperature around 98.6 degrees F.
When someone is in a cold environment, this negative stimulus activates homeostatic mechanisms designed to hold onto the body's heat, like shivering, in an attempt to maintain body temperature.
The human body has a phenomenal ability to maintain internal balance in response to disruptive outside forces and different types of internal or external negative stimuli.
Examples of Homeostasis
Several types of homeostatic regulation maintain homeostasis in healthy human bodies, including:
Body temperature homeostasis (thermoregulation): Keeps the body's temperature stable at around 98.6 degrees F and helps offset the risks of heat exhaustion or hypothermia (low body temperature)
Water and electrolyte homeostasis (osmoregulation): Keeps fluid levels and electrolyte balance stable within the body by filtering and removing excess fluids via the kidneys (electrolytes are minerals that carry a charge dissolved in water, such as in the bloodstream, body fluids, and cells, including sodium, potassium, calcium, phosphorus, chloride, and magnesium)
Oxygen (O₂) homeostasis: Keeps oxygen levels within a healthy range and helps the body avoid low oxygen levels (hypoxia)
Blood sugar homeostasis (pancreatic regulation): Keeps blood sugar (glucose) at stable and healthy levels of between 70 and 120 milligrams per deciliter (mg/dL) via the pancreas
Blood pressure homeostasis (baroreflex regulation): Sends homeostatic signals from the hypothalamus to the heart, blood vessels, and kidneys that keep blood pressure in a healthy range that isn't too high (hypertension) or too low (hypotension)
Calcium homeostasis: Maintains serum calcium homeostasis via the synthesis and release of parathyroid hormone (PTH) from the parathyroid gland
Potassium homeostasis: Keeps potassium levels within a healthy range of 3.6 to 5.2 milliequivalents per liter (mEq/L) and helps the body avoid having too much potassium in the blood (hyperkalemia) or too little (hypokalemia)
It's impossible to overstate the importance of homeostasis. Every living thing relies on homeostatic processes for its survival. When homeostasis fails to function properly, internal imbalances can lead to sickness and even death.
For example, when the body can't maintain blood sugar homeostasis due to low production of insulin or poor response to insulin, diabetes results. The inability to maintain potassium homeostasis can affect the heart's rhythm and nervous system activity, which can lead to death.
George E. Billman, a U.S. physiologist, describes homeostasis as "the central organizing principle upon which the discipline of physiology is built."
Centuries ago, Claude Bernard identified the importance of living organisms having the ability to maintain a stable inner environment, which he called milieu intérieur, meaning constant internal environment. In the early 20th century, Walter B. Cannon built on Bernard's concept of milieu intérieur and coined the term "homeostasis," which combines the Greek words "homeo" (similar to) and "stasis" (standing still).
Homeostatic mechanisms are triggered by negative feedback or any stimuli that throw off the body's inner balance. There are seven types of homeostasis that maintain a stable and constant internal environment regardless of external environmental changes.
Every living thing relies on homeostasis for its real-time and long-term survival. It helps organisms regulate themselves in response to changes in their environment. Even something as simple as sweating on a hot day is key to maintaining this balance and staying healthy.