What Is Homeostasis? - Definition & Examples

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  • 0:01 Homeostasis
  • 1:56 How Is It Achieved?
  • 3:50 Failure of Mechanisms
  • 4:34 Lesson Summary
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Lesson Transcript
Instructor: Natalia Caporale
Homeostasis can be defined as a property of an organism or system that helps it maintain its parameters within a normal range of values. It is key to life, and failures in homeostasis can lead to diseases like hypertension and diabetes.

Definition of Homeostasis

Homeostasis is a key concept in understanding how our body works. It means keeping things constant and comes from two Greek words: 'homeo,' meaning 'similar,' and 'stasis,' meaning 'stable.' A more formal definition of homeostasis is a characteristic of a system that regulates its internal environment and tends to maintain a stable, relatively constant, condition of properties.

Homeostasis is happening constantly in our bodies. We eat, sweat, drink, dance, eat some more, have salty fries, and yet our body composition remains almost the same. If someone were to draw your blood on ten different days of a month, the level of glucose, sodium, red blood cells and other blood components would be pretty much constant, regardless of your behavior (assuming fasting before drawing blood, of course).

No matter how much water you drink, your body doesn't swell up like a balloon if you drink tons, and it doesn't shrivel like a raisin if you drink very little. Have you ever wondered about this? Somehow, our bodies know how much fluid we need to keep, and then maintain a constant level regardless of how much water we drink.

This maintenance of body size is an example of homeostasis. And we don't even have to think about it for this to happen! Aren't our bodies amazing?

There are several other examples of homeostasis. For example, our concentration of salts and glucose (sugar) is constant; our body temperature is usually around 37 degrees Celsius (98.6 degrees Fahrenheit); the amount of blood in our bodies is about 5 liters, the osmolarity (number of solutes) of our blood remains about 300mOsm. The normal value of a physiological variable is called its set point.

How is Homeostasis Achieved?

So, how does our body regulate all these variables and compensate for changes in the environment? Well, it turns out we have tons of sensors in our body that monitor the temperature, salt composition of blood, blood pressure, osmolarity, and other things. These detectors signal the brain, the control center, when some value has deviated from normality and trigger compensatory changes that will try to restore that value to normal.

For example, imagine that you go outside and it's really hot. This will start changing your body temperature. Temperature sensors in our brain monitor body temperature, and if it starts rising (moving away from its supposed set point), this activates an effector tissue or organ that will help bring the temperature back to its set point. For example, if your body temperature rises, then you start sweating. This is a compensatory response by your body to lower your temperature back to normal.

The control center, sensors, and effector together form what is known as a control system. Control systems are everywhere; a thermostat that regulates room temperature is a classic example of a control system. Control systems that tend to reduce the difference between the desired value of a variable and the observed value are called negative feedback systems, or error correction systems.

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