Homeostasis

Homeostasis Definition

Homeostasis is an organism’s process of maintaining a stable internal environment suitable for sustaining life. The word homeostasis derives from Greek, with home meaning “similar,” and stasis, meaning “stable.” When used as an adjective, it is homeostatic.

We normally think about homeostasis in terms of the whole body, but individual systems – that is, groups of organs – also maintain homeostatic conditions. Nonetheless, prolonged imbalance in just one system can negatively impact the homeostasis of the entire organism.

Examples of Homeostasis

Homeostasis is a regulatory procedure. In the human body, homeostatic processes regulate:

• Ratios of water and minerals


• Body temperature


• Chemical levels

Example #1: The Formation of a Kidney Stone

Vitamins and minerals provide our bodies with the nutrients essential to thrive. While our large intestine and salivary glands absorb most of these nutrients, excess quantities leave our bodies through sweat and urination.

Of course, minerals vary in size. Calcium, phosphorus, and sodium are considered stone-promoting compounds, because they form crystals in the urinary tract that pass through the bladder. Technically, most humans always have kidney stones; not all of them are painful.

This is where homeostasis comes in. Under homeostatic conditions, our kidney stones (or crystals, in technical terms) are so small, we urinate them without a second thought. On the other hand, an overabundance of stone-promoting compounds or a lack of fluids in the urinary system can cause crystals to build and combine in the urinary tract, forming a stone. These stones, while excruciatingly painful, usually pass naturally. Sometimes, however, due to location or size, they require surgery.

Example #2: Running a Fever

You are exposed to over a million germs and bacteria cells per day – more if you work in a school, barn, doctor’s office or other high-contact area. Thankfully, the human immune system – lymph nodes, enzymes, t-cells, and b-cells – protects your body from the diseases these organisms may cause.

But some germs are tougher than the rest. Whether as mild as the common cold or as severe as tuberculosis, some strains, or varieties of disease, overcome your first line of defense and make you their host.

Microscopic invasions definitely disrupt homeostasis, often enough that the body knows exactly how to restore normal conditions. The hypothalamus raises the body’s temperature, making your insides both unwelcome to and uninhabitable for any uninvited guests. Furthermore, your immune system records these diseases in its “memory,” making it more difficult for you to catch the same bug twice.

Example #3: Producing Insulin in Response to High Blood Sugar

In homeostatic conditions, our bodies keep our blood sugar within a tight range – between 70 and 100 mg/dL, to be exact. However, this is a delicate balance. Our weight, diet, age, and activity levels can easily push us out of these normal levels.

Of the blood-glucose-affecting factors listed above, diet plays the largest role. Whether old or young, underweight or overweight, diabetic or non-diabetic, we use food to manage our blood glucose. We typically recognize its ability to raise levels, but even this benefit can be taken too far.

Especially since the dawn of processed foods, our diets have become increasingly sugary. While we have consumed complex sugars – like the ones that come from fruits and grains – for centuries, simple sugars – like those in candy and cereal – only hit our systems a few decades ago.

Simple sugars reach our bloodstream fast, and can therefore cause blood glucose levels to surge in as little as half an hour. To balance our blood sugar and maintain homeostasis, our pancreas produces insulin, a hormone that converts glucose to energy or stores it for future use. People with diabetes, a condition characterized by chronic high blood sugar, inject insulin after eating in order to maintain this same state of homeostasis.

Related Biology Terms

• Osmoregulation – Also called excretion, the maintenance by an organism of an internal balance between water and dissolved minerals regardless of environmental conditions.


• Thermoregulation – Maintaining an optimal internal temperature.


• Glucoregulation – The regulation of blood sugar.


• Filtration – The mass movement of water and solutes into the kidney, where they are processed into urine.

Test Your Knowledge

1. What is an example of disrupted homeostasis?
A. The body raising its temperature to ward off viruses or bacteria.
B. High blood sugar after a night of trick-or-treating.
C. A full bladder after drinking a gallon of water.
D. Crying after your significant other breaks up with you.

Answer to Question #1

B is correct. A fever is the body’s way of restoring homeostasis, and a full bladder is a way of maintaining it. While a break-up might cause some emotional disruption, it is not thought to disrupt homeostasis.

2. A body that maintains homeostasis in all systems is said to be in…
A. …perfect mode.
B. …normal homeostatic conditions.
C. …the risk pool.
D. …deep water.

Answer to Question #2

B is correct. “Homeostatic” is the adjectival form of homeostasis, and is used to describe animals and humans whose internal physical states do not fall outside of the normal range.

3. Homeostasis means maintaining ideal _________ conditions.
A. Internal
B. Diurnal
C. External
D. Plural

Answer to Question #3

A is correct. Although some disruptions to homeostasis may seem external, like cuts and bruises, the real damage happens inside the organism. This is why infection from a laceration sometimes spreads to other organs, or even other tissue areas.

Homeostasis