A great example of a homeostasis system is a building or house thermostat system. The thermostat is set on the temperature the house or building needs to stay. If the area gets too hot, the thermostat detects the temperature deviation and turns off the heater, while turning on the air conditioner. If the area gets too cold, the opposite happens: the air conditioner turns off, and the heater turns on. This system of homeostasis, or balance, keeps the area at the appropriate temperature.
Maintaining room temperature is similar to how the human body maintains a constant internal temperature. Sure, there can be fluctuations, such as heat stroke in hotter temperatures and frostbite in colder temperatures; but, overall, the body does a good job of keeping things close to 37 degrees C (98.6 degrees F).
Whenever body temperature starts to rise, receptors and signal neurons can sense the change, and take the message to the brain. The brain sends signals to the skin to open its pores and start sweating, so heat can be released. If body temperature drops below normal, the brain can tell the muscles to start twitching to generate body heat by motion. This action is called shivering.
Regulation of hormones is also an example of homeostasis in action. While people walk around, go to work, or sit and watch television, hormones are being regulated, and controlled, so the body functions properly. When any hormone level gets too high, the endocrine gland responsible for producing and secreting that hormone temporarily stops production. Circulating hormone concentration is decreased, and the levels go back to normal. If a hormone concentration gets too low, receptors stimulate the endocrine gland to secrete more hormone into the body. This is done until hormone levels return to normal.
An example for this system would be the fight or flight response. When people are startled, or faced with danger, their body prepares for them to either run away from danger or to fight. One of the ways it prepares is via neuronal signals, such as epinephrine (also known as adrenaline) stimulating the adrenal glands. These glands start secreting hormones, which help increase heart rate and blood pressure, providing energy for a situation.
Another example of body hormones in action is blood glucose (sugar) levels. If a person has lower blood glucose levels, which can occur when skipping a meal, the pancreas releases glucagon into the blood. This molecule signals the release of glucose from the liver and into the bloodstream. If a person has higher blood glucose levels, such as after eating a meal, the pancreas will secrete insulin, which tells the body's cells to take up and store the excess glucose. When one or both of these hormones aren't performing their jobs correctly, it can lead to the condition called diabetes.