Negative feedback is a key regulatory mechanism for physiological function in living things. Learn the definition, explore some examples and find out how this process happens in your body. Test your new knowledge at the end with a quiz.

What is Negative Feedback

Most of us have, at some point, experienced the infamous thermostat battle in our homes. Someone likes it warm, someone else likes it cool, maybe you like it somewhere in between. If the temperature in the house is 70 degrees, and someone changes the thermostat to 68 degrees, then the thermostat kicks on the AC to cool the house down two degrees. When someone else comes along and turns the thermostat to 75, it will kick on the heat to warm the house (or maybe just stop the AC for a little while).

The thermostat is a prime example of negative feedback, and we see the same thing happen in the biochemistry of living things. Negative feedback is a regulatory mechanism in which a ‘stimulus’ causes an opposite ‘output’ in order to maintain an ideal level of whatever is being regulated.

Steps of Negative Feedback Loops

All negative feedback loops occur in a series of steps. Let’s continue to use a thermostat as an example.

  1. You have a stimulus, in which a change occurs. In this case, the temperature in the house increases.
  2. You have a sensor, or the change is detected. In our scenario, the thermostat registers the increase in temperature.
  3. There’s a control, which is just a response to the change: the thermostat sends a signal to decrease the temperature.
  4. There’s an effector, or the effect of the response. This could be the AC turning on to bring the temperature in the house back down to normal or the heater stopping for a period of time until the temperature is brought back down to normal.

If the temperature were to keep dropping down until it is too cold, then the process would repeat itself, but this time, the response (or control) would be to increase the temperature to bring it back to normal. A negative feedback loop serves to keep a certain variable in check, temperature in this case.

Negative Feedback in Living Things

Your body has its own internal controller for maintaining its temperature, pH, hormone levels, blood sugar and other internal variable levels at homeostasis, which is the optimal internal state at which your body operates best. The controller of homeostasis in most animals is the hypothalamus. Without this structure in the brain, organisms would have great difficulty functioning normally.

There are many negative feedback pathways in biological systems, including:

  • Temperature regulation
  • Blood pressure regulation
  • Blood sugar regulation
  • Thyroid regulation
  • Photosynthesis in response to increased carbon dioxide
  • Predator/prey population dynamic

Examples of Negative Feedback Loops

This diagram shows the steps of the negative feedback loop, as well as how it works in temperature regulation.

As you can see, the body exceeds a certain temperature. This is detected by nerve cells that report back to the part of the brain that regulates temperature, and the brain sends out a signal for the body to cool itself down by sweating. Pretty efficient!

Another common example of a negative feedback loop in biology is thyroid regulation of metabolism, which you can see in this diagram. This is a negative feedback loop that controls the release of thyroid hormones T3 and T4, which stimulate metabolic activity. When these hormones are low in the bloodstream (stimulus), the hypothalamus (sensor) is triggered and releases the TRH hormone (control) to the anterior pituitary gland, which then causes the release of the TSH hormone (control), which causes the thyroid gland to release the T3 and T4 hormones (effector), increasing metabolic function. When T3 and T4 are at their optimum level (homeostasis) in the bloodstream, or higher, the hypothalamus is not triggered.

Lesson Summary

Negative feedback is a regulatory mechanism in which a ‘stimulus’ causes an opposite ‘output’ in order to maintain an ideal level of whatever is being regulated. Negative feedback loops occur in a series of steps.

  1. You have a stimulus, in which a change occurs.
  2. You have a sensor, or the change is detected.
  3. There’s a control, which is just a response to the change.
  4. There’s an effector, or the effect of the response.

Negative feedback loops occur in your body through its own internal controller for maintaining temperature, pH, hormone levels, blood sugar and other internal variable levels at homeostasis, which is the optimal internal state at which your body operates best. The controller of homeostasis in most animals is the hypothalamus.

In all ways that it occurs, negative feedback serves to maintain a ‘normal’ status of a variable. When that variable increases, a series of reactions take place – similar to a domino effect – that cause the variable to decrease, and vice versa.

Learning Outcomes

After learning about negative feedback in biology, you could achieve these goals:

  • Write the definition of negative feedback
  • List some of the negative feedback loops and pathways in biology
  • Realize the way in which your body maintains homeostasis
  • Provide examples of negative feedback loops