A negative-feedback loop is a cycle where a change is detected and a response opposes it, so the condition returns towards its set point. Once you can read one loop, you can read any example, because temperature, glucose and water control all use the same pattern.
This skill builds on kidney filtration and selective reabsorption and is applied to the skin in temperature regulation and to blood sugar in glucose regulation.
What are the parts of a loop?
Read every loop in the same five steps.
- Set point: the value the body keeps returning towards.
- Change: the condition moves above or below the set point.
- Detector: a receptor senses the change and passes the information on.
- Response: an effector, such as a muscle or gland, does something that opposes the change.
- Return: the condition moves back towards the set point, and the response eases.
The word “feedback” refers to step 5 passing information back to step 3. Because the response eases when the condition returns, the system does not overshoot for long.
Why is it called negative?
Because the response goes the other way. A rise leads to a response that lowers, and a fall leads to a response that raises. A system that amplified the change instead would be positive feedback, which is not how the body holds steady conditions.
Worked example
Use this invented loop for core body temperature, with a set point of 37.0 °C. The figures are made up to show the pattern.
| Stage | What happens |
|---|---|
| Set point | 37.0 °C |
| Change | temperature rises to 37.6 °C |
| Detector | temperature receptors detect the rise |
| Response | sweat glands release more sweat, so more heat is lost by evaporation |
| Return | temperature falls to 37.1 °C and the sweating eases |
Step 1: state the direction of the change. It rose, by 37.6 − 37.0 = 0.6 °C above the set point.
Step 2: check that the response opposes it. More heat loss lowers temperature, so the response opposes a rise. This is negative feedback.
Step 3: check the return. The temperature fell by 37.6 − 37.1 = 0.5 °C towards the set point, so the loop is working.
You can practise ordering a loop like this with the mechanism and feedback builder.
The mistake to watch for
The common error is to describe the response but stop before saying what it does or what happens next.
Mistaken answer: “Temperature goes up, so the body sweats.”
This gives a cause and a response but never says what the response does or what happens next.
The correction is to add the opposing effect and the return: “Temperature rises above the set point. Receptors detect it. Sweat glands respond, cooling the body by evaporation, so temperature falls back towards the set point.”
Check yourself
Try these, then open each answer.
1. Put in order: response, change detected, return to set point, condition changes.
Show answer
Condition changes, change detected, response, return to set point.
2. A condition falls below its set point. State whether a negative-feedback response would raise or lower it.
Show answer
It would raise it. A negative-feedback response always opposes the change, so a fall triggers a response that increases the condition.
3. In the invented loop above, which part is the effector?
Show answer
The sweat glands are the effectors, because they carry out the response.
Where this leads next
With the pattern clear, move to explaining temperature regulation using competing effects, where two responses act together. Some students can label a loop but lose marks on wording. Our teachers work on that kind of sentence-level precision in online one-to-one Biology tuition.