Negative Feedback & Homeostasis
Your body temperature barely moves from 37 °C whether you are shivering in the snow or sweating in the sun. Your blood glucose, water balance and blood pH are all held within narrow limits the same way. The trick is a control loop that always pushes back against change, negative feedback. This lesson shows you how to draw and read these loops, the single most important diagram in homeostasis.
Orient yourself
Predict, scan the goals and key terms, and clear the misconception this lesson exists to fix.
Before You Read
warm-upYou step out of an air-conditioned room into 38 °C heat. Within minutes you start to sweat and your skin flushes.
Before reading: list, in order, the steps your body must go through to bring your temperature back down, and identify which step "detects" the heat and which step "does something about it".
Learning Intentions
goalsKnow
- What homeostasis and a set point mean
- The components of a negative feedback loop in order
- The convention for drawing a feedback-loop diagram
Understand
- Why the response opposes (reverses) the original change
- Why it is called "negative" feedback
- How the loop returns a variable to its set point
Can Do
- Construct a labelled negative feedback loop diagram
- Interpret a given feedback diagram to explain homeostasis
- Apply the loop to thermoregulation (and other variables)
Scan these before reading
vocabMisconceptions To Fix
watch outTwo truths, one lie: Three of these statements about negative feedback are true. Which one is the lie?
What Negative Feedback Does
The response always reverses the change
Core Content
What Negative Feedback Does
+5 XPThe response always reverses the change
Negative feedback keeps a variable steady by detecting when it drifts away from its set point and then triggering a response that pushes it back the other way.
In negative feedback, a change in a variable away from its set point is detected, and the body responds in a way that opposes (reverses) that change, returning the variable toward the set point. It is called "negative" because the response acts in the opposite direction to the stimulus, not because anything is wrong.
This is exactly how a thermostat works: if the room gets too hot the heater switches off (or the cooler switches on), and if it gets too cold the heater switches on. The system constantly corrects itself, so the value oscillates gently around the set point rather than running away.
Pause, copy the highlighted definition of negative feedback into your book before moving on.
In a negative feedback loop, the response acts in the _____ direction to the change that triggered it.
Constructing the Loop Diagram
Stimulus → receptor → control centre → effector → response → back to set point
Constructing the Loop Diagram
+5 XPStimulus → receptor → control centre → effector → response → back to set point
We just saw that the response reverses the change. That raises a question: how do we lay this out as a diagram an examiner can mark? This card answers it → a closed loop of five labelled components.
A negative feedback diagram is a closed loop: each component passes information to the next, and the loop closes when the response returns the variable to the set point.
Text description
- Start: the variable is held at its set point.
- 1 Stimulus: a change away from the set point.
- 2 A receptor detects the change.
- 3 The control centre processes it and signals a response.
- 4 An effector (muscle or gland) acts.
- 5 The response opposes the change; the arrow on the right returns the variable to the set point, closing the loop.
To construct a negative feedback diagram, draw a loop with: (1) stimulus, the change away from the set point; (2) receptor, detects the change; (3) control centre, processes it and signals a response; (4) effector, the muscle or gland that acts; (5) response, opposes the original change, returning the variable to the set point. Arrows show the direction of information flow, and the loop closes back to the set point.
Pause, copy the highlighted loop and the order of the five components.
"Negative" feedback means the controlled variable is always decreasing.
In a feedback loop the effector is the structure that carries out the response.
A correctly drawn negative feedback diagram is a closed loop that returns the variable to its set point.
Draw the Thermoregulation Loop
Do the activity in your book, then check what you have understood.
Activity 1
Draw the Thermoregulation Loop
Pattern C, Construct and label
In your book, construct a labelled negative feedback loop for body temperature rising above 37 °C on a hot day. Fill in each component: stimulus (body temp rises), receptor (temperature receptors in skin/hypothalamus), control centre (hypothalamus), effector (sweat glands, skin blood vessels), and response (sweating and vasodilation cool the body). Draw arrows for the loop, then write one sentence stating how the loop returns temperature to the set point.
Match each part of the thermoregulation loop to its label:
- Body temperature rises above 37 °C
- Temperature receptors in skin and hypothalamus
- The hypothalamus compares and signals
- Sweating and vasodilation cool the body
- Control centre
- Stimulus
- Response carried out by the effectors
- Receptor
Interpreting a Loop, Thermoregulation
Reading a worked example both ways
Interpreting a Loop, Thermoregulation
+5 XPReading a worked example both ways
We just constructed a loop. That raises a question: can the same loop also explain the opposite change, getting too cold? This card answers it → a negative feedback loop works in both directions around the set point.
A single negative feedback system corrects a variable whether it rises or falls, because the response always opposes the change in whichever direction it occurs.
Thermoregulation: if body temperature rises above 37 °C, receptors detect it, the hypothalamus signals sweat glands to sweat and skin arterioles to dilate (vasodilation), losing heat and cooling the body. If temperature falls below 37 °C, the hypothalamus triggers shivering and vasoconstriction (and reduced sweating), generating and conserving heat. Both responses oppose the change and return temperature to the set point, the hallmark of negative feedback maintaining homeostasis.
When you interpret a feedback diagram in an exam, name each component, state the direction of the change, and explain how the response opposes it to restore the set point. That structure earns full marks.
Add the highlighted two-way thermoregulation example to your notes before the check below.
When body temperature falls below the set point, which response would a negative feedback loop trigger?
When negative feedback can't keep up: heatstroke
Where this biology is doing real work outside the classroom.
When negative feedback can't keep up: heatstroke
Negative feedback is powerful but not unlimited. On extreme heatwave days in Australia, the body's cooling responses, sweating and vasodilation, can be overwhelmed: if the air is also very humid, sweat cannot evaporate, so heat is not lost. Core temperature then climbs above the range the feedback loop can correct, leading to heatstroke, a medical emergency. Understanding the loop explains both why our bodies usually stay at 37 °C and why, when the loop is pushed past its limits, the consequences are so dangerous, a theme you will return to in L25 on tolerance limits.
Construct a negative feedback loop for the control of body temperature, and use it to explain how the loop maintains homeostasis when a person becomes too hot.
The question asks you to construct a loop and then explain with it. The construction earns marks on its own — components in the right order, arrows showing the direction of information — and the explanation must then use it rather than start again.
6 marks: roughly two for the loop's structure, two for correct thermoregulation detail, and two for explaining how the response opposes the change. Write the loop out as a labelled sequence.
Set point: body temperature about 37 degrees Celsius. Stimulus: body temperature rises above the set point. Receptor: temperature receptors in the skin and in the hypothalamus detect the rise. Control centre: the hypothalamus compares the temperature with the set point and signals a response. Effectors: the sweat glands and the smooth muscle of the skin arterioles. Response: sweating and vasodilation. The loop then closes, because temperature falls back toward the set point.
Both responses remove heat. Sweat secreted onto the skin surface evaporates, and evaporation absorbs heat from the body, cooling it. Vasodilation widens the arterioles supplying the skin, so more warm blood flows close to the surface and more heat is radiated away to the surroundings.
These responses act in the opposite direction to the stimulus: the stimulus was a rise in temperature, and the response causes a fall. This is precisely what makes the mechanism negative feedback — the word "negative" refers to the response acting against the change, not to anything decreasing or being harmful.
As temperature falls back toward 37 degrees, the original stimulus is reduced. The receptors detect less deviation, the hypothalamus reduces its signalling, and sweating and vasodilation diminish. The loop is self-limiting: the response switches itself down as it succeeds, so temperature settles close to the set point rather than overshooting into the cold.
This is the maintenance of homeostasis: a variable is held within a narrow range around a set point despite disturbances from outside. The same loop operates in the opposite direction — if temperature falls below the set point, the hypothalamus triggers shivering and vasoconstriction instead — so one system corrects deviations either way, which is what maintaining a stable internal environment requires.
With the set point at about 37 degrees Celsius, the loop runs: stimulus, body temperature rises above the set point; receptor, temperature receptors in the skin and hypothalamus detect the rise; control centre, the hypothalamus compares the temperature with the set point and signals a response; effectors, the sweat glands and the smooth muscle of the skin arterioles; response, sweating and vasodilation; and the loop closes as temperature falls back toward the set point. Both responses remove heat: sweat secreted onto the skin evaporates, and evaporation absorbs heat from the body, while vasodilation widens the arterioles supplying the skin so that more warm blood flows near the surface and more heat is radiated away. These responses act in the opposite direction to the stimulus, since the stimulus was a rise and the response produces a fall, and that opposition is what makes the mechanism negative feedback — "negative" refers to the direction of the response, not to anything decreasing or harmful. As temperature falls back toward 37 degrees the original stimulus is reduced, so the receptors detect less deviation, the hypothalamus reduces its signalling, and sweating and vasodilation diminish; the loop is therefore self-limiting, switching itself down as it succeeds, so temperature settles close to the set point rather than overshooting into the cold. This is the maintenance of homeostasis, a variable held within a narrow range around a set point despite outside disturbance, and the same loop operates in the opposite direction, triggering shivering and vasoconstriction when temperature falls below the set point, so a single system corrects deviations either way.
Distinguish between negative and positive feedback, and explain why positive feedback would be unsuitable for the control of body temperature.
Distinguish asks for the point of difference — the criterion that separates the two. Here it is the direction of the response relative to the stimulus, and everything else follows from it.
4 marks. State the criterion, give each mechanism in those terms, then apply positive feedback to temperature and show what goes wrong.
The two are distinguished by the direction in which the response acts relative to the change that triggered it. In negative feedback the response opposes the change, acting to reverse it; in positive feedback the response reinforces the change, acting to amplify it.
Because a negative feedback response reverses the change, it returns the variable toward its set point and the system is self-correcting and stable, with the variable oscillating gently around the set point. Because a positive feedback response amplifies the change, it drives the variable further from its starting value, so the system is self-reinforcing and runs away until some external event halts it. Positive feedback is not abnormal — it drives childbirth contractions and blood clotting — but it produces escalation rather than stability.
Under positive feedback, a rise in body temperature above 37 degrees would trigger a response that raised it further — more heat generated rather than less. Receptors would detect a still greater deviation, the hypothalamus would signal a still stronger heating response, and temperature would climb without limit. The same would occur downward: a small fall would trigger further cooling and the body would continue to lose heat. In either direction the variable would run away from the set point instead of returning to it, and within a few degrees it would cross the critical tolerance limit at which enzymes denature and cells die. Homeostasis requires a mechanism that opposes change, so only negative feedback can maintain body temperature.
Negative and positive feedback are distinguished by the direction in which the response acts relative to the change that triggered it: in negative feedback the response opposes the change and acts to reverse it, while in positive feedback the response reinforces the change and acts to amplify it. Because a negative feedback response reverses the change, it returns the variable toward its set point, so the system is self-correcting and the variable oscillates gently around that point; because a positive feedback response amplifies the change, it drives the variable further from its starting value, so the system escalates until some external event halts it. Positive feedback is not abnormal — it drives childbirth contractions and blood clotting — but it produces escalation rather than stability. Applied to body temperature, positive feedback would mean that a rise above 37 degrees triggered a response raising it further: receptors would detect a still greater deviation, the hypothalamus would signal a still stronger heating response, and temperature would climb without limit; a small fall would likewise trigger further cooling. In either direction the variable would run away from the set point rather than returning to it, and within a few degrees it would cross the critical tolerance limit at which enzymes denature and cells die. Homeostasis requires a mechanism that opposes change, so only negative feedback can maintain body temperature.
Practise independently
Answer in your own words first. The model answers are for checking, not for copying.
Multiple Choice
+5 XPA fresh set drawn from this lesson's question bank, feedback shown immediately. +5 XP per correct · +25 XP all correct
Pick your answer, then rate your confidence, that tells the system what to drill next.
Short Answer, 3 questions · 14 marks
+5 XPAnalyseBand 6(6 marks) 1. Construct a negative feedback loop for the control of body temperature, and use it to explain how the loop maintains homeostasis when a person becomes too hot.
2 marks: loop includes all components (stimulus, receptor, control centre, effector, response) in correct order · 2 marks: correct thermoregulation detail (receptors, hypothalamus, sweating/vasodilation) · 2 marks: explains that the response opposes the change to return temperature to the set point
UnderstandBand 4(3 marks) 2. Explain why the mechanism is called negative feedback, and explain why positive feedback would be unsuitable for maintaining body temperature.
1 mark: negative refers to the response acting in the opposite direction to the change, not to anything decreasing or being harmful · 1 mark: explains that positive feedback amplifies the change rather than opposing it · 1 mark: applies this to temperature, a rise would trigger further heating and the variable would run away from the set point
ApplyBand 5–6(5 marks) 3. Construct a negative feedback loop for the control of body temperature when a person becomes too cold, naming each component, and then explain how the same loop demonstrates the maintenance of homeostasis when the person becomes too hot.
1 mark: the cold loop names stimulus and receptor correctly · 1 mark: names the hypothalamus as control centre and correct effectors · 1 mark: names shivering and vasoconstriction as the response and states that it opposes the change · 1 mark: gives the hot-direction response (sweating and vasodilation) with the same components · 1 mark: concludes that a single system corrects deviations in both directions, which is what maintaining homeostasis means
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Short Answer Model Answer
Q1 (6 marks): Loop: Stimulus (body temperature rises above the set point of ~37 °C) → Receptor (temperature receptors in the skin and hypothalamus detect the rise) → Control centre (the hypothalamus compares the temperature to the set point and signals a response) → Effector (sweat glands and the smooth muscle of skin arterioles) → Response (sweating increases evaporative heat loss and vasodilation increases blood flow to the skin, radiating heat away) → temperature falls back toward the set point, closing the loop. Explanation: this is negative feedback because the response (cooling) acts in the opposite direction to the stimulus (heating), opposing and reversing the original change. By detecting the deviation and responding to oppose it, the loop returns body temperature to its set point and so maintains a stable internal environment, that is, it maintains homeostasis. The same loop works in reverse if the person becomes too cold (shivering and vasoconstriction), showing how negative feedback holds the variable around the set point.
Q2 (3 marks): "Negative" describes the direction of the response relative to the change: the response acts in the opposite direction to the stimulus and therefore cancels it. A rise above the set point triggers a response that lowers the variable, and a fall below it triggers a response that raises it. It does not mean the variable is decreasing, and it does not mean anything is wrong, negative feedback is the normal, stabilising mechanism that keeps a person healthy. Positive feedback would be unsuitable because it amplifies the change instead of opposing it. Applied to body temperature, a rise above 37 °C would trigger a response that raised the temperature further, which would raise it further again, so the variable would accelerate away from the set point rather than returning to it. Within minutes it would pass the critical tolerance limit at which enzymes denature. Positive feedback does occur in the body, in childbirth and in blood clotting, but only where a process needs to be driven rapidly to completion, never where a variable must be held steady.
Q3 (5 marks): When a person becomes too cold: the stimulus is a fall in core body temperature below the set point of about 37 °C; the receptors are temperature sensors in the skin and in the hypothalamus itself; the control centre is the hypothalamus, which compares the measured temperature with the set point and signals a response; the effectors are skeletal muscle and the smooth muscle of skin arterioles; and the response is shivering, which generates heat through rapid muscle contraction, together with vasoconstriction, which reduces blood flow to the skin and so reduces heat loss. Both actions raise body temperature back toward the set point, opposing the original change and closing the loop. When the person becomes too hot, exactly the same components operate, but the response reverses: receptors detect the rise, the hypothalamus signals the sweat glands and skin arterioles, and the response is sweating, which loses heat by evaporation, and vasodilation, which increases blood flow to the skin so heat is radiated away. The loop maintains homeostasis because one system corrects deviations in both directions: whichever way the variable moves, the response opposes it, so body temperature oscillates in a narrow band around the set point rather than drifting. That is precisely what a stable internal environment means.
Retrieve and reflect
Use the spaced-review session, then compare how your thinking has changed since your opening prediction.
Check what actually stuck
A short retrieval session mixing this lesson with earlier ones, so the ideas move into long-term memory instead of fading by the exam.
Lock it in
bossYou can now construct and interpret negative feedback loop diagrams and use them to explain how homeostasis is maintained. Next lesson looks at the hypothalamus and pituitary gland, the master control centres that drive many of these loops through hormones.
↩ Back to focus-area hubHow did your thinking change?
At the start you listed the steps to cool down on a hot day. In feedback terms these are: the receptor detects the heat, the control centre (hypothalamus) processes it, and the effectors (sweat glands and skin blood vessels) carry out the response (sweating and vasodilation), which opposes the rise and returns temperature to the set point.
If you thought "negative" feedback meant something was going wrong, revisit the misconception box: negative simply means the response reverses the change, and it is the normal mechanism that keeps you stable.