The big idea: Your blood glucose must be kept within narrow limits — too high or too low is dangerous — even though you eat in bursts and burn glucose all the time.
The pancreas does this. It constantly monitors blood glucose and releases one of two hormones to correct any change:
Insulin — released when glucose is too high; it lowers it.
Glucagon — released when glucose is too low; it raises it.
The two hormones pull in opposite directions (they are antagonistic), so the level is held close to a set point — this is negative feedback.
Blood glucose is held near its set point by negative feedback: a change (glucose too high or too low) is detected by the pancreas, which releases a hormone whose effect OPPOSES the change and pushes glucose back to normal.
Interactive diagram
Explore the labelled diagram, charts and maps for this topic in full study mode.
- Blood glucose
- The amount of glucose (sugar) dissolved in the blood; it must be kept within narrow limits around a set point.
- Homeostasis
- Keeping the body's internal conditions (such as blood glucose) steady, close to a set point.
- Pancreas
- The organ that monitors blood glucose and secretes insulin and glucagon to control it.
- Insulin
- A hormone from the pancreas, released when glucose is too high. It makes the liver and muscles take up glucose and store it as glycogen, lowering blood glucose.
- Glucagon
- A hormone from the pancreas, released when glucose is too low. It makes the liver break glycogen down into glucose, raising blood glucose.
- Glycogen
- The storage form of glucose, kept mainly in the liver and muscles. It is built up by insulin and broken down by glucagon.
- Antagonistic hormones
- A pair of hormones with opposite effects — here insulin lowers glucose while glucagon raises it.
Don't mix up the two 'gluc-' words: Glucagon is the hormone that raises blood glucose.
Glycogen is the storage molecule (made of many glucose units).
Memory hook: glucaGON means glucose is gone (low) — so it brings glucose back.
The control loop runs in two directions — one for when glucose is too high, one for when it is too low.
Read each as a chain of cause and effect: a change is detected by the pancreas, which releases a hormone, and the hormone's effect opposes the change and brings glucose back to normal.
When glucose is TOO HIGH (after a meal)
- You eat — glucose is absorbed and blood glucose rises above the set point.
- The pancreas detects the rise and releases insulin.
- Insulin makes liver and muscle cells take up glucose from the blood.
- These cells store the glucose as glycogen (and use more for respiration).
- Blood glucose falls back to normal — and as it does, insulin release stops.
The high-glucose arm: after a meal glucose rises above normal → the pancreas detects it and releases INSULIN → the liver and muscles take up glucose and store it as glycogen → glucose falls back to the set point.
Interactive diagram
Explore the labelled diagram, charts and maps for this topic in full study mode.
When glucose is TOO LOW (between meals)
- Time passes / you exercise — glucose is used up and blood glucose falls below the set point.
- The pancreas detects the fall and releases glucagon.
- Glucagon makes liver cells break glycogen down into glucose.
- The glucose is released into the blood.
- Blood glucose rises back to normal — and as it does, glucagon release stops.
The low-glucose arm: between meals glucose falls below normal → the pancreas detects it and releases GLUCAGON → the liver breaks glycogen back down to glucose → glucose rises back to the set point.
Interactive diagram
Explore the labelled diagram, charts and maps for this topic in full study mode.
Why this is negative feedback: In both arms the response opposes the change:
A rise triggers insulin, which lowers glucose. A fall triggers glucagon, which raises glucose.
Because the correction always pushes glucose back towards the set point, the level is held steady within narrow limits. That self-correcting pattern is negative feedback.
The two hormones are antagonistic — opposite effects — which is exactly what lets the body correct a change in either direction.
| Insulin | Glucagon | |
|---|---|---|
| Released when | Blood glucose is too HIGH (e.g. after a meal) | Blood glucose is too LOW (e.g. between meals, exercising) |
| Made by | The pancreas (β cells) | The pancreas (α cells) |
| Main targets | Liver and muscle cells | Liver cells |
| What it makes cells do | Take up glucose from the blood and store it as glycogen | Break glycogen back down into glucose and release it into the blood |
| Effect on blood glucose | LOWERS it back to normal | RAISES it back to normal |
The role of the liver: The liver is the body's glucose bank.
Under insulin it takes glucose out of the blood and locks it away as glycogen (deposit).
Under glucagon it breaks glycogen back down and releases glucose into the blood (withdrawal).
So most of the actual storing and releasing happens in the liver — the hormones just give the orders.
Reading a blood-glucose graph: On a Paper 1 graph you may be asked to explain a trend over a time window.
A fall in glucose (e.g. in the hours after a meal) is explained by: glucose rose → insulin was released → cells took up glucose and stored it as glycogen → so glucose fell.
A rise between meals is explained the other way: glucose fell → glucagon released → glycogen broken down → glucose rose.
Know your predicted grade
Take timed mock exams and get detailed feedback on every answer. See exactly where you're losing marks.
How this is tested: The big one is a 7-mark Describe/Explain on Paper 2: describe how blood glucose is kept within narrow limits, or explain how tissue glucose is regulated. Score points for both arms of the loop — pancreas detects; insulin on a rise (uptake + glycogen storage); glucagon on a fall (glycogen → glucose); antagonistic; negative feedback.
A 4-mark Describe asks for the role of two named hormones — name insulin AND glucagon and give each one's effect.
On Paper 1 a 1-mark item may ask you to identify a function of the pancreas (it monitors glucose and secretes insulin and glucagon), or to read a glucose graph / bar chart and explain a trend or deduce a drug's effect.
IB-style question — how blood glucose is kept within narrow limits
Describe how blood glucose concentration is kept within narrow limits in humans. [7]
How to score all seven marks
- Set point + monitor. Blood glucose is kept close to a set point; the pancreas monitors the blood glucose level.
- Rise detected → insulin. When glucose rises (e.g. after a meal), the pancreas releases insulin.
- Insulin's effect. Insulin makes liver and muscle cells take up glucose and store it as glycogen, so blood glucose falls back to normal.
- Fall detected → glucagon. When glucose falls (e.g. between meals), the pancreas releases glucagon.
- Glucagon's effect. Glucagon makes the liver break glycogen down into glucose and release it, so blood glucose rises back to normal.
- Antagonistic pair. Insulin and glucagon have opposite effects (antagonistic), so glucose can be corrected in either direction.
- Negative feedback. Because each response opposes the change and returns glucose to the set point, the level is held within narrow limits — this is negative feedback. (Award 1 mark per distinct point, up to 7.)
Final answer
The pancreas monitors blood glucose. A rise releases insulin → liver/muscle take up glucose and store it as glycogen → glucose falls. A fall releases glucagon → liver breaks glycogen down to glucose → glucose rises. The two hormones are antagonistic, and each response opposes the change (negative feedback), so the level stays within narrow limits.
✓ Why this scores full marks: It covers both arms of the loop (insulin on a rise, glucagon on a fall), names the store (glycogen) and the organ (liver), and ties it together with the two key terms antagonistic and negative feedback.
A common way to lose marks is to describe only insulin — a 7-mark answer needs the glucagon (low-glucose) arm too.
| Situation | Hormone released | Response (what cells do) | Result |
|---|---|---|---|
| Glucose too HIGH (after eating) | Insulin (pancreas) | Liver and muscle take up glucose → store as glycogen | Glucose falls to set point |
| Glucose too LOW (between meals) | Glucagon (pancreas) | Liver breaks glycogen down → glucose into blood | Glucose rises to set point |