Explain glucagon and liver release when glucose falls
Follow glycogen breakdown and return glucose to the blood.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall hormone production and blood transport, respiration, liver storage and electrical impulses along neurones.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is glycogen in this pathway?
What you will learn
- Trace the pancreatic glucagon signal
- Connect liver glycogen breakdown with rising blood glucose
Explain glucagon and liver release when glucose falls
| Feature | Meaning |
|---|---|
| Hormone | Glucagon from pancreas |
| Liver reaction | Glycogen → glucose |
| Release | Glucose enters blood |
| Result | Blood glucose concentration increases |
Trace the pancreatic glucagon signal
When blood glucose concentration falls below its regulated level, the pancreas secretes more glucagon. Glucagon travels in blood to the liver and changes its activity. It is a different pancreatic hormone from insulin. A low-glucose response needs a mechanism that raises concentration rather than one that stores more of the available glucose.
Glucagon promotes breakdown of liver glycogen to glucose. The liver releases this glucose into the blood, increasing blood glucose concentration. Both the breakdown and release links matter: simply naming glycogen does not explain the direction of the blood change. The required arrow is glycogen → glucose, followed by release into circulating blood.
Connect liver glycogen breakdown with rising blood glucose
The liver acts as a storage and release organ, whereas the pancreas supplies the hormone signal. Do not claim that glucagon is glycogen or that the liver secretes glucagon. This lesson focuses on liver glycogen as required by the syllabus; it does not claim that muscle glycogen is directly exported as free glucose to the blood in the same way.
As blood glucose moves back towards its regulated level, the stimulus for increased glucagon secretion decreases. Negative feedback can therefore produce an increase in the controlled value when the original departure was downward. The word negative describes opposition to the departure, not a requirement that every concentration change must be negative.
Pause and explain
Which chain corrects a low concentration?
Worked example
Explain how the low-glucose response raises concentration.
Show the worked solution
- Pancreas secretes glucagon, carried to the liver.
- Liver glycogen is broken down to glucose and glucose is released into blood.
Answer Pancreatic glucagon promotes liver glycogen → glucose and release into blood, increasing blood glucose concentration.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Trace the low-glucose branch through pancreas, glucagon and liver.
Give me a hint
Include glucose release into blood.
Compare my reasoning
- Pancreatic glucagon reaches liver in blood.
- Liver glycogen becomes glucose, which enters blood.
Low blood glucose → pancreatic glucagon → liver glycogen → glucose → release into blood → increased blood glucose concentration.
Look for these in your work
- Name the correct hormone
- Include breakdown and blood release
Distinguish glucagon, glycogen and glucose.
Give me a hint
Identify signal, store and released substrate.
Compare my reasoning
- Glucagon is a pancreatic hormone.
- Glycogen is stored carbohydrate; glucose is the released respiratory substrate.
Glucagon: pancreatic hormone. Glycogen: stored carbohydrate. Glucose: substrate released from liver stores into blood.
Look for these in your work
- Distinguish all three names
- Connect store and released substrate
Explain why increasing blood glucose in this branch is still negative feedback.
Give me a hint
The initial departure is below the reference.
Compare my reasoning
- The concentration is below its regulated level.
- An increase reduces that departure.
The increase opposes the initial fall and moves concentration towards its regulated level; it is therefore negative feedback.
Look for these in your work
- Identify the initial departure
- Explain the opposing response
Common mistakes
- Treating glucagon and glycogen as interchangeable names.
- Omitting release into blood after glycogen breakdown.
What can you explain now?
Which chain corrects a low concentration?
Compare with the explanation
Glucagon → liver glycogen breakdown → glucose release
The final effect raises blood glucose concentration.
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Make it stick
Trace low-glucose correction and distinguish hormone, stored carbohydrate and released glucose.
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