GCSE · Biology · Edexcel · Spec 1BI0

Glucagon control of blood glucose

You skipped breakfast, then sprinted for the bus. Your blood glucose is dropping, so what stops it sliding too far? Meet glucagon.

Low blood glucose

Rebuild the loop, then break it

3 stages are missing. Use the rest of the loop to work out which goes where.

Stage 1: Blood glucose concentration falls
This happens during fasting, and during exercise, when respiration speeds up to supply the contracting muscles with energy.
Stage 3: The pancreas secretes glucagon into the blood plasma
It does this because blood glucose is too low.
Stage 6: Blood glucose rises back to normal
The pancreas keeps detecting increases and decreases, so the loop can start again whenever blood glucose drops.

…and stage 6 leads back to stage 1.

Opposite hormones, opposite jobs

GlucagonvsInsulin

Both come from the pancreas. They push blood glucose in opposite directions.

Focus

Effect on blood glucose

Glucagon

Raises it

Insulin

Lowers it

The insight

This is the headline difference: the two hormones have opposite effects, so they pull blood glucose back from opposite sides.

What it causes

Glucagon

Glycogen is converted into glucose

Insulin

Glucose is converted into glycogen

Secreted when blood glucose is

Glucagon

Too low

Insulin

Too high

Target cells

Glucagon

The liver

Insulin

The liver and the muscles

Predict, then check

Commit to an answer before you look.

Jo skipped breakfast and then ran a hard cross-country race. What is happening to Jo's blood glucose, and what does the pancreas do about it?

Untangle the look-alikes

Which idea sounds closest to yours?

Blood glucose has dropped and the body is putting it right.

Which of these is closest to what you think right now?

Glucagon and glycogen are basically the same thing, just spelled differently.Glucagon is there to bring blood glucose down.The liver notices that blood glucose has dropped.The pancreas detects the drop and secretes glucagon. Glucagon makes the liver turn its glycogen into glucose.

How sure are you?

I'm sureI think soI'm guessing

Glucagon and glycogen are basically the same thing, just spelled differently.

This is a common misconception

They look almost identical, which is why this trips people up, but they are different kinds of thing. Glucagon is a hormone secreted by the pancreas. Glycogen is a stored form of glucose found in liver and muscle cells. One is the message, the other is the store the message unlocks.

Glucagon is there to bring blood glucose down.

This is a common misconception

This one is easy to mix up with insulin. It is insulin that lowers blood glucose. Glucagon has the opposite effect: it raises blood glucose by causing glycogen to be converted into glucose.

The liver notices that blood glucose has dropped.

This is a common misconception

The liver does the responding, so it feels like it should be doing the noticing too. But the pancreas is the organ that detects changes in blood glucose concentration. The liver acts once glucagon reaches it.

The pancreas detects the drop and secretes glucagon. Glucagon makes the liver turn its glycogen into glucose.

This matches the evidence

Yes. Glucagon is the hormone, glycogen is the store, and the liver releases glucose into the blood so blood glucose rises back to normal.

Glucagon is the hormone from the pancreas. Glycogen is the stored glucose in liver and muscle cells. Glucagon raises blood glucose by acting on the liver.

Why bother?

Reason it through

Why does the body work so hard to keep blood glucose within narrow limits?

Link 1 of 4

First link · your turn

What do your cells use the glucose from the blood for, and when do they need it?

Locked — reveal the link above first

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The pancreas gives the signal, the liver opens its glycogen store, and blood glucose climbs back to normal.

What you need to know

Glucose is a sugar carried in the blood plasma to cells, which need a constant supply for respiration, even at rest.
Homeostasis regulates internal conditions to keep them optimum for enzyme action and all cell functions; blood glucose concentration is one of them.
Blood glucose rises after sugary or carbohydrate food, and falls during fasting, and during exercise as respiration speeds up.
Have a goA classmate swears that wolfing down a big bowl of pasta (a carbohydrate food) makes your blood glucose fall. Are they right?
No. Blood glucose rises after carbohydrate food.
Sugary and carbohydrate foods push blood glucose up; fasting and exercise are what make it fall.
The pancreas is a gland that detects changes in blood glucose and secretes the hormones insulin and glucagon.
Glycogen is a stored form of glucose, found in liver and muscle cells.
When blood glucose is too low, the pancreas secretes glucagon, which travels in the blood plasma to the liver.
Glucagon stops liver cells absorbing glucose, and makes the liver turn glycogen into glucose and release it.
Have a goGlucagon stops liver cells absorbing glucose from the blood. If that glucose stays in the blood instead, does blood glucose go up or down?
Up. The glucose stays in the blood instead of being taken in.
Absorbing glucose takes it out of the blood, so stopping that, and releasing glucose from glycogen, both push the level up.
Insulin does the opposite: the pancreas secretes it when blood glucose is too high, and it lowers blood glucose.
Have a goThe pancreas has just secreted insulin. Was blood glucose too high or too low a moment ago?
Too high.
Insulin is the answer to blood glucose that is too high; blood glucose that is too low gets glucagon instead.
Too low, and a person could fall into a coma, which can be fatal. High for long, and organs can stop functioning properly.

The big picture

When blood glucose concentration is too low, the pancreas secretes the hormone glucagon. Glucagon travels in the blood plasma to the liver, where it stops liver cells absorbing glucose and makes the liver turn stored glycogen into glucose and release it, so blood glucose rises back to normal. Insulin does the opposite job when blood glucose is too high, and all of this matters because blood glucose that is too low could lead to a coma, while blood glucose that stays high for a long time can stop organs functioning properly.

Key points

1Low blood glucose: the pancreas secretes glucagon, glucagon reaches the liver, the liver turns glycogen into glucose and releases it, and blood glucose rises back to normal.

2Glucagon is a hormone. Glycogen is a stored form of glucose in liver and muscle cells.

3Glucagon and insulin have opposite effects: glucagon raises blood glucose and insulin lowers it.

4The pancreas keeps blood glucose in an ideal range by detecting increases and decreases and secreting insulin or glucagon.

5Blood glucose too low could lead to a coma, which can be fatal; blood glucose high for a long time can stop organs functioning properly.

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Worked example

Problem

Zoe drinks a large bottle of sugary drink. Explain how her body brings her blood glucose concentration back to normal.

⚠ Watch out

Mixing up the names. Glucagon is the hormone and glycogen is the store. Watch for two more traps: saying glucagon lowers blood glucose (it is insulin that does that), and saying the liver detects the change (the pancreas detects it).

🧠

Memory hook

Glucagon is the key, glycogen is the locked store. The pancreas turns the key, the liver opens the store, and glucose flows back into the blood.

✓

Check yourself

Close the page and tell the low-blood-glucose story in four beats: what happens to blood glucose, which organ detects it, what that organ secretes, and what the liver then does.

Flashcards

(12)

Where does glucose travel in the body, and what do cells use it for?

It travels in the blood plasma and is delivered to cells for respiration. Cells need a constant supply, even at rest.

What is homeostasis?

The regulation of internal conditions to maintain the optimum for enzyme action and all cell functions.

Which organ detects changes in blood glucose concentration?

The pancreas, a gland that secretes the hormones insulin and glucagon.

What is glycogen, and where is it found?

A stored form of glucose, found in liver and muscle cells.

Glucagon or glycogen: which is the hormone and which is the store?

Glucagon is the hormone. Glycogen is the store of glucose.

What does the pancreas secrete when blood glucose is too low, and where does it travel?

Glucagon, which travels in the blood plasma to the liver.

What does glucagon do to liver cells?

It stops them absorbing glucose from the blood and causes the liver to turn glycogen into glucose and release it.

What happens to blood glucose when glucagon reaches the liver?

It rises back to normal.

Which cells are insulin's target cells?

Cells in the liver and muscles.

How do glucagon and insulin compare?

They have opposite effects. Glucagon raises blood glucose (glycogen to glucose); insulin lowers it (glucose to glycogen).

When does blood glucose concentration rise, and when does it fall?

It rises after eating or drinking foods containing sugar or carbohydrates. It falls during fasting and during exercise.

Why must blood glucose be kept within narrow limits?

Too low, a person could fall into a coma, which can be fatal. High for a long time, organs can stop functioning properly.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Rebuild the loop, then break it

Which idea sounds closest to yours?

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