11.2 The Control of Blood Glucose Levels

A free GCSE Biology lesson for AQA (8461) from OBA School: how the pancreas uses insulin and glucagon to keep blood glucose steady. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Explain why the blood glucose concentration must be kept within narrow limits
• Describe how the pancreas and insulin lower a high blood glucose concentration
• Explain how glucagon raises a low blood glucose concentration and how it interacts with insulin (Higher tier)
• Interpret graphs of blood glucose and insulin concentration

Key words

• Blood glucose concentration: How much glucose is dissolved in the blood, often measured in mmol per litre.
• Pancreas: The organ that monitors and controls the blood glucose concentration.
• Insulin: Hormone from the pancreas that makes glucose move from the blood into cells.
• Glycogen: An insoluble store of carbohydrate made from glucose in liver and muscle cells.
• Glucagon: (Higher tier) Hormone from the pancreas that makes liver cells convert glycogen into glucose.
• Negative feedback: A change away from the normal level causes a response that brings it back towards normal.

Why blood glucose must be controlled

Every cell needs glucose for respiration, to release energy. The blood carries glucose to cells. Keeping the conditions inside the body steady is called homeostasis, and the blood glucose concentration is one thing that must be kept within narrow limits.

• Too low: cells, especially brain cells, do not get enough glucose for respiration. A person may feel shaky and confused and can lose consciousness.
• Too high for long periods: this damages blood vessels, nerves, the eyes and the kidneys.
• For most healthy people the level stays at roughly 4 to 7 mmol per litre.

• Eating and digesting carbohydrates (starch and sugars), which are absorbed into the blood as glucose; Makes blood glucose fall Exercise: muscle cells respire faster and take more glucose from the blood
• Glucagon making the liver release glucose (Higher tier); Makes blood glucose fall Insulin making cells take in glucose; going a long time without food

Lowering blood glucose: insulin

The pancreas monitors the blood glucose concentration. If it is too high, the pancreas secretes the hormone insulin into the blood.

• Insulin causes glucose to move from the blood into cells, where it can be used for respiration.
• In liver and muscle cells, excess glucose is converted into glycogen for storage.
• So the blood glucose concentration falls back towards normal.

Key fact: Insulin lowers blood glucose. Glycogen is a store; glucose is the sugar; glucagon is a hormone.

Raising blood glucose: glucagon (Higher tier)

If the blood glucose concentration is too low, the pancreas secretes a second hormone, glucagon. Glucagon causes liver cells to convert glycogen into glucose, which is released into the blood. The level rises back towards normal.

Insulin and glucagon work against each other in a negative feedback cycle. A rise causes insulin release, which brings the level down; a fall causes glucagon release, which brings it up. The level keeps swinging back towards normal.

• Released when blood glucose is…; Insulin too high; Glucagon (Higher tier) too low
• Made by; Insulin the pancreas; Glucagon (Higher tier) the pancreas
• Main effect; Insulin glucose moves into cells; liver and muscles make glycogen; Glucagon (Higher tier) liver converts glycogen into glucose
• Effect on blood glucose; Insulin falls; Glucagon (Higher tier) rises

Worked example: exam tip

“Explain how blood glucose is returned to normal after a long run.” (3 marks)
Pancreas detects the low level (1) and secretes glucagon (1). Glucagon makes the liver convert glycogen into glucose, which is released into the blood (1).

Answer: Spell glycogen and glucagon carefully: examiners will not guess.

Reading glucose and insulin graphs

The graph shows made-up but realistic data for a healthy person who ate a meal at time 0.

• Glucose rises first as the meal is digested and glucose is absorbed into the blood.
• Insulin rises after glucose, because the pancreas responds to the rise.
• Once insulin is high, glucose falls back towards the starting level; then insulin falls too.

Worked example: a rate from a graph

Calculate the mean rate of increase in blood glucose in the first 45 minutes.
Change = 7.6 − 5.0 = 2.6 mmol per litre. Rate = 2.6 ÷ 45 = 0.0578…
Percentage increase = 2.6 ÷ 5.0 × 100 = 52%.

Answer: 0.058 mmol per litre per minute (2 s.f.)

Common mistakes

• Mixing up glucose (the sugar), glycogen (the store) and glucagon (the hormone).
• Saying insulin “turns glucose into glycogen in the blood”. The conversion happens inside liver and muscle cells.
• Saying the liver makes insulin. Both insulin and glucagon are made by the pancreas.
• Saying glucagon is released after a meal. It is released when blood glucose is too low.

Revision questions

Try these, then check your answers below each one.

Question 1. Which organ monitors and controls the blood glucose concentration? (Choose from: Liver, Pancreas, Kidney, Stomach.)

Answer: Pancreas

Working: The pancreas monitors blood glucose and releases insulin (and glucagon) to control it.

Question 2. What is the effect of insulin? (Choose from: It makes glucose move from the blood into cells, It makes the liver convert glycogen into glucose, It raises the blood glucose concentration, It is made by the liver.)

Answer: It makes glucose move from the blood into cells

Working: Insulin causes glucose to move from the blood into cells, and liver and muscle cells store excess as glycogen, so blood glucose falls.

Question 3. Name the insoluble storage carbohydrate made from excess glucose in liver and muscle cells.

Answer: glycogen

Working: Excess glucose is converted into glycogen for storage in the liver and muscles.

Related lessons

• Previous lesson: 11.1 Principles of Hormonal Control
• Next lesson: 11.3 Treating Diabetes
• In this chapter: 11.4 The Role of Negative Feedback
• In this chapter: 11.5 Human Reproduction
• In this chapter: 11.6 Hormones and the Menstrual Cycle

Continue in the full course

This lesson is section 11.2 (AGCBH1102) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.