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Learn9700Paper 4 · A Level Structured QuestionsHomeostasisBlood glucose control
Homeostasis · Subtopic 2 of 2

Blood Glucose Control

Blood glucose is kept near 5 mmol dm⁻³ by the islets of Langerhans in the pancreas. High glucose: β cells release insulin, which binds receptors on liver, muscle and fat cells; more GLUT4 transporters move to membranes; glucose is converted to glycogen (glycogenesis) and fat, and respiration increases. Low glucose: α cells release glucagon, which binds liver receptors; via the second messenger cyclic AMP and an enzyme cascade (protein kinase), glycogen is broken down (glycogenolysis) and glucose is made from amino acids and glycerol (gluconeogenesis). Adrenaline also raises glucose via cAMP. Type 1 diabetes: no insulin (autoimmune), treated with insulin injections. Type 2: cells less responsive to insulin, linked to obesity; treated with diet, exercise and drugs. Glucose is measured with test strips/biosensors using glucose oxidase.

Cambridge 9700 Paper 4Edexcel YBI11 WBI15AQA 7402 Paper 2≈ 45 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe how insulin and glucagon control blood glucose.
  • Explain the cAMP second messenger cascade.
  • Compare type 1 and type 2 diabetes.
  • Describe glucose testing.
Pause and think

Why does one glucagon molecule cause so many glucose molecules to be released?

Section 2 of 14

Core idea

Start hereStaying at 5

Eat a cake or skip lunch, and your blood glucose still returns to about 5 mmol dm⁻³.

The big idea

Insulin lowers blood glucose; glucagon raises it. Glucagon works through cyclic AMP, a second messenger that amplifies the signal.

Glucagon signalling in a liver cell

Each step amplifies the signal.

Worked exampleAfter a meal

Glucose rises from 5.0 to 9.0 mmol dm⁻³. % increase and response?

Goal
% and hormone.
Strategy
Change ÷ original.
  1. 9.0−5.05.0×100=80%\frac{9.0-5.0}{5.0}\times100=80\%
    Percentage change.
  2. β cells release insulin\beta\text{ cells release insulin}
    Glucose uptake and glycogenesis lower it.
Answer80% rise; insulin released.
✓ CheckNegative feedback ✓.

Summary

  • Insulin vs glucagon.
  • cAMP cascade.
  • Type 1 vs type 2.
Key words
Second messenger
Molecule inside a cell that relays a hormone signal.
Glycogenolysis
Breakdown of glycogen to glucose.
HistoryBanting and Best, 1921. Frederick Banting and Charles Best extracted insulin from dog pancreases; a year later it saved the life of 14-year-old Leonard Thompson.
Fun factContinuous monitors. Many people with diabetes now wear a skin sensor that reads glucose every few minutes and sends it to their phone.
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