GCSE & A-Level Biology

Hormonal Control of Blood Glucose – The Role of Insulin and Glucagon

Keeping blood glucose within a narrow, safe range is one of the body’s most important homeostatic processes. Too high, and cells and tissues are damaged; too low, and vital organs such as the brain are starved of energy.

At both GCSE and A-Level, this topic brings together hormones, negative feedback, and metabolism in a way that exam boards love to test.

Why blood glucose must be controlled

Glucose is the main fuel for respiration. However:

High blood glucose can damage blood vessels and organs.

Low blood glucose can lead to dizziness, confusion, or loss of consciousness.

The body therefore uses hormonal control, coordinated by the pancreas, to keep glucose levels stable.

The pancreas: the control centre

The pancreas contains clusters of cells called the islets of Langerhans, which act as glucose sensors and hormone secretors.

Two key hormones are involved:

Insulin – lowers blood glucose

Glucagon – raises blood glucose

They work as an elegant antagonistic pair.

Insulin – lowering blood glucose

Insulin is released when blood glucose levels rise, for example after a carbohydrate-rich meal.

Its main effects:

Increases uptake of glucose by muscle and fat cells

Stimulates glycogenesis (conversion of glucose to glycogen) in the liver and muscles

Increases use of glucose in respiration

👉 Overall effect: blood glucose falls back to normal

Glucagon – raising blood glucose

Glucagon is released when blood glucose levels fall, such as between meals or during exercise.

Its main effects:

Stimulates glycogenolysis (breakdown of glycogen to glucose) in the liver

Stimulates gluconeogenesis (production of glucose from non-carbohydrate sources)

👉 Overall effect: blood glucose rises back to normal

Negative feedback in action

This system is a classic example of negative feedback:

If glucose rises → insulin is released → glucose falls

If glucose falls → glucagon is released → glucose rises

Once normal levels are restored, hormone secretion is reduced.

🔁 This constant adjustment keeps conditions inside the body stable.

GCSE vs A-Level focus

GCSE students should be able to:

Name insulin and glucagon

State where they are produced

Describe their effects on blood glucose

Explain negative feedback in simple terms

A-Level students also need to:

Explain cellular mechanisms (e.g. receptor binding, second messengers)

Describe glycogenesis, glycogenolysis, and gluconeogenesis in detail

Link failures in this system to diabetes mellitus

Analyse data and feedback loops in exam questions

Exam tip 💡

If a question mentions:

After a meal → think insulin

Fasting or exercise → think glucagon

Control or regulation → mention negative feedback

Why this topic matters

Beyond exams, this system underpins our understanding of:

Diabetes

Diet and metabolism

Hormonal coordination across the body

It’s a perfect example of how biology balances complexity with precision.

05 January 2026