Blood Glucose Regulation and Diabetes

This lesson covers how the body regulates blood glucose concentration and the causes and treatments of diabetes, as required by the AQA GCSE Combined Science Trilogy specification (8464). Blood glucose regulation is one of the most important examples of homeostasis and negative feedback.

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Why Must Blood Glucose Be Controlled?

Blood glucose concentration must be maintained within a narrow range:

• Too high (hyperglycaemia) — can damage blood vessels, nerves, and organs over time; can be immediately dangerous in extreme cases.
• Too low (hypoglycaemia) — cells cannot carry out respiration, leading to weakness, confusion, loss of consciousness, and potentially death.

The pancreas is the organ responsible for monitoring and regulating blood glucose concentration.

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The Role of the Pancreas

The pancreas contains specialised cells that continuously monitor the concentration of glucose in the blood and respond accordingly:

Blood Glucose Level	Pancreas Response	Hormone Released	Effect on the Body
Too high (e.g. after a meal)	Beta cells detect the rise	Insulin	Insulin causes glucose to move from the blood into cells; excess glucose is converted to glycogen and stored in the liver and muscles
Too low (e.g. during exercise)	Alpha cells detect the fall	Glucagon	Glucagon causes glycogen in the liver to be converted back to glucose and released into the blood

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Insulin and Glucagon — A Negative Feedback System

Blood glucose regulation is an excellent example of negative feedback:

flowchart TD
    A["Normal blood glucose level"] --> B{"Blood glucose changes"}
    B -->|"Blood glucose RISES\n(e.g. after eating)"| C["Pancreas detects rise"]
    C --> D["Beta cells release INSULIN"]
    D --> E["Liver and muscle cells take up glucose\nGlucose → Glycogen (stored)"]
    E --> A
    B -->|"Blood glucose FALLS\n(e.g. during exercise)"| F["Pancreas detects fall"]
    F --> G["Alpha cells release GLUCAGON"]
    G --> H["Liver converts glycogen → glucose\nGlucose released into blood"]
    H --> A

Exam Tip: Insulin and glucagon have opposite effects. Think of them as a seesaw: insulin lowers blood glucose; glucagon raises it. They work antagonistically.

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Key Terminology

Term	Definition
Glycogen	A storage polysaccharide made from many glucose molecules joined together; stored in the liver and muscles
Insulin	A hormone produced by the pancreas that lowers blood glucose concentration
Glucagon	A hormone produced by the pancreas that raises blood glucose concentration
Negative feedback	A process where the response counteracts the original change, returning the system to its set point

Worked Example

A student eats a meal containing a large amount of carbohydrate. Describe how their blood glucose concentration is returned to normal.

Model answer:

1. Carbohydrates are digested into glucose, which is absorbed into the blood, causing blood glucose concentration to rise.
2. The pancreas detects the rise in blood glucose.
3. Beta cells in the pancreas secrete insulin into the blood.
4. Insulin travels to the liver (and muscle cells), where it causes cells to take up glucose from the blood.
5. Excess glucose is converted to glycogen for storage.
6. Blood glucose concentration falls back to the normal level.
7. When the normal level is restored, the pancreas stops releasing insulin (negative feedback).

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Diabetes

Diabetes is a condition where the body cannot regulate blood glucose concentration properly. There are two types:

Type 1 Diabetes

Feature	Detail
Cause	The immune system destroys the beta cells in the pancreas
Result	The pancreas produces little or no insulin
Onset	Usually develops in childhood or young adulthood
Risk factors	Largely genetic — not linked to lifestyle
Treatment	Regular insulin injections (or insulin pump) and careful monitoring of blood glucose and diet

Type 2 Diabetes

Feature	Detail
Cause	Body cells become resistant to insulin (insulin is still produced but cells do not respond to it properly)
Result	Blood glucose concentration remains high after meals
Onset	Usually develops in adulthood (but increasingly seen in younger people)
Risk factors	Obesity, lack of exercise, high-sugar diet, genetic predisposition
Treatment	Controlled by diet (low sugar, high fibre), regular exercise, and sometimes medication (e.g. metformin); in severe cases, insulin injections

Comparing Type 1 and Type 2 Diabetes

Feature	Type 1	Type 2
Insulin production	None (or very little)	Insulin is produced but cells are resistant
Age of onset	Childhood / young adulthood	Usually adulthood
Main risk factor	Genetic / autoimmune	Obesity and lifestyle
Treatment	Insulin injections	Diet, exercise, medication
Can it be prevented?	No	Often — through healthy lifestyle

Exam Tip: Type 2 diabetes is much more common than Type 1 and is increasing in prevalence. The examiners often ask about risk factors for Type 2 diabetes — always mention obesity and lack of exercise.

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Common Mistakes

• Confusing insulin and glucagon — insulin lowers blood glucose; glucagon raises it. Never mix them up.
• Saying "insulin breaks down glucose" — insulin does not break down glucose. It causes glucose to be taken up by cells and converted to glycogen for storage.
• Confusing glycogen and glucagon — glycogen is a storage molecule; glucagon is a hormone. They sound similar but are very different.
• Saying Type 2 diabetics "don't produce insulin" — they do produce insulin, but their cells are resistant to it.

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Summary

• The pancreas monitors blood glucose and releases insulin (to lower it) or glucagon (to raise it).
• This is an example of negative feedback — the response counteracts the original change.
• Type 1 diabetes: autoimmune destruction of beta cells → no insulin → treated with insulin injections.
• Type 2 diabetes: cells become resistant to insulin → treated with diet, exercise, and medication.
• Obesity and inactivity are major risk factors for Type 2 diabetes.
• This is a key topic in AQA GCSE Combined Science Trilogy (8464), Paper 1: Biology.

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Extended Examples and Exam Technique

Extended Worked Example — Graph Interpretation

A student measures blood glucose concentration every 15 minutes after eating a high-carbohydrate meal. The mean trace is summarised below: