Blood Glucose Regulation

This lesson explains how the body regulates blood glucose concentration using hormones produced by the pancreas. Understanding negative feedback in the context of blood glucose is a core part of the AQA GCSE Biology specification. This lesson also covers Type 1 and Type 2 diabetes.

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Why Must Blood Glucose Be Controlled?

Blood glucose concentration must be kept within a narrow range to ensure cells have a constant supply of glucose for cellular respiration, but not so much that it causes damage.

Condition	What Happens
Blood glucose too high	Water moves out of cells by osmosis, causing dehydration of cells; excess glucose can damage blood vessels and organs
Blood glucose too low	Cells do not have enough glucose for respiration; this can lead to unconsciousness or death
Normal range	Sufficient glucose is available for cellular respiration; cells function optimally

Sources of blood glucose:

• Eating carbohydrate-containing foods (digested to glucose and absorbed into the blood)
• Glycogen breakdown in the liver (glycogen is converted back to glucose)

Uses of blood glucose:

• Cellular respiration in all cells
• Stored as glycogen in the liver and muscles
• Converted to fat for long-term storage

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The Role of the Pancreas

The pancreas is an organ that acts as both an endocrine gland (producing hormones) and a digestive gland (producing enzymes). For blood glucose regulation, it contains clusters of cells called the Islets of Langerhans that monitor blood glucose levels and produce two key hormones:

• Insulin — produced by beta cells when blood glucose is too high.
• Glucagon — produced by alpha cells when blood glucose is too low.

Exam Tip: Do not confuse glucagon (a hormone that raises blood glucose) with glycogen (a storage molecule made from glucose). They sound similar but are completely different. Glucagon tells the liver to convert glycogen into glucose.

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When Blood Glucose Is Too High

After eating a meal rich in carbohydrates, blood glucose concentration rises. The body responds:

1. The pancreas detects the rise in blood glucose.
2. Beta cells in the pancreas release insulin into the blood.
3. Insulin travels in the blood to target cells, especially the liver and muscle cells.
4. Insulin causes cells to take up more glucose from the blood.
5. In the liver, insulin stimulates the conversion of glucose into glycogen (glycogenesis) for storage.
6. Blood glucose concentration falls back to the normal level.
7. The pancreas detects the return to normal and reduces insulin production.

flowchart TD
    A[Blood glucose rises after eating] --> B[Pancreas detects high glucose]
    B --> C[Beta cells release insulin]
    C --> D[Insulin travels in blood to liver and muscle cells]
    D --> E[Cells take up more glucose]
    D --> F[Liver converts glucose to glycogen]
    E --> G[Blood glucose falls to normal]
    F --> G
    G --> H[Pancreas reduces insulin production]

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When Blood Glucose Is Too Low

Between meals or during exercise, blood glucose concentration falls. The body responds:

1. The pancreas detects the fall in blood glucose.
2. Alpha cells in the pancreas release glucagon into the blood.
3. Glucagon travels to the liver.
4. Glucagon stimulates the liver to convert stored glycogen back into glucose (glycogenolysis).
5. Glucose is released into the blood.
6. Blood glucose concentration rises back to the normal level.
7. The pancreas detects the return to normal and reduces glucagon production.

flowchart TD
    A[Blood glucose falls during exercise or fasting] --> B[Pancreas detects low glucose]
    B --> C[Alpha cells release glucagon]
    C --> D[Glucagon travels in blood to liver]
    D --> E[Liver converts glycogen to glucose]
    E --> F[Glucose released into blood]
    F --> G[Blood glucose rises to normal]
    G --> H[Pancreas reduces glucagon production]

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Negative Feedback in Blood Glucose Regulation

The regulation of blood glucose is an excellent example of negative feedback — the response always acts to oppose the change and bring the level back to normal.

• If glucose goes up, insulin brings it down.
• If glucose goes down, glucagon brings it up.

Insulin and glucagon have opposing (antagonistic) effects, working together to keep blood glucose within a narrow range around the set point.

flowchart LR
    subgraph Too_High
        A1[Blood glucose rises] --> A2[Insulin released]
        A2 --> A3[Glucose to glycogen in liver]
        A3 --> A4[Blood glucose falls]
    end
    subgraph Normal
        N[Normal blood glucose level]
    end
    subgraph Too_Low
        B1[Blood glucose falls] --> B2[Glucagon released]
        B2 --> B3[Glycogen to glucose in liver]
        B3 --> B4[Blood glucose rises]
    end
    A4 --> N
    B4 --> N

Exam Tip: A very common 6-mark question asks you to describe how blood glucose is regulated after a meal and during exercise. Make sure you name both hormones, their source (pancreas), their target (liver), and the process they trigger (glucose to glycogen or glycogen to glucose).

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Diabetes

Diabetes is a condition in which the body cannot control its blood glucose concentration properly. There are two types.

Type 1 Diabetes

Feature	Details
Cause	The pancreas produces little or no insulin because the immune system has destroyed the beta cells
Type of condition	Autoimmune disease
Age of onset	Usually develops in childhood or early adulthood
Treatment	Regular insulin injections (or insulin pump) to control blood glucose; careful monitoring of diet and blood glucose levels
Can it be prevented?	No — it is not linked to lifestyle
Can it be cured?	No — it is a lifelong condition

People with Type 1 diabetes must:

• Monitor their blood glucose regularly (using finger-prick blood tests or continuous glucose monitors).
• Inject insulin before meals to prevent blood glucose rising too high.
• Adjust insulin doses based on food intake and physical activity.
• Be careful about exercise, as it can cause blood glucose to drop dangerously low (hypoglycaemia).

Type 2 Diabetes

Feature	Details
Cause	The body's cells become resistant to insulin, so they do not respond to it properly; the pancreas may also produce insufficient insulin
Type of condition	Metabolic disorder linked to lifestyle
Age of onset	Usually develops in adulthood (but increasingly in young people)
Treatment	Controlled by diet and exercise; medication may be prescribed to increase insulin sensitivity; insulin injections in severe cases
Can it be prevented?	Yes — healthy diet, regular exercise, and maintaining a healthy weight reduce risk
Risk factors	Obesity, lack of exercise, high-sugar diet, family history, age, ethnicity

Comparing Type 1 and Type 2 Diabetes