Blood Glucose Regulation and Diabetes

This lesson covers one of the most important homeostatic mechanisms: the regulation of blood glucose concentration. You will learn how insulin and glucagon work together through negative feedback to keep blood glucose within safe limits, and how this system fails in Type 1 and Type 2 diabetes. This is a critical topic for Edexcel GCSE Biology (1BI0) Topic 7.

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Why Must Blood Glucose Be Controlled?

Blood glucose is the concentration of glucose dissolved in the blood. Glucose is essential because it is the substrate for cellular respiration — the process that releases energy for all cell functions.

If Blood Glucose Is Too High	If Blood Glucose Is Too Low
Glucose can damage blood vessels and organs (kidneys, eyes, nerves)	Cells do not have enough glucose for respiration
Water moves out of cells by osmosis, causing dehydration	Brain cells are particularly affected (they rely almost entirely on glucose)
Long-term: cardiovascular disease, nerve damage	Symptoms: dizziness, confusion, loss of consciousness
	In severe cases: coma and death

The body must therefore keep blood glucose within a narrow, safe range at all times.

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The Role of the Pancreas

The pancreas is the organ responsible for monitoring and controlling blood glucose concentration. It acts as both the receptor (detecting changes in blood glucose) and the coordination centre (producing the hormonal response).

The pancreas contains specialised clusters of cells called the islets of Langerhans, which include:

Cell Type	Hormone Produced	Released When
Beta (β) cells	Insulin	Blood glucose is too high
Alpha (α) cells	Glucagon	Blood glucose is too low

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When Blood Glucose Is Too HIGH

This typically happens after eating a meal rich in carbohydrates. Carbohydrates are digested into glucose, which is absorbed into the blood from the small intestine.

The Response — Insulin

1. The pancreas (beta cells in the islets of Langerhans) detects the rise in blood glucose.
2. The beta cells release insulin into the blood.
3. Insulin travels in the blood to target cells — mainly liver cells and muscle cells.
4. Insulin binds to receptors on the surface of these cells.
5. This causes the cells to:
   • Take up more glucose from the blood (by increasing the number of glucose transport proteins in the cell membrane).
   • Convert glucose into glycogen for storage — a process called glycogenesis.
6. The liver and muscles store the glycogen.
7. Blood glucose concentration falls back to the normal level.
8. Once normal levels are reached, the pancreas reduces insulin production.

Key Term: Glycogenesis

Glycogenesis = the conversion of glucose into glycogen for storage. This occurs mainly in the liver and muscle cells.

Exam Tip: Insulin lowers blood glucose. Think "Insulin → glucose goes In to cells." It causes cells to take up glucose and convert it to glycogen.

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When Blood Glucose Is Too LOW

This can happen between meals, during exercise (muscles use up glucose for respiration), or after fasting.

The Response — Glucagon

1. The pancreas (alpha cells in the islets of Langerhans) detects the fall in blood glucose.
2. The alpha cells release glucagon into the blood.
3. Glucagon travels to the liver (its main target organ).
4. Glucagon binds to receptors on liver cells.
5. This causes the liver to convert stored glycogen back into glucose — a process called glycogenolysis.
6. The glucose is released into the bloodstream.
7. Blood glucose concentration rises back to the normal level.
8. Once normal levels are reached, the pancreas reduces glucagon production.

Key Term: Glycogenolysis

Glycogenolysis = the conversion of glycogen back into glucose. This occurs in the liver.

Exam Tip: Glucagon raises blood glucose. Think "Glucagon → Glucose released." It causes the liver to break down glycogen and release glucose into the blood.

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Insulin and Glucagon — Negative Feedback

Insulin and glucagon work together as an antagonistic pair through negative feedback:

Condition	Hormone Released	Effect on Blood Glucose
Blood glucose too high (e.g. after eating)	Insulin (from beta cells)	Lowers blood glucose — cells take up glucose; glucose → glycogen
Blood glucose too low (e.g. during exercise)	Glucagon (from alpha cells)	Raises blood glucose — glycogen → glucose; released into blood

This is negative feedback because:

• A rise in blood glucose triggers insulin, which lowers it (opposing the change).
• A fall in blood glucose triggers glucagon, which raises it (opposing the change).
• In both cases, the response reverses the original change.

graph TD
    A["Normal blood glucose"] -->|"After eating"| B["Blood glucose TOO HIGH"]
    B --> C["Pancreas beta cells detect rise"]
    C --> D["Insulin released"]
    D --> E["Liver and muscle cells take up glucose"]
    E --> F["Glucose converted to glycogen"]
    F --> A

    A -->|"During exercise or fasting"| G["Blood glucose TOO LOW"]
    G --> H["Pancreas alpha cells detect fall"]
    H --> I["Glucagon released"]
    I --> J["Liver converts glycogen to glucose"]
    J --> K["Glucose released into blood"]
    K --> A

    style A fill:#2ecc71,color:#fff
    style B fill:#e74c3c,color:#fff
    style G fill:#3498db,color:#fff
    style D fill:#e67e22,color:#fff
    style I fill:#9b59b6,color:#fff

Exam Tip: Do not confuse glycogen (the storage molecule) with glucagon (the hormone). They sound similar but are completely different: glycogen is a large, insoluble storage carbohydrate; glucagon is a hormone from the pancreas.

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Diabetes

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

Type 1 Diabetes

Feature	Detail
Cause	An autoimmune condition — the body's immune system attacks and destroys the beta cells in the pancreas
Result	The pancreas produces little or no insulin
Age of onset	Usually develops in childhood or early adulthood
Treatment	Insulin injections (or an insulin pump) to replace the missing insulin; blood glucose must be monitored regularly
Can it be prevented?	No — it is not linked to lifestyle; it cannot be prevented
Can it be cured?	No — it is a lifelong condition (though pancreas transplants are being researched)

People with Type 1 diabetes must:

• Inject insulin before meals (the dose depends on what they eat and their blood glucose level).
• Monitor blood glucose regularly using a glucose meter or continuous glucose monitor.
• Balance their insulin dose with food intake and physical activity.

Type 2 Diabetes

Feature	Detail
Cause	The body's cells become resistant to insulin (they no longer respond properly to it), OR the pancreas does not produce enough insulin
Result	Blood glucose remains too high after meals because cells do not take up glucose effectively
Age of onset	Usually develops in adulthood (although increasingly seen in younger people)
Risk factors	Obesity, poor diet (high in sugar and fat), lack of exercise, family history (genetics), age, ethnicity
Treatment	Diet and exercise (first-line); medication (e.g. metformin) to increase insulin sensitivity or reduce glucose production; in some cases, insulin injections
Can it be prevented?	Often yes — through maintaining a healthy weight, eating a balanced diet, and exercising regularly
Can it be cured?	No — but it can be managed and, in some cases, put into remission through significant lifestyle changes

Exam Tip: A very common exam question asks you to compare Type 1 and Type 2 diabetes. The key differences are: Type 1 is autoimmune (body destroys beta cells, no insulin produced, treated with injections, cannot be prevented); Type 2 is related to insulin resistance (often linked to lifestyle, managed with diet/exercise/medication, can often be prevented).

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Comparison: Type 1 vs Type 2 Diabetes

Feature	Type 1 Diabetes	Type 2 Diabetes
Cause	Autoimmune destruction of beta cells	Cells become resistant to insulin; or insufficient insulin produced
Insulin production	None (or very little)	Some, but not enough or cells do not respond to it
Age of onset	Usually childhood/young adulthood	Usually adulthood (increasingly in younger people)
Link to lifestyle	No	Yes — obesity, poor diet, lack of exercise
Treatment	Insulin injections + monitoring	Diet, exercise, medication (e.g. metformin); sometimes insulin
Prevention	Cannot be prevented	Can often be prevented through healthy lifestyle
Prevalence	~10% of diabetes cases	~90% of diabetes cases

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The Role of Adrenaline in Blood Glucose

It is worth noting that adrenaline also affects blood glucose. During the fight or flight response, adrenaline stimulates the liver to convert glycogen to glucose, raising blood glucose levels rapidly. This provides the extra energy needed for the muscles during a stressful situation. However, this is not part of the normal homeostatic regulation of blood glucose — it is an emergency response.

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Summary